Vasopressin in the brain of the golden hamster: the distribution of vasopressin binding sites and of immunoreactivity to the vasopressin-related glycopeptide

Using Receptor Autoradiography to Visualize and Quantify Oxytocin and Vasopressin 1a Receptors in the Human and Nonhuman Primate Brain

Despite its development almost 40 years ago, receptor autoradiography remains a regular and reliable practice for the localization of oxytocin and vasopressin receptors in brain tissue sections. It is used across many laboratories, institutions, and animal species to characterize and quantify the distribution and density of these receptors at baseline and/or in response to experimental manipulations or lived experience. This powerful tool and the neuroanatomical receptor maps that it generates have allowed researchers to more accurately investigate and understand the neural substrates upon which oxytocin and vasopressin act to affect behavior. Researchers have used these maps to design site-specific pharmacological manipulations and electrophysiological recordings in animal studies to directly probe the underlying neural mechanisms in this system. This methods chapter describes the specific procedures by which a pharmacologically optimized, competitive binding modification to receptor autoradiography can be used to reliably localize oxytocin and vasopressin receptors in the human brain and in the brains of nonhuman primates. The ability to reliably perform receptor autoradiography for these targets in human brain tissue can finally inform our interpretation of past intranasal oxytocin neuroimaging studies and allows us to move past the reliance on transcriptomic studies using brain tissue homogenates so that we can directly investigate the involvement of oxytocin and vasopressin receptors in human behavior, physiology, and neuropsychiatric disease.

Distribution of Vasopressin and Oxytocin Neurons in the Basal Forebrain and Midbrain of Spiny Mice (Acomys cahirinus)

The nonapeptides vasopressin (VP) and oxytocin (OT) are present in some form in most vertebrates. VP and OT play critical roles in modulating physiology and are well-studied for their influences on a variety of social behaviors, ranging from affiliation to aggression. Their anatomical distributions have been mapped for numerous species across taxa, demonstrating relatively strong evolutionary conservation in distributions throughout the basal forebrain and midbrain. Here we examined the distribution of VP-immunoreactive (-ir) and OT-ir neurons in a gregarious, cooperatively breeding rodent species, the spiny mouse (Acomys cahirinus), for which nonapeptide mapping does not yet exist. Immunohistochemical techniques revealed VP-ir and OT-ir neuronal populations throughout the hypothalamus and amygdala of males and females that are consistent with those of other rodents. However, a novel population of OT-ir neurons was observed in the median preoptic nucleus of both sexes, located dorsally to the anterior commissure. Furthermore, we found widespread sex differences in OT neuronal populations, with males having significantly more OT-ir neurons than females. However, we observed a sex difference in only one VP cell group - that of the bed nucleus of the stria terminalis (BST), a VP neuronal population that exhibits a phylogenetically widespread sexual dimorphism. These findings provide mapping distributions of VP and OT neurons in Acomys cahirinus. Spiny mice lend themselves to the study of mammalian cooperation and sociality, and the nonapeptide neuronal mapping presented here can serve as a basic foundation for the study of nonapeptide-mediated behavior in a group of highly social rodents.

Sex-dependent effects of social status on the regulation of arginine-vasopressin (AVP) V1a, oxytocin (OT), and serotonin (5-HT) 1A receptor binding and aggression in Syrian hamsters (Mesocricetus auratus)

Dominance status in hamsters is driven by interactions between arginine-vasopressin V1a, oxytocin (OT), and serotonin 1A (5-HT1A) receptors. Activation of V1a and OT receptors in the anterior hypothalamus (AH) increases aggression in males, while decreasing aggression in females. In contrast, activation of 5-HT1A receptors in the AH decreases aggression in males and increases aggression in females. The mechanism underlying these differences is not known. The purpose of this study was to determine if dominance status and sex interact to regulate V1a, OT, and 5-HT1A receptor binding. Same-sex hamsters (N = 47) were paired 12 times across six days in five min sessions. Brains from paired and unpaired (non-social control) hamsters were collected immediately after the last interaction and processed for receptor binding using autoradiography. Differences in V1a, OT, and 5-HT1A receptor binding densities were observed in several brain regions as a function of social status and sex. For example, in the AH, there was an interaction between sex and social status, such that V1a binding in subordinate males was lower than in subordinate females and V1a receptor density in dominant males was higher than in dominant females. There was also an interaction in 5-HT1A receptor binding, such that social pairing increased 5-HT1A binding in the AH of males but decreased 5-HT1A binding in females compared with unpaired controls. These results indicate that dominance status and sex play important roles in shaping the binding profiles of key receptor subtypes across the neural circuitry that regulates social behavior.

