The neurophysin-containing innervation of the forebrain of the mouse

Neurobiology of sociability

Sociability consists of behaviors that bring animals together and those that keep animals apart. Remarkably, while the neural circuitry that regulates these two "faces" of sociability differ from one another, two neurohormones, oxytocin (Oxt) and vasopressin (Avp), have been consistently implicated in the regulation of both. In this chapter the the structure and function of the Oxt and Avp systems, the ways in which affiliative and aggressive behavior are studied and the roles of Oxt and Avp in the regulation of sociability will be briefly reviewed. Finally, work implicating Oxt and Avp in sociability in humans, with a focus on neuropsychiatric disorders will be highlighted.

Cyto- and chemoarchitecture of the hypothalamic paraventricular nucleus in the C57BL/6J male mouse: a study of immunostaining and multiple fluorescent tract tracing

The paraventricular nucleus of the hypothalamus (PVH) plays a critical role in the regulation of autonomic, neuroendocrine, and behavioral activities. This understanding has come from extensive characterization of the PVH in rats, and for this mammalian species we now have a robust model of basic PVH neuroanatomy and function. However, in mice, whose use as a model research animal has burgeoned with the increasing sophistication of tools for genetic manipulation, a comparable level of PVH characterization has not been achieved. To address this, we employed a variety of fluorescent tract tracing and immunostaining techniques in several different combinations to determine the neuronal connections and cyto- and chemoarchitecture of the PVH in the commonly used C57BL/6J male mouse. Our findings reveal a distinct organization in the mouse PVH that is substantially different from the PVH of male rats. The differences are particularly evident with respect to the spatial relations of two principal neuroendocrine divisions (magnocellular and parvicellular) and three descending preautonomic populations in the PVH. We discuss these data in relation to what is known about PVH function and provide the work as a resource for further studies of the neuronal architecture and function of the mouse PVH.

Vasopressin innervation of the mouse (Mus musculus) brain and spinal cord

The neuropeptide vasopressin (AVP) has been implicated in the regulation of numerous physiological and behavioral processes. Although mice have become an important model for studying this regulation, there is no comprehensive description of AVP distribution in the mouse brain and spinal cord. With C57BL/6 mice, we used immunohistochemistry to corroborate the location of AVP-containing cells and to define the location of AVP-containing fibers throughout the mouse central nervous system. We describe AVP-immunoreactive (-ir) fibers in midbrain, hindbrain, and spinal cord areas, which have not previously been reported in mice, including innervation of the ventral tegmental area, dorsal and median raphe, lateral and medial parabrachial, solitary, ventrolateral periaqueductal gray, and interfascicular nuclei. We also provide a detailed description of AVP-ir innervation in heterogenous regions such as the amygdala, bed nucleus of the stria terminalis, and ventral forebrain. In general, our results suggest that, compared with other species, the mouse has a particularly robust and widespread distribution of AVP-ir fibers, which, as in other species, originates from a number of different cell groups in the telencephalon and diencephalon. Our data also highlight the robust nature of AVP innervation in specific regulatory nuclei, such as the ventral tegmental area and dorsal raphe nucleus among others, that are implicated in the regulation of many behaviors.

Vasopressin cell groups exhibit strongly divergent responses to copulation and male-male interactions in mice

Arginine vasopressin (AVP) and its nonmammalian homolog arginine vasotocin influence social behaviors ranging from affiliation to resident-intruder aggression. Although numerous sites of action have been established for these behavioral effects, the involvement of specific AVP cell groups in the brain is poorly understood, and socially elicited Fos responses have not been quantified for many of the AVP cell groups found in rodents. Surprisingly, this includes the AVP population in the posterior part of the medial bed nucleus of the stria terminalis (BSTMP), which has been extensively implicated, albeit indirectly, in various aspects of affiliation and other social behaviors. We examined the Fos responses of eight hypothalamic and three extra-hypothalamic AVP-immunoreactive (-ir) cell groups to copulation, nonaggressive male-male interaction, and aggressive male-male interaction in both dominant and subordinate C57BL/6J mice. The BSTMP cells exhibited a response profile that was unlike all other cell groups: from a control baseline of approximately 5% of AVP-ir neurons colocalizing with Fos, colocalization increased significantly to approximately 12% following nonaggressive male-male interaction, and to approximately 70% following copulation. Aggressive interactions did not increase colocalization beyond the level observed in nonaggressive male mice. These results suggest that BSTMP neurons in mice may increase AVP-Fos colocalization selectively in response to affiliation-related stimuli, similar to findings in finches. In contrast, virtually all other cell groups were responsive to negative aspects of interaction, either through elevated AVP-Fos colocalization in subordinate animals, positive correlations of AVP-Fos colocalization with bites received, and/or negative correlations of AVP-Fos colocalization with dominance. These findings greatly expand what is known of the contributions of specific brain AVP cell groups to social behavior.

Absence of progestin receptors alters distribution of vasopressin fibers but not sexual differentiation of vasopressin system in mice

Perinatal estrogens increase the number of vasopressin-expressing cells and the density of vasopressin-immunoreactive fibers observed in adult male rodents. The mechanism of action of estrogens on sexual differentiation of the extra-hypothalamic vasopressin system is unknown. We hypothesized that the sexually dimorphic expression of progestin receptors (PRs) during development would masculinize vasopressin expression in mice. We compared the number of vasopressin-expressing cells in the bed nucleus of the stria terminalis (BNST) and medial amygdala and the density of vasopressin-immunoreactive fibers in several brain regions of male and female wild type and PRKO mice using in situ hybridization and immunohistochemistry. As expected, sex differences in vasopressin cell number were observed in the BNST and medial amygdaloid nucleus. Vasopressin-immunoreactive fiber density was sexually dimorphic in the lateral septum, lateral habenular nucleus, medial amygdaloid nucleus, and mediodorsal thalamus. Sex differences were also observed in the principal nucleus of the BNST and medial preoptic area but not in the dorsomedial hypothalamus, which are thought to receive vasopressin innervation from the suprachiasmatic nucleus. Deletion of PRs did not alter the sex difference in vasopressin mRNA expression and vasopressin fiber immunoreactivity in any area examined. However, deletion of PRs increased the density of vasopressin fiber immunoreactivity in the lateral habenular nucleus. Our data suggest that PRs modulate vasopressin levels, but not sexual differentiation of vasopressin innervation in mice.

