Gene expression profiles of estrogen receptors α and ß in the fetal bovine hypothalamus and immunohistochemical characterization during development.

Steroid hormones intervene in the structural and functional regulation of neuronal processes during development and thus determine brain differentiation. The effects of estrogens are mediated by two transcription factors, namely estrogen receptor α (ER-α) and estrogen receptor ß (ER-ß), that regulate the expression of target genes through their binding to specific DNA target sequences. We describe the mRNA expression of ER-α and ER-ß in the hypothalamus of developing male and female bovines as revealed by quantitative real-time polymerase chain reaction, and the distribution of the two ERs in hypothalamic sections of all fetal stages as shown by immunohistochemistry. The expression profiles of the mRNAs of both ERs are mutually correlated throughout the gestation period, and their levels increase significantly in the last stages of gestation. No sexual differences in the mRNA expression of either ER-α or ER-ß have been found in our fetal specimens. The use of specific antisera against ER-α and ER-ß has allowed us to characterize and confirm the distribution of these receptors in the hypothalami of all fetal stages considered. Our results offer detailed information concerning the distribution of ER-α and ER-ß in the developing bovine hypothalamus and provide additional insights into the processes involved in the hypothalamic development of a mammal with a long gestation and a highly gyrencephalic brain.

Distribution of vasoactive intestinal peptide (VIP) immunoreactivity in the rat pallial and subpallial amygdala and colocalization with γ-aminobutyric acid (GABA).

The amygdaloid complex, also known as the amygdala, is a heterogeneous group of distinct nuclear and cortical pallial and subpallial structures. The amygdala plays an important role in several complex functions including emotional behavior and learning. The expression of calcium-binding proteins and peptides in GABAergic neurons located in the pallial and subpallial amygdala is not uniform and is sometimes restricted to specific groups of cells. Vasoactive intestinal polypeptide (VIP) is present in specific subpopulations of GABAergic cells in the amygdala. VIP immunoreactivity has been observed in somatodendritic and axonal profiles of the rat basolateral and central amygdala. However, a comprehensive analysis of the distribution of VIP immunoreactivity in the various pallial and subpallial structures is currently lacking. The present study used immunohistochemical and morphometric techniques to analyze the distribution and the neuronal localization of VIP immunoreactivity in the rat pallial and subpallial amygdala. In the pallial amygdala, VIP-IR neurons are local inhibitory interneurons that presumably directly and indirectly regulate the activity of excitatory pyramidal neurons. In the subpallial amygdala, VIP immunoreactivity is expressed in several inhibitory cell types, presumably acting as projection or local interneurons. The distribution of VIP immunoreactivity is non-homogeneous throughout the different areas of the amygdaloid complex, suggesting a distinct influence of this neuropeptide on local neuronal circuits and, consequently, on the cognitive, emotional, behavioral and endocrine activities mediated by the amygdala.

Connections of the sheep basolateral amygdala: A diffusion tensor imaging study.

BACKGROUND: A large amount of anatomic data published over the past decade has provided novel insight into the connections of the basolateral amygdala (BLA) in the rat, cat, and monkey. The mammalian (rat, cat, and monkey) BLA has strong connections with the cortex (especially piriform, and frontal cortices), the hippocampal region (especially perirhinal cortex, entorhinal cortex, and subiculum), the thalamus (in particular, the posterior internuclear nucleus and medial geniculate nucleus) and, to some extent, the hypothalamus. An important question remains as to how well the data obtained in rodents and primates can be extrapolated to ruminants. NEW METHOD: To address this issue the connections of the sheep BLA has been determined by Magnetic Resonance Imaging (MRI) and Diffusion Tensor Imaging (DTI, Tractography). RESULTS: Tractography showed ipsilateral connections between the BLA and several areas. COMPARISON WITH EXISTING METHOD(S): Reviews based mainly on description of the results obtained using anterograde and retrograde neuronal tracers. In the present research, we prefer to use a non-invasive technique (DTI). CONCLUSIONS: This report shows the existence of specific amygdaloid connections in the sheep.

Cytoarchitectureal changes in hippocampal subregions of the NZB/W F1 mouse model of lupus.