Sex-dependent effects of social isolation on the regulation of arginine-vasopressin (AVP) V1a, oxytocin (OT) and serotonin (5HT) 1a receptor binding and aggression

It is widely held that social isolation produces higher rates of mortality and morbidity and has deleterious effects on an individual's sociality. Relatedly, it is widely observed that socially isolated adult rodents display significantly higher levels of aggression when placed in a social situation than do their conspecifics living in social groups. In the following study, we investigated the effects of social isolation on several neurochemical signals that play key roles in the regulation of social behavior in adults. More specifically, we examined the effects of social isolation on vasopressin (AVP) V1a, oxytocin (OT) and serotonin (5-HT)1a receptor binding within the neural circuit controlling social behavior. Male and female Syrian hamsters were housed individually or with two other hamsters for four weeks and were then tested with a same-sex nonaggressive intruder in a neutral arena for 5 min. Social isolation significantly increased aggression in both males and females and altered receptor binding in several brain regions in a sex-dependent manner. For example, V1a receptor binding was greater in socially isolated males in the anterior hypothalamus than it was in any other group. Taken together, these data provide substantial new support for the proposition that the social environment can have a significant impact on the structural and neurochemical mechanisms regulating social behavior and that the amount and type of social interactions can produce differential effects on the circuit regulating social behavior in a sex-dependent manner.

Comparing vasopressin and oxytocin fiber and receptor density patterns in the social behavior neural network: Implications for cross-system signaling

Vasopressin (AVP) and oxytocin (OXT) regulate social behavior by binding to their canonical receptors, the vasopressin V1a receptor (V1aR) and oxytocin receptor (OTR), respectively. Recent studies suggest that these neuropeptides may also signal via each other's receptors. The extent to which such cross-system signaling occurs likely depends on anatomical overlap between AVP/OXT fibers and V1aR/OTR expression. By comparing AVP/OXT fiber densities with V1aR/OTR binding densities throughout the rat social behavior neural network (SBNN), we propose the potential for cross-system signaling in four regions: the medial amygdala (MeA), bed nucleus of the stria terminalis (BNSTp), medial preoptic area, and periaqueductal grey. We also discuss possible implications of corresponding sex (higher in males versus females) and age (higher in adults versus juveniles) differences in AVP fiber and OTR binding densities in the MeA and BNSTp. Overall, this review reveals the need to unravel the consequences of potential cross-system signaling between AVP and OXT systems in the SBNN for the regulation of social behavior.

Cross-talk among oxytocin and arginine-vasopressin receptors: Relevance for basic and clinical studies of the brain and periphery

Oxytocin (OT) and arginine-vasopressin (AVP) act in the brain to regulate social cognition/social behavior and in the periphery to influence a variety of physiological processes. Although the chemical structures of OT and AVP as well as their receptors are quite similar, OT and AVP can have distinct or even opposing actions. Here, we review the increasing body of evidence that exogenously administered and endogenously released OT and AVP can activate each other's canonical receptors (i.e., cross-talk) and examine the possibility that receptor cross-talk following the synaptic and non-synaptic release of OT and AVP contributes to their distinct roles in the brain and periphery. Understanding the consequences of cross-talk between OT and AVP receptors will be important in identifying how these peptides control social cognition and behavior and for the development of drugs to treat a variety of psychiatric disorders.

Animal models of social stress: the dark side of social interactions

Social stress occurs in all social species, including humans, and shape both mental health and future interactions with conspecifics. Animal models of social stress are used to unravel the precise role of the main stress system - the HPA axis - on the one hand, and the social behavior network on the other, as these are intricately interwoven. The present review aims to summarize the insights gained from three highly useful and clinically relevant animal models of psychosocial stress: the resident-intruder (RI) test, the chronic subordinate colony housing (CSC), and the social fear conditioning (SFC). Each model brings its own focus: the role of the HPA axis in shaping acute social confrontations (RI test), the physiological and behavioral impairments resulting from chronic exposure to negative social experiences (CSC), and the neurobiology underlying social fear and its effects on future social interactions (SFC). Moreover, these models are discussed with special attention to the HPA axis and the neuropeptides vasopressin and oxytocin, which are important messengers in the stress system, in emotion regulation, as well as in the social behavior network. It appears that both nonapeptides balance the relative strength of the stress response, and simultaneously predispose the animal to positive or negative social interactions.

