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Yacubova, E. & Komuro, H. Stage-specific control of neuronal migration by somatostatin. Nature 415, 77-81
Abstract
Developing neurons transiently express somatostatin and its receptors, but little is known about their function at these early stages. As we thought that endogenous somatostatin might control the migratory behaviour of immature neurons, we have examined the effects of somatostatin in cerebellar granule cells of early postnatal mice, because these cells express all five types of somatostatin receptors before the initiation of their migration. Here we show that somatostatin has opposite and stage-specific effects on the migration of cerebellar granule cells. Activation of somatostatin receptors increases the rate of granule cell migration near their birthplace, but decreases the rate near their final destination. Furthermore, somatostatin enhances the size and frequency of spontaneous Ca2+ fluctuations in the early phase of migration, whereas it eliminates spike-like Ca2+ transients in the late phase. Somatostatin-induced changes at both early and late phases are reversed by a blockade of K+ channel activity. These results indicate that somatostatin may provide an essential cue for accelerating the movement of granule cells in the early phase and for terminating the movement in the late phase through altering intracellular Ca2+ concentrations and K+ channel activity.
... Il a été montré par des études en microscopie sur tranches organotypiques que leur activation entraîne un effet opposé sur la migration en fonction des couches du cortex (Fig. 6B). En effet, alors que la SST augmente la migration tangentielle des neurones dans la CGE, elle inhibe la migration radiale dans la CGI, permettant aux cellules de s'arrêter dans cette couche (Yacubova and Komuro 2002). Cet effet modulateur différentiel de la migration passe par une régulation du Ca 2+ intracellulaire et serait dû à un changement d'expression des récepteurs. ...
... , and, in the IGL, promotes survival and differentiation ) of CGN. At the same time, somatostatin increases CGN migration in the EGL but decreases their migration in the IGL, inducing the final stop of the cells in this layer (Yacubova and Komuro 2002). Although considerable progress has been made towards understanding the guidance systems that regulate development of granule neurons, many molecules involved remain to be identified. ...
... But even if further investigation are needed to elucidate the exact contribution of nociceptin in brain development, the present results demonstrate the transient expression of the nociceptinergic system in the postnatal cerebellum IGL and provide first evidence that this peptide can, in this structure, promote CGN differentiation and survival. Yacubova, E., and Komuro, H. (2002). Stage-specific control of neuronal migration by somatostatin. ...
Le cervelet est une structure cérébrale impliquée dans de multiples fonctions motrices mais aussi cognitives et dont le développement postnatal est sous le contrôle de divers types de facteurs dont les neuropeptides. Les peptides capables d’agir sur le développement du cortex cérébelleux présentent généralement un profil d’expression particulier, avec chez le rongeur un pic d’expression au cours des 2 premières semaines postnatales. L’objectif de cette étude était d’identifier d’autres peptides présentant ce même type d’expression et de caractériser leurs potentiels effets au cours du développement du cortex cérébelleux, et plus particulièrement dans la mise en place des neurones en grain qui sont les plus abondants de cette structure. Pour cela, des cervelets de rats âgés de 8 à 90 jours ont été analysés par spectrométrie de masse. Parmi les 33 peptides identifiés, 4 présentent le profil recherché et nous avons choisi d’étudier l’un d’entre eux, la nociceptine. La mesure de l’expression du gène de la nociceptine et de son récepteur montre un profil d’expression similaire à celui observé en peptidomique. De plus, ces 2 gènes sont retrouvés principalement exprimés dans la couche granulaire interne du cortex cérébelleux par microdissection et qPcr. La recherche de la fonction de la nociceptine montre qu’elle exerce un effet neurotrophique en augmentant la survie et la différenciation des neurones en grain, sans affecter la motilité de ces cellules. Des tests préliminaires réalisés in vivo indiquent que la nociceptine est aussi capable de bloquer la toxicité induite par l’alcool. La dernière partie de l’étude avait pour but d’identifier de nouveaux neuropeptides exprimés dans le cervelet en utilisant une approche par séquençage de novo. L’application de filtres comme la récurrence des séquences peptidiques ou leur régulation au cours du développement a permis de ne retenir que 6 séquences pour la suite de l’analyse. Des études génomiques permettront de restreindre encore ce nombre afin de focaliser les tests d’activité biologique sur la ou les cibles qui ont la plus grande probabilité de correspondre à des peptides biologiquement actifs.
... This puzzle was eventually solved by the seminal work of Pasco Rakic who showed that granule cells use Bergman fibers as a substratum on their route through the nascent molecular layer (Rakic 1971). This study not only established a fundamental and extremely fruitful paradigm for neuronal migration throughout the CNS; it also paved the way for the identification of a wealth of genetic constituents and molecular regulators of granule cell migration, and neuronal motility in general (e.g., Hatten and Mason 1990;Miller 1992;Zheng et al. 1996;Rakic 1996, 1998b;Yacubova and Komuro 2002). ...
... Among modulators of the motility and speed of granule cell migration, the neurotransmitter glutamate, somatostatin (Yacubova and Komuro 2002) and PACAP (Cameron et al. 2007), but also ion channel activity are the most prominent and best characterized. Much of our knowledge here is based on a series of studies pioneered by Hoshino Komuro and associates (e.g., Komuro and Rakic 1992, 1998b; for reviews, see; Komuro and Yacubova 2003;Komuro et al. 2015; see also; Mancini and Atchison 2007;Tarnok et al. 2008). ...
... Finally, we note that not only speed and mode of migration (the latter inferred primarily from cell shape), but also the sensitivity and reaction of granule cells to modulators of their migration, notably PACAP (Raoult et al. 2014) and 1 3 somatostatin (Yacubova and Komuro 2002), differ in the layers they have to transit on their descent into the nascent granule cell layer. ...
The enormous expansion the vertebrate nervous system goes through from its first anlage to its adult shape and organization goes along with extensive rearrangements of its constituent cells and typical cellular migrations, often over long distances, and by convoluted pathways. Here, I try to summarize how the cells that form the cerebellum move and migrate during normal cerebellar histogenesis. The cerebellum is made up of a limited set of clearly distinguishable classes of cells, some of which are also readily accessible by genetic tools. Its structure and development have been the focus of studies dating back to at least Ramon y Cajal which have yielded fundamental insights into basic mechanisms of the development of the nervous. During cerebellar histogenesis, several distinct and well-discernable modes of migration may be recognized, some of which have been studied in considerable morphological and molecular detail. Still, often grace to the detail known, a wealth of open questions remains, and the cerebellar anlage remains a highly accessible and promising paradigm for those interested in nervous system development and cell migration in general. I also point out some of the issues that may warrant consideration when results from technically distinct studies are compared and integrated.
... The transient arrest phase of granule cells in the PCL could be necessary for initiation of a differentiation program and/or for a correct integration of granule cells in the IGL. In particular, the somatostatinergic system exerts a stimulatory effect on tangential granule cell migration in the EGL but somatostatin is the stop signal of granule cells in the IGL [45]. Therefore, PACAP could be responsible for the switch of the somatostatinergic control of granule cell migration. ...
... (2) the silencing of genes in knock-out animals; and (3) the administration of exogenous synthetic or purified compounds with potential effect. In particular, the role of somatostatin [45], PACAP [13,17], tPA [13] and IGF-1 [25] on interneuron migration has been examined ex vivo or in vivo by real-time monitoring of the cell after inhibition of the endogenous molecule ( Figure 6). Mainly by comparing the thickness of cerebellar cortical layers, the effects of MMP-2/3/9 [48][49][50], BDNF [51], SDF-1 [52], tPA [53] or astrotactin [54] have been evidenced in knock-out (KO) animals or after in vivo patch implantation for neurotrophin-3 [55] (Figure 6). ...
... Both SST-14 and SST-28 bind to all five SSTRs. During postnatal cerebellar development, SST-14 is present in Purkinje cells (ML and PCL), Golgi cells, and climbing fibres (IGL), while SST-28 is detected in Golgi cells and mossy fiber terminals (IGL) [45]. Three binding sites, including SSTR1, SSTR4, and mainly SSTR2 are expressed during cerebellar development [62]. ...
Due to its continuing development after birth, the cerebellum represents a unique model for studying the postnatal orchestration of interneuron migration. The combination of fluorescent labeling and ex/in vivo imaging revealed a cellular highway network within cerebellar cortical layers (the external granular layer, the molecular layer, the Purkinje cell layer, and the internal granular layer). During the first two postnatal weeks, saltatory movements, transient stop phases, cell-cell interaction/contact, and degradation of the extracellular matrix mark out the route of cerebellar interneurons, notably granule cells and basket/stellate cells, to their final location. In addition, cortical-layer specific regulatory factors such as neuropeptides (pituitary adenylate cyclase-activating polypeptide (PACAP), somatostatin) or proteins (tissue-type plasminogen activator (tPA), insulin growth factor-1 (IGF-1)) have been shown to inhibit or stimulate the migratory process of interneurons. These factors show further complexity because somatostatin, PACAP, or tPA have opposite or no effect on interneuron migration depending on which layer or cell type they act upon. External factors originating from environmental conditions (light stimuli, pollutants), nutrients or drug of abuse (alcohol) also alter normal cell migration, leading to cerebellar disorders.
... However, until recently, little was known about the role of SST in brain development. The real-time observation of cell migration and the use of pharmacological tools have revealed that endogenous SST regulates granule cell migration in a corticallayer-specific manner (Yacubova and Komuro, 2002b). Postmitotic granule cells express all five types of SSTRs before the initiation of migration, while differentiated granule cells in the adult do not express the receptors. ...
... Postmitotic granule cells express all five types of SSTRs before the initiation of migration, while differentiated granule cells in the adult do not express the receptors. High levels of SST are present along the migratory route of granule cells and in their final destination (Yacubova and Komuro, 2002b). During periods of granule cell migration, SST-14 is present in Purkinje cells, Golgi cells, and climbing fibers, and SST-28 is present in Golgi cells and mossy fiber terminals. ...
... During periods of granule cell migration, SST-14 is present in Purkinje cells, Golgi cells, and climbing fibers, and SST-28 is present in Golgi cells and mossy fiber terminals. The time-lapse recording of granule cell migration in acute cerebellar slices of P10 mice demonstrates that the addition of 1 mM of SST-14 or SST-28 to the medium significantly increases the speed of granule cell movement in the EGL, slightly decreases the speed in the ML, and significantly decreases the speed in the IGL (Yacubova and Komuro, 2002b). In contrast, the addition of an SST antagonist, AC-178,335, to the medium significantly decreases the speed of granule cell migration in the EGL, slightly increases the speed in the ML, and significantly increases the speed in the IGL. ...
During development, cerebellar neurons migrate from their birthplaces (the cerebellar plate ventricular zone and the upper rhombic lip) to their final destinations (the cerebellar cortexes and deep cerebellar nuclei). The active movement of cerebellar neurons is essential for the formation of neuronal cytoarchitecture and their proper differentiation. In this chapter, we focus on recent findings from studies that investigated (1) when, where, and how cerebellar neurons migrate from their origin to their resident destinations, (2) the mechanisms underlying the migration of cerebellar neurons, and (3) how the exposure to toxic materials, such as alcohol, affects the migration of cerebellar neurons.
... Mice expressing enhanced green fluorescent protein (EGFP) from the Pax2 locus were originally obtained from Peter Pfeffer and Meinrad Busslinger, Vienna ( [16]; BAC line no. 30). These animals were kept as heterozygotes on a C57Bl/6 background. ...
... As many of the tracks observed, or parts thereof, were rather obliquely oriented, it might be necessary to adequately multiply these numbers to arrive at realistic time estimates. For comparison, immature granule cells have been reported to transit the ML, if in the opposite direction, in about 8.3 h with a speed of some 11-15 μm/h, and migrate at a somewhat lower speed (some 10 μm/h) in the nascent GL at the developmental stage analyzed presently [9,30]. And while the faster Pax2 cells that we observed in the ML migrated with a speed comparable to that reported for ML interneuron precursors in slice cultures (1 5 μm/h) [4], the average speed we observed for our large sample was about ten times lower. ...
The cerebellum arguably constitutes one of the best characterized central nervous circuits, and its structure, cellular function, and histogenesis have been described in exceptional quantitative detail. A notable exception to this is the development of its inhibitory interneurons, and in particular the extensive migrations of future basket and stellate cells. Here, we used acute slices from 8-day-old mice to assess the migration of Pax2-EGFP-tagged precursors of these cells en route to the molecular layer during their transit through the nascent cerebellar cortex. We document that movement of these cells is highly directed. Their speed and directional persistence are larger in the nascent granule cell layer than in the molecular layer. And they migrate periodically, with periods of effective, directed translocation separated by bouts of rather local movement. Finally, we document that the arrangement of these cells in the adult molecular layer is characterized by clustering. These data are discussed with a focus on potential generative mechanisms for the developmental pattern observed.