Over 50% of clinical patients affected by the systemic lupus erythematosus disease display impaired neurological cognitive functions and psychiatric disorders, a form called neuropsychiatric systemic lupus erythematosus. Hippocampus is one of the brain structures most sensitive to the cognitive deficits and psychiatric disorders related to neuropsychiatric lupus. The purpose of this study was to compare, layer by layer, neuron morphology in lupus mice model NZB/W F1 versus Wild Type mice. By a morphometric of cells identified on Nissl-stained sections, we evaluated structural alterations between NZB/W F1 and Wild Type mice in seven hippocampal subregions: Molecular dentate gyrus, Granular dentate gyrus, Polymorph dentate gyrus, Oriens layer, Pyramidal layer, Radiatum layer and Lacunosum molecular layer. By principal component analysis we distinguished healthy Wild Type from NZB/W F1 mice. In NZB/W F1 mice hippocampal cytoarchitecture, the neuronal cells resulted larger in size and more regular than those of Wild Type. In NZB/W F1, neurons were usually denser than in WT. The Pyramidal layer neurons were much denser in Wild Type than in NZB/W F1. Application of principal component analysis, allowed to distinguish NZB/W F1 lupus mice from healthy, showing as NZBW subjects presented a scattered distribution and intrasubject variability. Our results show a hypertrophy of the NZB/W F1 hippocampal neurons associated with an increase in perikaryal size within the CA1, CA2, CA3 region and the DG. These results help advance our understanding on hippocampal organization and structure in the NZB/W F1 lupus model, suggesting the hypothesis that the different subregions could be differentially affected in neuropsychiatric systemic lupus erythematosus disease. Leveraging an in-depth analysis of the morphology of neural cells in the hippocampal subregions and applying dimensionality reduction using PCA, we propose an efficient methodology to distinguish pathological NZBW mice from WT mice."

Stereology of the neocortex in Odontocetes: qualitative, quantitative, and functional implications.

We investigated the quantitative morphology of the neocortex (gray matter) in 2 toothed whale (odontocete) species (harbor porpoise, Phocoena phocoena; bottlenose dolphin, Tursiops truncatus) with stereological methods. The 4 primary projection areas (motor, somatosensory, auditory, and visual fields) are analyzed for their cell densities in layers III and V with standard design-based stereology methods. Along cortical areas M1, S1, A1, and V1 in Tursiops, neuron density is always higher in layer III than in layer V, whereas the data in Phocoena are variable. Moreover, neuron density in layer III is generally around 1.5 times higher in Tursiops than in Phocoena. Maximal density values are seen in layer III of A1 and V1 in Tursiops and the ratio of layer III/layer V density is maximal in A1 of this species. Thus, layer III could have a higher capacity in the bottlenose dolphin with regard to intrinsic connectivity. Extant knowledge on toothed whale neurobiology and behavior suggests that quantitative/stereological differences between the 2 odontocete species regarding the neuron density of standard cortical units may be correlated with specific adaptations to their respective habitats. In contrast to layers V and VI which mainly serve as an executive system, layer III could represent an intermediate level in sensory and premotor processing which works more tangentially in the cortices via horizontal connections with other cortical areas, respectively. The generally higher density of cortical layer III in Tursiops suggests a higher connectivity of this layer in view of the more agile and complicated behavior of these gregarious animals including versatile phonation by complex sound and ultrasound signals.

Expression and localization of aromatase P450AROM, estrogen receptor-α, and estrogen receptor-ß in the developing fetal bovine frontal cortex.