Sex Differences in the Regulation of Offensive Aggression and Dominance by Arginine-Vasopressin

Arginine-vasopressin (AVP) plays a critical role in the regulation of offensive aggression and social status in mammals. AVP is found in an extensive neural network in the brain. Here, we discuss the role of AVP in the regulation of aggression in the limbic system with an emphasis on the critical role of hypothalamic AVP in the control of aggression. In males, activation of AVP V1a receptors (V1aRs) in the hypothalamus stimulates offensive aggression, while in females activation of V1aRs inhibits aggression. Serotonin (5-HT) also acts within the hypothalamus to modulate the effects of AVP on aggression in a sex-dependent manner. Activation of 5-HT1a receptors (5-HT1aRs) inhibits aggression in males and stimulates aggression in females. There are also striking sex differences in the mechanisms underlying the acquisition of dominance. In males, the acquisition of dominance is associated with the activation of AVP-containing neurons in the hypothalamus. By contrast, in females, the acquisition of dominance is associated with the activation of 5-HT-containing neurons in the dorsal raphe. AVP and 5-HT also play critical roles in the regulation of a form of social communication that is important for the maintenance of dominance relationships. In both male and female hamsters, AVP acts via V1aRs in the hypothalamus, as well as in other limbic structures, to communicate social status through the stimulation of a form of scent marking called flank marking. 5-HT acts on 5-HT1aRs as well as other 5-HT receptors within the hypothalamus to inhibit flank marking induced by AVP in both males and females. Interestingly, while AVP and 5-HT influence the expression of aggression in opposite ways in males and females, there are no sex differences in the effects of AVP and 5-HT on the expression of social communication. Given the profound sex differences in the incidence of many psychiatric disorders and the increasing evidence for a relationship between aggressiveness/dominance and the susceptibility to these disorders, understanding the neural regulation of aggression and social status will have significant import for translational studies.

Oxytocin (OT) and arginine-vasopressin (AVP) act on OT receptors and not AVP V1a receptors to enhance social recognition in adult Syrian hamsters (Mesocricetus auratus)

Social recognition is a fundamental requirement for all forms of social relationships. A majority of studies investigating the neural mechanisms underlying social recognition in rodents have investigated relatively neutral social stimuli such as juveniles or ovariectomized females over short time intervals (e.g., 2h). The present study developed a new testing model to study social recognition among adult males using a potent social stimulus. Flank gland odors are used extensively in social communication in Syrian hamsters and convey important information such as dominance status. We found that the recognition of flank gland odors after a 3min exposure lasted for at least 24h, substantially longer than the recognition of other social cues in rats and mice. Intracerebroventricular injections of OT and AVP prolonged the recognition of flank gland odor for up to 48h. Selective OTR but not V1aR agonists, mimicked these enhancing effects of OT and AVP. Similarly, selective OTR but not V1aR antagonists blocked recognition of the odors after 20min. In contrast, the recognition of non-social stimuli was not blocked by either the OTR or the V1aR antagonists. Our findings suggest both OT and AVP enhance social recognition via acting on OTRs and not V1aRs and that the recognition enhancing effects of OT and AVP are limited to social stimuli.

Species, sex and individual differences in the vasotocin/vasopressin system: relationship to neurochemical signaling in the social behavior neural network

Arginine-vasotocin (AVT)/arginine vasopressin (AVP) are members of the AVP/oxytocin (OT) superfamily of peptides that are involved in the regulation of social behavior, social cognition and emotion. Comparative studies have revealed that AVT/AVP and their receptors are found throughout the "social behavior neural network (SBNN)" and display the properties expected from a signaling system that controls social behavior (i.e., species, sex and individual differences and modulation by gonadal hormones and social factors). Neurochemical signaling within the SBNN likely involves a complex combination of synaptic mechanisms that co-release multiple chemical signals (e.g., classical neurotransmitters and AVT/AVP as well as other peptides) and non-synaptic mechanisms (i.e., volume transmission). Crosstalk between AVP/OT peptides and receptors within the SBNN is likely. A better understanding of the functional properties of neurochemical signaling in the SBNN will allow for a more refined examination of the relationships between this peptide system and species, sex and individual differences in sociality.