... The absence of liver kinase B1 (Lkb1), also known as serine/threonine kinase 11, in GCPs was shown to increase cerebellar size and foliation without affecting proliferation, but through delayed radial migration of GCs (Ryan et al., 2017). A theoretical study also predicted that GC migration at the experimentally observed speed (Yacubova and Komuro, 2002) resulted in non-uniform GC accumulation in the IGL and consequent folia lengthening (Takeda et al., 2021). Moreover, cerebellar gross structures are also regulated by two chromodomain helicase DNA-binding (CHD) proteins, CHD7 and CHD8, which are associated with cerebellum-related neurodevelopmental disorders. ...
The well-organized cerebellar structures and neuronal networks are likely crucial for their functions in motor coordination, motor learning, cognition, and emotion. Such cerebellar structures and neuronal networks are formed during developmental periods through orchestrated mechanisms, which include not only cell-autonomous programs but also interactions between the same or different types of neurons. Cerebellar granule cells (GCs) are the most numerous neurons in the brain and are generated through intensive cell division of GC precursors (GCPs) during postnatal developmental periods. While GCs go through their own developmental processes of proliferation, differentiation, migration, and maturation, they also play a crucial role in cerebellar development. One of the best-characterized contributions is the enlargement and foliation of the cerebellum through massive proliferation of GCPs. In addition to this contribution, studies have shown that immature GCs and GCPs regulate multiple factors in the developing cerebellum, such as the development of other types of cerebellar neurons or the establishment of afferent innervations. These studies have often found impairments of cerebellar development in animals lacking expression of certain molecules in GCs, suggesting that the regulations are mediated by molecules that are secreted from or present in GCs. Given the growing recognition of GCs as regulators of cerebellar development, this review will summarize our current understanding of cerebellar development regulated by GCs and molecules in GCs, based on accumulated studies and recent findings, and will discuss their potential further contributions.
... Many of the markers used for the Hannum clock are within or near genes that have functions in aging-related conditions, such as Alzheimer's disease [17]. Specifically, two methylation markers used for the aging clock are located in the somatostatin (SST) gene region, which encodes somatostatin, a peptide hormone that regulates exocrine, endocrine, and nervous system function [33]. Somatostatin is highly expressed in the brain, and its actions include inhibiting the release of excitatory neurotransmitters through voltage-gated calcium channels [34,35]. ...
DNA methylation age acceleration, the discrepancy between epigenetic age and chronological age, is associated with mortality and chronic diseases, including diabetes, hypertension, and hyperlipidemia. In this study, we investigate whether medications commonly used to treat these diseases in 15 drug categories are associated with four epigenetic age acceleration measures: HorvathAge acceleration (HorvathAA), HannumAge acceleration (HannumAA), PhenoAge acceleration, and GrimAge acceleration (GrimAA) using cross-sectional (Phase 1, N=1,100) and longitudinal (Phases 1 and 2, N=266) data from African Americans in the Genetic Epidemiology Network of Arteriopathy (GENOA) study. In cross-sectional analyses, the use of calcium channel blockers was associated with 1.27 years lower HannumAA after adjusting for covariates including hypertension (p=0.001). Longitudinal analyses showed that, compared to those who never used antihypertensives, those who started to take antihypertensives after Phase 1 had a 0.97-year decrease in GrimAA (p=0.007). In addition, compared to those who never used NSAID analgesics, those who started to take them after Phase 1 had a 2.61-year increase in HorvathAA (p=0.0005). Our study demonstrates that three commonly used medications are associated with DNAm age acceleration in African Americans and sheds light on the potential epigenetic effects of pharmaceuticals on aging at the cellular level.
... To understand the contribution of GC migration along the BG fibers (oriented based on tissue deformation) to cerebellar morphogenesis, we performed numerical analyses of cerebellar tissue morphogenesis, by altering the cell migration velocity 0 as 10 μm/h with reference to the experimental measurement (Yacubova and Komuro, 2002b) and as 5 and 0 μm/h for comparison. Our simulation data showed that GC proliferation in the EGL and their subsequent migration from the EGL to the IGL, caused folia formation (Fig. 2 A-C). ...
The cerebellum has a unique morphology characterized by fine folds called folia. During cerebellar morphogenesis, folia formation (foliation) proceeds with granule cell (GC) proliferation in an external granular layer, and subsequent cell migration to an internal granular layer (IGL). GC migration is guided along Bergmann glial (BG) fibers, whose orientation depends on the deformation of cerebellar tissue during folia formation. The aim of this study is to investigate the contribution of the fiber-guided GC migration on folia formation from a mechanical viewpoint. Based on a continuum mechanics model of cerebellar tissue deformation and GC dynamics, we simulated foliation process caused by GC proliferation and migration. By changing migration speeds, we showed that the fiber-guided GC migration caused the non-uniform accumulation of GCs and folia lengthening. Furthermore, the simulation of impaired GC migration under pathological conditions, where GCs did not migrate along BG fibers, revealed that fiber-guided GC migration was necessary for folia lengthening. These simulation results successfully recapitulated the features of physiological and pathological foliation processes and validated the mechanisms that guidance of GC migration by BG fibers causes folia lengthening accompanied by non-uniform IGL. Our computational approach will help us understand biological and physical morphogenesis mechanisms, facilitated by interactions between cellular activities and tissue behaviors.
... In addition to the flow of CSF fluid generated by motile cilia, spontaneous Ca 2+ fluctuations have been shown to be important for neural migration along with other regulated developmental events, such as axonal outgrowth and maturation of signaling properties [106][107][108][109][110][111]. Additionally, embryonic stem cell-derived neural progenitors were found to form networks with concurrent oscillating Ca 2+ activity that stimulated proliferation [112]. ...
The calcium ion (Ca2+) is a diverse secondary messenger with a near-ubiquitous role in a vast array of cellular processes. Cilia are present on nearly every cell type in either a motile or non-motile form; motile cilia generate fluid flow needed for a variety of biological processes, such as left–right body patterning during development, while non-motile cilia serve as the signaling powerhouses of the cell, with vital singling receptors localized to their ciliary membranes. Much of the research currently available on Ca2+-dependent cellular actions and primary cilia are tissue-specific processes. However, basic stimuli-sensing pathways, such as mechanosensation, chemosensation, and electrical sensation (electrosensation), are complex processes entangled in many intersecting pathways; an overview of proposed functions involving cilia and Ca2+ interplay will be briefly summarized here. Next, we will focus on summarizing the evidence for their interactions in basic cellular activities, including the cell cycle, cell polarity and migration, neuronal pattering, glucose-mediated insulin secretion, biliary regulation, and bone formation. Literature investigating the role of cilia and Ca2+-dependent processes at a single-cellular level appears to be scarce, though overlapping signaling pathways imply that cilia and Ca2+ interact with each other on this level in widespread and varied ways on a perpetual basis. Vastly different cellular functions across many different cell types depend on context-specific Ca2+ and cilia interactions to trigger the correct physiological responses, and abnormalities in these interactions, whether at the tissue or the single-cell level, can result in diseases known as ciliopathies; due to their clinical relevance, pathological alterations of cilia function and Ca2+ signaling will also be briefly touched upon throughout this review.
... However, in the case of global neuron ablation, we also observed a decline in beta cell mass likely due to secondary effects from the extensive levels of neuronal cell death. Given the potential role of Somatostatin signaling in mediating migration of developing neurons (Yacubova and Komuro, 2002), it is possible that delta cell loss could worsen the decline in innervation density. Similar to what has been reported in rodents (Hsueh et al., 2017;Tang et al., 2018), a dense supply of nerve fibers could be observed within the endocrine pancreas of developing and adult zebrafish. ...
Pancreatic islets are innervated by autonomic and sensory nerves that influence their function. Analyzing the innervation process should provide insight into the nerve-endocrine interactions and their roles in development and disease. Here, using in vivo time-lapse imaging and genetic analyses in zebrafish, we determined the events leading to islet innervation. Comparable neural density in the absence of vasculature indicates that it is dispensable for early pancreatic innervation. Neural crest cells are in close contact with endocrine cells early in development. We find these cells give rise to neurons that extend axons towards the islet as they surprisingly migrate away. Specific ablation of these neurons partly prevents other neurons from migrating away from the islet resulting in diminished innervation. Thus, our studies establish the zebrafish as a model to interrogate mechanisms of organ innervation, and reveal a novel mode of innervation whereby neurons establish connections with their targets before migrating away.
... How TrkB mediates BDNF-induced OEC migration? There are increasing evidence that calcium signaling regulates the motility and direction of migratory cells (Ariano et al., 2006;Brundage et al., 1991;Komuro and Rakic, 1996;Yacubova and Komuro, 2002) and mediates the signals of extracellular factors such as BDNF (Jin et al., 2005) and Slit-2 (Huang et al., 2011a). TRPC channels are a family of nonselective Ca 21 -permeable cation channels (Huang, 2004;Montell, 2001). ...
Olfactory ensheathing cells (OECs) are a unique type of glial cells with axonal growth-promoting properties in the olfactory system. Organized migration of OECs is essential for neural regeneration and olfactory development. However, the molecular mechanism of OEC migration remains unclear. In the present study, we examined the effects of brain-derived neurotrophic factor (BDNF) on OEC migration. Initially, the "scratch" migration assay, the inverted coverslip and Boyden chamber migration assays showed that BDNF could promote the migration of primary cultured OECs. Furthermore, BDNF gradient attracted the migration of OECs in single-cell migration assays. Mechanistically, TrkB receptor expressed in OECs mediated BDNF-induced OEC migration, and BDNF triggered calcium signals in OECs. Finally, transient receptor potential cation channels (TRPCs) highly expressed in OECs were responsible for BDNF-induced calcium signals, and required for BDNF-induced OEC migration. Taken together, these results demonstrate that BDNF promotes the migration of cultured OECs and an unexpected finding is that TRPCs are required for BDNF-induced OEC migration. GLIA 2016.
... Vascular scaffolding was implicated in the islet innervation of developing mouse pancreas (Reinert et al. 2014). Somatostatin was implicated in the regulation of neuronal migration in developing central nervous system (Yacubova & Komuro 2002). Potential role of somatostatin in the pancreatic neuronal regulation needs to be investigated. ...
Human pancreatic islets show unique architecture in which α and δ cells are mostly at the peripheral and perivascular areas. It has remained unknown how such prototype is realized in every islet. Here, I report that fetal islets develop first in two distinct types consisting of β or α/δ cells, respectively. The α/δ islets are variable in shape, composed of α and δ cells evenly intermixed. They are vascularized better but encapsulated poorer than β islets in general. During the development, the β and α/δ islets adjoin and fuse with each other in such a way that α and δ cells form a crescent on β cells and, then, progress to encompass and encroach into β cells. Most mature-form islets appear to develop through the fusion. Islets at various stages of fusion are present concurrently until late gestation, suggesting that the islet fusion is an ongoing developmental process. The α/δ islets appear to play a primary role for the process, approaching toward the fusion partner actively. Direct connection is present between the α/δ islets and neural ganglia undergoing active neurogenesis, suggesting an organ-wide neuroendocrine network development. The fusion of precursor islets appears to be a principle of human pancreatic development providing the prototype of mature islets. The complex development might be a reference for in vitro reproduction of biologically competent islets.
... The somatostatin mRNA precursor is translated to produce a large inactive pre-prosomatostatin peptide (116 amino acids; PPSST); its posttranslational enzymatic cleavage yields two biologically active products, somatostin 14 (14 amino acids; and somatostin 28 (28 amino acids; SST-28), which have neurotransmitter and neuromodulator roles (Kumar and Grant 2010). SST is known to be involved in granule cell migration during cerebellar development (Epelbaum et al. 1994;Yacubova and Komuro 2002;Le Verche et al. 2009). Several mapping studies performed in embryonic, postnatal, and adult mice showed that SST has a wide central nervous system distribution that includes cerebral cortex, hippocampus, striatum, amygdala, olfactory system, hypothalamus, diencephalon, midbrain, and brainstem (Roberts et al. 1982, Moga and Gray 1985, Gray and Magnuson 1992Garcia-Lopez et al. 2008;Viollet et al. 2008;Real et al. 2009;Bupesh et al. 2011a, b;Morales-Delgado et al. 2011). ...
... The somatostatin mRNA precursor is translated to produce a large inactive pre-prosomatostatin peptide (116 amino acids; PPSST); its posttranslational enzymatic cleavage yields two biologically active products, somatostin 14 (14 amino acids; and somatostin 28 (28 amino acids; SST-28), which have neurotransmitter and neuromodulator roles (Kumar and Grant 2010). SST is known to be involved in granule cell migration during cerebellar development (Epelbaum et al. 1994;Yacubova and Komuro 2002;Le Verche et al. 2009). Several mapping studies performed in embryonic, postnatal, and adult mice showed that SST has a wide central nervous system distribution that includes cerebral cortex, hippocampus, striatum, amygdala, olfactory system, hypothalamus, diencephalon, midbrain, and brainstem (Roberts et al. 1982, Moga and Gray 1985, Gray and Magnuson 1992Garcia-Lopez et al. 2008;Viollet et al. 2008;Real et al. 2009;Bupesh et al. 2011a, b;Morales-Delgado et al. 2011). ...
