[Show abstract][Hide abstract] ABSTRACT: Granule neurons of the dentate gyrus (DG) of the hippocampus undergo continuous renewal throughout life. Among cell cycle regulators, cyclin-dependent kinase 2 (Cdk2) is considered as a major regulator of S-phase entry. We used Cdk2-deficient mice to decipher the requirement of Cdk2 for the generation of new neurons in the adult hippocampus. The quantification of cell cycle markers first revealed that the lack of Cdk2 activity does not influence spontaneous or seizure-induced proliferation of neural progenitor cells (NPC) in the adult DG. Using bromodeoxyuridine incorporation assays, we showed that the number of mature newborn granule neurons generated de novo was similar in both wild-type (WT) and Cdk2-deficient adult mice. Moreover, the apparent lack of cell output reduction in Cdk2(-/-) mice DG did not result from a reduction in apoptosis of newborn granule cells as analyzed by TUNEL assays. Our results therefore suggest that Cdk2 is dispensable for NPC proliferation, differentiation and survival of adult-born DG granule neurons in vivo. These data emphasize that functional redundancies between Cdks also occur in the adult brain at the level of neural progenitor cell cycle regulation during hippocampal neurogenesis.
[Show abstract][Hide abstract] ABSTRACT: This study was designed to document convulsant and neurotoxic properties of extracts of a tropical tree, Magnistipula butayei subsp. Montana, and to investigate the involvement of the glutamatergic system in these effects. Continuous behavioral observations and electroencephalographic (EEG) records were obtained after per os administration of an aqueous extract of Magnistipula (MBMAE) in rats. MBMAE (800 mg/kg) induced behavioral changes resembling motor limbic seizures: staring and head tremor, automatisms, forelimb clonic movements and violent tonic-clonic seizures leading to death in all animals. Concomitantly, important seizure activity that gradually evolved to epileptiform activity was recorded on the EEG. Moreover, c-Fos immunohistochemistry has revealed an increased c-Fos expression in the dentate gyrus and in piriform, peri- and entorhinal cortices 2 and 4h after treatment. This expression pattern suggested that the mechanism of action for the MBMAE is similar to that observed in glutamate-induced models of epilepsy. The MBMAE increased cell death also in hippocampal cell cultures. Furthermore, the build-up of convulsive activity and epileptic discharges induced by MBMAE in rat were abolished by MK-801, an NMDA receptor antagonist. Our study suggests that MBMAE contains a potent toxin, with a powerful neurotoxic activity in rat, and corresponding to a new natural component(s) that act as an NMDA-mediated convulsant molecule.
[Show abstract][Hide abstract] ABSTRACT: The present study aimed at characterizing the acute and intermittent psychomotor responsiveness to cocaine in mice lacking the MCHR1 receptor, which is thought to modulate the mesocorticolimbic sytem functioning [Smith DG, Tzavara ET, Shaw J, Luecke S, Wade M, Davis R, et al. Mesolimbic dopamine super-sensitivity in melanin-concentrating hormone-1 receptor deficient mice. J Neurosci 2005;25:914-22]. On a first free-drug session, MCHR1-deficient mice exhibited significantly higher levels of locomotor activity elicited by the novelty of the test chambers than their wild-type counterparts. On the following day session, a first injection of 6 or 12 mg/kg cocaine induced comparable dose-related psychomotor activations in both genotypes, without significant difference in the relative increase in locomotion. Over the following eight once-daily test sessions, the slight psychomotor increase induced by 6 mg/kg was equivalent in both genotypes and constant over the sessions. At 12 mg/kg, cocaine induced a clear-cut incremental responsiveness to cocaine in both genotypes on the three first sessions; on the following sessions, only the wild-types displayed an incremental responsiveness until the last session, a sensitized effect that was confirmed for the wild-types but not for the knockouts on a subsequent sensitization test (cocaine challenge). Finally, the knockouts did not exhibit any sign of cocaine-conditioning (saline challenge), contrarily to the wild-types. It is speculated that MCHR1 may contribute to the neurobiological mechanisms of conditioned cocaine-induced psychomotor effects, possibly to those underpinning sensitization, and to a lesser extent to those sub-serving acute pharmacological cocaine action.