The role of serotonin, vasopressin, and serotonin/vasopressin interactions in aggressive behavior

Aggression control has been investigated across species and is centrally mediated within various brain regions by several neural systems that interact at different levels. The debate over the degree to which any one system or region affects aggressive responding, or any behavior for that matter, in some senses is arbitrary considering the plastic and adaptive properties of the central nervous system. Nevertheless, from the reductionist point of view, the compartmentalization of evolutionarily maladaptive behaviors to specific regions and systems of the brain is necessary for the advancement of clinical treatments (e.g., pharmaceutical) and novel therapeutic methods (e.g., deep brain stimulation). The general purpose of this chapter is to examine the confluence of two such systems, and how their functional interaction affects aggressive behavior. Specifically, the influence of the serotonin (5HT) and arginine vasopressin (AVP) neural systems on the control of aggressive behavior will be examined individually and together to provide a context by which the understanding of aggression modulation can be expanded from seemingly parallel neuromodulatory mechanisms, to a single and highly interactive system of aggression control.

Sociality and oxytocin and vasopressin in the brain of male and female dominant and subordinate mandarin voles

The dominant-subordinate hierarchy in animals often needs to be established via agonistic encounters and consequently affects reproduction and survival. Differences in brain neuropeptides and sociality among dominant and subordinate males and females remain poorly understood. Here we explore neuropeptide levels and sociality during agonistic encounter tests in mandarin voles. We found that dominant mandarin voles engaged in higher levels of approaching, investigating, self-grooming and exploring behavior than subordinates. Dominant males habituated better to a stimulus vole than dominant females. Dominant males displayed significantly less oxytocin-immunoreactive neurons in the paraventricular nuclei and more vasopressin-immunoreactive neurons in the paraventricular nuclei, supraoptic nuclei, and the lateral and anterior hypothalamus than subordinates. Dominant females displayed significantly more vasopressin-immunoreactive neurons in the lateral hypothalamus and anterior hypothalamus than subordinates. Sex differences were found in the level of oxytocin and vasopressin. These results indicate that distinct parameters related to central nervous oxytocin and vasopressin are associated with behaviors during agonistic encounters in a sex-specific manner in mandarin voles.

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.

The regulation of social recognition, social communication and aggression: vasopressin in the social behavior neural network

Neuropeptides in the arginine vasotocin/arginine vasopressin (AVT/AVP) family play a major role in the regulation of social behavior by their actions in the brain. In mammals, AVP is found within a circuit of recriprocally connected limbic structures that form the social behavior neural network. This review examines the role played by AVP within this network in controlling social processes that are critical for the formation and maintenance of social relationships: social recognition, social communication and aggression. Studies in a number of mammalian species indicate that AVP and AVP V1a receptors are ideally suited to regulate the expression of social processes because of their plasticity in response to factors that influence social behavior. The pattern of AVP innervation and V1a receptors across the social behavior neural network may determine the potential range and intensity of social responses that individuals display in different social situations. Although fundamental information on how social behavior is wired in the brain is still lacking, it is clear that different social behaviors can be influenced by the actions of AVP in the same region of the network and that AVP can act within multiple regions of this network to regulate the expression of individual social behaviors. The existing data suggest that AVP can influence social behavior by modulating the interpretation of sensory information, by influencing decision making and by triggering complex motor outputs. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

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.