The telencephalic subpallium is the source of various GABAergic interneuron cohorts that invade the pallium via tangential migration. Based on genoarchitectonic studies, the subpallium has been subdivided into four major domains: striatum, pallidum, diagonal area and preoptic area (Puelles et al. 2013; Allen Developing Mouse Brain Atlas), and a larger set of molecularly distinct progenitor areas (Flames et al. 2007). Fate mapping, genetic lineage-tracing studies, and other approaches have suggested that each subpallial subdivision produces specific sorts of inhibitory interneurons, distinguished by differential peptidic content, which are distributed tangentially to pallial and subpallial target territories (e.g., olfactory bulb, isocortex, hippocampus, pallial and subpallial amygdala, striatum, pallidum, septum). In this report, we map descriptively the early differentiation and apparent migratory dispersion of mouse subpallial somatostatin-expressing (Sst) cells from E10.5 onward, comparing their topography with the expression patterns of the genes Dlx5, Gbx2, Lhx7-8, Nkx2.1, Nkx5.1 (Hmx3), and Shh, which variously label parts of the subpallium. Whereas some experimental results suggest that Sst cells are pallidal, our data reveal that many, if not most, telencephalic Sst cells derive from de diagonal area (Dg). Sst-positive cells initially only present at the embryonic Dg selectively populate radially the medial part of the bed nucleus striae terminalis (from paraseptal to amygdaloid regions) and part of the central amygdala; they also invade tangentially the striatum, while eschewing the globus pallidum and the preoptic area, and integrate within most cortical and nuclear pallial areas between E10.5 and E16.5.
Electronic supplementary material
The online version of this article (doi:10.1007/s00429-015-1086-8) contains supplementary material, which is available to authorized users.
... Apart from the hypothalamic locations, STT has a wide distribution in other brain regions such as the amygdala, preoptic area, hippocampus, striatum, cerebral cortex, olfactory regions, and brainstem, where it acts as a neurotransmitter or neuromodulator (Viollet et al., 2008). STT and its receptors have also been implicated in brain development (Yacubova and Komuro, 2002;Le Verche et al., 2009). ...
... As PACAP is involved in neuritogenesis (Gonzalez et al. 1997;Falluel-Morel et al. 2005), the transient arrest phase could be necessary for the initiation of a differentiation program and/or for a correct integration of GN in the IGL. As an example, somatostatin is the stop signal for GN in the IGL, but the subtype of receptor that mediates the inhibitory effect on GN migration is still a matter of debate (Viollet et al. 1997;Yacubova and Komuro 2002b). In fact, somatostatin stimulates the tangential migration of GN in the EGL through sst2 receptors but exerts an opposite effect in the IGL through a different type of receptor. ...
During early post‐natal development of the cerebellum, granule neurons (GN) execute a centripetal migration toward the internal granular layer, whereas basket and stellate cells (B/SC) migrate centrifugally to reach their final position in the molecular layer (ML). We have previously shown that pituitary adenylate cyclase‐activating polypeptide (PACAP) stimulates in vitro the expression and release of the serine protease tissue‐type plasminogen activator ( tPA ) from GN, but the coordinated role of PACAP and tPA during interneuron migration has not yet been investigated. Here, we show that endogenous PACAP is responsible for the transient arrest phase of GN at the level of the Purkinje cell layer (PCL) but has no effect on B/SC. tPA is devoid of direct effect on GN motility in vitro , although it is widely distributed along interneuron migratory routes in the ML, PCL, and internal granular layer. Interestingly, plasminogen activator inhibitor 1 reduces the migration speed of GN in the ML and PCL, and that of B/SC in the ML. Taken together, these results reveal for the first time that tPA facilitates the migration of both GN and fast B/SC at the level of their intersection in the ML through degradation of the extracellular matrix. image
Crucial role of tissue plasminogen activator (tPA) in interneuron migration. Interneuron migration is a critical step for normal establishment of neuronal network. This study indicates that, in the post‐natal cerebellum, tPA facilitates the opposite migration of immature excitatory granule neurons (GN) and immature inhibitory basket/stellate cells (B/SC) along the same migratory route. These data show that tPA exerts a pivotal role in neurodevelopment.
... Spontaneous activity has been shown to regulate many aspects of neural development, including the proliferation of precursors (Liu and others 2005; LoTurco and others 1995; Weissman and others 2004), neuronal survival (Mennerick and Zorumski 2000;Spitzer 2006) and migration ( Komuro and Rakic 1996;Manent and others 2005;Yacubova and Komuro 2002;Zheng and Poo 2007), neurotransmitter specification ( Borodinsky and others 2004;Marek and others 2010;Spitzer 2012), and axon and dendrite growth and branching (Hua and others 2005;Lohmann and others 2002;Ruthazer and others 2003;Uesaka and others 2006;Wong and Ghosh 2002). All these processes influence how neurons connect to each other. ...
Throughout development, the nervous system produces patterned spontaneous activity. Research over the past two decades has revealed a core group of mechanisms that mediate spontaneous activity in diverse circuits. Many circuits engage several of these mechanisms sequentially to accommodate developmental changes in connectivity. In addition to shared mechanisms, activity propagates through developing circuits and neuronal pathways (i.e., linked circuits in different brain areas) in stereotypic patterns. Increasing evidence suggests that spontaneous network activity shapes synaptic development in vivo. Variations in activity-dependent plasticity may explain how similar mechanisms and patterns of activity can be employed to establish diverse circuits. Here, I will review common mechanisms and patterns of spontaneous activity in emerging neural networks and discuss recent insights into their contribution to synaptic development.
... Together, these signals converge and cause changes such as calcium influx into granule cells, and ultimately control the initiation, termination, and rate of migration of granule cells. 83,84 Granule cell migration is completed by ∼P20 in mice, which corresponds to the final stages of foliation. ...
The internal structure of the cerebellum reflects an intriguing paradox; its cytoarchitecture is relatively simple and repeated throughout, yet the connections between its neurons are wired into a complex array of gene expression domains and functional circuits. The developmental mechanisms that coordinate the establishment of cerebellar structure and circuitry provide a powerful model for understanding how functional brain networks are formed. Two primary germinal zones generate the cells that make up the cerebellum. Each zone expresses a specific set of genes that establish the cell lineages within the cerebellar anlage. Then, cohorts of differentiated projection neurons and interneuron progenitors migrate into the developing cerebellum. Thereafter, a number of remarkable patterning events occur including transformation of the smooth cerebellar surface into an intricately patterned series of folds, formation of three distinct cellular layers, and the demarcation of parasagittal gene expression domains. Together, these structural and molecular organizations are thought to support the proper connectivity between incoming afferent projections and their target cells. After birth, genetic programs and neural activity repattern synaptic connections into topographic neural networks called modules, which are organized around a longitudinal zone plan and are defined by their molecular, anatomic, and functional properties. WIREs Dev Biol 2013, 2:149–164. doi: 10.1002/wdev.65
This article is categorized under: Nervous System Development > Vertebrates: Regional Development
... Granule cells are, by far, the major population of interneurons in the cerebellum and they represent the main source of glutamate, the second most abundant population being GABAergic neurons (Voogd and Glickstein, 1998). Previous studies have demonstrated that plasticity of granule cells can be modulated by neuropeptides (Cote et al., 1999;Yacubova and Komuro, 2002). In particular, in cerebellar granule cells, PACAP has been shown to inhibit proliferation (Nicot et al., 2002), stop migration (Cameron et al., 2007), protect from apoptosis (Vaudry et al., 2000), and promote differentiation (Gonzalez et al., 1997). ...
High concentrations of pituitary adenylate cyclase-activating polypeptide (PACAP) and a high density of PACAP binding sites have been detected in the developing rat cerebellum. In particular, PACAP receptors are actively expressed in immature granule cells, where they activate both adenylyl cyclase and phospholipase C. The aim of the present study was to investigate the ability of PACAP to induce calcium mobilization in cerebellar granule neurons. Administration of PACAP-induced a transient, rapid, and monophasic rise of the cytosolic calcium concentration ([Ca(2+)]i), while vasoactive intestinal peptide was devoid of effect, indicating the involvement of the PAC1 receptor in the Ca(2+) response. Preincubation of granule cells with the Ca(2+) ATPase inhibitor, thapsigargin, or the d-myo-inositol 1,4,5-trisphosphate (IP3) receptor antagonist, 2-aminoethoxydiphenyl borate, markedly reduced the stimulatory effect of PACAP on [Ca(2+)]i. Furthermore, addition of the calcium chelator, EGTA, or exposure of cells to the non-selective Ca(2+) channel blocker, NiCl2, significantly attenuated the PACAP-evoked [Ca(2+)]i increase. Preincubation of granule neurons with the N-type Ca(2+) channel blocker, ω-conotoxin GVIA, decreased the PACAP-induced [Ca(2+)]i response, whereas the L-type Ca(2+) channel blocker, nifedipine, and the P- and Q-type Ca(2+) channel blocker, ω-conotoxin MVIIC, had no effect. Altogether, these findings indicate that PACAP, acting through PAC1 receptors, provokes an increase in [Ca(2+)]i in granule neurons, which is mediated by both mobilization of calcium from IP3-sensitive intracellular stores and activation of N-type Ca(2+) channel. Some of the activities of PACAP on proliferation, survival, migration, and differentiation of cerebellar granule cells could thus be mediated, at least in part, through these intracellular and/or extracellular calcium fluxes.
... Also, grafted neural stem cells exhibit spontaneous Ca 2+ activity that depends on gap junctions (38). Moreover, different patterns of spontaneous activity has been reported in regions of the developing visual cortex (39), and amplitude and frequency of Ca 2+ oscillations were correlated positively with the rate of neuronal migration (25,26). Our findings show that the spontaneous Ca 2+ activities in each cell are not uncorrelated, independent cell signals, but rather highly ordered signaling events creating small-world networks that follow a scalefree topology. ...
Significance
Synchronized activity among groups of interconnected cells is essential for diverse functions in the brain. Most studies on neuronal networks have been performed in the mature brain when chemical synapses have been established. However, less is known about networking during embryonic development. We have studied neural progenitors and found that they form gap junction-mediated small-world networks, which, via electrical depolarization, drive spontaneous calcium activity to stimulate cell proliferation. Our data underscore the critical role of intricate cell signaling during embryonic development and show that complex networks of immature cells exist in the brain before birth.
... Nearly all markers in the model lay within or near genes with known functions in aging-related conditions, including Alzheimer's disease, cancer, tissue degradation, DNA damage, and oxidative stress. By way of example, two markers lay within the gene somatostatin (SST), a key regulator of endocrine and nervous system function (Yacubova and Komuro, 2002). SST is known to decline with age and has been linked to Alzheimer's disease (Saito et al., 2005). ...
The ability to measure human aging from molecular profiles has practical implications in many fields, including disease prevention and treatment, forensics, and extension of life. Although chronological age has been linked to changes in DNA methylation, the methylome has not yet been used to measure and compare human aging rates. Here, we build a quantitative model of aging using measurements at more than 450,000 CpG markers from the whole blood of 656 human individuals, aged 19 to 101. This model measures the rate at which an individual's methylome ages, which we show is impacted by gender and genetic variants. We also show that differences in aging rates help explain epigenetic drift and are reflected in the transcriptome. Moreover, we show how our aging model is upheld in other human tissues and reveals an advanced aging rate in tumor tissue. Our model highlights specific components of the aging process and provides a quantitative readout for studying the role of methylation in age-related disease.
... Griffiths et al. (1977) first suggested that SST might play a role within the CNS that extends beyond the hypothalamic-anterior pituitary axis. Expression of SST and its receptors is highest during development of the cerebellum (Inagaki et al., 1989) and their downregulation coincides with the development of lobulation and the onset of granule cell migration from the external granular layer (Gonzalez et al., 1988): indeed, one role of somatostatin in the developing cerebellum appears to be in controlling the speed of migrating cerebellar granule cells (Yacubova and Komuro, 2002). ...
The object of this review is to assemble much of the literature concerning Purkinje cell death in cerebellar pathology and to relate this to what is now known about the complex topography of the cerebellar cortex. A brief introduction to Purkinje cells, and their regionalization is provided, and then the data on Purkinje cell death in mouse models and, where appropriate, their human counterparts, have been arranged according to several broad categories--naturally-occurring and targeted mutations leading to Purkinje cell death, Purkinje cell death due to toxins, Purkinje cell death in ischemia, Purkinje cell death in infection and in inherited disorders, etc. The data reveal that cerebellar Purkinje cell death is much more topographically complex than is usually appreciated.