Distribution of oxytocin in the brain of a eusocial rodent

Naked mole-rats are highly social rodents that live in large colonies characterized by a rigid social and reproductive hierarchy. Only one female, the queen, breeds. Most colony members are non-reproductive subordinates that work cooperatively to rear the young and maintain an underground burrow system. Little is known about the neurobiological basis of the complex sociality exhibited by this species. The neuropeptide oxytocin (Oxt) modulates social bonding and other social behaviors in many vertebrates. Here we examined the distribution of Oxt immunoreactivity in the brains of male and female naked mole-rats. As in other species, the majority of Oxt-immunoreactive (Oxt-ir) cells were found in the paraventricular and supraoptic nuclei, with additional labeled cells scattered throughout the preoptic and anterior hypothalamic areas. Oxt-ir fibers were found traveling toward and through the median eminence, as well as in the tenia tecta, septum, and nucleus of the diagonal band of Broca. A moderate network of fibers covered the bed nucleus of the stria terminalis and preoptic area, and a particularly dense fiber innervation of the nucleus accumbens and substantia innominata was observed. In the brainstem, Oxt-ir fibers were found in the periaqueductal gray, locus coeruleus, parabrachial nucleus, nucleus of the solitary tract, and nucleus ambiguus. The high levels of Oxt immunoreactivity in the nucleus accumbens and preoptic area are intriguing, given the link in other rodents between Oxt signaling in these regions and maternal behavior. Although only the queen gives birth or nurses pups in a naked mole-rat colony, most individuals actively participate in pup care.

Oxytocin deficiency mediates hyperphagic obesity of Sim1 haploinsufficient mice

Single-minded 1 (Sim1) encodes a transcription factor essential for formation of the hypothalamic paraventricular nucleus (PVN). Sim1 haploinsufficiency is associated with hyperphagic obesity and increased linear growth in humans and mice, similar to the phenotype of melanocortin 4 receptor (Mc4r) mutations. PVN neurons in Sim1(+/-) mice are hyporesponsive to the melanocortin agonist melanotan II. PVN neuropeptides oxytocin (Oxt), TRH and CRH inhibit feeding when administered centrally. Consequently, we hypothesized that altered PVN neuropeptide expression mediates the hyperphagia of Sim1(+/-) mice. To test this hypothesis, we measured hypothalamic expression of PVN neuropeptides in Sim1(+/-) and wild-type mice. Oxt mRNA and peptide were decreased by 80% in Sim1(+/-) mice, whereas TRH, CRH, arginine vasopressin (Avp), and somatostatin mRNAs were decreased by 20-40%. Sim1(+/-) mice also showed abnormal regulation of Oxt but not CRH mRNA in response to feeding state. A selective Mc4r agonist activated PVN Oxt neurons in wild-type mice, supporting involvement of these neurons in melanocortin feeding circuits. To test whether Oxt itself regulates feeding, we measured the effects of central administration of an Oxt receptor antagonist or repeated doses of Oxt on food intake of Sim1(+/-) and wild-type mice. Sim1(+/-) mice were hypersensitive to the orexigenic effect of the Oxt receptor antagonist. Oxt decreased the food intake and weight gain of Sim1(+/-) mice at a dose that did not affect wild-type mice. Our results support the importance of Oxt neurons in feeding regulation and suggest that reduced Oxt neuropeptide is one mechanism mediating the hyperphagic obesity of Sim1(+/-) mice.

Distribution of vasopressin in the brain of the eusocial naked mole-rat

Naked mole-rats are eusocial rodents that live in large subterranean colonies in which one queen breeds with one to three males. All other animals are nonbreeding subordinates. The external features of male and female subordinates, including their genitalia, are remarkably monomorphic, as is their behavior. Because vasopressin (VP) is associated with social behaviors and sex differences in other species, its distribution in naked mole-rats was of interest. We used immunohistochemistry to examine VP in the brains of subordinate and breeding naked mole-rats of both sexes. As in other mammals, VP-immunoreactive (-ir) somata were found in the paraventricular (PVN) and supraoptic nuclei (SON) and VP-ir projections from these nuclei ran through the internal and external zone of the median eminence. However, naked mole-rats had very few VP-ir cells in the bed nucleus of the stria terminalis (BST) and none in the suprachiasmatic nucleus (SCN); the extensive network of fine-caliber VP-ir fibers usually seen in projection sites of the BST and SCN were also absent. Equally unexpected was the abundance of large-caliber VP-ir fibers in the dorsomedial septum. VP immunoreactivity was generally similar in all groups, with the exception of VP-ir cell number in the dorsomedial hypothalamus (DMH). Breeders had a population of labeled cells in the DMH that was absent, or nearly absent, in subordinates. Future studies on the function of VP in these areas are needed to determine how the atypical distribution of VP immunoreactivity relates to eusociality and the unusual physiology of naked mole-rats.

The Neurosecretory System Is Hypertrophied in Senescence-Accelerated Mice

The hypothalamic supraoptic and paraventricular nuclei form the neurosecretory system and synthesize the neurohormones oxytocin and arginine-vasopressin. The senescence-accelerated mouse is a model of rapid aging that displays senile amyloidosis and memory problems. This paper presents the characterization of the neurosecretory system and describes the presence of a bilateral constant cluster of neurosecretory neurons in these mice. The stereologic analysis revealed that these groups contain 197 +/- 18 cells (87% synthesize arginine-vasopressin and 13% oxytocin). The presence of these clusters of neurosecretory neurons suggests that these mice could present greater neurohormone synthesis, increasing the deleterious effects of accelerated aging in this strain.

Dendritic peptide release and peptide-dependent behaviours

Neuropeptides that are released from dendrites, such as oxytocin and vasopressin, function as autocrine or paracrine signals at their site of origin, but can also act at distant brain targets to evoke long-lasting changes in behaviour. Oxytocin, for instance, has profound effects on social bonding that are exerted at sites that richly express oxytocin receptors, but which are innervated by few, if any, oxytocin-containing projections. How can a prolonged, diffuse signal have coherent behavioural consequences? The recently demonstrated ability of neuropeptides to prime vesicle stores for activity-dependent release could lead to a temporary functional reorganization of neuronal networks harbouring specific peptide receptors, providing a substrate for long-lasting effects.

Chronic exposure to Delta9-tetrahydrocannabinol downregulates oxytocin and oxytocin-associated neurophysin in specific brain areas

Cannabinoids are widely abused drugs. Our goal was to identify genes modulated by Delta9-tetrahydrocannabinol (Delta9-THC) treatment. We found that chronic administration of Delta9-THC (1.5 mg/kg/day, i.p.; 7 days) to rats, downregulates the expression of oxytocin-neurophysin (OT-NP) mRNA and of OT and oxytocin-associated NP (NPOT) immunoreactivity in nucleus accumbens (NAc) and ventral tegmental area (VTA), brain areas involved in reward and addiction. Real-time PCR revealed a 60% and 53% reduction of OT-NP mRNA in NAc and VTA, respectively, under chronic treatment, while no changes were observed in NAc after 24 h. Immunohistochemistry showed a large decrease in number of OT and NPOT-stained fibers in NAc (by 59% and 52%, respectively) and VTA (by 50% and 56%, respectively). No changes in cell staining were observed in the paraventricular nucleus and supraoptic nucleus. As OT is known to inhibit development of drug tolerance and attenuate withdrawal symptoms, we suggest that OT downregulation could play a role during the establishment of the chronic effects of Delta9-THC.