The enzyme aromatase (P450(AROM)) converts testosterone (T) into 17-ß estradiol (E(2)) and is crucial for the control of development of the central nervous system during ontogenesis. The effects of E(2) in various brain areas are mediated by the estrogen receptor alpha (ER-α) and the estrogen receptor beta (ER-ß). During fetal development, steroids are responsible for the sexual differentiation of the hypothalamus. Estrogens are also able to exert effects in other brain areas of the fetus including the frontal cortex, where they act through estrogen receptors (ERs) modulating cognitive function and affective behaviors. In this study we have determined the expression profiles of P450(AROM) and ERs in the fetal bovine frontal cortex by quantitative Real-Time PCR (qRT-PCR) throughout the prenatal development. The data show that the patterns of expression of both ERs are strongly correlated during pregnancy and increase in the last stage of gestation. On the contrary, the expression of P450(AROM) has no correlation with ERs expression and is not developmentally regulated. Moreover, we performed immunochemical studies showing that fetal neurons express P450(AROM) and the ERs. P450(AROM) is localized in the cytoplasm and only seldom present in the fine extensions of the cells; ER-α is detected predominantly in the soma whereas ER-ß is only present in the nucleus of a few cells. This study provides new data on the development of the frontal cortex in a long gestation mammal with a large convoluted brain.

Multi-aspect testing and ranking inference to quantify dimorphism in the cytoarchitecture of cerebellum of male, female and intersex individuals: a model applied to bovine brains.

The dimorphism among male, female and freemartin intersex bovines, focusing on the vermal lobules VIII and IX, was analyzed using a novel data analytics approach to quantify morphometric differences in the cytoarchitecture of digitalized sections of the cerebellum. This methodology consists of multivariate and multi-aspect testing for cytoarchitecture-ranking, based on neuronal cell complexity among populations defined by factors, such as sex, age or pathology. In this context, we computed a set of shape descriptors of the neural cell morphology, categorized them into three domains named size, regularity and density, respectively. The output and results of our methodology are multivariate in nature, allowing an in-depth analysis of the cytoarchitectonic organization and morphology of cells. Interestingly, the Purkinje neurons and the underlying granule cells revealed the same morphological pattern: female possessed larger, denser and more irregular neurons than males. In the Freemartin, Purkinje neurons showed an intermediate setting between males and females, while the granule cells were the largest, most regular and dense. This methodology could be a powerful instrument to carry out morphometric analysis providing robust bases for objective tissue screening, especially in the field of neurodegenerative pathologies.

Distribution of Calretinin Immunoreactivity in the Lateral Nucleus of the Bottlenose Dolphin (Tursiops truncatus) Amygdala.

The amgdaloid complex consists of different nuclei, each with unique cytoarchitectonic, chemoarchitectonic and connectional characteristics. Most of the inputs coming from cortical and subcortical areas enter the amygdala via the lateral nucleus, which makes it the main receiving structure of the complex. The activity of its neurons is coordinated and modulated by different inhibitory, GABAergic-interneurons, which can be classified for their expression of various calcium-binding proteins, as well as by morphological characteristics. This research based on the analysis of the amygdala of three bottlenose dolphins, provides the first description of the topography, cytoarchitecture and distribution of calretinin immunoreactivity of the lateral nucleus. Our observations on the bottlenose dolphin confirmed the general topography of the mammalian amygdala and of the lateral nucleus. Notably, we identified six subdivision of the nucleus, more than those reported until now in the rat, monkey and human lateral nucleus. This could reveal an outstanding capability of integration and elaboration of external stimuli. In addition, we observed a strong presence of CR-immunoreactive (-ir) neurons and fibres. CR-ir neurons were mainly non-pyramidal inhibitory neurons; in particular, 80% of IR-cells were represented by large and small polygonal neurons. In the lateral nucleus of the human amygdala, CR-ir neurons form inhibitory synapses on calbindin-D28k-IR inhibitory interneurons. Since calbindin-D28k-ir interneurons make inhibitory synapses on the pyramidal cells, the final goal of the CR-ir interneurons could be the synchronization of cells activity, thus playing an important role in the control of information flow in the lateral amygdalar nucleus. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:2008-2016, 2017. © 2017 Wiley Periodicals, Inc.

The Inferior Alveolar Nerve of the Horse: Course and Anatomical Relationship with Mandibular Cheek Teeth.

