Serotonin and GABA are colocalized in restricted groups of neurons in the larval sea lamprey brain: Insights into the early evolution of neurotransmitter colocalization in vertebrates

Department of Cell Biology and Ecology, Faculty of Biology, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain.
Journal of Anatomy (Impact Factor: 2.1). 07/2009; 215(4):435-43. DOI: 10.1111/j.1469-7580.2009.01119.x
Source: PubMed


Colocalization of the classic neurotransmitters serotonin (5-HT) and gamma-aminobutyric acid (GABA) (or the enzyme that synthesizes the latter, glutamate decarboxylase) has been reported in a few neurons of the rat raphe magnus-obscurus nuclei. However, there are no data on the presence of neurochemically similar neurons in the brain of non-mammalian vertebrates. Lampreys are the oldest extant vertebrates and may provide important data on the phylogeny of neurochemical systems. The colocalization of 5-HT and GABA in neurons of the sea lamprey brain was studied using antibodies directed against 5-HT and GABA and confocal microscopy. Colocalization of the neurotransmitters was observed in the diencephalon and the isthmus. In the diencephalon, about 87% of the serotonergic cells of the rostral tier of the dorsal thalamus (close to the zona limitans) exhibited GABA immunoreactivity. In addition, occasional cells double-labelled for GABA and 5-HT were observed in the hypothalamic tuberal nucleus and the pretectum. Of the three serotonergic isthmic subgroups already recognized in the sea lamprey isthmus (dorsal, medial and ventral), such double-labelled cells were only observed in the ventral subgroup (about 61% of the serotonergic cells in the ventral subgroup exhibited GABA immunoreactivity). An equivalence between these lamprey isthmic cells and the serotonergic/GABAergic raphe cells of mammals is suggested. Present findings suggest that serotonergic/GABAergic neurons are more extensive in lampreys than in the rat and probably appeared before the separation of agnathans and gnathostomes. Cotransmission by release of 5-HT and GABA by the here-described lamprey brain neurons is proposed.

