Distribution and morphometric characteristics of oxytocin- and vasopressin-immunoreactive neurons in the rabbit hypothalamus

Oxytocinergic Cells of the Hypothalamic Paraventricular Nucleus Are Involved in Food Entrainment

When food is presented at a specific time of day subjects develop intense locomotor behavior before food presentation, termed food anticipatory activity (FAA). Metabolic and hormonal parameters, as well as neural structures also shift their rhythm according to mealtime. Food-entrained activity rhythms are thought to be driven by a distributed system of central and peripheral oscillators sensitive to food cues, but it is not well understood how they are organized for the expression of FAA. The hormone Oxytocin plays an important role in food intake, satiety and homeostatic glucose metabolism and although it is recognized that food is the main cue for food entrainment this hormone has not been implicated in FAA. Here we investigated the activity of oxytocinergic (OTergic) cells of the hypothalamus in relation to the timing of feeding in rabbit pups, a natural model of food entrainment. We found that OTergic cells of the supraoptic nucleus and the main body of the paraventricular nucleus (PVN) are activated after feeding which suggests that OT may be an entraining signal for food synchronization. Moreover, a detailed analysis of the PVN revealed that OTergic cells of the caudal PVN and a subpopulation in the dorsal part of the main body of this nucleus shows activation before the time of food but not 12 h later. Moreover this pattern persists in fasted subjects at the time of the previous scheduled time of nursing. The fact that those OTergic cells of the dorsal and caudal part of the PVN contain preautonomic cells that project to the adrenal, pancreas and liver perhaps may be related to the physiological changes in preparation for food ingestion, and synchronization of peripheral oscillators, which remains to be determined; perhaps they play a main role in the central oscillatory mechanism of FAA as their activity persists in fasted subjects at the time of the next feeding time.

The bovine anterior hypothalamus: Characterization of the vasopressin-oxytocin containing nucleus and changes in relation to sexual differentiation

In an effort to systematically describe the neurochemical anatomy of the bovine anterior hypothalamus, we used a series of immunocytochemical markers such as acetylcholine esterase (AChE), arginine-vasopressin (AVP), calbindin (Calb), galanin (Gal), neuropeptide-Y (NPY), oxytocin (OXT), somatostatin (SST), and vasoactive intestinal peptide (VIP). We also investigated the potential sex difference present in the suprachiasmatic nucleus (SCN) and the vasopressin-oxytocin containing nucleus (VON) of six male and six female Bos taurus. Our study revealed that the cytochemical structure of the cattle anterior hypothalamus follows the blueprint of other mammals. The VON, which was never described before in cattle, showed a sex difference with a 33.7% smaller volume and 23.2% fewer magnocellular neurons (approximately 20-30 μm) in the male. The SCN also did show a sex difference in VIP neurons and volume with a 36.1% larger female nucleus with 28.1% more cells. Additionally, we included five heifers with freemartin syndrome as a new animal model relevant to sexual differentiation in the brain. This is, to the best of our knowledge, the first freemartin study in relation to the brain. Surprisingly, the SCN of freemartin heifers was 32.5% larger than its control male and female counterparts with 29% more VIP cells. Conversely, the freemartin VON had an intermediary size between male and female. To analyze our data, a classical statistical analysis and a novel multivariate and multi-aspect approach were applied. These findings shed new light on sexual dimorphism in the bovine brain and present this species with freemartins as a valuable animal model in neuroscience.