The precise location of neurovascular structures within the relatively long mandibular canal of the horse is of paramount importance in surgical procedures of the area. The inferior alveolar nerve (IAN) enters the mandibular canal on the medial (lingual) surface of the mandible and innervates all the mandibular teeth. During its course, the nerve moves laterally, crossing the roots of the inferior cheek teeth. However, the exact anatomical relationships occurring between the IAN and the roots of the equine mandibular cheek teeth have not been described in detail. In this study, the mandibles of 40 horses were examined with CT scans and then used for bilateral detailed anatomical dissection, to assess the path of the IAN and its relationship to the roots of the lower cheek teeth. The data obtained show that the equine IAN is located ventral to the apices of the molar teeth (311/411, 310/410, 309/409 according to the Triadan numerical system). At the level of PM(4) (308/408), the IAN is located on the lingual side of the roots and coronally to its apices. At the level of PM(3) (307/407), the IAN is then found on the lingual side of the roots but in proximity to the apices. In 2 of 40 horses (=5%), the IAN moves towards the lingual side between the mesial and the distal root of PM(4). Our observations are valuable for planning a surgical approach to the ventral side of the mandible in the horse and to avoid potential post-operative complications.

Melatonin signal transduction and mechanism of action in the central nervous system: using the rabbit cortex as a model.

The cortex of the rabbit (Oryctolagus cuniculus) is rich in melatonin binding sites, and particularly abundant is the parietal cortex. Consequently, we characterized the putative melatonin receptor in the parietal cortex by a series of in vitro ligand-receptor binding experiments and biochemical and electrophysiological studies. The in vitro saturation and competition experiments demonstrated that the binding in the crude cortical membrane preparations was of high affinity and specificity. Guanine nucleotides (GDP, GTP, and GTP gamma S) inhibited the specific 2-[125I]iodomelatonin binding in a dose-dependent manner. Coincubation with a nonhydrolyzable GTP analog provoked a shift in the binding affinity; the numerical values of the Kd increased from 20-30 to 200-600 pM. Melatonin, in nanomolar concentrations, was able to inhibit the forskolin-stimulated accumulation of cAMP in parietal cortex explants, and preincubation with pertussis toxin counteracted this effect of melatonin. Apparently, the melatonin binding site in the rabbit parietal cortex is linked to its second messenger via a pertussis toxin-sensitive G-protein, probably of the inhibitory Gi class, similar to what has been described for different parts of the brain of other vertebrates. The experiments on the spontaneous firing activity of single neurons in the third to fourth layer of the parietal cortex in anesthetized animals showed that melatonin and its potent agonist 2-iodomelatonin exhibited gamma-aminobutyric acid (GABA)-like effects and were able alone, in nanomolar concentrations, to significantly slow the neuronal firing activity. Moreover, both melatonin and 2-iodomelatonin potentiated the effect of GABA on the neuronal activity, leading to powerful inhibition of the tested neurons. Undoubtedly, the binding site in the rabbit parietal cortex possesses all of the characteristics of a functional receptor. We suggest that melatonin is involved in the control of fundamental cortical functions and that it acts in concert with GABA, one of the two major inhibitory neurotransmitters in the central nervous system.

Cytosolic androgen receptors in the neuroendocrine tissues of the golden hamster: influence of photoperiod and melatonin treatment.

Hamsters exposed for eight weeks to short photoperiod (LD 10:14) or treated with melatonin in the late afternoon under long photoperiod (LD 14:10) had significantly higher number of cytosolic androgen receptors in the pituitaries, hypothalami and harderian glands, as compared to the long photoperiod (LD 14:10) exposed controls. The numerical value of the apparent Kd was two to three times lower in the hypothalami and pituitaries, but not in the harderian glands of the animals from these groups. These results indicate that alterations in receptor numbers and affinity constants may be responsible for the dramatic changes in the sensitivity of the hypothalamo-pituitary axis to the negative feedback actions of the gonadal steroids, observed under inhibitory photoperiods and that this effect could be duplicated by late afternoon melatonin treatment.

Neuropeptide Y (NPY) and C-flanking peptide of NPY in the pineal gland of normal and ganglionectomized sheep.

