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ABSTRACT: The ontogeny of the gamma-aminobutyric acid (GABA)-positive neurons in the brain of Xenopus laevis tadpoles was investigated by means of immunohistochemistry, using specific antibodies both against GABA and its biosynthetic enzyme, glutamate decarboxylase (GAD). The results obtained with the two antisera were comparable. The GABA system differentiates very early during development. At stages 35/36, numerous GABA-positive neurons were seen throughout the prosencephalon and formed two main bilateral clusters within the lateral walls of the forebrain that ran caudally toward the hindbrain. Other GABA-immunolabeled cell bodies, together with a conspicuous network of GABAergic fibers, were seen in the posterior hypothalamus. In the spinal cord, the lateral marginal zone was GABA-positive, as were Rohon-Beard neurons, interneurons, and Kolmer-Agdhur cells. A very rich GABA innervation was observed in the pars intermedia of the pituitary. At stage 50, plentiful immunopositive neurons and fibers were found in the telencephalic hemispheres, the diencephalon, and the mesencephalon (optic tectum and tegmentum). By stage 54, the number of GABA-immunoreactive neurons in the posterior hypothalamus had decreased, so that, at stage 58, there were very few GABA-labeled cell bodies in the dorsolateral walls of the infundibulum, despite a strong GABAergic innervation within the median eminence and the pars intermedia. From stage 58 to stage 66, the distribution pattern was very similar to that described in the adult X. laevis and in other amphibian species. These results point to transient GABA expression within the hypothalamus, possibly related to either 1) a naturally occurring cell death or 2) a phenotypic switch.
The Journal of Comparative Neurology 05/1996; 368(2):285-94. · 3.81 Impact Factor
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ABSTRACT: The connections of the posterior pallial regions were studied in the crested newt, Triturus carnifex, by means of the horseradish peroxidase technique. The tracer was injected into the lateral and medial pallia, caudal to the interventricular foramen. In addition, the connections between the posterior pallium and the infundibular hypothalamus were investigated with both horseradish peroxidase and the fluorescent dye DiI. The results show important differences between the connection patterns of the medial and lateral pallia. The lateral pallium receives inputs from the main olfactory bulb and send fibers to the contralateral hemisphere through the anterior commissure. It also shows modes extra-telencephalic connections. Conversely, the medial pallium receives direct afferent inputs from the amygdala (pars medialis) and the anterior dorsal thalamus. It is reciprocally connected to the contralateral homologue region through the hippocampal commissure, and its main efferent system is the medial forebrain bundle, which reaches the infundibular hypothalamus. The infundibulum also receives a prominent projection from the amygdala (pars lateralis). The connectivity of the posterior pallium is comparable to that reported previously for the anterior pallium, although a few differences are noted. These differences in the connectivity of the lateral pallium and the medial pallium may reflect different functional properties of these telencephalic regions.
Brain Behavior and Evolution 02/1995; 45(4):195-208. · 2.21 Impact Factor
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ABSTRACT: By using a histochemical procedure, the distribution of neurons containing dihydronicotinamide adenine dinucleotide diaphorase (NADPHd) was examined in the brain, retina and olfactory epithelium of the urodele amphibian Triturus carnifex. Positive nerve fibers and terminals were observed throughout the brain and cell bodies were seen within the telencephalon, optic tectum, brain stem, cerebellum and spinal cord. In the retina, NADPHd labeling was localized in the outer segment of photoreceptors and in some amacrine cells as well as in the outer and inner plexiform layers. In the olfactory epithelium, NADPHd labeling was found in the olfactory neurons. By comparing NADPHd distribution with nitric oxide synthase (NOS) immunoreactivity (using a polyclonal antiserum raised against mouse cerebellar NOS) it was found that NADPHd labeling and NOS immunoreaction patterns generally matched. The organization of NADPHd and NOS containing neurons in the central nervous system of the crested newt, which is simpler than in other vertebrates investigated, shows some peculiarities, such as the occurrence of NADPHD in the pinealocytes of the epiphysis, nucleus rubber of the brain stem and eminentia cerebellaris ventralis of the cerebellum.