Behavioural Brain Research 11/2006; 173(1):94-103. · 3.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Can a gene defect be responsible for the occurrence in an individual, at a particular age, of such a muscle twitch followed by relaxation called: "myoclonus" and defined as sudden, brief, shock-like movements? Genetic defects could indeed determine a subsequent cascade of molecular events (caused by abnormal encoded proteins) that would produce new aberrant cellular relationships in a particular area of the CNS leading to re-built "myoclonogenic" neuronal networks. This can be illustrated reviewing some inherited neurological entities that are characterized by a predominant myoclonic picture and among which a clear gene defect has been identified. In the second part of this chapter, we will also propose a new point of view on how some structural genes could, under certain conditions, when altered, produced idiopathic generalized epilepsy with myoclonic jerks, taking juvenile myoclonic epilepsy (JME) and the myoclonin (EFHC-1) gene as examples.
[Show abstract][Hide abstract] ABSTRACT: In order to investigate the physiological properties of the melanin-concentrating hormone (MCH) we have generated and used mice from which the MCH receptor 1 gene was deleted (MCHR1(Neo/Neo) mice). Complementary experimental approaches were used to investigate alterations in the learning and memory processes of our transgenic model. The ability of the knockout strain to carry out the inhibitory passive avoidance test was found to be considerably impaired although no significant differences were observed in anxiety levels. This impaired cognitive property prompted us to explore modifications in N-methyl D-aspartate (NMDA) responses in the hippocampus. Intracellular recordings of CA1 pyramidal neurons in hippocampal slices from the MCHR1(Neo/Neo) mice revealed significantly decreased NMDA responses. Finally, using in situ hybridization we found a 15% reduction in NMDAR1 subunit in the CA1 region. These results show for the first time a possible role for MCH in the control of the function of the NMDA receptor.
European Journal of Neuroscience 06/2005; 21(10):2837-44. · 3.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In seasonally breeding songbirds, seasonal fluctuations occur in serum testosterone (T) concentrations and reproductive behaviours. Many T-dependent behaviours are regulated by the activity of androgenic and oestrogenic metabolites within specific brain regions. Male European starlings breed in spring when circulating T concentrations peak. T and its metabolites act within portions of the diencephalon to regulate the pituitary-gonadal axis and to activate courtship and copulation. Song in male starlings is critical for mate attraction during the breeding season and is regulated by steroid-sensitive nuclei in the telencephalon and diencephalon. Outside the breeding season, T is undetectable, however, males continue to sing at high levels. This suggests that singing outside of the breeding season might not be T-dependent as it appears to be in the spring. Alternatively, singing when T is low might continue to be regulated by T due to increased sensitivity of the brain to the action of the steroid. This increased sensitivity could be mediated by changes in intracellular T metabolism leading to increased production of active or decreased production of inactive metabolites. To explore the relationship between T-metabolism and reproductive behaviour, we analysed seasonal changes in the activity of four brain T-metabolizing enzymes: aromatase, 17beta-hydroxysteroid dehydrogenase (17beta-HSDH), 5alpha-reductase (all three convert T into active metabolites) and 5beta-reductase (converts T into an inactive metabolite) in the diencephalon and telencephalon. In the anterior and posterior diencephalon, the highest aromatase was observed in spring when this region is critical for courtship and copulation. In the telencephalon, aromatase was highest and 5beta-reductase was lowest throughout the winter months well prior to the reproductive season and these enzymes presumably maximize T-activity within this region. Although these data do not indicate whether the metabolic changes occur specifically within song nuclei, these findings are compatible with the idea that singing in male starlings outside the breeding season may be regulated by steroids despite the presence of low serum T concentrations. Overall, seasonal changes in T-metabolizing enzymes appear to play a significant role in seasonal changes in behaviour and reproductive physiology.