Oxytocin and vasopressin immunoreactive staining in the brains of Brandt's voles (Lasiopodomys brandtii) and greater long-tailed hamsters (Tscherskia triton)

Immunoreactive (ir) staining of the neuropeptides oxytocin (OT) and vasopressin (AVP) was performed in the brains of Brandt's voles (Lasiopodomys brandtii) and greater long-tailed hamsters (Tscherskia triton)-two species that differ remarkably in social behaviors. Social Brandt's voles had higher densities of OT-ir cells in the medial preoptic area (MPOA) and medial amygdala (MeA) as well as higher densities of AVP-ir cells in the lateral hypothalamus (LH) compared to solitary greater long-tailed hamsters. In contrast, the hamsters had higher densities of OT-ir cells in the anterior hypothalamus (AH) and LH and higher densities of AVP-ir cells in the MPOA than the voles. OT-ir and AVP-ir fibers were also found in many forebrain areas with subtle species differences. Given the roles of OT and AVP in the regulation of social behaviors in other rodent species, our data support the hypothesis that species-specific patterns of central OT and AVP pathways may underlie species differences in social behaviors. However, despite a higher density of OT-ir cells in the paraventricular nucleus of the hypothalamus (PVN) in females than in males in both species, no other sex differences were found in OT-ir or AVP-ir staining. These data failed to support our prediction that a sexually dimorphic pattern of neuropeptide staining in the brain is more apparent in Brandt's voles than in greater long-tailed hamsters.

The bed nucleus of the stria terminalis in the Syrian hamster (Mesocricetus auratus): absence of vasopressin expression in standard and wild-derived hamsters and galanin regulation by seasonal changes in circulating sex steroids

The bed nucleus of the stria terminalis (BNST) is a nucleus of the forebrain highly sensitive to sex steroids and containing vasopressin neurons implicated in several social- and reproduction-related behaviours such as scent-marking, aggression, pair bonding and parental behaviour. Sexually dimorphic vasopressin expression in BNST neurons has been reported in almost all rodents, with the notable exception of the Syrian hamster. In this species, vasopressin expression is completely absent in the BNST. Because almost all Syrian hamsters used in research are derived from a very small breeding stock captured in 1930, we compared commercially available Syrian hamsters with a recently captured, wild-derived breeding stock. We checked for vasopressin expression using in situ hybridization and immunohistochemistry. Vasopressin expression in BNST neurons was completely absent in both breeding stocks, confirming the absence of BNST vasopressin expression in Mesocricetus auratus and ruling out a breeding artefact. Because vasopressin expression in BNST neurons appears to be strictly dependent on circulating sex steroids, the absence of vasopressin expression in Syrian hamster BNST neurons might be due to an insensitivity of these neurons to sex steroids. BNST vasopressin neurons also express galanin. Although galanin expression in the BNST is not sexually dimorphic in the Syrian hamster, it appears to be regulated by sex steroids. In the Djungarian hamster, photoperiodically driven seasonal variations of circulating sex steroids result in a seasonal rhythm of galanin expression in BNST neurons. We analysed the sex steroid dependence of galanin expression in the Syrian hamster. Castration and short photoperiod-induced sexual quiescence both resulted in downregulation of galanin mRNA in cell bodies (BNST) and immunoreactivity in the fibres (lateral septum). Testosterone supplementation of short photoperiod-adapted animals was able to restore galanin expression. Thus Syrian hamster BNST neurons respond to circulating sex steroids and their seasonal variations as observed in other rodent species.

Neural distribution of nonapeptide binding sites in two species of songbird

Vasotocin (VT) and its mammalian homologue, vasopressin (VP), modulate many social behaviors in a variety of vertebrate species. In songbirds, the effects of centrally administered VT vary according to species, which may reflect species-specific distributions of VT binding sites. Different radioligands used to map receptors in previous autoradiographical studies have revealed nonoverlapping distributions of VT binding, suggesting a heterogeneous population of more than one type of VT receptor. For two model songbird species, the white-throated sparrow (Zonotrichia albicollis) and zebra finch (Taeniopygia guttata), we labeled putative VT receptors with two radioligands, [(125)I]ornithine vasotocin analog ([(125)I]OVTA) and [(125)I]linear VP antagonist ([(125)I]HO-LVA). Competitive binding assays in the lateral septum showed that both ligands were effectively displaced by both VT and a related nonapeptide, mesotocin (MT), showing that these radioligands, which were developed to label mammalian nonapeptide receptors, label at least one population of related receptors in songbirds. [(125)I]OVTA labeled receptors throughout the telencephalon, diencephalon, midbrain, and brainstem, with a similar distribution in both species. In contrast, the binding of [(125)I]HO-LVA was restricted to the septal area, dorsal arcopallium, and optic tectum in sparrow and was essentially undetectable in zebra finch. Because the avian brain is likely to express multiple types of VT receptors, we hypothesize that the binding patterns of these radioligands represent a heterogeneous receptor population.