... However, knowledge about which signalling pathway(s) is affected by 9acGD3 remains speculative. As the migration of neural progenitor cells has also been shown to be dependent on intracellular calcium transients (Komuro and Rakic, 1993, 1998 Yacubova and Komuro, 2002; Scemes et al., 2003; Kumada and Komuro, 2004; Agresti et al., 2005b; Agresti et al., 2005a; Striedinger et al., 2007 ), we evaluated whether the interference of 9acGD3- mediated neuronal migration affected Ca 2+ signalling in GCPs derived from postnatal cerebellar explants. Here, we show for the first time that in mouse cerebellar neuroblasts, immunoblockade of 9acGD3 or the lack of this ganglioside reduce GCP migration rate and the frequency of P2Y 1 R (P2Y 1 receptor)-mediated spontaneous calcium oscillations . ...
Previous studies indicated that a ganglioside 9-O-acetyl GD3 (9acGD3) antibody (the Jones antibody) reduces granule cell progenitor (GCP) migration in vitro and in vivo. We here investigated, using cerebellar explants of post-natal day (P) 6 mice, the mechanism by which 9acGD3 reduces GCP migration. We found that immunoblockade of the ganglioside with the Jones antibody or the lack of GD3 synthase reduced GCP in vitro migration and the frequency of Ca2+ oscillations. Immunocytochemistry and pharmacological assays indicated that GCPs expressed P2Y1 receptors and that deletion or blockade of these receptors decreased the migration rate of GCPs and the frequency of Ca2+ oscillations. The reduction in P2Y1 -mediated calcium signals seen in Jones-treated and GD3 synthase-null GCPs were paralleled by P2Y1R internalization. We conclude that 9acGD3 controls GCP migration by influencing P2Y1R cellular distribution and function.
... The somatostatin system subserves neuromodulatory roles in the brain, influencing motor activity, sleep, sensory processes, and cognitive functions. Sst expression has been found altered in bipolar disorder [39] and shown to control the migration of developing neurons [40]. A deficiency of mature BDNF and its receptor TrkB has been implicated in increased anxiety-related behavior and decreased neuronal complexity of hippocampal neurons [31,41]. ...
MAP kinase signaling has been implicated in brain development, long-term memory, and the response to antidepressants. Inducible Braf knockout mice, which exhibit protein depletion in principle forebrain neurons, enabled us to unravel a new role of neuronal MAPK signaling for emotional behavior. Braf mice that were induced during adulthood showed normal anxiety but increased depression-like behavior, in accordance with pharmacological findings. In contrast, the inducible or constitutive inactivation of Braf in the juvenile brain leads to normal depression-like behavior but decreased anxiety in adults. In juvenile, constitutive mutants we found no alteration of GABAergic neurotransmission but reduced neuronal arborization in the dentate gyrus. Analysis of gene expression in the hippocampus revealed nine downregulated MAPK target genes that represent candidates to cause the mutant phenotype.
Our results reveal the differential function of MAPK signaling in juvenile and adult life phases and emphasize the early postnatal period as critical for the determination of anxiety in adults. Moreover, these results validate inducible gene inactivation as a new valuable approach, allowing it to discriminate between gene function in the adult and the developing postnatal brain.
... The frequency and mode of CGC migration differs among the cerebellar cortical layers (Komuro and Yacubova, 2003). The uniform impairment induced by MeHg is unlike manipulation of specific neurotrophic factors such as somatostatin, to which migration responds in a stage-specific manner (Yacubova and Komuro, 2002). ...
... During the last 2 decades, real-time observation of cell movement demonstrated that granule cells display a distinct mode, tempo, and rate of migration as they traverse different cortical layers (13)(14)(15)(16)(17). It became apparent that granule cell migration is controlled by the orchestrated activity of multiple molecular events at the right time and right place, including pathway selection, activation of specific receptors and channels, and assembly and disassembly of cytoskeletal components (18)(19)(20)(21)(22). However, the question of how natural environmental stimuli are involved in controlling granule cell migration has been poorly understood. ...
The role of genetic inheritance in brain development has been well characterized, but little is known about the contributions of natural environmental stimuli, such as the effect of light-dark cycles, to brain development. In this study, we determined the role of light stimuli in neuronal cell migration to elucidate how environmental factors regulate brain development. We show that in early postnatal mouse cerebella, granule cell migration accelerates during light cycles and decelerates during dark cycles. Furthermore, cerebellar levels of insulin-like growth factor 1 (IGF-1) are high during light cycles and low during dark cycles. There are causal relationships between light-dark cycles, speed of granule cell migration, and cerebellar IGF-1 levels. First, changes in light-dark cycles result in corresponding changes in the fluctuations of both speed of granule cell migration and cerebellar IGF-1 levels. Second, in vitro studies indicate that exogenous IGF-1 accelerates the migration of isolated granule cells through the activation of IGF-1 receptors. Third, in vivo studies reveal that inhibiting the IGF-1 receptors decelerates granule cell migration during light cycles (high IGF-1 levels) but does not alter migration during dark cycles (low IGF-1 levels). In contrast, stimulating the IGF-1 receptors accelerates granule cell migration during dark cycles (low IGF-1 levels) but does not alter migration during light cycles (high IGF-1 levels). These results suggest that during early postnatal development light stimuli control granule cell migration by altering the activity of IGF-1 receptors through modification of cerebellar IGF-1 levels.
... Somatostatin is a pleiotropic hormone, exerting a variety of systemic effects, including control of hormone secretion and influencing the proliferation, motility and development of a wide variety of cells (8)(9)(10). Somatostatin has also been shown to act as a chemoattractant for hematopoietic progenitor cells, HOC, and immature neurons (11)(12)(13). Physiological effects of somatostatin are mediated through a family of seven transmembrane spanning Gprotein coupled receptors (GPCR) (8). Increasing evidence has shown that the distant effects on cell response elicited by the individual receptor types were correlated with activation of the various intracellular signaling pathways (14). ...
Somatostatin is a pleiotropic peptide, exerting a variety of effects through its receptor subtypes. Recently, somatostatin has been shown to act as a chemoattractant for haematopoietic progenitor cells and hepatic oval cells (HOC) via receptor subtype 2 and subtype 4 (SSTR4) respectively.
We investigated the in vivo effect of somatostatin/SSTR4 on HOC migration in the injured liver model of rats and the type of signalling molecules associated with the chemotactic function.
Migration assay, HOC transplantation and phosphatidylinositol-3-kinase (PI3K) signalling were assessed with or without somatostatin and an analogue of somatostatin (TT232) that specifically binds to SSTR4.
TT232 was shown to have an antimigratory action on HOC induced by somatostatin in vitro. In HOC transplantation experiments, a lower number of donor-derived cells were detected in TT232-treated animals, as compared with control animals. Activation of PI3K was observed in HOC exposed to somatostatin, and this activation was suppressed by either SSTR4 antibody or TT232-pretreatment. In addition, a PI3K inhibitor abrogated the motility of HOC.
Together, these data suggest that somatostatin stimulates the migration of HOC within injured liver through SSTR4, and this action appears to be mediated by the PI3K pathway.
... The spontaneous Ca 2+ transients in migrating granule cells are mediated by NMDA receptors and by N-type Ca 2+ VDCCs [10,34]. Other agonists that can trigger an elevation in [Ca 2+ ] i involved in motility control are the neurotransmitter GABA, that exerts an excitatory action in immature cells due to the high intracellular Cl -concentration, the neuropeptide somatostatin that influences Ca 2+ fluctuations in a stage-dependent manner, and neurotrophins , like Brain Derived Neurotrophic Factor [13,434445. The ErbB4 receptor, like other members of the ErbB family [46,47] , upon ligand activation could elicit calcium release from intracellular stores and calcium influx. ...
A number of studies have separately shown that the neuregulin1 (NRG1)/ErbB4 system and NMDA-type glutamate receptors (NMDARs) are involved in several aspects of neuronal migration. In addition, intracellular calcium fluctuations play central roles in neuronal motility. Stable expression of the tyrosine kinase receptor ErbB4 promotes migratory activity in the neural progenitor cell line ST14A upon NRG1 stimulation. In this work we analyzed the potential interactions between the NRG1/ErbB4 system and NMDARs in the ST14A migratory process as well as its calcium dependence.
RT-PCR studies have shown that both native ST14A cells (non-expressing ErbB4), as well as ErbB4-transfected cells express low levels of a restricted number of NMDAR subunits: NR1, NR2C, NR2D and NR3B. The resulting NMDAR would form Ca(2+) channels characterized by low Mg(2+)-sensitivity and low Ca(2+)-permeability, generating small, long-lasting currents. Ca(2+)-imaging experiments showed slow [Ca(2+)](i) increases in 45% of the cells following 8 μM NMDA stimulation. Basal migration of ErbB4-transfected ST14A cells was unaffected by 18 hrs NMDA incubation. However, over the same incubation time, NMDA was able to significantly enhance NRG1-induced migration. Pre-incubation with the intracellular calcium chelator BAPTA-AM reduced both NRG1- and NRG1/NMDA-stimulated migration, suggesting the involvement of Ca(2+) in these processes. NRG1 stimulation of ErbB4-transfected ST14A cells induced a sustained, long-lasting increase in [Ca(2+)](i), in 99% of the cells. These intracellular Ca(2+) signals could be ascribed to both release from intracellular stores and influx from the extracellular medium trough a mechanism of store-operated calcium entry (SOCE). Short-time co-incubation of NMDA and NRG1 did not substantially modify the NRG1-induced intracellular calcium signals.
In summary, NRG1 stimulation of the ErbB4 receptor exerts a sustained [Ca(2+)](i) increase in ST14A neural progenitors; NRG1-induced migration is Ca(2+)-dependent and can be positively modulated by activation of the NMDA receptor.
... NT cell bodies in this region are negligible (Mai et al., 1987;Zech et al., 1986) 7.4.2 Somatostatin-SST is found in developing neurons (Le Verche et al., 2009;Yacubova and Komuro, 2002) and is also a potent neuromodulator (Epelbaum et al., 1994). In the monkey PL, immunoreactivity for biologically active SST peptides, SS14 and SS28, is found in both cell bodies and fibers in moderate to high densities, particularly in caudal sections of the PL (Amaral et al., 1989;McDonald et al., 1995). ...
The primate amygdala is composed of multiple subnuclei that play distinct roles in amygdala function. While some nuclei have been areas of focused investigation, others remain virtually unknown. One of the more obscure regions of the amygdala is the paralaminar nucleus (PL). The PL in humans and non-human primates is relatively expanded compared to lower species. Long considered to be part of the basal nucleus, the PL has several interesting features that make it unique. These features include a dense concentration of small cells, high concentrations of receptors for corticotropin releasing hormone and benzodiazepines, and dense innervation of serotonergic fibers. More recently, high concentrations of immature-appearing cells have been noted in the primate PL, suggesting special mechanisms of neural plasticity. Following a brief overview of amygdala structure and function, this review will provide an introduction to the history, embryology, anatomical connectivity, immunohistochemical and cytoarchitectural properties of the PL. Our conclusion is that the PL is a unique subregion of the amygdala that may yield important clues about the normal growth and function of the amygdala, particularly in higher species.
... In addition, neuronostatin and somatostatin have some similar physiological functions. For example, somatostatin also decreases food intake [42], increases mean arterial pressure [6,38], depresses cardiac contractile [40] and involves in neuronal migration in the cerebellum [52]. Despite the ratios are variable in different tissues, neuronostatin and somatostatin are widely expressed in similar tissues [40]. ...
Neuronostatin, a recently discovered endogenous bioactive peptide, was encoded by pro-mRNA of somatostatin that contributes to modulation of nociception. However, nociceptive effect of neuronostatin is still not fully known. The aim of this study was to evaluate effect of neuronostatin on nociception and elucidate its possible mechanism of action. Intracerebroventricular (i.c.v.) administration of neuronostatin (0.3, 3, 6, 12nmol/mouse) produced a dose- and time-related antinociceptive effect in the tail immersion assay in mice, an acute pain model. The antinociceptive effect of neuronostatin was significantly antagonized by naloxone, and was strongly inhibited by co-injection with β-funaltrexamine or nor-binaltorphimine, but not by naltrindole. Also, melanocortin 3/4 receptor antagonist, SHU9119, completely blocked the effect of neuronostatin. These data indicated the involvement of both μ- and κ-opioid receptors and central melanocortin system in the analgesic response induced by neuronostatin. In addition, neuronostatin (6nmol, i.c.v.) increased c-Fos protein expression in the periaqueductal gray (PAG) and the nucleus raphe magnus (NRM) that have a pivotal role in regulating descending pain pathways. Taken together, this study is the first to reveal that neuronostatin produces antinociceptive effect via opioid and central melanocortin systems, which is associated with an increase in neuronal activity the PAG and NRM.
