Studies on the distribution of vasopressin-immunoreactive neuronal perikarya and their fibers in the hypothalamus of Tupaia belangeri

Distribution of vasotocin- and vasoactive intestinal peptide-like immunoreactivity in the brain of blue tit (Cyanistes coeruleus)

Blue tits (Cyanistes coeruleus) are songbirds, used as model animals in numerous studies covering a wide field of research. Nevertheless, the distribution of neuropeptides in the brain of this avian species remains largely unknown. Here we present some of the first results on distribution of Vasotocine (AVT) and Vasoactive intestinal peptide (VIP) in the brain of males and females of this songbird species, using immunohistochemistry mapping. The bulk of AVT-like cells are found in the hypothalamic supraoptic, paraventricular and suprachiasmatic nuclei, bed nucleus of the stria terminalis, and along the lateral forebrain bundle. Most AVT-like fibers course toward the median eminence, some reaching the arcopallium, and lateral septum. Further terminal fields occur in the dorsal thalamus, ventral tegmental area and pretectal area. Most VIP-like cells are in the lateral septal organ and arcuate nucleus. VIP-like fibers are distributed extensively in the hypothalamus, preoptic area, lateral septum, diagonal band of Broca. They are also found in the bed nucleus of the stria terminalis, amygdaloid nucleus of taenia, robust nucleus of the arcopallium, caudo-ventral hyperpallium, nucleus accumbens and the brainstem. Taken together, these results suggest that both AVT and VIP immunoreactive structures show similar distribution to other avian species, emphasizing evolutionary conservatism in the history of vertebrates. The current study may enable future investigation into the localization of AVT and VIP, in relation to behavioral and ecological traits in the brain of tit species.

Distribution of vasopressin, oxytocin and vasoactive intestinal polypeptide in the hypothalamus and extrahypothalamic regions of tree shrews

Vasopressin (VP), oxytocin (OXT) and vasoactive intestinal polypeptide (VIP) in the brain modulate physiological and behavioral processes in many vertebrates. Day-active tree shrews, the closest relatives of primates, live singly or in pairs in territories that they defend vigorously against intruding conspecifics. However, anatomy concerning peptidergic neuron distribution in the tree shrew brain is less clear. Here, we examined the distribution of VP, OXT and VIP immunoreactivity in the hypothalamus and extrahypothalamic regions of tree shrews (Tupaia belangeri chinensis) using the immunohistochemical techniques. Most of VP and OXT immunoreactive (-ir) neurons were found in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. In addition, VP-ir or OXT-ir neurons were scattered in the preoptic area, anterior hypothalamic areas, dorsomedial hypothalamic nucleus, stria terminalis, bed nucleus of the stria terminalis and medial amygdala. Interestingly, a high density of VP-ir fibers within the ventral lateral septum was observed in males but not in females. Both VP-ir and VIP-ir neurons were found in different subdivisions of the suprachiasmatic nucleus (SCN) with partial overlap. VIP-ir cells and fibers were also scattered in the cerebral cortex, anterior olfactory nucleus, amygdala and dentate gyrus of the hippocampus. These findings provide a comprehensive description of VIP and a detailed mapping of VP and OXT in the hypothalamus and extrahypothalamic regions of tree shrews, which is an anatomical basis for the participation of these neuropeptides in the regulation of circadian behavior and social behavior.

Distribution of orexin/hypocretin immunoreactivity in the brain of a male songbird, the house finch, Carpodacus mexicanus

Previous research has shown orexin/hypocretin immunoreactive (orexin-ir) neurons in domesticated Galliformes. However, these findings may not be representative of other birds and these studies did not include a distribution of orexin-ir projections throughout the brain. The present study was carried out in a wild-caught passerine, the house finch, Carpodacus mexicanus, and includes a detailed description of orexin-ir neurons and their projections. Orexin A and B-ir neurons were located in a single population centered on the paraventricular nucleus of the hypothalamus extending into the lateral hypothalamic area, consistent with other studies in birds. Orexin A and B-ir fibers were similarly visible across the brain, with the highest density within the preoptic area, hypothalamus and thalamus. Orexin-ir projections extended from the paraventricular nucleus rostrally to the preoptic area, laterally towards the medial striatum, nidopallium, and dorsally along the lateral ventricle towards the mesopallium. Caudally, the highest densities of orexin-ir fibers were found along the third ventricle. The periaqueductal grey, substantia nigra pars compacta and the locus coeruleus also showed a high density of orexin-ir fibers. This study showed a detailed fiber distribution previously unreported in birds and showed that orexin-ir neurons were located in similar areas regardless of phylogeny or domestication in birds. The apparently conserved neural distribution of orexins suggests that these peptides play similar roles among birds. The widespread distribution of the projections in brain areas serving various roles indicates the potential involvement of these peptides in multiple behavioral and physiological functions.

Comparative neuroanatomy of vasotocin and vasopressin in amphibians and other vertebrates

This review focuses on the neuroanatomical distribution of vasotocin (VT) and vasopressin (VP) and presents a comparative analysis of brain areas in which VT and VP cell bodies have been reported in fish, amphibians, reptiles, birds and mammals. A comparison of information from previous neuroanatomical studies of VT and VP with findings from a recent study of VT in an amphibian (Taricha granulosa) supports the conclusions that the VT/VP system can be subdivided into identifiable groups of cell bodies, based on neuroanatomical and cell morphology characteristics, and that these cell groups are not necessarily delimited by classical neuroanatomical boundaries. The comparative neuroanatomy of the distribution of VT and VP cell bodies also indicates that the neuroanatomy of the VT/VP system is fairly conserved among vertebrates. The review uses comparative data to present a series of tentative hypotheses about the homology of the VT cell groups and VP cell groups in the different vertebrate taxa.