European journal of histochemistry: EJH 02/1995; 39(3):183-94. · 1.69 Impact Factor
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ABSTRACT: The amphibian Xenopus laevis is able to adapt the colour of its skin to the light intensity of the background, by releasing alpha-melanophore-stimulating hormone from the pars intermedia of the hypophysis. In this control various inhibitory (dopamine, gamma-aminobutyric acid, neuropeptide Y, noradrenaline) and stimulatory (thyrotropin-releasing hormone and corticotropin-releasing hormone) neural factors are involved. Dopamine, gamma-aminobutyric acid and neuropeptide Y are present in suprachiasmatic neurons and co-exist in synaptic contacts on the melanotrope cells in the pars intermedia, whereas noradrenaline occurs in the locus coeruleus and noradrenaline-containing fibres innervate the pars intermedia. Thyrotropin-releasing hormone and corticotropin-releasing hormone occur in axon terminals in the pars nervosa. In the present study, the neuronal origins of these factors have been identified using axonal tract tracing. Application of the tracers 1,1'dioctadecyl-3,3,3',3' tetramethyl indocarbocyanine and horseradish peroxidase into the pars intermedia resulted in labelled neurons in two brain areas, which were immunocytochemically identified as the suprachiasmatic nucleus and the locus coeruleus, indicating that these areas are involved in neural inhibition of the melanotrope cells. Thyrotropin-releasing hormone and corticotropin-releasing hormone were demonstrated immunocytochemically in the magnocellular nucleus. This area appeared to be labelled upon tracer application into the pars nervosa. This finding is in line with the idea that corticotropin-releasing hormone and thyrotropin-releasing hormone stimulate melanotrope cell activity after diffusion from the neural lobe to the pars intermedia. After anterograde filling of the optic nerve with horseradish peroxidase, labelled axons were traced up to the suprachiasmatic area where they showed to be in contact with suprachiasmatic neurons. These neurons showed a positive reaction with anti-neuropeptide Y and the same held for staining with anti-tyrosine hydroxylase. It is suggested that a retino-suprachiasmatic pathway is involved in the control of the melanotrope cells during the process of background adaptation.
Neuroscience 08/1994; 61(2):411-20. · 3.38 Impact Factor
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ABSTRACT: Quantitative receptor autoradiography was used to study the binding of 2-[125I] iodomelatonin in the brain of the castrated and gonadally intact male Japanese quail Coturnix japonica exposed to both long- and short-day photoperiod cycles. The distribution study displayed that these conditions were responsible for a heterogeneous binding pattern as shown by elevated receptor levels being located in visual brain centers, such as the stratum opticum, nucleus pretectalis, and nucleus geniculatus lateralis, pars ventralis, while lower values were found in the nucleus lateralis hypothalami and nucleus isthmi pars magnocellularis. Closer examination of the 2-[125I] iodomelatonin-binding pattern following the different gonadal and photic influences showed that combination of the gonadally intact condition and a 16L:8D (long-day) photoperiod cycle was required for the greater binding changes. These differences occurred in brain sites such as the area preoptica, paleostriatum primitivum, and nucleus ectomamillaris. Saturation binding studies, which were carried out only in some of the above areas, revealed that the combined gonadal- and photic-induced changes are basically due to the modifications of total number of binding sites. The importance of a gonadal steroid modulatory role in the photic-dependent melatonin binding activity suggests that other types of neuronal mechanisms might be involved in the regulation of neuroendocrine and socio-sexual behaviors in nonmammalian vertebrates.
Journal of Experimental Zoology 08/1994; 269(4):383-8.
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ABSTRACT: Afferent projections to the pituitary pars intermedia were studied using the DiI tract-tracing technique in two amphibian species, the urodelan Triturus carnifex, and the anuran Rana esculenta. After DiI crystal application into the pituitary intermediate lobe, in both species cells were retrogradely labeled in the preoptic nucleus, in the supra- and retro-chiasmatic hypothalamus and in the brainstem (especially in the area indicated as locus coeruleus). The findings are discussed in relation to data on the neurochemical nature of the innervation of the pars intermedia in amphibians.