... Apart from the hypothalamic locations, STT has a wide distribution in other brain regions such as the amygdala, preoptic area, hippocampus, striatum, cerebral cortex, olfactory regions, and brainstem, where it acts as a neurotransmitter or neuromodulator (Viollet et al., 2008). STT and its receptors have also been implicated in brain development (Yacubova and Komuro, 2002; Le Verche et al., 2009). ...
The hypothalamus comprises alar, basal, and floor plate developmental compartments. Recent molecular data support a rostrocaudal subdivision into rostral (terminal) and caudal (peduncular) halves. In this context, the distribution of neuronal populations expressing somatostatin (Sst) mRNA was analyzed in the developing mouse hypothalamus, comparing with the expression pattern of the genes Orthopedia (Otp), Distal-less 5 (Dlx5), Sonic Hedgehog (Shh), and Nk2 homeobox 1 (Nkx2.1). At embryonic day 10.5 (E10.5), Sst mRNA was first detectable in the anterobasal nucleus, a Nkx2.1-, Shh-, and Otp-positive basal domain. By E13.5, nascent Sst expression was also related to two additional Otp-positive domains within the alar plate and one in the basal plate. In the alar plate, Sst-positive cells were observed in rostral and caudal ventral subdomains of the Otp-positive paraventricular complex. An additional basal Sst-expressing cell group was found within a longitudinal Otp-positive periretromamillary band that separates the retromamillary area from tuberal areas. Apart of subsequent growth of these initial populations, at E13.5 and E15.5 some Sst-positive derivatives migrate tangentially into neighboring regions. A subset of cells produced at the anterobasal nucleus disperses ventralward into the shell of the ventromedial hypothalamic nucleus and the arcuate nucleus. Cells from the rostroventral paraventricular subdomain reach the suboptic nucleus, whereas a caudal contingent migrates radially into lateral paraventricular, perifornical, and entopeduncular nuclei. Our data provide a topologic map of molecularly defined progenitor areas originating a specific neuron type during early hypothalamic development. Identification of four main separate sources helps to understand causally its complex adult organization.
... [25]. Another neuropeptide, somatostatin, also affects migration of granule cells by inhibiting the cAMP signalling pathway [26] and reduces the effect of PACAP [23]; moreover, alteration of the cAMP/PKA system affects motility and chemotaxis of various other cells types [27,28]. More recently, the small GTPase protein Rap via the cAMP/Epac1 pathway has been found to play a crucial role as a negative regulator of migration in epithelial cells and in ovarian tumor cells [29,30]. ...
This study was aimed at characterizing the effect of purinergic transmission on migration of embryonic ciliary ganglion satellite glial cells. Application of adenosine significantly decreased the rate of migration of glial cells whereas no differences were observed in the presence of ATP. The A(2B) receptor antagonist reverted this action, but application of an A(2A) receptor antagonist or a cAMP-protein kinase inhibitor had no effect on the agonist's stimulation. Forskolin, which stimulates adenylate cyclase activity, and the cAMP analogue 8-CPT-2'-O-Me-cAMP, which selectively activates the guanine exchange factor Epac1, mimicked the effect of adenosine. In addition, intracellular calcium measurements studies revealed that application of either adenosine or ATP induced an increase in [Ca(2+)]i and that the adenosine-induced [Ca(2+)]i response was due to Ca(2+) entry and was blocked by an A(2A) receptor antagonist, SCH 58261, or by high Gd(3+) concentrations. Furthermore, forskolin, but not 8-CPT-2'-O-Me-cAMP, activated the Ca(2+) entry which was blocked by Gd(3+) and was independent of cAMP-protein kinase activity. These results demonstrate the involvement of purinergic P1 signalling in the regulation of cellular migration, and point to the importance of adenosine as a negative modulator of migration of peripheral developing glial cells and as an activator of Ca(2+) entry.
Transient expression of somatostatin (SST) has been observed in the olfactory epithelium (OE) and nerves of chick embryos. Intense expression of SST in these regions on embryonic days (E) 5–8 coincides with the migration of neurons producing gonadotropin‐releasing hormone (GnRH) from the OE to the forebrain (FB), suggesting that SST plays a role in the development of GnRH neurons. Using in ovo electroporation of small interfering RNA, we found that the suppression of SST mRNA in the olfactory placode (OP) of E3.5 chick embryos significantly reduced the number of GnRH and Islet‐1‐immunoreactive neurons in the nasal region without affecting the entry of GnRH neurons into the FB at E5.5–6. SST knockdown did not lead to changes in the number of apoptotic, proliferating, or HuC/D‐positive neuronal cells in the OE; therefore, it is possible that SST is involved in the neurogenesis/differentiation of GnRH neurons and OP‐derived GnRH‐negative migratory neurons. In whole OP explant cultures, we also found that SST or its analog octreotide treatment significantly increased the number of migratory GnRH neurons and the migratory distance from the explants. The co‐application of an SST antagonist blocked the octreotide‐induced increase in the number of GnRH neurons. Furthermore, the fasciculation of polysialylated neural cell adhesion molecule‐immunoreactive fibers emerging from the explants was dependent on octreotide. Taken together, our results provide evidence that SST exerts facilitatory effects on the development of neurons expressing GnRH or Islet‐1 and on GnRH neuronal migration, in addition to olfactory‐related fiber fasciculation.
Neurogenesis persists throughout life in the hippocampi of all mammals, including humans. In the healthy hippocampus, relatively quiescent Type-1 neural stem cells (NSCs) can give rise to more proliferative Type-2a neural progenitor cells (NPCs), which generate neuronal-committed Type-2b NPCs that mature into Type-3 neuroblasts. Many Type-3 neuroblasts survive and mature into functionally integrated granule neurons over several weeks. In kindling models of epilepsy, neurogenesis is drastically upregulated and many new neurons form aberrant connections that could support epileptogenesis and/or seizures. We have shown that sustained vector-mediated hippocampal somatostatin (SST) expression can both block epileptogenesis and reverse seizure susceptibility in fully kindled rats. Here we test whether adeno-associated virus (AAV) vector-mediated sustained SST expression modulates hippocampal neurogenesis and microglial activation in fully kindled rats. We found significantly more dividing Type-1 NSCs and a corresponding increased number of surviving new neurons in the hippocampi of kindled versus sham-kindled rats. Increased numbers of activated microglia were found in the granule cell layer and hilus of kindled rats at both time points. After intrahippocampal injection with either eGFP or SST-eGFP vector, we found similar numbers of dividing Type-1 NSCs and -2 NPCs and surviving BrdU⁺ neurons and glia in the hippocampi of kindled rats. Upon observed variability in responses to SST-eGFP (2/4 rats exhibited Grade 0 seizures in the test session), we conducted an additional experiment. We found significantly fewer dividing Type-1 NSCs in the hippocampi of SST-eGFP vector-treated responder rats (5/13 rats) relative to SST-eGFP vector-treated non-responders and eGFP vector-treated controls that exhibited high-grade seizures on the test session. The number of activated microglia was upregulated in the GCL and hilus of kindled rats, regardless of vector treatment. These data support the hypothesis that sustained SST expression exerts antiepileptic effects potentially through normalization of neurogenesis and suggests that abnormally high proliferating Type-1 NSC numbers may be a cellular mechanism of epilepsy.
The cerebellum is a brain structure involved in motor and cognitive functions. The development of the cerebellar cortex (the external part of the cerebellum) is under the control of numerous factors. Among these factors, neuropeptides including PACAP or somatostatin modulate the survival, migration and/or differentiation of cerebellar granule cells. Interestingly, such peptides contributing to cerebellar ontogenesis usually exhibit a specific transient expression profile with a low abundance at birth, a high expression level during the developmental processes, which take place within the first two postnatal weeks in rodents, and a gradual decline toward adulthood. Thus, to identify new peptides transiently expressed in the cerebellum during development, rat cerebella were sampled from birth to adulthood, and analyzed by a semi-quantitative peptidomic approach. A total of 33 peptides were found to be expressed in the cerebellum. Among these 33 peptides, 8 had a clear differential expression pattern during development, 4 of them i.e. cerebellin 2, nociceptin, somatostatin and VGF [353-372], exhibiting a high expression level during the first two postnatal weeks followed by a significative decrease at adulthood. A focus by a genomic approach on nociceptin, confirmed that its precursor mRNA is transiently expressed during the first week of life in granule neurons within the internal granule cell layer of the cerebellum, and showed that the nociceptin receptor is also actively expressed between P8 and P16 by the same neurons. Finally, functional studies revealed a new role for nociceptin, acting as a neurotrophic peptide able to promote the survival and differentiation of developing cerebellar granule neurons.
The present review examines various aspects of the developmental expression of neuropeptides and of their receptors in mammalian retinas, emphasizing their possible roles in retinal maturation. Different peptidergic systems have been investigated with some detail during retinal development, including substance P (SP), somatostatin (SRIF), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), neuropeptide Y (NPY), opioid peptides and corticotrophin-releasing factor (CRF). Overall, the developmental expression of most peptides is characterized by early appearance, transient features and achievement of the mature pattern at the time of eye opening. Concerning possible developmental actions of neuropeptides, recent studies imply a role of SP in the modulation of cholinergic neurotransmission in early postnatal rabbit retinas, when cholinergic cells participate in the retinal spontaneous waves of activity. In addition, the presence of transient SRIF expressing ganglion cells and recent observations in SRIF receptor knock-out mice indicate variegated roles of this peptide in the development of the retina and of retinofugal projections. Furthermore, VIP and PACAP exert protective and growth-promoting actions that may sustain retinal neurons during their development, and opioid peptides may control cell proliferation in the developing retina. Finally, a peak in the expression of certain peptides, including VIP, NPY and CRF, is present around the time of eye opening, when the retina begins the analysis of structured visual information, suggesting important roles of these peptides during this delicate phase of retinal development. In summary, although the physiological actions of peptides during retinal development are far from being clarified, the data reviewed herein indicate promising perspectives in this field of study.
Cell migration plays an essential role in tissue formation during development, most prominently in complex organs such as the nervous system. Thus, the extraordinary degree of organization of the vertebrate brain reflects the complexity of the migratory movements required to generate it. This article summarizes basic mechanisms controlling neuronal migration, both during development and in the adult brain, with a focus on the mammalian cerebral cortex. Special emphasis is also made on new ideas suggesting that evolution may have had an impact on this basic cellular process and transformed brain organization in different vertebrate species.
In the developing cerebellum, granule cells migrate from their birth place to their final destination. The active translocation of granule cells is essential for the formation of cerebellar cortical layers and their proper differentiation. This chapter will review (1) how granule cells migrate from their origin to their resident destinations in the developing cerebellum, (2) the mechanisms involved in normal and abnormal migration of granule cells, and (3) the mechanisms underlying the differentiation of granule cells.
In the developing brain, immature neurons migrate from their sites of origin to their final destination, where they reside for the rest of their lives. This active movement of immature neurons is essential for the formation of normal neuronal cytoarchitecture and proper differentiation. Deficits in migration result in the abnormal development of the brain, leading to a variety of neurological disorders. A myriad of extracellular guidance molecules and intracellular effector molecules is involved in controlling the migration of immature neurons in a cell type, cortical layer and birth-date-specific manner. To date, little is known about how extracellular guidance molecules transfer their information to the intracellular effector molecules, which regulate the migration of immature neurons. In this article, to fill the gap between extracellular guidance molecules and intracellular effector molecules, using the migration of cerebellar granule cells as a model system of neuronal cell migration, we explore the role of second messenger signaling (specifically Ca2+ and cyclic nucleotide signaling) in the regulation of neuronal cell migration. We will, first, describe the cortical layer-specific changes in granule cell migration. Second, we will discuss the roles of Ca2+ and cyclic nucleotide signaling in controlling granule cell migration. Third, we will present recent studies showing the roles of Ca2+ and cyclic nucleotide signaling in the deficits in granule cell migration in mouse models of fetal alcohol spectrum disorders and fetal Minamata disease. © 2014 Wiley Periodicals, Inc. Develop Neurobiol, 2014
Schwann cells migrate along axons before initiating myelination during development and their migration facilitates peripheral nerve regeneration after injury. Axon guidance molecule Slit-2 is highly expressed during peripheral development and nerve regeneration; however, whether Slit-2 regulates the migration of Schwann cells remains a mystery. Here we show that Slit-2 receptor Robo-1 and Robo-2 were highly expressed in Schwann cells in vitro and in vivo. Using three distinct migration assays, we found that Slit-2 repelled the migration of cultured Schwann cells. Furthermore, frontal application of a Slit-2 gradient to migrating Schwann cells first caused the collapse of leading front, and then reversed soma translocation of Schwann cells. The repulsive effects of Slit-2 on Schwann cell migration depended on a Ca(2+) signaling release from internal stores. Interestingly, in response to Slit-2 stimulation, the collapse of leading front required the loss of F-actin and focal adhesion, whereas the subsequent reversal of soma translocation depended on RhoA-Rock-Myosin signaling pathways. Taken together, we demonstrate that Slit-2 repels the migration of cultured Schwann cells through RhoA-Myosin signaling pathways in a Ca(2+) -dependent manner.