Brain anatomy of the 4-day-old European rabbit

The European rabbit (Oryctolagus cuniculus) is a widely used model in fundamental, medical and veterinary neurosciences. Besides investigations in adults, rabbit pups are relevant to study perinatal neurodevelopment and early behaviour. To date, the rabbit is also the only species in which a pheromone - the mammary pheromone (MP) - emitted by lactating females and active on neonatal adaptation has been described. The MP is crucial since it contributes directly to nipple localisation and oral seizing in neonates, i.e. to their sucking success. It may also be one of the non-photic cues arising from the mother, which stimulates synchronisation of the circadian system during pre-visual developmental stages. Finally, the MP promotes neonatal odour associative and appetitive conditioning in a remarkably rapid and efficient way. For these different reasons, the rabbit offers a currently unique opportunity to determine pheromonal-induced brain processing supporting adaptation early in life. Therefore, it is of interest to create a reference work of the newborn rabbit pup brain, which may constitute a tool for future multi-disciplinary and multi-approach research in this model, and allow comparisons related to the neuroethological basis of social and feeding behaviour among newborns of various species. Here, in line with existing experimental studies, and based on original observations, we propose a functional anatomical description of brain sections in 4-day-old rabbits with a particular focus on seven brain regions which appear important for neonatal perception of sensory signals emitted by the mother, circadian adaptation to the short and single daily nursing of the mother in the nest, and expression of specific motor actions involved in nipple localisation and milk intake. These brain regions involve olfactory circuits, limbic-related areas important in reward, motivation, learning and memory formation, homeostatic areas engaged in food anticipation, and regions implicated in circadian rhythm and arousal, as well as in motricity.

Evolution of a vertebrate social decision-making network

Animals evaluate and respond to their social environment with adaptive decisions. Revealing the neural mechanisms of such decisions is a major goal in biology. We analyzed expression profiles for 10 neurochemical genes across 12 brain regions important for decision-making in 88 species representing five vertebrate lineages. We found that behaviorally relevant brain regions are remarkably conserved over 450 million years of evolution. We also find evidence that different brain regions have experienced different selection pressures, because spatial distribution of neuroendocrine ligands are more flexible than their receptors across vertebrates. Our analysis suggests that the diversity of social behavior in vertebrates can be explained, in part, by variations on a theme of conserved neural and gene expression networks.

Distribution of oxytocin- and vasopressin-immunoreactive neurons in the brain of the eusocial mole rat (Fukomys anselli)

Fukomys anselli, also known as Ansell's mole rat, is a subterranean, highly social (so-called eusocial) rodent that lives in Africa. These mole rats typically form multigenerational families consisting of a single monogamous breeding pair and their nonreproductive offspring. Research on other mammals suggests that oxytocin (OT) and vasopressin (VP) as well as the distribution of OT- and VP-receptors may influence social behavior and pair bonding. Recent studies on eusocial naked mole rats have shown a possible relation between sociality and OT-immunoreactive (OT-ir) processes. In this study, we examined expression patterns of OT and VP in the brains of F. anselli and the common Sprague-Dawley (SD) laboratory rat. As in other species, the majority of OT-ir and VP-ir neurons was found in the paraventricular (Pa) and supraoptic (SO) nuclei, and scattered labeling throughout the preoptic and anterior hypothalamic areas. We found no difference in either quality or quantity of OT- and VP-ir neurons between individuals of different social and reproductive ranks. Equally unexpected was the finding of specific OT-immunoreactivity in neurons of the mammillary complex of F. anselli that was not found in SD rats. Further studies are needed to determine whether these mammillary OT-ir neurons are causally related to monogamy in F. anselli and whether these correlates of monogamy are found in other species.

Brain processing of the mammary pheromone in newborn rabbits

Chemosignals strongly contribute to social interactions in mammals, including mother-young relationships. In the European rabbit, a volatile compound emitted by lactating females in milk, the 2-methylbut-2-enal, has been isolated. Carrying the properties of a pheromone, in particular the spontaneous ability to release critical sucking-related movements in newborns, it has been called the mammary pheromone (MP). Lesion of the vomeronasal organ and preliminary 2-deoxyglucose data suggested that the MP could be processed by the main olfactory system. However, the neuronal substrate that sustains the MP-induced response of neonates remained unknown. Here, we evaluated Fos expression in 4-day-old-rabbits exposed to the MP (in comparison with control neonates exposed to non-relevant odorant, no odorant or unmanipulated pups) both at the level of the olfactory bulb and central brain regions. Evidence of high and widespread Fos immunoreactivity in the main olfactory bulb appear in MP pups while the accessory olfactory bulb exhibits a negligible staining. However, no obvious bulbar pattern of Fos expression is observed, when in contrast a certain pattern emerges with the neutral odorant. Compared to this latter, the MP exposure increases Fos expression in the anterior piriform cortex, the organum vasculosum of the lamina terminalis and the habenula, with a tendency in the lateral preoptic region. For the first time, a pheromone essential for mother-young interaction is thus highlighted for its processing by the main olfactory system, the whole olfactory bulb, and by brain regions involved in osmoregulation, thirst and motivation-guided motor responses.