Journal of Neuroendocrinology 12/2001; 13(11):985-97. · 3.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We recently demonstrated that dopamine (DA) as well as different DA receptor agonists and antagonists are able to decrease within a few minutes the aromatase activity (AA) measured in vitro in homogenates or in explants of the quail preoptic area — hypothalamus. In addition, DA also appears to regulate AA, in vivo presumably by modifying enzyme synthesis. The cellular mechanisms and the anatomical substrate that mediate these controls of AA by DA are poorly understood. Tyrosine hydroxylase-immunoreactive (TH-ir) fibers and punctate structures have been previously observed in close vicinity of aromatase-immunoreactive (ARO-ir) cells in the quail medial preoptic nucleus (POM) and bed nucleus striae terminalis (BST) but these fibers could reflect a noradrenergic innervation. We also do not know whether aromatase cells are dopaminoceptive. The main goal of the present study was therefore to bring more information on the anatomical relationships between aromatase expressing neurons and the dopaminergic system in the quail brain. The visualization by immunocytochemistry of DA and of the D1 receptor associated protein DARPP-32 was used to address these questions. DA-ir fibers were observed in the quail forebrain and overlapped extensively with nuclei that contain high densities of ARO-ir cells such as the POM and BST. This confirms that the previously reported TH-ir innervation of ARO-ir cells is, at least in part, of dopaminergic nature. DARPP-32-immunoreactive cells were found in periventricular position throughout the hypothalamus. DARPP-32-ir cells were also observed in telencephalic and mesencephalic areas (hyperstriatum accessorium, paleostriatum, nucleus intercollicularis, optic tectum). DARPP-32-ir fibers were widespread in tel-, di-, and mes-encephalic areas. The highest densities of immunoreactive fibers were detected in the lobus parolfactorius, paleostriatum augmentatum and substantia nigra/area ventralis of Tsai. In double-labeled sections, appositions between DARPP-32 fibers and ARO-ir cells were present in the dorsolateral POM and BST but DARPP-32 immunoreactivity was not detected in the ARO-ir perikarya (no colocalization). These data confirm the presence of a dopaminoceptive structures within the main cell clusters of ARO-ir cells in the quail brain but provide no evidence that these ARO-ir cells are themselves dopaminoceptive. Because DARPP-32 is not present in all types of cells expressing DA receptors, the presence of DA receptors that would not be associated with DARPP-32 in ARO-ir cells still remains to be investigated
Journal of Chemical Neuroanatomy 02/2001; · 2.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The excitatory amino acid glutamate is implicated in the central control of many neuroendocrine and behavioral processes. The ionotropic glutamate receptors are usually divided into the N-methyl-D-aspartate (NMDA) and non-NMDA (kainate and AMPA) subtypes. Subunits of these receptors have been cloned in a few mammalian species. Information available in birds is more limited. In quail, we recently demonstrated that glutamate agonists (kainate, AMPA, and NMDA) rapidly (within minutes) and reversibly decrease in vitro aromatase activity like several other manipulations affecting intracellular HCa(2+) pools. Aromatase catalyzes the conversion of androgens into estrogens which is a limiting step in the control by testosterone of many behavioral and physiologic processes. Therefore, glutamate could control estrogen production in the brain, but the anatomic substrate supporting this effect is poorly understood. In quail, aromatase is mainly localized in the preoptic-hypothalamic-limbic system. We visualized here the distribution of the major ionotropic glutamate receptors in quail by immunocytochemical methods by using commercial primary antibodies raised against rat glutamate receptor 1 and receptors 2-3 (GluR1, GluR2/3: AMPA subtype, Chemicon, CA), rat glutamate receptors 5-7 (GluR5-7: kainate subtype, Pharmingen, CA), and rat NMDA receptors (NMDAR1, Pharmingen, CA). Dense and specific signals were obtained with all antibodies. The four types of receptors are broadly distributed in the brain, and, in particular, immunoreactive cells are identified within the major aromatase cell groups located in the medial preoptic nucleus, ventromedial hypothalamus, nucleus striae terminalis, and nucleus taeniae. Dense specific populations of glutamate receptor-immunoreactive cells are also present with a receptor subtype-specific distribution in broad areas of the telencephalon. The distribution of glutamate receptors, therefore, is consistent with the idea that these receptors could be located at the surface of aromatase-containing cells and mediate the rapid regulation of aromatase activity in a direct manner.