Receptors and neural effects of oxytocin in the rodent hypothalamus and preoptic region

Vasopressin and oxytocin are produced in and secreted from not only hypothalamo-hypophysial neurons which shed their products into the circulation to act as hormones or releasing factors, but also from neurons whose axons form tracts which remain within the central nervous system. Using tritiated or radioiodinated ligands, binding sites for vasopressin and for oxytocin have been detected by in vitro autoradiography. In the rat hypothalamus binding sites for vasopressin are present in the suprachiasmatic, sigmoid and arcuate nuclei, and oxytocin receptors in the area of the ventromedial nucleus. Electrophysiological evidence obtained using single cell recordings in slices suggests that oxytocin-binding sites present in the ventromedial hypothalamus and in the bed nucleus of the stria terminalis mostly represent functional, neuronal receptors. The expression of these receptors (but not of the vasopressin receptors) depends on gonadal steroid hormones, as does that of uterine and mammary gland oxytocin receptors. Modifications of the hormonal status associated with, for example, puberty and lactation cause 'up-regulation' of central and peripheral oxytocin receptors. The central administration of oxytocin facilitates (and the administration of oxytocin agonists inhibits) maternal behaviour and the milk ejection reflex, therefore the hormonal and neural actions of oxytocin appear to be complementary in ensuring the birth and development of the offspring.

Vasopressin 1a receptor knockout mice have a subtle olfactory deficit but normal aggression

Two receptors for vasopressin (Avp) are expressed in the brain, the Avp 1a receptor (Avpr1a) and the Avp 1b receptor (Avpr1b). To investigate the role of Avpr1a in behaviors in mice more extensively, we generated a line of mice lacking a functional Avpr1a (knockout, Avpr1a(-/-)). We first performed a baseline phenotypic screen of the Avpr1a knockouts followed by a more detailed analysis of their circadian rhythms and olfactory function. When free-running in constant darkness, the Avpr1a(-/-) mice have a longer circadian tau than the wild types. There are also subtle olfactory deficits in Avpr1a(-/-) mice as measured in an olfactory habituation/dishabituation test and in the discrimination of female urine from male urine using an operant testing paradigm. An extensive body of research has shown that manipulation of the Avpr1a alters behavior, including aggression and social recognition. Therefore, we expected profound behavioral deficits in mice lacking the Avpr1a gene. Contrary to our expectations, social aggression, anxiety-like behavior and social recognition are unaffected in this line of Avpr1a knockout mice. These data suggest either that the Avpr1a is not as critical as we thought for social behavior in mice or, more likely, that the neural circuitry underlying aggression and other social behaviors compensates for the life-long loss of the Avpr1a. However, the olfactory deficits observed in the Avpr1a(-/-) mice suggest that Avp and Avpr1a drugs may affect behavior, in part, by modulation of chemosensory systems.

Anterior hypothalamic vasopressin modulates the aggression-stimulating effects of adolescent cocaine exposure in Syrian hamsters

Repeated low-dose cocaine treatment (0.5 mg/kg/day) during adolescence induces offensive aggression in male Syrian hamsters (Mesocricetus auratus). This study examines the hypothesis that adolescent cocaine exposure predisposes hamsters to heightened levels of aggressive behavior by increasing the activity of the anterior hypothalamic-vasopressinergic neural system. In a first experiment, adolescent male hamsters were treated with low-dose cocaine and then scored for offensive aggression in the absence or presence of vasopressin receptor antagonists applied directly to the anterior hypothalamus. Adolescent cocaine-treated hamsters displayed highly escalated offensive aggression that could be reversed by blocking the activity of vasopressin receptors within the anterior hypothalamus. In a second set of experiments, adolescent hamsters were administered low-dose cocaine or vehicle, tested for offensive aggression, and then examined for differences in vasopressin innervation patterns and expression levels in the anterior hypothalamus, as well as the basal- and stimulated-release of vasopressin in this same brain region. Aggressive, adolescent cocaine-treated hamsters showed no differences in vasopressin afferent innervation and/or peptide levels in the anterior hypothalamus compared with non-aggressive, saline-treated littermates. Conversely, significant increases in stimulated, but not basal, vasopressin release were detected from the anterior hypothalamus of aggressive, cocaine-treated animals compared with non-aggressive, saline-treated controls. Together, these data suggest that adolescent cocaine exposure increases aggression by increasing stimulated release of vasopressin in the anterior hypothalamus, providing direct evidence for a causal role of anterior hypothalamic-vasopressin activity in adolescent cocaine-induced offensive aggression. A model for how alterations in anterior hypothalamic-vasopressin neural functioning may facilitate the development of the aggressive phenotype in adolescent-cocaine exposed animals is presented.