The present immunohistochemical study describes the presence and distribution of nerve fibers containing neuropeptide Y (NPY), and C-Flanking Peptide Of NPY (CPON) in the pineal gland of the sheep. Nerve fibers were detected by using a series of antisera directed against NPY or against CPON. Many positive immunoreactive nerve fibers were identified in the pial capsule of the pineal, in connective septae and in the parenchyma between pinealocytes. The intraparenchymal fibers were particularly evident and created an extensive network throughout the gland. Nerve fibers immunoreactive for all the peptides were also observed in the posterior commissure and in the stria medullaris thalami. No NPY- or CPON-positive neurons were found in the pineal gland. In order to study the site of origin of NPY- and CPON-immunoreactive nerve fibers, the superior cervical ganglia were bilaterally removed in a series of animals. Sympathetic denervation was checked by using an antiserum against tyrosine hydroxylase (TH). Nearly all TH-immunoreactive elements disappeared in the pineal glands of animals sacrificed 15 days after surgery. Also the density of NPY- and CPON-immunoreactive nerve fibers decreased in the animals after the ganglionectomy. However, a number of nerve fibers still remained in the gland. These data indicate that some NPY- and CPON-immunoreactive nerve fibers of the sheep pineal gland derive from an extrasympathetic origin. The very dense innervation of the sheep pineal gland with nerve fibers containing NPY and CPON strongly indicates a functional role for this family of peptides in the pineal gland of this species.

Density of peptide histidine-isoleucine- and vasoactive intestinal peptide-immunoreactive nerve fibers in the sheep pineal gland is not affected by superior cervical ganglionectomy.

Peptide histidine-isoleucine (PHI) is a regulatory peptide, synthesized as part of the same propeptide that includes also vasoactive intestinal peptide (VIP). The present study describes the distribution of PHI-immunoreactive nerve fibers in the sheep pineal organ and compares their location with the distribution of VIP-immunoreactive fibers in both normal and superior cervical ganglionectomized sheep in order to elucidate the origin of the PHI/VIP immunoreactive nerve fibers. Several PHI-immunoreactive nerve fibers were present in the meninges and in the pineal capsule. Numerous positive nerve fibers entered the pineal gland and travelled within connective tissue spaces. Individual PHI-positive nerve fibers were either smooth, without specialization, or varicose. Generally VIP- and PHI-immunoreactive fibers were located close to connective septa and blood vessels. However, many PHIergic and VIPergic fibers possessing varicosities of variable sizes were also dispersed between pinealocytes. The distribution, density, and morphology of PHI- and VIP-immunoreactive fibers in the sheep pineal gland were similar. In superior cervical ganglionectomized animals, intrapineal VIP- and PHI-immunoreactive nerve fibers were present with the same density as in control animals. In agreement, the concentration of immunoreactive VIP and PHI did not change after ganglionectomy. No VIP- and PHI-immunoreactive cell bodies were observed in the superior cervical ganglia. Thus this study shows that the intrapineal VIP- and PHI-immunoreactive nerve fibers do not originate from the sympathetic superior cervical ganglion.

Autoradiographic localization of putative melatonin receptors in the brains of two Old World primates: Cercopithecus aethiops and Papio ursinus.

The distribution of putative melatonin receptors in the brains of two Old World primates of the superfamily Catarrhina, Cercopithecus aethiops and Papio ursinus, was characterized using 2-[125I]iodomelatonin autoradiography. The specific binding demonstrated a discrete distribution pattern. The median eminence was intensely labelled, and examination at the light microscopic level demonstrated that the binding was confined to the small layer of cells comprising the pars tuberalis of the pituitary gland. The collar of pars distalis, present in the baboon (Papio ursinus), was diffusely labelled. No binding was detected in the pars distalis proper or the neural lobe of the pituitary gland. The binding in the suprachiasmatic nuclei was weaker, but well discernible. Diffuse faint specific binding was found in the frontal cortex and the dentate gyrus of the hippocampus. Two non-neural sites expressed strong, well-delineated binding: the walls of some brain blood vessels (the vertebral and spinal arteries, the inferior cerebellar and acoustic arteries, the basilar, pericallosal, internal carotid arteries, the arteries forming the circle of Willis) and the choroid plexuses. Binding in the arteries of the circle of Willis, the pars tuberalis and the suprachiasmatic nuclei was readily displaceable. Addition of 1 microM unlabelled 2-iodomelatonin following 45 min of preincubation with the radioactive ligand completely abrogated the binding. Co-incubation with guanosine 5'-O-(3-thiotriphosphate) led to a significant decrease in the apparent binding density in the pars tuberalis and abolished binding in the suprachiasmatic nuclei, but was without effect on the binding in the walls of the adjacent arteries, forming the circle of Willis, in the cortex and in the hippocampus. This qualitative distribution pattern demonstrates that in the two primate species studied, melatonin high-affinity, G-protein-linked binding sites are present in the pars tuberalis and the hypothalamic suprachiasmatic nuclei, and that melatonin may be acting as a synchronizer of the endogenous pacemakers' circadian activity, apart from its possible reproductive effects at the level of pars tuberalis, where the highest receptor density was observed. The strongly labelled arterial walls, and the flimsy labelled cortex and hippocampus, expressed different characteristics: though the binding was readily reversible, it was apparently not regulated by a guanine nucleotide-binding protein.