Migration of neurons and neuronal precursors from the site of origin to their final location is a key process in the development of the nervous system and in the correct organization of neuronal structures and circuits. Different modes of migration (mainly radial and tangential) have been described in the last 40 years; for these, as for motility processes involving other cellular types, calcium signalling plays a key role, with influx from the extracellular medium representing the main mechanism, and a more delimited but specific role played by release from intracellular stores. Deciphering the involvement of the different calcium influx pathways has been a major task for cellular neurobiologists, and the availability or lack of reliable and selective pharmacological tools has represented the main limiting factor. This review addresses the strategies employed to investigate the role of voltage-dependent calcium channels and of neurotransmitter activated channels, either calcium permeable or not, that directly or indirectly can elicit cytosolic calcium increases; in addition, reference to recent findings on the involvement of other families of calcium permeable channels (such as the transient receptor potential superfamily) is presented. Finally, a brief description of the present - and limited - knowledge of the perturbations of calcium signalling involved in neuronal migration pathologies is provided.
During the past 40 years, somatostatin (SST) has been a subject of intensive research. Apart from its substantial role in the neuroendocrine system, due to its dense localization in various areas in the brain, its functions as a neuromodulator have also been thoroughly investigated. Increasing evidence suggests that SST plays a crucial role in memory and cognition. Synthetic forms, biologically active peptide sequences, SST receptor agonists and SST depleting agents have been applied in animal models and in human studies of a number of neuropsychiatric disorders. The translation of experimental data into clinical use could provide novel therapies in neurodegenerative disorders involving cognitive dysfunctions. However in view of the controversial data reported concerning the different roles of the SST receptor subtypes, and the lack of SST analogs that are able to cross diffusion barriers and act selectively at these receptor subtypes, broader clinical use of SST analogs as cognitive enhancers is limited. This review covers the whole range of available experimental results relating to the behavioral effects of SST, and highlights the potential for further investigations.
We show that alpha3 integrin mutation disrupts distinct aspects of neuronal migration and placement in the cerebral cortex. The preplate develops normally in alpha3 integrin mutant mice. However, time lapse imaging of migrating neurons in embryonic cortical slices indicates retarded radial and tangential migration of neurons, but not ventricular zone-directed migration. Examination of the actin cytoskeleton of alpha3 integrin mutant cortical cells reveals aberrant actin cytoskeletal dynamics at the leading edges. Deficits are also evident in the ability of developing neurons to probe their cellular environment with filopodial and lamellipodial activity. Calbindin or calretinin positive upper layer neurons as well as the deep layer neurons of alpha3 integrin mutant mice expressing EGFP were misplaced. These results suggest that alpha3beta1 integrin deficiency impairs distinct patterns of neuronal migration and placement through dysregulated actin dynamics and defective ability to search and respond to migration modulating cues in the developing cortex.
Ectopic neurons are often found in the brains of fetal alcohol spectrum disorders (FASD) and fetal alcohol syndrome (FAS) patients, suggesting that alcohol exposure impairs neuronal cell migration. Although it has been reported that alcohol decreases the speed of neuronal cell migration, little is known about whether alcohol also affects the turning of neurons. Here we show that ethanol exposure inhibits the turning of cerebellar granule cells in vivo and in vitro. First, in vivo studies using P10 mice demonstrated that a single intraperitoneal injection of ethanol not only reduces the number of turning granule cells but also alters the mode of turning at the EGL-ML border of the cerebellum. Second, in vitro analysis using microexplant cultures of P0-P3 mouse cerebella revealed that ethanol directly reduces the frequency of spontaneous granule cell turning in a dose-dependent manner. Third, the action of ethanol on the frequency of granule cell turning was significantly ameliorated by stimulating Ca(2+) and cGMP signaling or by inhibiting cAMP signaling. Taken together, these results indicate that ethanol affects the frequency and mode of cerebellar granule cell turning through alteration of the Ca(2+) and cyclic nucleotide signaling pathways, suggesting that the abnormal allocation of neurons found in the brains of FASD and FSA patients results, at least in part, from impaired turning of immature neurons by alcohol.
Transient elevations of intracellular Ca2+ levels play critical roles in neuronal development, but such elevations have not been demonstrated in migrating neurons. Here, we show that the amplitude and frequency components of Ca2+ fluctuations are correlated positively with the rate of granule cell movement in cerebellar microexplant cultures. Moreover, depression of the amplitude and frequency components of Ca2+ fluctuations by blockade of Ca2+ influx across the plasma membrane results in a reversible retardation of cell movement. These results indicate that the combination of amplitude and frequency components of intracellular Ca2+ fluctuations may provide an intracellular signal controlling the rate of neuronal cell migration.
Somatostatin and somatostatin receptors are transiently expressed in the immature rat cerebellar cortex but virtually undetectable in the cerebellum of adults. Although somatostatin binding sites have been visualized during the postnatal period in the external granule cell layer, the type of cell that expresses somatostatin receptors has never been identified; thus, the potential function of somatostatin in the developing cerebellum remains unknown. In the present study, we have taken advantage of the possibility of obtaining a culture preparation that is greatly enriched in immature cerebellar granule cells to investigate the presence of somatostatin receptors and the effect of somatostatin on intracellular messengers on cerebellar neuroblasts in primary culture. Autoradiographic labeling revealed the occurrence of a high density of binding sites for radioiodinated Tyr-[D-Trp8]somatostatin-(1-14) on 1-day-old cultured immature granule cells. Saturation and competition studies showed the existence of a single class of high-affinity binding sites (Kd = 0.133 +/- 0.013 nM, Bmax = 3038 +/- 217 sites per cell). Somatostatin induced a dose-dependent inhibition of forskolin-evoked cAMP formation (ED50 = 10 nM), and this effect was prevented by preincubation of cultured immature granule cells with pertussis toxin. Somatostatin also caused a marked reduction of intracellular calcium concentration. These results show the presence of functionally active somatostatin receptors on immature granule cells. Our data suggest the possible involvement of somatostatin in the regulation of proliferation and/or migration of neuroblasts during the development of the cerebellar cortex.
Real-time examination of Dil-labeled, immature granule cells in cerebellar slice preparations reveals several temporal and cytological aspects of neuronal migration that have not been observed in previous in vivo or in vitro systems. Using confocal microscopy we have obtained evidence that rates of cell movement depend critically on the age of the cerebellum. Although there were considerable variations in the speed of individual cells, the average rate of cell migration increased systematically from 9.6 +/- 3.0 microns/hr in cerebella from 7-d-old mice to 18.0 +/- 2.9 microns/hr in cerebella from 13-d-old mice. Consequently, granule cells traversed the developing molecular layer within a relatively constant time period despite the doubling in width of the molecular layer during the second week of postnatal life. Granule cell movement was characterized by alternations of short stationary phases with movement in a forward or backward direction. The net displacement of a cell depended on the duration and frequency of these phases as well as on the speed of movement. Changes in the relative position of Dil crystals attached to the surface of granule cells suggested the existence of a complex topographical flow of plasma membrane during migration. Although a large portion of the plasma membrane seemed to move in register with the nucleus and surrounding cytoplasm, new membrane appeared to be incorporated primarily at the leading process. However, the pattern of membrane flow at the interface between migrating neurons and Bergmann glial fibers could not be determined, since these sites could not be labeled by Dil crystals. The present results are in harmony with the concept that multiple cellular/molecular mechanisms may be engaged in granule cell migration.
Among CNS neuronal populations, the cerebellar granule cell provides a simple model for analysing the molecular regulation of CNS neurogenesis. In this study, polyclonal antisera raised against immature granule cell precursors, purified from early postnatal mouse cerebellum, were used to isolate 39 unique cDNA clones from a lambda gt11 cDNA expression library made from the same cell population. Northern blot analysis revealed developmental stage and tissue-specific expression of 28 of the clones. In situ localization of mRNAs encoded by these novel cDNAs, as well as those encoding the axonal glycoprotein TAG-1 and the alpha 6 subunit of the GABAA receptor, reveal four distinct stages in cerebellar granule cell differentiation. The developmentally transient and spatially restricted expression of clones GC9 and GC44 identify a previously unrecognized step in cerebellar histogenesis.
Although numerous Ca2+ channels have been identified in cerebellar granule cells, their role in regulating excitability remained unclear. We therefore investigated the excitable response in granule cells using whole cell patch-clamp recordings in acute rat cerebellar slices throughout the time of development (P4-P21, n = 183), with the aim of identifying the role of Ca2+ channels and their activation mechanism. After depolarizing current injection, 46% of granule cells showed Ca2+ action potentials, whereas repetitive Na+ spikes were observed in an increasing proportion of granule cells from P4 to P21. Because Ca2+ action potentials were no longer observed after P21, they characterized an immature granule cell functional stage. Ca2+ action potentials consisted of an intermediate-threshold spike (ITS) activating at -60/-50 mV and sensitive to voltage inactivation and of a high-threshold spike (HTS), activating at above -30 mV and resistant to voltage inactivation. Both ITS and HTS comprised transient and protracted Ca2+ channel-dependent depolarizations. The Ca2+ action potentials could be activated synaptically by excitatory postsynaptic potentials, which were significantly slower and had a proportionately greater N-methyl-D-aspartate (NMDA) receptor-mediated component than those recorded in cells with fast repetitive Na+ spikes. The NMDA receptor current, by providing a sustained and regenerative current injection, was critical for activating the ITS, which was not self-regenerative. Moreover, NMDA receptors determined temporal summation of impulses during repetitive mossy fiber transmission, raising membrane potential into the range required for generating protracted Ca2+ channel-dependent depolarizations. The nature of Ca2+ action potentials was considered further using selective ion channel blockers. N-, L-, and P-type Ca2+ channels generated protracted depolarizations, whereas the ITS and HTS transient phase was generated by putative R-type channels (R(ITS) and R(HTS), respectively). R(HTS) channels had a higher activation threshold and were more resistant to voltage inactivation than R(ITS) channels. At a mature stage, most of the Ca2+-dependent effects depended on the N-type current, which promoted spike repolarization and regulated the Na+-dependent discharge frequency. These observations relate Ca2+ channel types with specific neuronal excitable properties and developmental states in situ. Synaptic NMDA receptor-dependent activation of Ca2+ action potentials provides a sophisticated mechanism for Ca2+ signaling, which might be involved in granule cell development and plasticity.
As postmitotic neurons migrate to their final destinations, they encounter different cellular microenvironments, but functional responses of migrating neurons to changes in local environmental cues have not been examined. In the present study, we used a confocal microscope on acute cerebellar slice preparations to examine real-time changes in the shape of granule cells, as well as the mode and rate of their migration as they transit different microenvironments. The rate of granule cell movement is fastest in the molecular layer, whereas their elongated somata and long leading processes remain in close contact with Bergmann glial fibers. Cell movement is slowest in the Purkinje cell layer after granule cells detach from the surface of Bergmann glia and the somata become transiently round, whereas the leading processes considerably shorten. Surprisingly, after entering the internal granular layer, granule cells re-extend both their somata and leading processes as they resume rapid movement independent of Bergmann glial fibers. In this last phase of migration, described here for the first time, most granule cells move radially for >100 micron (a distance comparable to that observed in the molecular layer) until they reach the deep strata of the internal granular layer, where they become rounded again and form synaptic contacts with mossy fiber terminals. These observations reveal that migrating neurons alter their shape, rate, and mode of movement in response to local environmental cues and open the possibility for testing the role of signaling molecules in cerebellar neurogenesis.
During neuronal differentiation and maturation, electrical excitability is essential for proper gene expression and the formation of synapses. The expression of ion channels is crucial for this process; in particular, voltage-gated K(+) channels function as the key determinants of membrane excitability. Previously, we reported that the A-type K(+) current (I(A)) and Kv4.2 K(+) channel subunit expression increased in cultured cerebellar granule cells with time. To examine the correlation between ion currents and the action potential, in the present study, we measured developmental changes of action potentials in cultured granule cells using the whole-cell patch-clamp method. In addition to an observed increment of I(A), we found that the Na(+) current also increased during development. The increase in both currents was accompanied by a change in the membrane excitability from the nonspiking type to the repetitive firing type. Next, to elucidate whether Kv4.2 is responsible for the I(A) and to assess the effect of Kv4 subunits on action potential waveform, we transfected a cDNA encoding a dominant-negative mutant Kv4.2 (Kv4.2dn) into cultured cells. Expression of Kv4.2dn resulted in the elimination of I(A) in the granule cells. This result demonstrates that members of the Kv4 subfamily are responsible for the I(A) in developing granule cells. Moreover, elimination of I(A) resulted in shortening of latency before the first spike generation. In contrast, expression of wild-type Kv4.2 resulted in a delay in latency. This indicates that appearance of I(A) is critically required for suppression of the excitability of granule cells during their maturation.