Sexual differentiation of central vasopressin and vasotocin systems in vertebrates: different mechanisms, similar endpoints

Vasopressin neurons in the bed nucleus of the stria terminalis and amygdala and vasotocin neurons in homologous areas in non-mammalian vertebrates show some of the most consistently found neural sex differences, with males having more cells and denser projections than females. These projections have been implicated in social and reproductive behaviors but also in autonomic functions. The sex differences in these projections may cause as well as prevent sex differences in these functions. This paper discusses the anatomy, steroid dependency, and sexual differentiation of these neurons. Although the final steps in sexual differentiation of vasopressin/vasotocin expression may be similar across vertebrate species, what triggers differentiation may vary dramatically. For example, during development, estrogen masculinizes vasopressin expression in rats but feminizes its counterpart in Japanese quail. Apparently, nature consistently finds a way of maintaining sex differences in vasopressin and vasotocin pathways, suggesting that the function of these differences is important enough that it was conserved during evolution.

TGFα and AVP in the mouse suprachiasmatic nucleus: Anatomical relationship and daily profiles

Daily rhythms in behavior and physiology are under control of the suprachiasmatic nucleus (SCN), the main mammalian circadian pacemaker located in the hypothalamus. The SCN communicates with the rest of the brain via various output systems. The aim of the present study was to determine the neuroanatomical and temporal relationship between two output systems, arginine-vasopressin (AVP) and transforming growth factor alpha (TGFalpha), in the mouse SCN. TGFalpha-positive cells were found throughout the SCN, but more abundantly in the core than the shell area, while AVP was predominantly found in the shell. Fluorescent double labeling revealed a total lack of co-expression for the two proteins in SCN cells. The circadian profile, studied by way of optical density in immunostaining at 3 h intervals, showed peak values for AVP shortly after the LD transitions. Immunoreactivity for TGFalpha was highly variable, especially at time points before the LD transitions. In addition, strong lateralization in TGFalpha immunostaining in the SCN was found in some individuals. Daily fluctuations in the paraventricular nucleus were absent for TGFalpha, and only weakly present for AVP. The main conclusion derived from this study is that these two output systems of the biological clock are anatomically separated with different daily profiles in expression.

Oxytocin and vasopressin immunoreactivity within the forebrain and limbic-related areas in the mustached bat, Pteronotus parnellii

The nonapeptides, oxytocin and arginine vasopressin, play an important role in mammalian social and reproductive behavior. Using immunocytochemical procedures, we identified oxytocin-immunoreactive neurons in the frontal and auditory cortices, limbic areas such as the medial septal nucleus, horizontal limb of the diagonal band and the amygdala. Only arginine vasopressin neurons were present in the bed nucleus of the stria terminalis. In limbic-related areas, the hypothalamic paraventricular and supraoptic nuclei and the nucleus centralis contained both oxytocin and arginine vasopressin neurons. The medial preoptic area showed a positive reaction for several arginine vasopressin fibers, but not oxytocin fibers, except in one female bat sacrificed during the breeding season. Arginine vasopressin fibers were observed in another limbic-related area, the periaqueductal gray. Furthermore, oxytocin was predominantly localized within sensory (e.g., auditory) and frontal cortex and limbic areas, whereas arginine vasopressin was restricted largely to known audiovocal regions of the periaqueductal gray. Classical neurosecretory nuclei in the hypothalamus contain both peptides. Oxytocin-immunoreactive neurons were also found in other structures such as the olfactory bulb, olfactory tubercle, primary and secondary motor cortex, fronto-parietal cortex, piriform cortex and the nucleus of the internal capsule. Both oxytocin and arginine vasopressin immunoreactivity was present in the suprachiasmatic nucleus, median eminence, neural lobe of the hypophysis and the pineal gland. Together with previous studies, the presence of these peptides within auditory areas of the cortex (sensory and frontal), and limbic as well as limbic-related regions provides anatomical evidence supporting their proposed role in social vocal behaviors and probably in auditory processing.

Transgenesis and the study of expression, cellular targeting and function of oxytocin, vasopressin and their receptors

The neuropeptides oxytocin and vasopressin and the neurons in the hypothalamus that synthesize them have been a rich source for the exploration and understanding of both the brain and the endocrine system. Because of their large size and compact nuclear organization the magnocellular neurons of the hypothalamoneurohypophysial system have traditionally attracted scientists using state-of-the-art techniques, including the subject of this review, transgenesis. We discuss the role of transgenics in deciphering gene elements necessary for the appropriate expression of oxytocin and vasopressin and to deliver exogenous genes, such as green fluorescent protein, selectively to secretory granules in the neurons in the hypothalamoneurohypophysial system. Finally, we review the studies of mice whose genes for oxytocin and, most recently, for the oxytocin and vasopressin receptors have been knocked out through homologous recombination.

Behavioral effects of arginine8-vasopressin in the Hebb-Williams maze

Arginine(8)-vasopressin (AVP) has been shown to improve memory consolidation in various mnemonic tasks. Our previous studies have pointed out the involvement of the hippocampus (with higher sensitivity of its ventral part) in memory consolidation and retrieval processes during discriminative learning in mice. The present study was designed to extend our knowledge, firstly, of the range of tasks and consequently the types of information for which the peptide improves consolidation processes, and secondly, the effects of AVP on information treatment processes such an information transfer. To this end, the effects of AVP were analyzed in the Hebb-Williams closed-field maze. Mice were initially trained on one of the mazes in the Hebb-Williams series (Maze 7) and subsequently tested on either that maze or another maze in the series (Maze 11). The effects of the peptide on both memory consolidation and information transfer processes were analyzed in relation to the route of administration: peripheral (subcutaneous, s.c.), central (intracerebroventricular, i.c.v.), and in situ (dorsal or ventral hippocampus). The results showed that AVP facilitated spatial memory consolidation following s.c., i.c.v, and dorsal, but not ventral hippocampal administration. This differential effect of AVP following injection into the hippocampus can be interpreted in regards to this structure's functions. In line with the involvement of the dorsal hippocampus in spatial memory, the effectiveness of the peptide in the Hebb-Williams maze, which contains spatial components, was better when the treatment was performed in this part of the structure. In contrast, whatever the route of administration, AVP had no effect on processes related to the transfer from one learning situation to another.