The Journal of Comparative Neurology 01/2001; 428(4):577-608. · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In adult male and female Japanese quail, aromatase-immunoreactive cells were identified in the spinal dorsal horns from the upper cervical segments to the lower caudal area. These immunoreactive cells are located mostly in laminae I-III, with additional sparse cells being present in the medial part of lamina V and, at the cervical level exclusively, in lamina X around the central canal. Radioenzyme assays based on the measurement of tritiated water release confirmed the presence of substantial levels of aromatase activity throughout the rostrocaudal extent of the spinal cord. Contrary to what is observed in the brain, this enzyme activity and the number of aromatase-immunoreactive cells in five representative segments of the spinal cord are not different in sexually mature males or females and are not influenced in males by castration with or without testosterone treatment. The aromatase activity and the numbers of aromatase-immunoreactive cells per section are higher at the brachial and thoracic levels than in the cervical and lumbar segments. These experiments demonstrate for the first time the presence of local estrogen production in the spinal cord of a higher vertebrate. This production was localized in the sensory fields of the dorsal horn, where estrogen receptors have been identified previously in several avian and mammalian species, suggesting an implication of aromatase in the modulation of sensory (particularly nociceptive) processes.
The Journal of Comparative Neurology 09/2000; 423(4):552-64. · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Many behavioral effects of testosterone on hypothalamic and limbic brain areas are mediated by the action, at the cellular level, of estrogens derived from local testosterone aromatization. Aromatase activity and cells containing the aromatase protein and mRNA have accordingly been identified in the brain areas involved in the control of behavior. The presence of an unusually high level of aromatase activity has been detected in the telencephalon of one songbird species, the zebra finch (Taeniopygia guttata), and it is suspected that this high telencephalic aromatase may be a specific feature of songbirds but this idea is supported only by few experimental data. The distribution of aromatase activity in the brain of zebra finches and of one nonsongbird species, the Japanese quail (Coturnix japonica), was compared with the distribution of aromatase activity in the brain of four species of free-living European songbirds, the chaffinch (Fringilla coelebs, Fringillidae), willow warbler (Phylloscopus trochilus, Sylviidae), great tit (Parus major, Paridae), and pied flycatcher (Ficedula hypoleuca, Muscicapidae). High levels of enzyme activity were observed in the diencephalon of all species. The high levels of aromatase activity that had been observed in the zebra finch telencephalon and were thought to be typical of songbirds were also present in the four wild oscine species but not in quail. None of these songbird species had, however, a telencephalic aromatase activity as high as that in the zebra finch, which may represent an extreme as far as the activity of this enzyme in the telencephalon is concerned. Measurable levels of aromatase activity were also detected in all songbird species in the liver and in the three other brain areas that were assayed, the optic lobes, cerebellum, and brain stem, with the exception of the cerebellum in willow warblers and quail, but no detectable activity was observed in the testes, muscle, and adrenals of all species. Additional studies will be needed to identify the functional significance of estrogen synthesis in areas that are not classically known to be implicated in the control of reproduction. Within a given species, the birds that had the highest plasma testosterone levels also displayed the highest levels of diencephalic aromatase activity and the interspecies differences in the two variables were positively related. This raises the possibility that the absolute level of diencephalic aromatase represents a species-specific characteristic under the control of plasma testosterone levels. There was, in contrast, no correlation between the aromatase activity in the telencephalon and the plasma testosterone levels but the enzyme activity was correlated with the plasma levels of luteinizing hormone. These data bring additional support to the idea that the diencephalic and telencephalic aromatases are controlled by independent mechanisms.