Innervation of the sheep pineal gland by nonsympathetic nerve fibers containing NADPH-diaphorase activity.

We used the NADPH-diaphorase histochemical method as a potential marker for nitric oxide synthase (NOS)-containing nerve fibers innervating the pineal gland of the sheep. Nerve fibers containing NADPH-diaphorase activity provide dense innervation of the sheep pineal gland. The nerve fibers were located in the pineal capsule, in the connective tissue septae separating the lobull of the gland, and penetrating between the pinealocytes. The nerve fibers were either smooth or endowed with boutons en passant. After bilateral removal of the superior cervical ganglion, the dense network of NADPH-diaphorase-positive fibers was still present in the gland. Ganglionectomy affected neither the distribution nor the appearance of the NADPH-diaphorase-positive fibers. Most of the NADPH-diaphorase-positive fibers also contained peptide histidine isoleucine and vasoactive intestinal polypeptide, and a comparatively smaller fraction contained neuropeptide Y. Pinealocytes never exhibited NADPH-diaphorase activity. These results demonstrate a major neural input to the sheep pineal gland with NADPH-diaphorase-positive nerve fibers of nonsympathetic origin.

The distribution of neuropeptide Y-immunoreactive neurons and nerve fibers in the forebrain of the carp Cyprinus carpio L.

The present study reports the distribution of Neuropeptide Y (NPY)-immunoreactive neurons and fibers in the forebrain of the adult carp Cyprinus carpio L. Serial Nissl-stained sections were used for cytoarchitecture and identification of anatomical structures. Immunostaining of NPY-containing neurons and fibers was used as neurochemical marker and tool for comparison with other species, including the goldfish. The general outline of the cytoarchitecture of the carp forebrain is similar to that of other Cypriniformes. However, using NPY immunohistochemistry, we found several specific differences with the goldfish, especially in the diencephalon. In the hypothalamus of the carp NPY-immunoreactive (NPYir) neurons were identified in the n. dorsolateralis thalami, and in the n. ventralis lateralis thalami. In the same location, we observed the n. anterior hypothalami and the n. preglomerulosus pars lateralis, described in the goldfish, as parts of n. prerotundus. However, in the carp we were not able to identify a n. preglomerulosus pars medialis, a n. preglomerulosus pars medialis commissuralis and a n. glomerulosus. We describe a n. rotundus, in which we did not find substructures typical of the goldfish. Further differences with the goldfish, trout and salmon were also noted.

The chemical neuroanatomy of the mammalian pineal gland: neuropeptides.