Modulation of synaptic transmission by oxytocin and vasopressin in the supraoptic nucleus

It is now generally accepted that magnocellular neurons of the supraoptic and paraventricular nuclei release the neuropeptides oxytocin and vasopressin from their dendrites. Peptide release from their axon terminals in the posterior pituitary and dendrites differ in dynamics suggesting that they may be independently regulated. The dendritic release of peptide within the supraoptic nucleus (SON) is an important part of its physiological function since the local peptides can regulate the electrical activity of magnocellular neurons (MCNs) which possess receptors for these peptides. This direct postsynaptic action would affect the output of peptide in the neurohypophysis. Another way that these peptides can regulate MCN activity would be to modulate afferent inputs unto themselves. Although the influence of afferent inputs (inhibitory and excitatory) on SON magnocellular neuron physiology has been extensively described in the last decade, a role for these locally released peptides on synaptic physiology of this nucleus has been difficult to show until recently, partly because of the difficulty of performing stable synaptic recordings from these cells in suitable preparations that permit extensive examination. We recently showed that under appropriate conditions, oxytocin acts as a retrograde transmitter in the SON. Oxytocin, released from the dendrites of MCNs, decreased evoked excitatory synaptic transmission by inhibiting glutamate release from the presynaptic terminals. It modulated voltage-dependent calcium channels, mainly N-type and to a lesser extent P/Q-type channels, located on glutamatergic terminals. Although evidence is less conclusive, it is possible that vasopressin has similar actions to reduce excitatory transmission. This synaptic depressant effect of oxytocin and/or vasopressin, released from dendrites, would ensure that MCNs regulate afferent input unto themselves using their own firing rate as a gauge. Alternatively, it may only be a subset of afferent terminals that are sensitive to these peptides, thereby providing a means for the MCNs to selectively filter their afferent inputs. Indeed its specificity is partly proven by our observation that oxytocin does not affect spontaneous glutamate release, or GABA release from inhibitory terminals (Brussaard et al., 1996). Thus, the dendrites of MCNs of the supraoptic nucleus serve a dual role as both recipients of afferent input and regulators of the magnitude of afferent input, allowing them to directly participate in the shaping of their output. This adds to a rapidly growing body of evidence in support of the concept of a two-way communication between presynaptic terminals and postsynaptic dendrites, and shows the potential of this nucleus as a model to study such form of synaptic transmission.

FOS and FOSB expression in the medial preoptic nucleus pars compacta of maternally active C57BL/6J and DBA/2J mice

C57BL/6J and DBA/2J inbred mice differ in aspects of maternal behavior and in the morphology of the medial preoptic nucleus (MPO), suggesting a possible association. DBA/2J mice have a compact subnucleus in the MPO, the MPOpc, that is sexually dimorphic and absent in C57BL/6J mice. To determine whether MPOpc cells are activated by maternal behavior, FOS and FOSB immunohistochemistry was performed on brain sections of C57BL/6J and DBA/2J mothers following the return of their pups after a separation of 2 days. In both light and dark phases of the daily cycle, stimulation of DBA/2J mothers evoked an increase in FOS- and FOSB-immunoreactivity in the MPOpc. Stimulated C57BL/6J mice, which lack the MPOpc, did not show an increase in cellular activity in the corresponding MPO region. Cells immediately lateral to the MPOpc were activated by pup stimulation, in both strains. These results suggest that MPOpc cells are active during maternal behavior, and that strain differences in maternal behavior are related to anatomical differences in the MPO.

Osmotic stress increases brain-derived neurotrophic factor messenger RNA expression in the hypothalamic supraoptic nucleus with differential regulation of its transcripts. Relation to arginine-vasopressin content

We have shown that osmotic stress increases brain-derived neurotrophic factor (BDNF) mRNA in the supraoptic nucleus and that this increase seems to be determined by the high expression of transcripts containing exon I. The paraventricular nucleus is another hypothalamic neuronal subset where BDNF mRNA is also sensitive to osmotic stress stimulation. In this nucleus, transcripts containing exon I were not modified but only those containing exon II. By contrast, transcripts containing exon III did not exhibit any variation in our experimental conditions. The presence of BDNF mRNA in both paraventricular and supraoptic hypothalamic nuclei was recently reported. These nuclei are extremely sensitive to osmotic stimuli and their neurons secrete oxytocin and arginine-vasopressin in the posterior pituitary gland. This study was thus designed to investigate the possible involvement of BDNF in the response of supraoptic nucleus to osmotic stress stimulus. Osmotic stress was induced by hypertonic saline injection (1.35% NaCl) administered to animals 3 h before analysis. We used non-isotopic in situ hybridization to study the expression of BDNF mRNA and its transcripts with antisense riboprobes on histological brain sections, including paraventricular and supraoptic nuclei from control and osmotic stress-stimulated animals. To investigate a possible correlation between the expression of BDNF mRNA and arginine-vasopressin, the peptide content was analyzed by immunohistochemistry in both paraventricular and supraoptic nuclei at two different times after hyperosmotic injection. The results showed that BDNF mRNA expression preceded the arginine-vasopressin increase. In addition, on serial adjacent histological sections of supraoptic nucleus (10 microm), both BDNF and arginine-vasopressin mRNAs were visualized by isotopic in situ hybridization and the images were overlaid, showing that almost all of the hybridization signals were overlapped. Taken together our results are in keeping with the hypothesis that activation of the different BDNF promoters seems to be region-specific. Besides, the temporal correlation between both BDNF mRNA expression and arginine-vasopressin content, as well as the morphological vicinity between their respective producing cells in the supraoptic nucleus, suggest an autocrine or paracrine action for this neurotrophin in the regulation of arginine-vasopressin secretion.

Transplanted clonal neural stem-like cells respond to remote photic stimulation following incorporation within the suprachiasmatic nucleus

Multipotent neural stem-like cells (NSCs) obtained from one brain region and transplanted to another region appear to differentiate into neuronal and glial phenotypes indigenous to the implantation site. Whether these donor-derived cells are appropriately integrated remains unanswered. In order to test this possibility, we exploited the suprachiasmatic nucleus (SCN) of the hypothalamus, site of a known circadian clock, as a novel engraftment target. When a clone of NSCs initially derived from neonatal mouse cerebellum was transplanted into mouse embryos, the cells incorporated within the SCN over a narrow gestational window that corresponded to the conclusion of SCN neurogenesis. Immunocytochemical staining suggested that donor-derived cells in the SCN synthesized a peptide neurotransmitter (arginine vasopressin) characteristic of SCN neurons. Donor-derived SCN cells reacted to light pulses by expressing immunoreactive c-Fos protein in a pattern that is appropriate for native SCN cells. This region-specific and physiologically appropriate response to the natural stimulation of a remote sensory input implies that donor-derived and endogenous cells formed true SCN chimeras, suggesting that exogenous NSCs engrafted to ectopic locations can integrate in a meaningful fashion.

Differential expression of vasopressin, oxytocin and corticotrophin-releasing hormone messenger RNA in the paraventricular nucleus of the prairie vole brain following stress

Forced swimming, as an effective stressor, has been found to facilitate the development of pair bonds in male but to interfere with this behaviour in female prairie voles (Microtus ochrogaster). In the present study, we found that forced swimming differentially influenced the expression of messenger RNA for vasopressin, oxytocin and corticotrophin-releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus (PVN) in the prairie vole brain. Forced swimming did not alter vasopressin mRNA labelling, but did induce a sustained decrease in oxytocin mRNA labelling and a progressive increase in CRH mRNA labelling in the PVN. The elevated CRH mRNA labelling appeared to be due to an increased number of cells synthesizing CRH mRNA and an enhanced ability of individual cells to produce CRH mRNA. Male and female prairie voles did not differ in the vasopressin, oxytocin or CRH mRNA expression either at the basal levels or in response to swimming stress. Together, these data indicate that the hypothalamic response of vasopressin, oxytocin and CRH messenger RNAs to swimming stress is regulated by distinct transcriptional factors. In addition, it seems unlikely that these changes are involved directly in the sex differences in pair bond formation.