The rabbit pup, a natural model of nursing-anticipatory activity

Mother rabbits nurse their young once a day with circadian periodicity. Nursing bouts are brief (ca. 3 min) and occur inside the maternal burrow. Despite this limited contact mother rabbits and their pups are tuned to each other to ensure that the capacities of each party are used efficiently to ensure the weaning of a healthy litter. In this review we present behavioral, metabolic and hormonal correlates of this phenomenon in mother rabbits and their pups. Research is revealing that the circadian rhythm of locomotion shifts in parallel to the timing of nursing in both parties. In pups corticosterone has a circadian rhythm with highest levels at the time of nursing. Other metabolic and hormonal parameters follow an exogenous or endogenous rhythm which is affected by the time of nursing. In the brain, clock genes and their proteins (e.g. Per1) are differentially expressed in specific brain regions (e.g. suprachiasmatic nucleus, paraventricular nucleus) in relation to providing or ingesting milk in mothers and young, respectively. These findings suggest that circadian activities are modulated, in the mothers, by suckling stimulation and, in the young, by the ingestion of milk and/or the perception of the mammary pheromone. In conclusion, the rabbit pup is an extraordinary model for studying the entraining by a single daily food pulse with minimal manipulations. The mother offers the possibility of studying nursing as a non-photic synchronizer, also with minimal manipulation, as suckling stimulation from the litter occurs only once daily.

The hypothalamic supraoptic and paraventricular nuclei of the echidna and platypus

The monotremes are an intriguing group of mammals that have major differences in their reproductive physiology and lactation from therian mammals. Monotreme young hatch from leathery skinned eggs and are nourished by milk secreted onto areolae rather than through nipples. Parturition and lactation are in part controlled through the paraventricular and supraoptic nuclei of the hypothalamus. We have used Nissl staining, enzyme histochemistry, immunohistochemistry for tyrosine hydroxylase, calbindin, oxytocin, neurophysin and non-phosphorylated neurofilament protein, and carbocyanine dye tracing techniques to examine the supraoptic and paraventricular nuclei and the course of the hypothalamo-neurohypophysial tract in two monotremes: the short-beaked echidna (Tachyglossus aculeatus) and the platypus (Ornithorhynchus anatinus). In both monotremes, the supraoptic nucleus consisted of loosely packed neurons, mainly in the retrochiasmatic position. In the echidna, the paraventricular nucleus was quite small, but had similar chemoarchitectural features to therians. In the platypus, the paraventricular nucleus was larger and appeared to be part of a stream of magnocellular neurons extending from the paraventricular nucleus to the retrochiasmatic supraoptic nucleus. Immunohistochemistry for non-phosphorylated neurofilament protein and carbocyanine dye tracing suggested that hypothalamo-neurohypophysial tract neurons in the echidna lie mainly in the retrochiasmatic supraoptic and lateral hypothalamic regions, but most neurophysin and oxytocin immunoreactive neurons in the echidna were found in the paraventricular, lateral hypothalamus and supraoptic nuclei and most oxytocinergic neurons in the platypus were distributed in a band from the paraventricular nucleus to the retrochiasmatic supraoptic nucleus. The small size of the supraoptic nucleus in the two monotremes might reflect functional aspects of monotreme lactation.