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Available from: Antón Barreiro-Iglesias,
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    • "In the ascidian tunicate tadpole, serotonergic neurons are found only in the hindbrain, while in amphioxus larvae they are found in the forebrain and hindbrain (Candiani et al., 2012); while this situation may resemble that found in Actinopterygii, the existence of forebrain serotonergic nuclei in the amphioxus is probably an apomorphism due to the absence of a midbrain–hindbrain organizer in protochordates (Butler and Hodos, 2005). In the sea lamprey, serotonin-like immunoreactivity is found in the pretectal area, zona limitans intrathalamica, tuberal and mammillary hypothalamus, isthmus and vagal group, as well as in the spinal cord (Barreiro-Iglesias et al., 2009; Cornide-Petronio et al., 2013); these populations are roughly equivalent to the nuclei found in basal actinopterygian fish (López and González, 2014) and teleosts (Lillesaar, 2011; Maximino et al., 2013a). Thus, the ancestral state of the vertebrate serotonergic system is characterized by well-defined nuclei in the raphe nuclei, the preoptic area and the basal hypothalamus (Lillesaar, 2011; López and González, 2014; Maximino et al., 2013a); in amniotes, this system is reduced, as bona fide 5-HTergic cells are found only in the retina, pineal and raphe nuclei of these species (Hale and Lowry, 2011). "
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    ABSTRACT: Due to the fish-specific genome duplication event (~320-350 mya), some genes which code for serotonin proteins were duplicated in teleosts; this duplication event was preceded by a reorganization of the serotonergic system, with the appearance of the raphe nuclei (dependent on the isthmus organizer) and prosencephalic nuclei, including the paraventricular and pretectal complexes. With the appearance of amniotes, duplicated genes were lost, and the serotonergic system was reduced to a more complex raphe system. From a comparative point of view, then, the serotonergic system of zebrafish and that of mammals shows many important differences. However, many different behavioral functions of serotonin, as well as the effects of drugs which affect the serotonergic system, seem to be conserved among species. For example, in both zebrafish and rodents acute serotonin reuptake inhibitors (SSRIs) seem to increase anxiety-like behavior, while chronic SSRIs decrease it; drugs which act at the 5-HT1A receptor seem to decrease anxiety-like behavior in both zebrafish and rodents. In this article, we will expose this paradox, reviewing the chemical neuroanatomy of the zebrafish serotonergic system, followed by an analysis of the role of serotonin in zebrafish fear/anxiety, stress, aggression and the effects of psychedelic drugs.
    Progress in Neuro-Psychopharmacology and Biological Psychiatry 03/2014; 55. DOI:10.1016/j.pnpbp.2014.03.008 · 3.69 Impact Factor
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    • "Over the past two decades, evidence indicating that transmission by multiple messengers released by single neurons was the norm rather than the exception has been accumulated [42]–[46]. The functional implications of neurotransmitter co-release are not clear but it likely plays an important role in the maturation and refinement of synapses, in precision of motor activity, in the homeostatic opposition to hyperexcitability during seizures [42] or possibly in reducing the metabolic cost and errors of signaling [43]. "
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    ABSTRACT: Glutamate is the main excitatory neurotransmitter involved in spinal cord circuits in vertebrates, but in most groups the distribution of glutamatergic spinal neurons is still unknown. Lampreys have been extensively used as a model to investigate the neuronal circuits underlying locomotion. Glutamatergic circuits have been characterized on the basis of the excitatory responses elicited in postsynaptic neurons. However, the presence of glutamatergic neurochemical markers in spinal neurons has not been investigated. In this study, we report for the first time the expression of a vesicular glutamate transporter (VGLUT) in the spinal cord of the sea lamprey. We also study the distribution of glutamate in perikarya and fibers. The largest glutamatergic neurons found were the dorsal cells and caudal giant cells. Two additional VGLUT-positive gray matter populations, one dorsomedial consisting of small cells and another one lateral consisting of small and large cells were observed. Some cerebrospinal fluid-contacting cells also expressed VGLUT. In the white matter, some edge cells and some cells associated with giant axons (Müller and Mauthner axons) and the dorsolateral funiculus expressed VGLUT. Large lateral cells and the cells associated with reticulospinal axons are in a key position to receive descending inputs involved in the control of locomotion. We also compared the distribution of glutamate immunoreactivity with that of γ-aminobutyric acid (GABA) and glycine. Colocalization of glutamate and GABA or glycine was observed in some small spinal cells. These results confirm the glutamatergic nature of various neuronal populations, and reveal new small-celled glutamatergic populations, predicting that some glutamatergic neurons would exert complex actions on postsynaptic neurons.
    PLoS ONE 10/2012; 7(10):e47898. DOI:10.1371/journal.pone.0047898 · 3.23 Impact Factor
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    • "Surprisingly, this map suggests that, at least in the developmental stages examined, neurotransmitters do not colocalize in the amphioxus CNS. This finding contrasts with some examples of neurochemical colocalization observed in mollusks and vertebrates [28-30]. "
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    ABSTRACT: Background Amphioxus, representing the most basal group of living chordates, is the best available proxy for the last invertebrate ancestor of the chordates. Although the central nervous system (CNS) of amphioxus comprises only about 20,000 neurons (as compared to billions in vertebrates), the developmental genetics and neuroanatomy of amphioxus are strikingly vertebrate-like. In the present study, we mapped the distribution of amphioxus CNS cells producing distinctive neurochemicals. To this end, we cloned genes encoding biosynthetic enzymes and/or transporters of the most common neurotransmitters and assayed their developmental expression in the embryo and early larva. Results By single and double in situ hybridization experiments, we identified glutamatergic, GABAergic/glycinergic, serotonergic and cholinergic neurons in developing amphioxus. In addition to characterizing the distribution of excitatory and inhibitory neurons in the developing amphioxus CNS, we observed that cholinergic and GABAergic/glycinergic neurons are segmentally arranged in the hindbrain, whereas serotonergic, glutamatergic and dopaminergic neurons are restricted to specific regions of the cerebral vesicle and the hindbrain. We were further able to identify discrete groups of GABAergic and glutamatergic interneurons and cholinergic motoneurons at the level of the primary motor center (PMC), the major integrative center of sensory and motor stimuli of the amphioxus nerve cord. Conclusions In this study, we assessed neuronal differentiation in the developing amphioxus nervous system and compiled the first neurochemical map of the amphioxus CNS. This map is a first step towards a full characterization of the neurotransmitter signature of previously described nerve cell types in the amphioxus CNS, such as motoneurons and interneurons.
    BMC Neuroscience 06/2012; 13(1):59. DOI:10.1186/1471-2202-13-59 · 2.67 Impact Factor
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