Neuroscience Letters 04/1994; 169(1-2):163-6. · 2.11 Impact Factor
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ABSTRACT: The type of mechanism(s) by which melatonin alone and/or through the intervention of other putative neurotransmitters is able to control circadian rhythms remains unresolved. Comparison of 2-[125I]iodomelatonin binding pattern in the brain of castrated and gonadally intact Japanese quail (Coturnix japonica), using quantitative receptor autoradiography, displayed that the combination of the intact gonadal condition and a long-day (16L:8D) photostimulatory schedule is responsible for major binding changes. In fact, high and low binding levels were obtained in the suprachiasmatic area and nucleus ectomamillaris (p < 0.01) and in the nucleus preopticus anterior and paleostriatum primitivum (p < 0.001), respectively. A gonadal modulatory role was not always evident in all brain areas as revealed by long-day photic cycles producing diminished (p < 0.01) binding levels in the anterior neostriatum and the nucleus rotundus of both castrated and gonadally intact animals, although elevated values were also found in the substantia grisea centralis (p < 0.05) of the same animals. Saturation binding studies revealed that gonadal and/or photic effects induce alterations in the number of binding sites, whereas the affinity constant varied only in some hypothalamic sites. Testing of GABAergic activity on 2-[125I] iodomelatonin binding levels showed that this inhibitory neurotransmitter was responsible for increasing low receptor values. Moreover, GABA-dependent influences were shown to be mediated via a GABAA receptor subtype since bicuculline (specific antagonist of this site) inhibited the elevated GABA-induced melatonin binding levels in the above brain sites of the gonadally intact quail exposed to both photoperiod cycles. Even in this case, melatonin binding changes were due to the variations in the number of binding sites. The apparent GABAergic-gonadal influence resulting in changes of the 2-[125I] iodomelatonin binding values, under the different photic conditions, provides evidences of other probable neural mechanisms that entrain circadian rhythmicity in neuroendocrine activities and in sociosexual behaviors.
Brain Research Bulletin 01/1994; 34(5):425-35. · 2.82 Impact Factor
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ABSTRACT: A polyclonal glial fibrillary acidic protein (GFAP) antiserum was used to study the distribution of GFAP-like immunoreactivity in the retina of adult vertebrates (teleosts, amphibians, reptiles, birds and mammals). GFAP-positive Müller cells were demonstrated in all the species studied, although with different degrees and patterns of immunoreactivity. In nonmammalian vertebrates, Müller cells were the only immunoreactive retinal elements. The staining was located throughout the retina of the species examined, with the exception of the rabbit, which exhibited regional variability in the expression of GFAP. The data indicate that GFAP expression in retinal Müller cells is a common feature of a wide variety of adult vertebrate species.
European journal of histochemistry: EJH 02/1992; 36(4):467-77. · 1.69 Impact Factor
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ABSTRACT: The distribution of the dipeptide carnosine was studied in the brain of the crested newt, Triturus carnifex, with immunohistochemical methods. Carnosine-like immunoreactivity (IR) is present in the cell bodies and processes of several areas of the central nervous system: in the telencephalon (especially in the medial pallium), in the diencephalon (pineal organ, thalamus, and hypothalamus), in the mesencephalon (optic tectum and tegmentum), and in the rhombencephalon (cerebellum, raphe region, and octavolateralis area). Double-labelling experiments show that carnosine IR is colocalized with tyrosine hydroxylase and neuropeptide Y IR in a few cells. Histochemical staining for heavy metals, the TIMM method, reveals that carnosine IR and TIMM labelling overlap in the medial pallium. These data indicate two primary conclusions: (a) In the crested newt brain, in contrast to those of mammals and birds, carnosine IR is not associated with glial cells but with neurons. Furthermore, carnosine is absent from the primary olfactory pathway in newts. (b) In the medial pallium of the crested newt, carnosine IR reliably identifies a population of neurons.