General and Comparative Endocrinology 02/2000; · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sexual interactions can cause changes in plasma hormone levels and activate immediate early genes within the mammalian brain. There are marked anatomical differences between the regions activated that relate directly to the sexual specific behaviour and neuroendocrinology of each sex. The aim of this study was to determine if such a sexual dimorphism exists in birds by examining the brain regions stimulated in adult virgin female Japanese quail (Coturnix japonica) during sexual behaviour and comparing this to previously reported data concerning males. Female quail were allowed to freely interact with adult males and both female and male sexual behaviour was recorded. Contrary to previous findings in male quail, no significant induction of Fos-like immunoreactive (FLI) cells was observed following sexual interactions in the preoptic area of females; this area is fundamentally involved in the control of male-type copulatory behaviour. Sexual interactions significantly induced FLI cells in the hyperstriatum ventrale, the part of the archistriatum just lateral to the anterior commissure, and the nucleus intercollicularis. Moreover, prominent activation was detected throughout most of the ventromedial nucleus of the hypothalamus, a region reported to be rich in oestrogen receptors. FLI induction was not a consequence of sexual behaviour induced changes in luteinizing hormone (LH) as plasma LH levels were unaltered. Instead, brain activation must be a consequence of copulation-associated somatosensory inputs or direct stimuli originating from the male. Male quail, like the majority of other birds, lack an intromittant organ (penis) so that the somatosensory inputs to the female are rather different from those in mammals; the precise nature of these inputs is yet to be determined.
Journal of Neuroendocrinology 11/1999; 11(10):771-84. · 3.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A partial estrogen receptor-beta (ERbeta) cDNA had been previously cloned and sequenced in Japanese quail. The 3'- and 5'-rapid amplification of cDNA ends techniques were used here to identify a cDNA sequence of the quail ERbeta that contains a complete open reading frame. For the first time in an avian species, this cDNA sequence and the corresponding amino acid sequence are described. They are compared with the known ERbeta sequences previously described in mammals and with the ERalpha sequences identified in a selection of mammalian and avian species. The analysis by Northern blotting of the ERbeta mRNA expression in the brain and kidneys revealed the presence of several transcripts. The presence of ERbeta identified by reverse transcriptase-polymerase chain reaction demonstrated a widespread distribution quite different from the distribution of ERalpha. The complete neuroanatomical distribution of ERbeta mRNA as determined by in situ hybridization with 35S- and 33P-labeled oligoprobes is also presented. Transcripts are present in many nuclei implicated in the control of reproduction such as the medial preoptic nucleus, the nucleus striae terminalis, and the nucleus taeniae, the avian homologue of the amygdala. These data demonstrate the presence of ERbeta in a nonmammalian species and indicate that the (neuro)-anatomical distribution of this receptor type has been conserved in these two classes of vertebrates. The role of this receptor in the control of reproduction and other physiological processes should now be investigated.
Journal of Neurobiology 10/1999; 40(3):327-42. · 3.05 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Male sexual behavior is determined by the interaction of endocrine and environmental stimuli originating from the female, yet it is unknown how and where these stimuli are integrated within the brain. Activation of copulatory behavior by testosterone is limited by its central aromatization into an estrogen in the preoptic area. We investigated whether mating-induced neuronal activation as identified by the expression of the immediate early gene Fos occurs in aromatase-immunoreactive (ARO-ir) cells of the male quail preoptic area. Fos-immunoreactive (ir) cells were observed within and lateral to these ARO-ir cells groups but few ARO-ir cells contained Fos-ir indicating that mating-related stimuli do not directly affect estrogen-synthesizing cells.