After their final mitosis, cerebellar granule cells remain in the external granular layer (EGL) for 20-48 hr before initiating their radial migration across the molecular layer (ML), but the significance of this latent period is not well understood. In the present study, we used a confocal microscope to examine morphogenetic changes and behavior of postmitotic granule cells restricted to the EGL in slice preparations of the postnatal mouse cerebellum. We found that, coincident with the extension of two uneven horizontal processes oriented parallel to the longitudinal axis of the folium, postmitotic granule cells start to migrate tangentially in the direction of the larger process. Interestingly, their morphology and the speed of cell movement change systematically with their position within the EGL. The rate of tangential cell movement is fastest (approximately 14.8 micrometer/hr) in the middle of the EGL, when cells have two short horizontal processes. As granule cells elongate their somata and extend longer horizontal processes at the bottom of the EGL, they move at a reduced rate (approximately 12.6 micrometer/hr). At the interface of the EGL and ML where cells migrate tangentially at the slowest rate (approximately 4.1 micrometer/hr), their somata round and then begin to extend couples of the descending processes into the ML. After the stationary period, granule cells abruptly extend a single vertical process and initiate the transition from tangential to radial migration, reshaping their rounded somata into a vertically elongated spindle. These observations suggest that tangential migration of granule cells within the EGL may provide the developmental mechanisms for their appropriate allocation across parasagittal compartments of the expanding cerebellar cortex.
I. Introduction SOMATOSTATIN [somatotropin release-inhibiting factor (SRIF)] is a 14-amino acid polypeptide that is widely distributed throughout the central nervous system and peripheral tissues (Ref. 1; reviewed in Refs. 2–4). It potently inhibits basal and stimulated secretion from a wide variety of endocrine and exocrine cells and functions as a neurotransmitter/neuromodulator in the central nervous system with effects on locomotor activity and cognitive functions (1–12). Somatostatin also has antiproliferative effects and may be an important hormonal regulator of cell proliferation and differentiation (Refs. 13–15 and reviewed in Ref. 16). The first evidence for somatostatin-like activity came from studies of Krulich et al. (17), reported in 1968, who while looking for GHRF described a factor in hypothalamic extracts that inhibited GH secretion from anterior pituitaries in culture. Based on the identification of this inhibitory activity, Krulich et al. (17) proposed that the secretion of GH was regul...
The neuropeptide somatostatin (SRIF) has diverse physiological actions in the brain and endocrine organs. A family of SRIF receptors has recently been cloned that may mediate the distinct biological effects of SRIF. These receptors have a high degree of amino acid sequence similarity among themselves, but their sequences are different from any other receptors, indicating that they represent a distinct neurotransmitter receptor subfamily. The availability of the cloned receptors will now allow for detailed structure-function analysis of SRIF receptors and will facilitate development of subtype-selective agonists and antagonists that could be useful in the treatment of central nervous system and endocrine disorders.
The distribution of [125I]SRIF-28 ([Leu8,d-Trp22,125I-Tyr25]somatostatin-28), [125I]204-090 ([Tyr3]octreotide) and [125I]CGP 23996 (c[Asu-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Tyr-Thr-Ser]) labelled recognition sites was studied by autoradiography in rat brain at embryonic day 18 (E 18) and postnatal day 5 (P 5). These results were compared with mRNA expression of somatostatin receptors SSTR1-5 (named sst1–5 now) as studied by in situ hybridization. [125I]SRIF-28, [125I]204-090 and [125I]CGP 23996 binding displayed different although partially overlapping distributions, and showed an increase between E 18 and P 5, which was less marked for [125I]204-090 binding. [125I]204-090 binding and sst2 receptor mRNA were similarly distributed, whereas [125I]CGP 23996 binding did not correlate with any single somatostatin receptor mRNA. The data suggest that most SRIF receptor subtypes in rat brain are present before birth, but evolve differently.
Analysis of neuronal migration in mouse cerebellar slice preparations by a laser scanning confocal microscope revealed that
postmitotic granule cells initiate their migration only after the expression of N-type calcium channels on their plasmalemmal
surface. Furthermore, selective blockade of these channels by addition of omega-conotoxin to the incubation medium curtailed
cell movement. In contrast, inhibitors of L- and T-type calcium channels, as well as those of sodium and potassium channels,
had no effect on the rate of granule cell migration. These results suggest that N-type calcium channels, which have been predominantly
associated with neurotransmitter release in adult brain, also play a transient but specific developmental role in directed
migration of immature neurons before the establishment of their synaptic circuits.
1. Somatotrophs from enzymatically dispersed anterior pituitary glands of rats, enriched to greater than 94% purity by density gradient centrifugation, were studied within 16 h of isolation using patch clamp recording methods in the conventional whole-cell and the perforated-patch configurations. 2. Rhythmic oscillations of membrane potential gave rise to action potentials in thirty-six of fifty-two cells studied with the perforated-patch technique. Membrane potential oscillated between approximately -70 mV and approximately -25 mV with an average frequency (mean +/- S.D.) of 0.9 +/- 0.9 s-1. 3. The current-voltage (I-V) relationship of cells was linear at negative potentials with outward rectification at potentials positive to -40 mV. Evidence that the outward current was due to K+ channels came from the deactivation tail currents, which reversed direction close to the K+ equilibrium potential (EK). The reversal potential shifted 60 mV per tenfold change of external K+ concentration ([K+]o), as expected for K+ current. 4. Suppression of outward current by tetraethylammonium (TEA) provided additional evidence for K+ current. Cd2+ reduced outward current, suggesting the presence of Ca(2+)-activated K+ conductance. 5. Depolarizing commands elicited transient inward Na+ current and a sustained Ca2+ current (ICa). ICa was recorded in isolation with Cs+ and TEA in the recording pipette and 10 mM-Ba2+ as the charge carrier. Activation of ICa began at approximately -40 mV, with peak inward current at 0 to +10 mV. The half-inactivation potential was approximately -35 mV. In addition, ICa was blocked by nifedipine. These characteristics indicate the presence of L-type Ca2+ channels in somatotrophs. 6. Somatostatin caused hyperpolarization and suppressed the spontaneous bursts of action potentials. Under voltage clamp, somatostatin activated an inwardly rectifying current that reversed direction near EK. When EK was altered by elevation of [K+]o, the reversal potential of the somatostatin-induced current shifted 55 mV per tenfold change of [K+]o, as predicted for a K+ current by the Nernst relation. The somatostatin-induced conductance (gK) was greater at more negative potentials, and the activation range shifted positive with elevation of [K+]o. 7. We conclude that freshly isolated rat somatotrophs possess Na+, Ca2+ and K+ currents. A large proportion of the cells exhibit spontaneous bursts of action potentials. Somatostatin activates an inwardly rectifying K+ conductance, causing hyperpolarization and cessation of spontaneous action potential activity, actions that would contribute to suppression of growth hormone release.
In order to study roles of the extracellular matrix (ECM) in the cerebellar granule cell migration, cerebellar microexplants of neonatal to postnatal 11-day-old mice were cultured on 3 kinds of substrata, poly-L-lysine (PL), PL/fibronectin and PL/laminin. A prominent outgrowth of small granule cells, which did not uptake GABA, was observed only on the PL/laminin substratum. The granule cells showed the following sequence of events: (1) Many polygonal undifferentiated cells migrated out from the microexplants. These blast cells differentiated into small bipolar neurons with long fine neurites which extended radially from the explants. (2) These cells then changed their orientation perpendicular to their radial neurites, by protruding a short process from the cell body at right angles. (3) Finally, cell bodies of these granule cells adhered to each other to form cell aggregates. Quantitative labelings by bromodeoxyuridine revealed that there were less mitotic cells in explants from the later postnatal cerebellar compared to the earlier postnatal ones. Anti-MAP2 immunoreactivity was localized in short perpendicular processes of the aggregated granule cells. Thus, this unique cell behavior exhibited on the PL/laminin substratum provides the first defined experimental system for studying the granule cell differentiation in vitro.
1. The effects of somatostatin and somatostatin analogues on a Ca2+ current from acutely isolated and short-term (24-48 h) cultured adult rat superior cervical ganglion (SCG) neurones were studied using the whole-cell variant of the patch-clamp technique. 2. [D-Trp8]Somatostatin (SOM) produced a rapid, reversible and concentration-dependent reduction of the Ca2+ current. Ca2+ current amplitude was reduced over the voltage range -15 to +40 mV with the greatest reduction occurring where the amplitude was maximal (ca +10 mV). In the presence of SOM, the Ca2+ current rising phase was slower and biphasic at potentials between 0 and +40 mV. 3. Application of 0.1 microM-SOM for greater than 10 s resulted in a desensitization of the response. During a 4 min application of 0.1 microM-SOM, Ca2+ current amplitude returned to about 90% of control. A second application of 0.1 microM-SOM produced less block than the initial application. 4. Concentration-response curves for SOM, somatostatin-14 (SOM-14) and somatostatin-28 (SOM-28) were fitted to a single-site binding isotherm. The concentrations producing half-maximal block and the maximal attainable blocks of the Ca2+ current for SOM, SOM-14 and SOM-28 were 3.3, 5.4 and 35 nM, respectively and 55, 51 and 54%, respectively. SOM-14 and SOM-28 slowed the Ca2+ current rising phase in a manner similar to that of SOM. Somatostatin-28 had no effect on the Ca2+ current at 1 microM. 5. The magnitude of the Ca2+ current block produced by 0.1 microM-SOM was not significantly altered in the presence of 1 microM-idazoxan, atropine, naloxone or the somatostatin antagonist aminoheptanoyl-Phe-D-Trp-Lys-O-benzyl-Thr. 6. Internal dialysis with solutions containing 500 microM-guanylyl-imidodiphosphate (Gpp(NH)p) or guanosine-5'-O-(3-thiotriphosphate)(GTP-gamma-S) decreased the Ca2+ current amplitude by 36 and 41%, respectively, and induced a biphasic rising phase in the Ca2+ current. Under these conditions, application of 0.1 microM-SOM produced significantly less block of Ca2+ current amplitude (7.1 and 14.7%, respectively) when compared with controls. 7. Internal dialysis with solutions containing 500 microM-guanosine-5'-O-(2-thiodiphosphate)(GDP-beta-S) had no significant effect on either the Ca2+ current amplitude or block produced by 0.1 microM-SOM. 8. Internal dialysis with solutions containing 500 microM-cyclic adenosine 3',5'-monophosphate (cyclic AMP) and 3-isobutyl-1-methylxanthine had no significant effect on either the Ca2+ current block produced by 0.1 microM-SOM or the Ca2+ current amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)
The distribution of somatostatin-immunoreactive (SOM-IR) elements in the cerebellar cortex of the rat has been studied at different stages of postnatal development (from birth to day 30) and in adult animals using immunohistochemistry. The results showed that in vermis of new born animals there are three main groups of SOM-IR structures within the cortex which subsequently spread along the Purkinje cell layer. In addition, both in the vermis and in the lateral lobes, numerous more evenly distributed SOM-positive cells and fibers could be seen. SOM-IR Golgi cells, Purkinje cells and climbing fibers could then be recognized during the subsequent developmental stages. In the vermal zone, SOM-IR Purkinje cells formed patches, which seemed to be part of a sagittal columnar or band-like organization. This was most obvious between days 5 and 21 of postnatal development. Subsequently there was a reduction in the number of immunoreactive Purkinje cells but a patchy disposition remained. In addition high numbers of SOM-IR Purkinje and Golgi cells and also climbing fibers were identified in the flocculus and paraflocculus at all stages of development studied, and they were also seen in the adult rats in these regions. In the lateral lobes expression of SOM-like immunoreactivity (LI) decreased and almost completely disappeared in adult animals. The present results demonstrate that a SOM or a SOM-LI peptide can be transiently detected in many Purkinje and Golgi cells in the cerebellar cortex, suggesting a role in events related to developmental processes. However, in some regions and structures SOM-LI can be seen also in adult animals.
We used in situ hybridization histochemistry to examine the postnatal development of the somatostatin (SRIF) synthesizing system in the cerebellum of rats. There are numerous hybridizing neurons from 1 to 9 days after birth. These occur throughout the cerebellum including the developing medulla and cortex except in the external granular cell layer. The lateral cerebellar nucleus also contains SRIF gene-containing cells. The intensity of the signals for SRIF mRNA in the cerebellum decreases with age. There is a drastic decrease in SRIF mRNA in the lateral cerebellar nucleus. SRIF cells cannot be detected in the lateral cerebellar nucleus of adult rats, whereas a small, yet significant number of SRIF cells are scattered in the cerebellar medulla. However, the cerebellum of adult rats still contains a significant number of labeled cells in the granular cell layer, although the intensity for SRIF mRNA decreases from 14 days after birth to adulthood. SRIF gene-expressing cells in the cerebellar cortex are located primarily in the granular cell layer and appear to correspond to Golgi cells judging from their characteristic features. These results are consistent with our previous immunohistochemical study on the decrease of SRIF immunoreactivity in the cerebellum of adult rats. These findings, together with a recent study of transient SRIF receptor-expressing cells in the developing cerebellum suggest that SRIF acts during cerebellar development.