Vasopressin into the preoptic area increases grooming behavior in mice

In mice, the neuropeptide arginine-8-vasopressin (AVP) induces excessive grooming, scratching, and hyperactivity when administered intracerebroventricularly. In hamsters, AVP infusion into the medial preoptic area/anterior hypothalamus (MPOA/AH) increases flank marking and flank mark grooming. We measured the behavioral effects of administration of AVP (0, 1, and 10 ng/250 nl) into the preoptic area (POA) of male C57BL/6 mice. Administration of AVP into the POA induced robust effects on grooming, including increased hindleg scratching and face washing. Rearing and olfactory investigation were inhibited by AVP into the POA. These findings indicate that the POA is one site in which AVP induces grooming behavior in mice.

Strain and sex differences in the morphology of the medial preoptic nucleus of mice

The medial preoptic nucleus (MPO), which is involved in sexual and maternal behaviors, contains neuronal clusters that have been described as being sexually dimorphic in size and neuropeptide content in a variety of species. A subnucleus in DBA/2J (D2) inbred mice, called the pars compacta of the MPO (MPOpc), is absent in C57BL/6J (B6) inbred mice (Robinson et al. [1985] J. Neurogenet. 2:381-388). We report here on experiments that further characterize strain and sex differences in medial preoptic morphology in D2 and B6 inbred mice. A prominent MPOpc, located within the caudal part of the MPO and dorsal to the suprachiasmatic nucleus, was present in both male and female D2 animals but was absent from B6 animals. MPOpc neurons were darkly stained for Nissl substance and larger than neurons in the surrounding MPO. In D2 brains, galanin-immunoreactive (-ir), oxytocin-ir, vasopressin-ir, and NADPH diaphorase-positive neurons were concentrated within the MPOpc. Fewer similar neurons in the comparable region of the MPO of B6 mice suggests that the absence of the MPOpc is due to absence of these neurons rather than a less compact organization. In D2 animals, the density of galanin-ir neurons in the MPOpc was sexually dimorphic, with higher numbers of galanin-ir neurons in females. Strain differences in galanin-ir, oxytocin-ir, vasopressin-ir, and NADPH diaphorase staining appeared to be limited to the MPOpc. Cholecystokinin-immunoreactive neurons, which have been reported to be numerous in the sexually dimorphic central subdivision of the MPO of rats, were sparse in the MPO of D2 and B6 mice. Confirmation of the MPOpc as an accessory magnocellular neurosecretory nucleus was obtained by finding labeling of MPOpc neurons after injection of DiI into the posterior pituitary.

Neuromodulation of memory in the hippocampus by vasopressin

The involvement of [Arg(8)]vasopressin in memory processes was analyzed in the hippocampal structure, since we have reported that this is one of the main central target structures of the vasopressin-enhancing effect on memory. This structure is functionally differentiated along its dorsoventral axis, and the expression of the vasopressinergic system is dependent upon whether the dorsal or ventral part of the hippocampus is involved. For this reason, the effect of vasopressin injected into hippocampus was evaluated on the basis of the site of injection. We have shown, using a Go-No Go visual discrimination task with mice that both parts of the hippocampus are involved in the effect of endogenous or exogenous vasopressin, but with higher sensitivity for the ventral part. Based on the expression of Fos protein following intracerebroventricular injection of vasopressin in unconditioned or conditioned mice, we confirmed the greater involvement of the ventral hippocampus in the enhancing effect of vasopressin on memory processes. The effect of the peptide seems specific, since only a few of the hippocampal cells that expressed Fos protein in the unconditioned mice did so in the conditioned mice (cells in the dentate gyrus and the CA3 hippocampal field). Moreover, we have shown that in the ventral hippocampus, vasopressin generates different behavioral effects whether treatment is performed at the beginning or in the middle of the learning process, suggesting that the mnemonic context is an important factor for understanding the effect of vasopressin on memory in the ventral hippocampus.

The role of Clock in the developmental expression of neuropeptides in the suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) is the dominant circadian pacemaker in mammals. To understand better the ontogeny of mouse SCN and the role of the pacemaker in peptide expression, the authors examined the distribution of cells that were immunoreactive for vasopressin (AVP) or vasoactive intestinal polypeptide (VIP) in wild type and Clock mutant mice at two developmental stages. Clock homozygous mice failed to show the dramatic increase in the number of VIP-immunoreactive (VIP-ir) neurons from postnatal day 6 (P6) to P30 that was found in the SCN of wild type mice. The number of AVP-ir neurons was relatively constant in the postnatal SCN but was significantly reduced in Clock/Clock mice. The effects of the Clock mutation varied with position in the SCN for both peptides. Densitometry of immunolabeled brains indicated that the Clock mutation reduced AVP expression specifically in the SCN and not in other brain areas. The SCN did not significantly change shape or size with age or Clock genotype. Taken together, these results indicate that the neonatal mouse SCN has its full complement of cells, some of which are not yet mature in their neuropeptide content. Furthermore, the observation that the Clock mutation appears to act on a subset of AVP and VIP cells suggests heterogeneity within these cell classes in the SCN.

Vasopressin preferentially depresses excitatory over inhibitory synaptic transmission in the rat supraoptic nucleus in vitro

Endogenous arginine-vasopressin (AVP) in the supraoptic nucleus is known to decrease the firing rate of some supraoptic nucleus neurones. To determine a possible mechanism by which this locally released AVP produces this change in neuronal excitability, we investigated the effects of AVP on evoked excitatory (e.p.s.c.) and inhibitory post-synaptic (i.p.s.c.) responses recorded in magnocellular neurones in a hypothalamic slice preparation, using the perforated-patch recording technique. Our data show that AVP produces a dose-dependent decrease in the evoked e.p.s.c. in about 80% of magnocellular neurones tested with an estimated EC50 of about 0.9 microM. The maximum decrease in e.p.s.c. amplitude was about 31% of control and was obtained with an AVP concentration of 2 microM. The AVP-induced synaptic depression was blocked by Manning Compound (MC), a non-selective antagonist of oxytocin (OXT) and vasopressin (AVP) receptors, but not by a selective OXT receptor antagonist. It was not mimicked by desmopressin (ddAVP), a V2-receptor subtype agonist. By contrast, AVP used at the same concentration (2 microM), had no global effect on pharmacologically isolated i.p.s.c.s in the majority of magnocellular neurones tested. These results show that AVP acts in the supraoptic nucleus to reduce excitatory synaptic transmission to magnocellular neurones by activating a non-OXT receptor, presumably the V1 receptor subtype.