Brain Behavior and Evolution 02/1991; 37(3):168-78. · 2.21 Impact Factor
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ABSTRACT: The amphibian Xenopus laevis is able to adapt the colour of its skin to the light intensity of the background, by releasing α-melanophore-stimulating hormone from the pars intermedia of the hypophysis. In this control various inhibitory (dopamine, γ-aminobutyric acid, neuropeptide Y, noradrenaline) and stimulatory (thyrotropin-releasing hormone and corticotropin-releasing hormone) neural factors are involved. Dopamine, γ-aminobutyric acid and neuropeptide Y are present in suprachiasmatic neurons and co-exist in synaptic contacts on the melanotrope cells in the pars intermedia, whereas noradrenaline occurs in the locus coeruleus and noradrenaline-containing fibres innervate the pars intermedia. Thyrotropin-releasing hormone and corticotropin-releasing hormone occur in axon terminals in the pars nervosa. In the present study, the neuronal origins of these factors have been identified using axonal tract tracing. Application of the tracers 1,1' dioctadecyl-3,3,3',3' tetramethyl indocarbocyanine and horseradish peroxidase into the pars intermedia resulted in labelled neurons in two brain areas, which were immunocytochemically identified as the suprachiasmatic nucleus and the locus coeruleus, indicating that these areas are involved in neural inhibition of the melanotrope cells. Thyrotropin-releasing hormone and corticotropin-releasing hormone were demonstrated immunocytochemically in the magnocellular nucleus. This area appeared to be labelled upon tracer application into the pars nervosa. This finding is in line with the idea that corticotropin-releasing hormone and thyrotropin-releasing hormone stimulate melanotrope cell activity after diffusion from the neural lobe to the pars intermedia. After anterograde filling of the optic nerve with horseradish peroxidase, labelled axons were traced up to the suprachiasmatic area where they showed to be in contact with suprachiasmatic neurons. These neurons showed a positive reaction with anti-neuropeptide Y and the same held for staining with anti-tyrosine hydroxylase.It is suggested that a retino-suprachiasmatic pathway is involved in the control of the melanotrope cells during the process of background adaptation.
Neuroscience.
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[show abstract]
[hide abstract]
ABSTRACT: Afferent projections to the pituitary pars intermedia were studied using the DiI tract-tracing technique in two amphibian species, the urodelan Triturus carnifex, and the anuran Rana esculenta. After DiI crystal application into the pituitary intermediate lobe, in both species cells were retrogradely labeled in the preoptic nucleus, in the supra- and retro-chiasmatic hypothalamus and in the brainstem (especially in the area indicated as locus coeruleus). The findings are discussed in relation to data on the neurochemical nature of the innervation of the pars intermedia in amphibians.
Neuroscience Letters.
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[show abstract]
[hide abstract]
ABSTRACT: The type of mechanism(s) by which melatonin alone and/or through the intervention of other putative neurotransmitters is able to control circadian rhythms remains unresolved. Comparison of 2-[125I] iodomelatonin binding pattern in the brain of castrated and gonadally intact Japanese quail (Coturnix j,ponica), using quantitative receptor autoradiograph, displayed that the combination of the intact gonadal condition and a long-day (16L:8D) photostimulatory schedule is responsible for major binding changes. In fact, high and low binding levels were obtained in th suprachiasmatic area and nucleus ectomamillaris (p < 0.01) and in the nucleus preopticus anterior and paleostriatum pnmitivum (p < 0.001), respectively. A gonadal modulatory role was not always evident in all brain areas as revealed by long-day photic cycles producing diminished (p < 0.01) binding levels in the anterior neostriatum and the nucleus rotundus of both castrated and gonadally intact animals, although elevated values were also found in the substantia grisea centralis (p < 0.05) of the same animals. Saturation binding studies revealed that gonadal and/or photic effects induce alterations in the number of binding sites, whereas the affinity constant varied only in some hypothalamic sites. Testing of GABAergic activity on 2-[125I] iodomelatonin binding levels showed that this inhibitory neurotransmitter was responsible for increasing low receptor values. Moreover, GABA-dependent influences were shown to be mediated via a GABAA receptor subtype since bicuculline (specific antagonist of this site) inhibited the elevated GABA-induced melatonin binding levels in the above brain sites of the gonadally intact quail exposed to both photoperiod cycles. Even in this case, melatonin binding changes were due to the variations in the number of binding sites. The apparent GABAergic-gonadal influence resulting in changes of the 2-[125I] iodomelatonin binding values, under the different photic conditions, provides evidences of other probable neural mechanisms that entrain circadian rhythmicity in neuroendocrine activities and in sociosexual behaviors.
Brain Research Bulletin.