Suckling and genital stroking induces Fos expression in hypothalamic oxytocinergic neurons of rabbit pups

Maternal behaviour in the rabbit is unusual among mammals because the doe visits her litter to nurse once every 24 h. In the present study we examined the consequences of milk intake on oxytocinergic (OT) and vasopressinergic (AVP) neurons of the supraoptic (SON) and paraventricular (PVN) nuclei of 7-day-old pups before suckling, after suckling and following anogenital stroking in un-nursed pups. To determine neuronal activation we assessed the expression of the Fos protein combined with antibodies against OT and AVP at two levels in the SON (supraoptic rostral, SOr, and supraoptic retrochiasmatic, SOrch), and three levels in the PVN (anterior, PVab; medial PVm and caudal, PVc). Daily nursing bouts lasted only 228+/-6 s throughout the observed 7 days, and pups ingested up to 34.95+/-9.0% of their body weight in milk on day 7, the day of perfusion. Suckling induced a significant increase in the number of double-labeled Fos/OT cells in both subdivisions of the SON (P<0.01) and in PVab and PVm (P<0.01). The effect in the SON was related to suckling, as it was not seen in stroked, un-nursed pups, which showed Fos increases only in PVab and PVm. All regions in the SON and PVN showed significant increases in the number of Fos/AVP neurons after suckling or stroking but, contrary to OT, the number of double-labeled Fos/AVP cells was very low. In conclusion, our results show that the oxytocinergic system of the SON and PVN is differentially activated by suckling of milk and anogenital stroking, and that the vagal-hypothalamic axis is mature in 7-day-old rabbits.

Endogenous expression of C-Fos in hypothalamic nuclei of neonatal rabbits coincides with their circadian pattern of suckling-associated arousal

Rabbits exhibit an unusually restricted form of maternal care. The newborn young are only nursed for about 3 min every 24 h and drink up to one third of their body weight in this time. They show a circadian increase in activity in anticipation of the doe's visit, which is entrained by suckling and appears analogous to feeding-entrained rhythms reported for other species. By investigating the expression of c-Fos protein in nursed and un-nursed pups at selected times before and after scheduled nursing, we were able to distinguish endogenous patterns of neuronal activation and patterns induced by suckling. Increased endogenous expression of c-Fos in the paraventricular thalamus and in the magnocellular neurons of the paraventricular hypothalamus coincided with the period of anticipatory arousal. By contrast, suckling induced c-Fos expression in the supraoptic nucleus and the parvocellular neurons of the paraventricular hypothalamus, whilst decreasing expression in the magnocellular neurons. Furthermore, the endogenous pattern of c-Fos expression was less distinct in 3-day-old compared to 7-day-old pups, suggesting maturational or experience-related influences on the neural correlates of the anticipatory arousal. In conclusion, the close correspondence between c-Fos expression and pups' endogenous rhythm of behaviour suggests that the rabbit's natural schedule of restricted nursing provides an ideal model in which to investigate the ontogeny of circadian function without disrupting the mother-offspring relationship or normal neonatal development.

Neuroanatomical distribution of vasotocin in a urodele amphibian (Taricha granulosa) revealed by immunohistochemical and in situ hybridization techniques

Immunohistochemical and in situ hybridization techniques were used to investigate the neuroanatomical distribution of arginine vasotocin-like systems in the roughskin newt (Taricha granulosa). Vasotocin-like-immunoreactive neuronal cell bodies were identified that, based on topographical position, most likely, are homologous to groups of vasopressin-immunoreactive neuronal cell bodies described in mammals, including those in the bed nucleus of the stria terminalis, medial amygdala, basal septal region, magnocellular basal forebrain-including the horizontal limb of the diagonal band of Broca, paraventricular and supraoptic nuclei, suprachiasmatic nucleus, and dorsomedial hypothalamic nucleus. Several additional vasotocin-like-immunoreactive cell groups were observed in the forebrain and brainstem regions; these observations are compared with previous studies of vasotocin- and vasopressin-like systems in vertebrates. Arginine vasotocin-like-immunoreactive fibers and presumed terminals also were widely distributed with high densities in the basal limbic forebrain, the ventral preoptic and hypothalamic regions, and the brainstem ventromedial tegmentum. Based on in situ hybridization studies with synthetic oligonucleotide probes for vasotocin and the related neuropeptide mesotocin, as well as double-labeling studies with combined immunohistochemistry and in situ hybridization, we conclude that the vasotocin immunohistochemical procedures used identify vasotocin-like, but not mesotocin-like, elements in the brain of T. granulosa. The distribution of arginine vasotocin-like systems in T. granulosa is greater than the distribution previously reported for any other single vertebrate species; however, it is consistent with an emerging pattern of distribution of vasotocin- and vasopressin-like peptides in vertebrates. Complexity in the vasotocinergic system adds further support to the conclusion that this peptide regulates multiple neurophysiological and neuroendocrinological functions.