Sexual dimorphism in numbers of vasotocin-immunoreactive neurons in brain areas associated with reproductive behaviors in the roughskin newt

Vasotocin (VT) and vasopressin control many endocrine and neuroendocrine functions, including the regulation of reproductive behaviors. In the roughskin newt (Taricha granulosa), VT administration can enhance courtship behaviors in males and egg-laying behaviors in females. This study used immunohistochemistry to investigate whether there are sex differences in VT in specific brain areas, and whether these differences persist in nonbreeding animals. Numbers of VT immunoreactive (ir) cell bodies were counted in males and females collected in February, April, June, and August. Radioimmunoassay of plasma samples confirmed that testosterone and 5alpha-dihydrotestosterone concentrations were higher in males than females, and that 17beta-estradiol concentrations were higher in females than males. In 11 brain areas, no sexual or seasonal differences in the number of VTir cells were found. But in 3 brain regions-the bed nucleus of the stria terminalis (BNST), the nucleus amygdalae dorsolateralis (AMYG), and the anterior preoptic area (aPOA)-there were significantly greater numbers of VTir cells in males than in females, and these differences did not change seasonally. In the aPOA, an area important to male sex behaviors, the sexual dimorphism in VTir was particularly pronounced. In four brain regions, there were significantly greater numbers of VTir cells in females than males, but only in specific seasons. In April-collected (breeding) animals, more VTir cells were found in females than in males in the populations of VT cells within the pars dorsalis hypothalami and ventromedial hypothalamus, brain regions frequently associated with stress responses and female mating behaviors. In August-collected (nonbreeding) animals, more VTir cells were found in females than in males, in the region of the bed nucleus of the decussation of the fasciculus lateralis telencephali and in the nucleus visceralis superior, nucleus isthmi region. Significantly greater numbers of VTir cells were observed in the magnocellular preoptic area of males and females collected in February. These results indicate that the functional interactions between gonadal steroid hormones and VT are complex and appear to involve site-, sex-, and season-specific regulatory mechanisms. Furthermore, it seems likely that populations of VT neurons in the BNST, AMYG, and aPOA are involved in regulating male-specific behaviors, and that the VT neurons in the pars dorsalis hypothalami/ventromedial hypothalamus may be involved in female-specific behaviors.

Species differences in paternal behavior and aggression in peromyscus and their associations with vasopressin immunoreactivity and receptors

Previous comparative studies have suggested that the distribution of arginine vasopressin (AVP) pathways within the brain is associated with species-typical patterns of social behavior. In the current study, male parental behavior and aggression were compared in two species of Peromyscus. As predicted based on other studies, male mice from a monogamous species, the California mouse Peromyscus californicus, spent more time providing parental care to offspring than males from a polygamous species, the white-footed mouse Peromyscus leucopus. Sexually naive male California mice also attacked opponents more rapidly than white-footed mice during resident-intruder and neutral aggression tests. Since AVP has been shown to modulate these behaviors, we compared the distribution of vasopressinergic neurons and receptors. We predicted that greater AVP-immunoreactive (AVP-ir) staining in the bed nucleus of the stria terminalis and AVP receptor density in the lateral septum would occur in the species with low levels of paternal care because this pattern was found in similar comparisons with sexually naive monogamous and polygamous voles. In contrast, in our study, monogamous male mice showed more AVP-ir staining in the bed nucleus of the stria terminalis than the polygamous species, as well as more AVP receptors in the lateral septum. Parental behavior therefore does not appear to predict differences in patterns of AVP-ir staining and receptor distribution across species or vice versa. We propose the hypothesis that aggression may be better correlated with species patterns of AVP-ir staining density and receptor distribution.

Fos protein expression induced by intracerebroventricular injection of vasopressin in unconditioned and conditioned mice

Arginine8-vasopressin (AVP) has been shown to improve memory consolidation in various mnemonic tasks. Our previous studies have pointed out the involvement of the hippocampus in memory consolidation and retrieval processes during discriminative learning by mice. The present study attempts to determine what other brain areas besides the hippocampus might be involved in the enhancing effect of intracerebroventricularly (i.c.v.) injected AVP on memory consolidation in a visual discrimination task using a polyclonal antibody that acts against Fos and Fos-like proteins. For behavioral testing, AVP was i.c.v. injected at the behaviorally active dose of 2 ng after the last learning session and improvement in consolidation processes was assessed in a retention session. Changes in Fos and Fos-like protein expression were determined in non-conditioned and conditioned mice. In non-conditioned mice, AVP i. c.v. injected at a dose of 2 ng evoked a time-dependent increase in Fos and Fos-like protein expression in the dentate gyrus (DG), CA1 and CA3 hippocampal fields, lateral septum (LS), bed nucleus of the stria terminalis, and basolateral and central amygdaloid nuclei, with a peak 120 min after the injection in most of the these brain areas. In contrast, in conditioned mice, an increase in the level of Fos expression, assessed 120 min after the end of learning and the injection of AVP, was detected only in the DG, ventral CA3 hippocampal field, and LS. Thus, the pattern observed after post-training injection of AVP was not the same as that evoked by AVP alone, since among the limbic structures activated following AVP alone, only the DG, the CA3 hippocampal field, and the LS seem to be involved in the enhancing effect of AVP on memory consolidation in discriminative learning.

Role of vasopressin in learning and memory in the hippocampus

The involvement of arginine8-vasopressin (VP) in learning and memory in the hippocampus is examined in mice using a discriminative learning task. Bilateral dorsal hippocampal lesion blocks the enhancing effect of intracerebroventricular (i.c.v.) injection of VP on retrieval and relearning processes. An additional study showed that immunoneutralization of dorsal hippocampal endogenous VP inhibited the facilitating effect of i.c.v. injection of VP, suggesting that hippocampus is essential for the expression of VP's behavioral effects. Using in situ microinjection, a greater sensitivity of the ventral part of the hippocampus to the memory enhancing effects of VP has been reported. This effect is mediated by vasopressin V1 type receptors and oxytocin receptors. Then, we examined the effects on behavior of VP applied to the ventral hippocampus, in relation to the time of treatment during learning. When the animals have no previous information about the task to learn, a deleterious effect of VP appears (pre-first session treatment). Regarding memory consolidation, the effects of VP may depend upon the previous level of performance acquired by the animals since, when injected after the first learning session, the peptide slightly delayed performance, whereas when the injection took place after the second learning session, it enhanced learning. Concerning memory retrieval, the effects of VP depend on the quality of the previously stored information. The fact that VP did not generate the same behavioral effects when the treatment was performed at the beginning or in the middle of the learning processes, suggests that mnemonic context is an important factor in understanding the effect of VP on memory in the ventral hippocampus. Finally, the role of hippocampal adrenergic receptors in the enhancing VP effects on memory retrieval has been examined. The facilitatory effects of VP seem to depend upon the functional state of both alpha- and beta-adrenergic receptors, but further studies will be necessary to clarify the role played by each receptor type in retrieval processes, and to determine the relationships that might exist between them.

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.