Somatostatin and somatostatin receptors have not been identified in adult rat cerebellum. In contrast, during the development, somatostatin-containing neurons have been visualized in the deep layers of the cerebellum. The present study shows that during ontogenesis, somatostatin receptors are present in close association with the external granule cell layer of the cerebellum. No correlation was found between the location of immunoreactive somatostatin and the distribution of somatostatin receptors. The disappearance of somatostatin receptors, from postnatal day 13 to 23, was concomitant with the involution of the external germinal layer.
Somatostatin and its receptors are transiently expressed at a high level in the cerebellum around birth, before declining to adult levels by 2-3 weeks postnatally. We therefore investigated the neurotrophic effects of somatostatin (SS) on rat cerebellar granule cells in culture by measuring the percentage of cells with processes, the content of mRNA and protein for neurofilament (NF) and mRNA for glutaminase, and the number of viable cells (MTS assay). SS increased the percentage of cells with processes at 8 h after plating. After 1 day in vitro (DIV), SS caused a 2-fold increase in NF mRNA, and a 23% increase in NF protein. The mRNA increase was maximal at DIV1 whereas by DIV7 the NF protein content of control cells reached that of SS-treated cells. SS had no effect on glutaminase mRNA or on the number of viable neurons from either postnatal day 5 or 8 animals. These results demonstrated that SS has a neurotrophic effect on neurite production, including initiation of neurite outgrowth, but no effect on neuronal survival, cell proliferation, or phenotype differentiation (glutaminase expression), and support the possibility that SS plays a role in the differentiation of immature cerebellar granule cells during central nervous system development.
The temporal pattern of distribution of somatostatin receptor was investigated using the somatostatin analogue [125I]Tyr0-DTrp8-somatostatin14 as a ligand and compared with that of somatostatin immunoreactivity during early developmental stages in the spinal cord and the sensory derivatives in rat fetuses. Qualitative and quantitative analysis showed that somatostatin receptors were detected in a transient manner. In the neural tube, they were clearly associated with immature premigratory cells and with the developing white matter. During the time-period examined (from day 10.5 to 16.5), the disappearance of somatostatin receptors followed a ventro to dorsal gradient probably linked to the regression of the ventricular zone. In sensory derivatives, they were expressed in the forming ganglia and their central and peripheral nerves from embryonic day 12.5 to 16.5 inclusive, with a peak around day 14.5 and low levels observed at day 16.5. Competition experiments performed at embryonic day 14.5 demonstrated that somatostatin1-14, somatostatin1-28, and Octreotide displaced specific binding with nanomolar affinities while CGP 23996 was only active at micromalar doses. Such displacements are compatible with the SSTR2 and/or SSTR4 pharmacology. During the time period examined, some transient somatostatin immunoreactive cell bodies and fibers were detected in the neural tube and in the sensory derivatives. These results demonstrate the existence, in neuronal derivatives, of a complex temporal and anatomical pattern of expression of somatostatin receptors, from the SSTR2/SSTR4 subtype(s), and somatostatin immunoreactivity. It appears that the transient expression of somatostatin receptors and/or somatostatin immunoreactivity characterizes critical episodes in the development of a cohort of neurons; a fact that unequivocally reinforces the notion that somatostatin plays a fundamental role during neurogenesis in vertebrates.
The N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor is essential for neuronal differentiation and establishment
or elimination of synapses in a developing brain. The activity of the NMDA receptor has now been shown to also regulate the
migration of granule cells in slice preparations of the developing mouse cerebellum. First, blockade of NMDA receptors by
specific antagonists resulted in the curtailment of cell migration. Second, enhancement of NMDA receptor activity by the removal
of magnesium or by the application of glycine increased the rate of cell movement. Third, increase of endogenous extracellular
glutamate by inhibition of its uptake accelerated the rate of cell migration. These results suggest that NMDA receptors may
play an early role in the regulation of calcium-dependent cell migration before neurons reach their targets and form synaptic
contacts.
The neuropeptide somatostatin (SRIF) has diverse physiological actions in the brain and endocrine organs. A family of SRIF receptors has recently been cloned that may mediate the distinct biological effects of SRIF. These receptors have a high degree of amino acid sequence similarity among themselves, but their sequences are different from any other receptors, indicating that they represent a distinct neurotransmitter receptor subfamily. The availability of the cloned receptors will now allow for detailed structure-function analysis of SRIF receptors and will facilitate development of subtype-selective agonists and antagonists that could be useful in the treatment of central nervous system and endocrine disorders.
Somatostatin was first identified chemically in 1973, since when much has been established about its synthesis, storage and release. It has important physiological actions, including a tonic inhibitory effect on growth hormone release from the pituitary. It has other central actions which are not well understood but recent cloning studies have identified at least five different types of cell membrane receptor for somatostatin. The identification of their genes has allowed studies on the distribution of the receptor transcripts in the central nervous system where they show distinct patterns of distribution, although there is evidence to indicate that more than one receptor type can co-exist in a single neuronal cell. Receptor selective radioligands and antibodies are being developed to further probe the exact location of the receptor proteins. This will lead to a better understanding of the functional role of these receptors in the brain and the prospect of determining the role, if any, of somatostatin in CNS disorders and the identification of potentially useful medicines.
The present study describes the expression pattern of somatostatin receptor genes during the development of rat cerebellum. Characterization of somatostatin receptors was carried out by binding studies using receptor subtype-selective ligands in the germinative epithelium and granule cell layer of the cerebellum from postnatal day 4 (P4) to P21 and in granule cell cultures. Quantitative reverse transcription-PCR carried out for the five receptor subtype mRNAs in cerebellar extracts showed that sst1 mRNAs are predominant at the end of gestation. A transient high expression of the sst2 gene was observed from P7 to P14. In parallel, high levels of binding sites sensitive to sst2 ligands were detected in the granule cell germinative epithelium and in granule cell cultures. sst3 mRNAs rapidly increased from P14 and became the predominant form at P21, but respective binding sites were not detected. Whereas sst4 mRNA levels were generally low, those of sst5 were nearly undetectable. Reverse transcription-PCR carried out in granule cell cultures revealed the relative abundance of sst mRNAs as follows: sst2 > sst1 > sst3 = sst4. sst5 mRNA was undetectable. The results show the expression of four somatostatin receptor genes, but only three receptors (sst1, sst4, and mainly sst2) were detected as binding sites during cerebellar development.
Somatostatin (SRIF) is the main inhibitory peptide regulating growth hormone (GH) secretion. It has been difficult to establish the role of endogenous SRIF release in the absence of pure SRIF antagonists. Although several SRIF antagonists have recently been described, none have been shown to possess in vivo activity in the absence of added SRIF. Here, an SRIF antagonist with no detectable agonist activity has been identified from a synthetic combinatorial hexapeptide library containing 6.4 x 10(7) unique peptides. Each peptide in the library is amino-terminally acetylated and carboxyl-terminally amidated and consists entirely of D-amino acids. A SRIF-responsive yeast growth assay was used as a primary screening tool, and cAMP accumulation, competitive binding, and microphysiometry also were used to confirm and further characterize SRIF antagonist activity. The hexapeptide library was screened in stepwise iterative fashion to identify AC-178,335, a pure SRIF antagonist of the sequence Ac-hfirwf-NH2. This D-hexapeptide bound SRIF receptor type 2 with an affinity constant (Ki) of 172 +/- 12 nM, blocked SRIF inhibition of adenylate cyclase in vitro (IC50 = 5.1 +/- 1.4 microM), and induced GH release when given alone (50 micrograms intravenously) to anesthetized rats with or without pretreatment with a long-acting SRIF agonist.
It has been proposed that neurotransmitters and neuromodulators may function as neurotrophic factors during the development of the nervous system. Somatostatin (SS) was known to increase neurite outgrowth in PC12 cells, rat pheochromocytoma cell line, and cerebellar granule cells as well as Helisoma neuron. To further investigate a neurotrophic role of SS, voltage-dependent K+ and Ca2+ channel expression was studied using whole-cell patch-clamp in PC12 cells and the effect of SS was compared to that of nerve growth factor (NGF). Cyclic AMP (cAMP) level and mitogen-activated protein (MAP) kinase phosphorylation were also studied following the treatment with SS and/or NGF. Whereas NGF (50 ng/ml) increased continually the current density of the voltage-dependent K+ channel throughout 8 days treatment, SS (1 microM) increased the K+ current density on day 2 to the peak. K+ current density was decreased thereafter and was not different on day 6 from that of undifferentiated cells. Although SS did not increase voltage-dependent Ca2+ current density, it potentiated NGF-induced increase of voltage-dependent Ca2+ channel current density as well as the K+ current density. cAMP level was decreased by NGF and/or SS treatment. An increased phosphorylation of MAP kinase induced by NGF was not changed by SS treatment. These results support functionally that SS may function as a neurotrophic factor in developing nervous system.
We have investigated the influence of voltage-dependent, potassium conductances on the migration of embryonic neurons, using a culture preparation taken from the acoustico-vestibular anlage long before the onset of electrical excitability and synaptic function. Whole-cell patch clamp recordings from migrating neuroblasts at Hamburger-Hamilton stage 28 (E 5.5) revealed the exclusive expression of voltage-dependent, high-threshold, outward currents, activating at potentials positive to -20 mV. These currents were completely suppressed by the potassium channel blockers, 1.0 mM tetraethylammonium chloride (TEA) or 1.0 mM 4-aminopyridine (4-AP). In control media, the active migration of individual neuroblasts was recorded at 27 +/- 6 microm per hr. Within minutes after adding either drug to the culture, normal migration completely stopped for several hours. Calcium channel blockers, omega-conotoxin (3 microM) or cadmium chloride (100 microM), slowed, but did not halt, migration, while nickel chloride (100 microM) or N-methyl-D-glucamine (1 mM) had no effect. However, within 8 hr after TEA exposure, migratory activity usually returned. This recovery was associated with the appearance of a previously undetected, low-threshold and 4-AP- sensitive potassium conductance. We suggest that high-threshold, TEA/4-AP-sensitive potassium channels may normally support the migration of these neurons, while their chronic blockade can be compensated by the appearance of novel potassium channels. Potassium currents may act in concert with N-type calcium channels to regulate neuronal migration.
The present study was aimed at identifying somatostatin receptor subtypes on the basis of their ligand-binding properties in the rat somatosensory cortex during fetal and postnatal development. Characterization of somatostatin-binding sites was performed in individual cortical layers by using three radioligands and eight competitors with known selectivities for the five somatostatin receptor subtypes. Binding sites sensitive to sst2-selective ligands were detected with high densities in the intermediate zone of the fetal cortex. From embryonic day 21 to 21 days postnatal (P21), mixed populations of receptors were detected in the cortical plate and emerging layers I-VI. Putative sst2 receptors were detected throughout the entire period but displayed different affinities for somatostatin and analogs, and a different sensitivity to GTP, depending on the developmental stage and the cortical layer considered. High densities of binding sites exhibiting characteristics of the sst1, sst3/5, and sst4 receptor subtypes were observed from P4 to P7, P7 to P14, and P7 to P21, respectively. In addition, each type of site exhibited a particular distribution pattern across the cortical layers that varied during the development. In the adult cortex, binding sites with sst1 and sst2 receptor characteristics were predominant. This study provides evidences of developmental expression windows of four sst receptor subtypes in selected areas of the rat cerebral cortex.
Embryonic and young postnatal mice were exposed once to thymidine-H3, to label cells preparing for division. Histogenesis of cerebellum was studied in autoradiograms. Purkinje cells and neurons of roof nuclei form simultaneously in the primitive ependyma of the young embryo and migrate outward to reach their final positions. A transient external granular layer arises by proliferation of cells on the lateral caudal cerebellar surface lining the fourth ventricle. These cells migrate over the external cerebellar surface, and continue to proliferate abundantly until a few weeks after birth. The layer disappears in the third postnatal week. Most external granule cells divide a few times and then migrate inward past the Purkinje cells to become granule cell neurons. A smaller population of cells arises in the granule layer itself and is characterized by an unusually long interval between deoxyribonucleic acid (DNA) synthesis and mitosis. These cells migrate short distances and may assume positions around the perikarya of Purkinje cells; cells of this class are probably neuroglia. An hypothesis is presented which accounts for the extensive cell migrations during histogenesis as a means for attaining particular synaptic contacts.