Immunohistochemical localization of corticotropin-releasing factor, [arginine8]-vasopressin and oxytocin neurons in the goat hypothalamus

Distribution patterns of corticotropin-releasing factor (CRF), [arginine8]-vasopressin (AVP) and oxytocin (OXY) neurons were examined immunohistochemically in the female goat hypothalamus. The majority of the CRF immunoreactive (-IR) cells were located in the parvocellular part of the paraventricular nucleus (PVN) with smaller population found in the magnocellular part of the PVN. CRF-IR cells were also found in the suprachiasmatic nucleus, the preoptic area and around the fornix in the caudal part of the hypothalamus. AVP- and OXY-IR cells were similarly distributed in the hypothalamus. The majority of AVP- and OXY-IR cells were observed in the magnocellular part of PVN and the supraoptic nucleus. Smaller numbers of AVP- and OXY-IR cells were found in the parvocellular part of the PVN and lateral hypothalamic area. AVP-IR but not OXY-IR cells were located in the suprachiasmatic nucleus. CRF-IR fibers were concentrated in the external palisade zone of the median eminence (ME) with a few fibers found in the internal palisade zone of the ME, whereas AVP- and OXY-IR fibers were concentrated in the internal palisade zone of the ME with a few fibers found in the external zone. These results support the view that not only CRF but also AVP and OXY are released into the hypophysial portal blood and involved in the control of pituitary endocrine function in ruminant species.

Oxytocin and vasopressin immunoreactivity in rabbit hypothalamus during estrus, late pregnancy, and postpartum

Mother rabbits construct an elaborate maternal nest before parturition and display a single, brief, daily nursing bout throughout lactation. These features present a unique model for investigating the relevance of changes in neuroendocrine secretion associated with pregnancy and parturition for the regulation of maternal behavior. In the present study we analyzed changes in the location, somal size, and number of oxytocin (OT)- and arginine vasopressin (AVP)-immunoreactive (IR) neurons in the hypothalamus of rabbits in estrus, late pregnancy (day 29), and postpartum day 1. From estrus to late pregnancy, the number of OT-IR neurons increased in the scattered cell groups located in the lateral hypothalamic area (LHA), but not in the magnocellular nuclei, i.e., paraventricular nucleus (PVN) and supraoptic nucleus (SON). On postpartum day 1 the increase in the number of OT-IR neurons was sustained in the LHA and became apparent also in the main body of the PVN, in which the number of OT-IR neurons doubled. Increases in the somal size of OT-IR cells were seen in all three nuclei only on postpartum day 1. No OT-IR cells were found in the suprachiasmatic nucleus (SCN). From late pregnancy and into postpartum day 1 increases in the somal size of AVP-IR neurons were detected in the PVN, SON, and LHA but not in the SCN. The number of AVP-IR neurons increased between late pregnancy and postpartum day 1 in the SON only. The changes observed in OT and AVP expression in specific hypothalamic nuclei may be related to specific somatic and behavioral events occurring around the time of parturition, e.g., nest-building, maintenance of homeothermy, elevation of blood volume, and nursing in mother rabbits.