Influences of the bed nucleus of the stria terminalis and of the paraventricular nucleus of the hypothalamus on the excitability of hippocampal-lateral septal synapses in mice

Previous experiments have shown that conditioning in aversive situations is associated with specific changes in excitability of hippocampal-septal synaptic transmission and that these changes might be related to a modulation of this synaptic transmission by afferents originating from the bed nucleus of the stria terminalis (BNST) and from the paraventricular nucleus (PVN) of the hypothalamus. Accordingly, the aim of the present experiment was to assess changes in excitability of hippocampal-septal synapses by varying the interval between the application of a conditioning pulse in either the BNST or the PVN, and a test pulse in fimbria fibers (FF). Electrical stimulation of FF, induces in the lateral septum (LS) a field potential characterized by two negative waves (N2 and N3) the magnitude of which is an index of excitability of two populations of target cells located in the ventral and dorsal lateral septum, respectively. Results showed that prestimulation of both the BNST and the PVN produced an increase in the amplitude of the N3 wave, although the optimal interpulse interval required for producing maximal increase was different as a function of the two structures. Only prestimulation of the BNST induced a significant increase in the amplitude of the N2 wave. These results suggest that the PVN projects mainly to the dorsal aspect of the LS, while the BNST projects to both dorsal and ventral parts of the LS. Together with results from previous experiments conducted in behaving mice exposed to conditioned aversive stimuli, it is concluded that these projections might play a role in the relief of contextual conditioned fear.

Dendritically released peptides act as retrograde modulators of afferent excitation in the supraoptic nucleus in vitro

Oxytocin (OXT) and vasopressin (VP) are known to be released from dendrites of magnocellular neurons. Here, we show that these peptides reduced evoked EPSCs by a presynaptic mechanism, an effect blocked by peptide antagonists and mimicked by inhibition of endogenous peptidases. Dendritic release of peptides, elicited with depolarization achieved by high frequency stimulation of afferents or with current injection into an individual neuron, induced short-term synaptic depression similar to that seen following exogenous peptide application and was prevented by peptide antagonists. Thus, dendritically released peptides depress evoked EPSCs in magnocellular neurons by activating presynaptic OXT and/or VP receptors. Such a retrograde modulatory action on afferent excitation may serve as a feedback mechanism to permit peptidergic neurosecretory neurons to autoregulate their own activity.

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.

Vasopressin receptors in the mouse (Mus musculus) brain: sex-related expression in the medial preoptic area and hypothalamus

We have investigated the distribution of vasopressin binding sites in the brain of male and female adult mice using a radio-iodinated ligand and film autoradiography. Vasopressin receptors were uncovered in various regions of the brain including the basal nucleus of Meynert, the substantia innominata, the hypothalamic paraventricular nucleus, the substantia nigra pars compacta and the hypoglossal nucleus. A sex-related difference in the expression of vasopressin receptors was seen in the medial preoptic area/anterior hypothalamus corresponding to the rat sexually dimorphic nucleus in the rat and in the hypothalamic mammillary nuclei. In both structures the autoradiographic labeling is more intense in females than in males. These observations confirm that vasopressin binding sites are present in the hypothalamic preoptic area of most species examined so far and that sex-related expression of neuropeptide receptors could trigger sex-related behavioral differences.

In situ hybridization analysis of vasopressin mRNA expression in the mouse hypothalamus: diurnal variation in the suprachiasmatic nucleus

The distribution, and diurnal variation of AVP mRNA-expressing neurons in the hypothalamus of the mouse has been investigated using in situ hybridization histochemistry. In general, cells hybridizing with an AVP mRNA-specific oligonucleotide probe in the mouse hypothalamus exhibit a similar distribution to the well-characterized distribution of AVP nuclei in the rat, but species-specific patterns of expression have been observed, a finding that confirms the results of earlier immunocytochemical studies. For example, prominent groups of AVP mRNA expressing cells are found in the region between the paraventricular (PVN) and suprachiasmatic (SCN) nuclei, forming the distinct mouse accessory nucleus, and a periventricular group that merges with the PVN neurons. Sampling of brains during both phases of the daily cycle (either 10.00 h (light) or 22.00 h (dark)) revealed a marked and significant variation in AVP mRNA abundance in the SCN whereas a similar variation was not consistently observed in the magnocellular neurons of the supraoptic nucleus (SON). This study has confirmed the distribution of AVP-synthesizing neurons in the mouse hypothalamus, and provided an anatomical substrate for molecular genetic studies in this species that are designed to investigate the basis of neuronal rhythmicity.

Peptidergic transmission: from morphological correlates to functional implications

Like non-peptidergic transmitters, neuropeptides and their receptors display a wide distribution in specific cell types of the nervous system. The peptides are synthesized, typically as part of a larger precursor molecule, on the rough endoplasmic reticulum in the cell body. In the trans-Golgi network, they are sorted to the regulated secretory pathway, packaged into so-called large dense-core vesicles, and concentrated. Large dense-core vesicles are preferentially located at sites distant from active zones of synapses. Exocytosis may occur not only at synaptic specializations in axonal terminals but frequently also at nonsynaptic release sites throughout the neuron. Large dense-core vesicles are distinguished from small, clear synaptic vesicles, which contain "classical' transmitters, by their morphological appearance and, partially, their biochemical composition, the mode of stimulation required for release, the type of calcium channels involved in the exocytotic process, and the time course of recovery after stimulation. The frequently observed "diffuse' release of neuropeptides and their occurrence also in areas distant to release sites is paralleled by the existence of pronounced peptide-peptide receptor mismatches found at the light microscopic and ultrastructural level. Coexistence of neuropeptides with other peptidergic and non-peptidergic substances within the same neuron or even within the same vesicle has been established for numerous neuronal systems. In addition to exerting excitatory and inhibitory transmitter-like effects and modulating the release of other neuroactive substances in the nervous system, several neuropeptides are involved in the regulation of neuronal development.

Inhibition of the vasopressin-enhancing effect on memory retrieval and relearning by a vasopressin V1 receptor antagonist in mice

We have previously shown that [Arg8]vasopressin bilaterally administered into the ventral hippocampus of mice at a dose of 0.025 ng/animal 10 min prior to the retention session, improved long-term retrieval processes and relearning of a Go-No-Go visual discrimination task. The purpose of the present study was to determine whether the vasopressin V1 receptor antagonist, -beta-mercapto-beta,beta-cyclopentamethylenepropionyl1, O-Me-Tyr2,Arg8]vasopressin, d(CH2)5Tyr(Me)vasopressin), is able to block the behavioral effect of arginine-vasopressin in the ventral hippocampus. We first tested the effect of three doses of d(CH2)5Tyr(Me)vasopressin (0.025, 1, and 6.3 ng/animal) in the same experimental conditions as used for arginine-vasopressin. The results showed a dose-dependent deleterious effect of the vasopressin V1 receptor antagonist on retrieval and relearning, suggesting the involvement of endogenous arginine-vasopressin in the ventral hippocampus for these memory processes. Second, we tested the ability of d(CH2)5Tyr(Me)vasopressin to block the enhancing effect of experimentally administered arginine-vasopressin. The antagonist was injected at a dose of 0.025 ng, which had no intrinsic effect on behavior, or at a dose of 1 ng, which had a weak deleterious effect on behavior, followed by administration of 0.025 ng of arginine-vasopressin. The results showed that even at the weakest dose (0.025 ng), d(CH2)5Tyr(Me)vasopressin blocked the enhancing effect of arginine-vasopressin on retrieval and relearning. Thus, as for other behaviors and structures, the antagonist microinjected into the ventral hippocampus prevents the enhancing effect of arginine-vasopressin on long-term retrieval and relearning. However, the exclusive involvement of the vasopressin V1 receptors remain to demonstrate vis-a-vis oxytocin receptors.