The mammalian pineal gland contains multiple afferent peptidergic nerve fibres. Sympathetic nerve fibres, with their origin in the superior cervical ganglia, contain neuropeptide Y colocalized with norepinephrine. Other pinealopetal nerve fibres, probably originating in the pterygopalatine ganglion, contain vasoactive intestinal peptide and peptide histidine isoleucine. Fibres containing substance P and calcitonin gene-related peptide have also been demonstrated in pinealopetal nerve fibres. These fibres might originate in the trigeminal ganglion. The neurotransmitter content of the fibres of the central innervation, innervating the gland from the brain via the pineal stalk, has not been elucidated. However, strong indications for the presence of neuropeptide Y, substance P, somatostatin, and vasopressin in these fibres have been presented. Recent immunohistochemical studies have further shown the presence of subtypes of pinealocytes containing neuropeptides. Thus, pinealocytes containing beta-endorphin, leu-enkephalin, and somatostatin have been demonstrated in the gland. Immunohistochemistry at the electron microscopical level has shown, that in some species, leu-enkephalin containing pinealocytes make synaptic contacts with other pinealocytes indicating of paracrine regulation of the pineal gland. It must however be emphasized that large interspecies variations exist with regard to the peptidergic pineal innervation and its content of peptidergic cells.

Vipergic innervation of the mammalian pineal gland.

The present article reviews the literature relative to VIP- and PHI-containing nerve fibers in the pineal gland of mammals. The article summarizes data on the presence and distribution of the two peptides in the brain of mammals, their role in neuronal metabolism, and the significance and origin of VIPergic and PHIergic cerebrovascular nerve fibers. Special emphasis is placed on VIP- and PHI-containing nerves in the pineal gland. The morphology of the fibers, the nature of the innervation, and the distribution of immunoreactive nerves within the pineal gland are examined. The review discusses the nature of the classical and "central" innervation of the pineal gland. The possible site of origin of pinealopetal VIPergic and PHIergic fibers is investigated, with special reference to ganglia of the head, and particularly to the pterygopalatine, otic, and trigeminal ganglia. The nature of VIP (and PHI) receptors is examined with reference to the most recent acquisitions in the field. Based on the data, a role for VIP (and PHI) in pineal metabolism is discussed.

Sexual differences and effect of photoperiod on melatonin receptor in avian brain.

Several data suggest that melatonin may influence avian reproduction by acting at the level of the hypothalamic-hypophisial-gonadal axis, and/or on neural circuits controlling reproductive behaviours. The action of melatonin is exerted through specific receptors whose distribution and pharmacological properties have been extensively investigated. This review will focus on the distribution, sexual dimorphism, and dependence upon the photoperiod of melatonin binding sites in avian species with a special emphasis on Japanese quail. Melatonin receptors are widely distributed in avian brain. They are mostly present in the visual pathways of all the investigated species and in the song controlling nuclei of oscine birds. Sexual dimorphism of melatonin binding sites (higher density in males than in females) was detected in some telencephalic nuclei of songbirds, in the visual pathways, and in the preoptic area of quail. The last region plays a key role in the activation of male quail copulatory behaviour and it hosts a large population of gonadotropin-releasing hormone-containing neurons. Sexual dimorphism of melatonin-binding sites in the above-mentioned regions suggests a differential role for this hormone in the modulation of visual perception, gonadotropin production, and seasonally activated behaviours in male and female quail. Further studies are necessary to understand interrelationships among photic cues, gonadal steroids, density, and sexually dimorphic distribution of melatonin receptors.

Localization and characterization of melatonin binding sites in the brain of the rabbit (Oryctolagus cuniculus) by autoradiography and in vitro ligand-receptor binding.

The distribution and the properties of the melatonin binding sites were characterized in the brain of the rabbit by combined use of autoradiography and in vitro ligand-receptor binding. Autoradiography revealed widespread specific binding in the brain. The pars tuberalis of the pituitary gland, suprachiasmatic nuclei, ventromedial hypothalamic nuclei, tapetum, hippocampus, indusium griseum, cingulate gyrus, cortex and the choroid plexus were intensely labelled. Diffuse specific binding was recorded in the olfactory bulb and the anterior hypothalamus. Series of in vitro ligand-receptor binding experiments, using the anterior hypothalamus, confirmed that the binding was of high affinity and specificity. Coincubation with a non-hydrolyzable GTP analogue provoked a shift in the binding affinity, the numerical values of the Kd increasing from 20-30 pM to 280-300 pM. Apparently the melatonin receptor in the rabbit brain is linked to its second messenger via a G protein, similarly to what has been described for the brain of other vertebrates.