Distribution of AVP and Ca(2+)-dependent PKC-isozymes in the suprachiasmatic nucleus of the mouse and rabbit

The suprachiasmatic nucleus (SCN) is the circadian pacemaker in mammals and contains a network of arginine-vasopressin-immunoreactive (AVP-ir) neurons. AVP-recipient cells contain the V1a class of receptors linked to phosphoinositol turnover and protein kinase C (PKC). The present study describes the localization of AVP and the four Ca(2+)-dependent PKC-isoforms in the mouse and rabbit SCN. An estimate of the numerical density of AVP-ir neurons at the rostral, medial, and caudal level of the SCN revealed that the mouse SCN contains more than twice the number of AVP-ir neurons than the rabbit SCN. Neurons immunostained for AVP or PKC dominated in the dorsomedial and ventrolateral aspects of the mouse SCN, while the central area of the SCN revealed only weakly stained neurons. The rabbit SCN was characterized by a more homogeneous distribution of AVP-ir and PKC-ir neurons. PKC alpha was the most abundantly expressed isozyme in both species, whereas the presence of the other isoforms differed (mouse: PKC alpha > PKC beta I >> PKC beta II > PKC gamma; rabbit: PKC alpha > PKC beta II > or = PKC gamma > PKC beta I). Clear PKC gamma-positive neurons were only observed in the rabbit SCN, while the mouse SCN predominantly contained immunolabeled fiber tracts for this PKC isozyme. Astrocytes immunoreactive for each PKC isoform were frequently encountered in the rabbit SCN, but were absent in mice. Immunofluorescence double labeling showed that numerous AVP-recipient cells in the mouse SCN were immunopositive for PKC alpha, and that nearly all AVP-ir neurons express PKC alpha abundantly. These results substantiate the putative role for PKC alpha in vasopressinergic signal transduction in the SCN. The differential expression in degree and cell type of the Ca(2+)-dependent PKC-isoforms in the mouse and rabbit SCN may be related to the differences observed in circadian timekeeping between the two species.

Vasopressin in the brain of a desert hibernator, the jerboa (Jaculus orientalis): presence of sexual dimorphism and seasonal variation

The distribution of vasopressin innervation in the brain of the jerboa (Jaculus orientalis) was investigated, with special attention to sex differences and seasonal variations. Vasopressin perikarya were observed in the paraventricular and supraoptic nuclei, the suprachiasmatic nucleus, the periventricular nucleus, the medial preoptic area, the bed nucleus of the stria terminalis, and the medial amygdaloid nucleus. In addition, vasopressin cell bodies were observed in the ventral retrochiasmatic area. After treatment with colchicine, vasopressin perikarya were also observed around the organum vasculosum laminae terminalis, in the medial diagonal band of Broca, and in the dorsal medial preoptic nucleus. Vasopressin fibers were also found to be more widespread in the jerboa brain than in other rodents. Fibers were observed in the medial diagonal band of Broca, the stria medullaris, the tuber cinerum, the area postrema, the medial vestibular nucleus, and the dorsal motor nucleus of the vagus. Sexual dimorphism and seasonal variation in vasopressin immunoreactivity were observed in areas that not only showed a testosterone-dependent vasopressin innervation in other rodents but also in the paratenial and mediodorsal thalamic nuclei, the tuber cinerum, the supramammillary complex, the zona incerta, the interpeduncular complex, and the dorsal and medial raphe nuclei. A denser vasopressin innervation was observed in spring/summer (sexual active period) than in autumn. Numerous brain structures contained vasopressin receptors (cerebral cortex, hypothalamus, substantia nigra, dentate gyrus, thalamic nuclei, superior colliculus, dorsal cochlear nucleus, and cerebellum); no sex- or season-related differences were observed. These data indicate a high level of vasopressin in the jerboa brain, which may reflect an adaptation to its harsh bioclimatic environment.