Ontogeny of oxytocin-like immunoreactivity in the Brazilian opossum brain

The neuropeptide oxytocin (OT) has been shown to function as a neurotransmitter and/or neuromodulator in addition to its hormonal function in the periphery in the adult central nervous system (CNS). Previously, we have studied the postnatal neurogenesis of the paraventricular and supraoptic nuclei and ontogeny of arginine vasopressin-like immunoreactivity in the Brazilian opossum brain, Monodelphis domestica. In this study, we have described the ontogeny of oxytocin-like immunoreactivity (OT-IR) in the opossum brain. As a marsupial, opossum pups are in an extremely immature state, with neurogenesis and morphogenesis continuing into the second week of postnatal life. Thus, opossum pups are a good model for developmental studies. In the adult opossum brain, OT-IR was localized in regions as reported for the adult rat and other species, except for a few differences. These findings suggest similar functional roles for OT in the adult opossum brain as in other mammals. Unlike the prenatal expression of arginine vasopressin, OT-IR was first detected in the forming median eminence on day 1 of postnatal life (1 PN). Between 3 and 5 PN, OT-IR was present in the hypothalamic supraoptic and paraventricular nuclei and posterior pituitary. At this time, neurogenesis of these nuclei is not completed. By 10 to 15 PN, OT-IR was seen in several brain areas, and begins to resemble that of the adult between 45 and 60 PN. These results indicate that the time course of appearance of the OTnergic system does not directly parallel the early expression of the vasopressinergic system. However, the expression of OT-IR in the opossum brain before neurogenesis and morphogenesis is completed suggests a potential role for OT in developmental events. Similar to arginine vasopressin, oxytocin may also be involved in the regulation of autonomic functions that are essential for the opossum's adaptation to an ex utero environment. Future studies utilizing experimental manipulations of the OTnergic system will help determine the significance of this peptide in the neonatal opossum.

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.

Postnatal development and sexual differentiation of pig hypothalamic nuclei

The postnatal development of some nuclei in the hypothalamus of the pig is described in relation to sexual differentiation. The vasopressin and oxytocin containing nucleus (VON), a nucleus that has only been described in the pig to date, showed a twofold increase in neuron number and volume during puberty in both sexes. After puberty, this increase in neuron number continued in the females, resulting in a VON that is twice as large in females as in males. The supraoptic nucleus (SON) does not show an increase in neuron number during puberty but in females an increase after puberty is seen, resulting in a sexual dimorphism of the SON in adulthood. Experiments showed that the number of neurons of the VON can be influenced by gonadal steroids. This study confirms that sexual differentiation of the hypothalamus occurs much later in the pig than reported in any other mammalian species so far.

Calcitonin gene-related peptide-like immunoreactive (CGRPI) elements in the circadian system of the mouse: an immunohistochemistry combined with retrograde transport study

This study was based on immunohistochemical detection of calcitonin gene-related peptide-like immunoreactive (CGRPI) neurons and fibers in the suprachiasmatic nucleus (SCN) and intergeniculate leaflet (IGL) of the mouse. CGRPI neurons and fibers were found within the ventrolateral part of the SCN, in the whole extent of IGL and sparsely distributed in ventral lateral geniculate body. The presence of CGRPI structures in the SCN and IGL of the mouse further supports the hypothesis of differences in the content of neuroactive substances in the circadian clock between mammalian species. Fluorogold retrograde transport combined with CGRP immunofluorescence demonstrates that CGRPI neurons in the IGL constitute a part of IGL reciprocal connections.

The effect of salt-loading on corticotropin releasing hormone and arginine vasopressin mRNA levels in the mouse hypothalamus: a quantitative in situ hybridization analysis

Previously, we showed that during salt-loading in mice there was an acute rise in plasma ACTH levels after 2 days followed by a transient decrease after 4 and 9 days. Pro-opiomelanocortin (POMC) mRNA levels in the anterior pituitary increased after 2 days and returned to normal thereafter. In this study, changes in hypothalamic CRH and AVP mRNA levels during salt-loading were investigated using quantitative in situ hybridization histochemistry. CRH mRNA was expressed only in the paraventricular nucleus (PVN), while AVP mRNA was expressed in both the supraoptic (SON) and paraventricular nuclei. CRH mRNA levels were unchanged after 2 days salt-loading, but declined to 77% of control levels after 9 days. AVP mRNA levels rose to 260% and 634% of control levels in the SON, and to 352% and 522% of control levels in the PVN, after 2 and 9 days salt-loading, respectively. These data suggest a major role of AVP in the acute stimulation of ACTH secretion and POMC mRNA levels seen after 2 days salt-loading. Desensitization of AVP receptors at the corticotroph level and a centrally mediated inhibition of CRH release may account for the decrease of ACTH secretion and POMC mRNA levels in the anterior pituitary with prolonged salt-loading.

Efferent projections of the suprachiasmatic nucleus in the golden hamster (Mesocricetus auratus)

The efferent projections of the suprachiasmatic nucleus (SCN) in the golden hamster have been examined by using the anterograde tracer Phaseolus vulgaris leucoagglutinin (Pha-L). SCN projections were further localized through a combination of restricted SCN-lesions and immunocytochemistry for three well-known peptidergic transmitters contained in SCN neurons, viz. vasopressin (VP), vasoactive intestinal peptide (VIP), and gastrin-releasing peptide (GRP). Thus, major terminal fields of SCN-derived VP were detected in the medial preoptic nucleus, the anterior part of the paraventricular nucleus of the thalamus (PVA), the medial parvicellular part of the paraventricular nucleus of the hypothalamus (PVN), and the medial part of the dorsomedial nucleus of the hypothalamus (DMH). VIP-containing projections from the SCN were discovered in the PVA, anterior and dorsal parvicellular divisions of the PVN, subparaventricular area, and medial DMH. Efferent fibers from the SCN containing GRP were restricted to the subparaventricular area, medial DMH, and supraoptic nucleus. In addition, Pha-L tracing indicated the existence of SCN projections which could not be ascribed to one of the presently investigated peptides. Furthermore, a pronounced innervation of the contralateral SCN was observed, of which the neurotransmitter remains to be established. The results of the present study indicate that the different neuronal populations in the SCN, as characterized by their transmitter content, also show a clear diversity in their preferential target areas.