[Show abstract][Hide abstract] ABSTRACT: Tyrosine hydroxylase (TH) activity, the rate-limiting step in the synthesis of catecholamines, was quantified in the preoptic area-hypothalamus of adult male Japanese quail by a new assay measuring the tritiated water production from 3,5-[3H]-L-tyrosine. Maximal levels of activity were observed at a 20-25 microM concentration of substrate, with more than 50% inhibition of the activity being recorded at a 100 microM concentration. TH activity was linear as a function of the incubation time during the first 20 min and maximal at a pH of 6.0. TH was heterogeneously distributed in the quail brain with highest levels of activity being found (in decreasing order) in the mesencephalon, diencephalon, and telencephalon. Given the large size of the telencephalon, this is the brain area that contains, as a whole, the highest level of enzyme activity. TH inhibitors that have been well-characterized in mammals, such as 3-iodo-L-tyrosine and L-alpha-methyl-p-tyrosine (AMPT) completely inhibited the enzyme activity at a 100 microM concentration. In mammals, the accumulation of catecholamines exerts a negative feedback control on TH activity. Similar controls were observed in the quail brain. Two inhibitors of the DOPA decarboxylase that should lead to accumulation of DOPA depressed TH activity by 60% or more, and the inhibitor of the dopamine beta-hydroxylase, fusaric acid that should cause an accumulation of dopamine, suppressed 90% of the TH activity. The addition of exogenous DOPA, dopamine, or norepinephrine to the brain homogenates also strongly inhibited TH activity, independently confirming the feedback effects of the enzyme products on the enzyme activity. These data demonstrate that TH activity in the quail brain is heterogeneously distributed and acutely regulated, as it is in mammals, by the accumulation of its products and of the derived catecholamines.
Brain Research Bulletin 02/1999; 48(1):31-7. · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Studies in avian species have often been useful in elucidating basic concepts relevant to the regulation of reproductive behaviors by sex steroid hormones. Once a link between a steroid hormone and a behavioral response has been established, one can use the localization of steroid hormone receptors in the brain to facilitate the identification of neural circuits that control behavior. The recent identification of a second type of estrogen receptor called estrogen receptor beta or ERbeta has raised new issues about the action of steroid hormones in the brain. A hypothesis has been proposed by Kuiper et al.  based on studies in mammalian species suggesting that ERalpha (the name given to the ER that was previously described) is important for reproduction while ERbeta is more important for non-reproductive functions. In this paper we apply this hypothesis more generally by examining possible functions of ERbeta in avian species. We have initiated studies of the ERbeta in the brain of two avian species, the Japanese quail (Coturnix japonica) and the European starling (Sturnus vulgaris). ERbeta was cloned in both species and the mRNA for this receptor type was localized in the brain employing in situ hybridization histochemistry methods. In both species ERbeta was found to be diffusely present in telencephalic areas consistent with a role for this receptor subtype in cognitive functions. However, ERbeta mRNA was also found in many brain areas that are traditionally thought to be important in the regulation of reproductive functions such as the preoptic region, the bed nucleus of the stria terminalis and the nucleus taeniae. Of the two receptor types, only mRNA for ERalpha was observed in the telencephalic vocal control nucleus HVc of male starlings. Steroid receptors in this nucleus are thought to be an example of an evolutionary specialization that has evolved to coordinate the production of courtship vocalizations with other aspects of reproduction. The lack of ERbeta mRNA expression in HVc is consistent with the hypothesis that ERalpha is preferentially involved in reproductive behaviors while ERbeta is involved in the steroid regulation of other neural functions. However, the widespread occurrence of ERbeta in other nuclei involved in reproductive function suggests that one must be cautious about the general applicability of the above hypothesis until more is known about ERbeta function in these other nuclei.
Brain Behavior and Evolution 02/1999; 54(1):28-40. · 2.89 Impact Factor