Hamster supraoptic nucleus: cytoarchitectural, morphometric, and three-dimensional reconstruction

BACKGROUND

The present paper describes the cytoarchitectonic, morphometric, and three-dimensional characteristics of the golden hamster supraoptic nucleus (SON) in order to provide an anatomical basis for subsequent morphofunctional studies that use this species as an experimental animal. The dimensions (volume and length) and the number of cells of each part of the supraoptic nucleus were obtained, as well as morphometric parameters of their neurons (cross-sectional area and maximum and minimum diameters). A three-dimensional reconstruction of hamster SON has been made in order to know the spatial morphology of this nucleus and to reveal the structural differences between both parts.

METHODS

Ten male adult golden hamsters (Mesocricetus auratus) were used. Animals were anaesthetized and transcardially perfused with 4% paraformaldehyde in 0.1 M phosphate buffer at pH 7.2. The hypothalamic area from seven animals was dissected out, dehydrated, and embedded in paraffin. Serial sections of 10 microns were cut in a coronal plane. Sections were stained with thionin, dehydrated, cleared in eucalyptol, and mounted with Eukitt. To prove the neurosecretory nature to the SON, every fourth section was immunostained against neurophysin by using the peroxidase-antiperoxidase method. To study the neuronal morphometric parameters, all magnocellular neurons of the SON were drawn in sections separated 80 microns with the aid of a camera lucida under 500x magnification. Serial 50 microns thick frozen sections of the hypothalamus from three animals were drawn with camera lucida to determine the volume of the two parts of the SON and to make the three-dimensional reconstruction.

RESULTS

The SON extends rostrocaudally 1.98 +/- 0.03 mm from the preoptic area to the tuberal hypothalamic area. Two classical parts can be clearly delimited: principal (SONp) and retrochiasmatic (SONr). The neuronal population of the two parts of the SON appears constituted only by magnocellular neurons. The volume of the SONp is 0.039 +/- 0.03 mm3 and contains about 762 +/- 93 magnocellular cells, with a density of 19,151.8 cells/mm3. The volume of the SONr is 0.126 +/- 0.03 mm3 and contains about 1,296 +/- 132 neurons with a density of 10,536.6 cells/mm3. The three-dimensional reconstruction reveals that the SONp appears located in a more cephalic, lateral, and dorsal position than the SONr, and a clear discontinuity between the two parts is observed.

CONCLUSIONS

The present study shows that the classically termed SON, in the hamster, clearly consists of two spatially separated neural populations. The SONr is longer than SONp and has the larger volume and higher number of neurons; however, the neurons of the SONr are smaller in cell area than those of the SONp.

Electrical stimulation of the paraventricular nucleus attenuates pyrogen fever in the rabbit

Arginine vasopressin (AVP) perfused within the ventral septal area (VSA) suppresses fever normally evoked by pyrogenic substances, including Salmonella abortus equi (SAE). Neurons containing AVP and located within the paraventricular nucleus (PVN) or the nearby bed nucleus of the stria terminalis (BnST) are believed to have projections to this septal region. A series of experiments was undertaken to determine whether electrical stimulation of these areas, which might be expected to cause the release of AVP within the VSA, would affect similarly the pathogenesis of fever. A stainless steel cannula was implanted surgically in each of 22 male New Zealand White rabbits and a monopolar electrode was lowered through this guide cannula to the PVN or BnST areas. Electrical stimulation (20 Hz, 10 s on, 10 s off, 2.6-3.2 V) was initiated 30 min prior to and was continued until 90 min after the intravenous (i.v.) administration of 0.1-1.0 micrograms of SAE (1.0 ml carrier vehicle). While afebrile body temperature remained unchanged, electrical stimulation of sites located in the rostral extension of the PVN effectively attenuated the pyrogen-induced fever. Stimulation of sites outside these areas did not affect either the absolute magnitude or the duration of the fever. Although the reduction in fever was most pronounced during the period of electrical stimulation, in some cases the fever remained suppressed beyond the application of the current. These experiments provide the first evidence that electrical stimulation of paraventricular areas with AVP-containing cell bodies is effective in suppressing a fever evoked by systemic administration of a pyrogen. Although untested, it is possible that a stimulus-induced release of AVP within the VSA is responsible for the attenuation of the fever.

Distribution of vasopressin and oxytocin cells and fibres in the hypothalamus of the domestic pig (Sus scrofa)

The distribution of vasopressin and oxytocin cells and fibres was studied in the pig hypothalamus by means of monoclonal antibodies, in order to prevent the non-specific staining that is characteristic for the pig. The nucleus circularis is described for the first time in the pig hypothalamus and consists of both oxytocin and vasopressin containing cell bodies. A cell group, characteristic for the pig and horse, lateral and caudal from the vascular organ of the lamina terminalis, was found to be continuous with the supraoptic nucleus. It contained only oxytocin and it is proposed that this group be called pars dorsomedialis of the supraoptic nucleus. In this study, vasopressin has been demonstrated for the first time in the suprachiasmatic nucleus of the pig. The discussion focusses on how our findings in the pig differ from vasopressin and oxytocin systems identified in other mammalian species.

Comparative analysis of the vasotocinergic and mesotocinergic cells and fibers in the brain of two amphibians, the anuran Rana ridibunda and the urodele Pleurodeles waltlii

To obtain more insight into the vasotocinergic and mesotocinergic systems of amphibians and the evolution of these neuropeptidergic systems in vertebrates in general, the distribution of vasotocin (AVT) and mesotocin (MST) was studied immunohistochemically in the brains of the anuran Rana ridibunda and the urodele Pleurodeles waltlii. In Rana, AVT-immunoreactive cell bodies are located in the nucleus accumbens, the dorsal striatum, the lateral and medial part of the amygdala, an area adjacent to the anterior commissure, the magnocellular preoptic nucleus, the hypothalamus, the mesencephalic tegmentum, and in an area adjacent to the solitary tract. In Pleurodeles, AVT-immunoreactive somata are confined to the medial amygdala, the preoptic area, and an area lateral to the presumed locus coeruleus. In both species, the distribution of MST-immunoreactive cell bodies is more restricted: in the frog, MST-immunoreactive somata are present in the medial amygdala and the preoptic area, whereas, in the urodele, cell bodies are found only in the preoptic area. Both in Rana and Pleurodeles, AVT- and MST-immunoreactive fibers are distributed throughout the brain and spinal cord. A major difference is that in Rana the number of MST-immunoreactive fibers is evidently higher than that of AVT-immunoreactive fibers, whereas the opposite is found in Pleurodeles. This holds, in particular, for the forebrain and the brainstem. The presence of several extrahypothalamic AVT-immunoreactive cell groups and the existence of well-developed extrahypothalamic networks of AVT- and MST-immunoreactive fibers are features that amphibians share with amniotes. However, this study has revealed that major differences exist not only between species of different classes of vertebrates, but also within a single class. In order to determine whether features of these neuropeptidergic systems are primitive or derived, a broad selection of species of each class of vertebrates is needed.

A vasopressin and oxytocin containing nucleus in the pig hypothalamus that shows neuronal changes during puberty

A vasopressin and oxytocin containing nucleus is described for the first time in the pig hypothalamus. It is located near the third ventricle, just dorsal to the suprachiasmatic nucleus, and consists of magnocellular neurons, similar to those of the supraoptic nucleus and paraventricular nucleus. Morphometric analysis of neuronal number, size, density, and volume was performed at four different ages: 1 day, 7 weeks, 16 weeks, and 30 weeks postnatally. No sex difference in these parameters was observed. In this period the volume of the nucleus increased gradually from 6.6 x 10(-3) to 54.2 x 10(-3) mm3. One day after birth 1,215 +/- 191 (mean +/- SEM) neurons were present in the vasopressin and oxytocin containing nucleus, followed by a decrease to 771 +/- 80 neurons at 7 weeks and 697 +/- 116 at 16 weeks. Between 16 and 30 weeks (puberty) there was a dramatic increase in neuron number up to 1,765 +/- 214 neurons. This increase in the number of vasopressin and oxytocin containing neurons in the pig hypothalamus is much later in development than has ever been reported so far.