Generation of the melatonin endocrine message in mammals: a review of the complex regulation of melatonin synthesis by norepinephrine, peptides, and other pineal transmitters

Melatonin, the major hormone produced by the pineal gland, displays characteristic daily and seasonal patterns of secretion. These robust and predictable rhythms in circulating melatonin are strong synchronizers for the expression of numerous physiological processes in photoperiodic species. In mammals, the nighttime production of melatonin is mainly driven by the circadian clock, situated in the suprachiasmatic nucleus of the hypothalamus, which controls the release of norepinephrine from the dense pineal sympathetic afferents. The pivotal role of norepinephrine in the nocturnal stimulation of melatonin synthesis has been extensively dissected at the cellular and molecular levels. Besides the noradrenergic input, the presence of numerous other transmitters originating from various sources has been reported in the pineal gland. Many of these are neuropeptides and appear to contribute to the regulation of melatonin synthesis by modulating the effects of norepinephrine on pineal biochemistry. The aim of this review is firstly to update our knowledge of the cellular and molecular events underlying the noradrenergic control of melatonin synthesis; and secondly to gather together early and recent data on the effects of the nonadrenergic transmitters on modulation of melatonin synthesis. This information reveals the variety of inputs that can be integrated by the pineal gland; what elements are crucial to deliver the very precise timing information to the organism. This also clarifies the role of these various inputs in the seasonal variation of melatonin synthesis and their subsequent physiological function.

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.

Sexual dimorphism in the central nervous system of marsupials

It is now evident that gonadal steroids, acting within a limited critical period during fetal or neonatal life, bring about sexual differentiation of both the reproductive tract and the central nervous system (CNS) in eutherians. This results in structural dimorphism in several regions of the brain and spinal cord and the programming of future patterns of adult reproductive behavior. At birth the CNS of marsupials is very underdeveloped and debate continues as to the importance of hormones in its sexual differentiation. Nevertheless, some sexually dimorphic regions have been identified, including the lateral septal nucleus in the hypothalamus and the spinal nucleus of the bulbocavernosus and dorsolateral nucleus in the spinal cord, but interestingly not the cremasteric nucleus, which is dimorphic in eutherians. To date, no apparent sex differences in estrogen and androgen receptor-immunoreactive structures have been detected in the marsupial brain; however, higher levels of aromatase activity during early development in male opossums have been reported. Sex differences have been identified in the localization of cholecystokinin-immunoreactive structures in the marsupial brain indicating that the expression of this neuropeptide is differentially regulated in each sex. A sex difference also exists in the density of arginine vasopressin-immunoreactive fibers. Arguments continue as to whether sexually dimorphic behavior in marsupials, as in eutherians, is largely predetermined by hormones acting on the CNS early in development or if it is entirely dependent on the adult steroid hormonal environment.

Vasopressin immunoreactivity and release in the suprachiasmatic nucleus of wild-type and tau mutant Syrian hamsters

Despite the prominent role of the Syrian hamster (Mesocricetus auratus) in studies of circadian rhythms, there are no data available on the temporal dynamics of the neuropeptide vasopressin (AVP), a major output system of the suprachiasmatic nucleus (SCN). We studied the hamster SCN-AVP system in vivo across the light period and in vitro using long-term organotypic SCN cultures. Additionally, we compared wild-type and tau mutant hamsters with an endogenous circadian period of approximately 24 h and approximately 20 h, respectively. The in vivo study revealed no differences in the number of SCN-AVP neurons between the two genotypes of hamsters studied at three time points across the light period of the circadian cycle. A significantly higher level of AVP-immunoreactivity, however, was found in the SCN of wild-type compared to tau mutant hamsters at the beginning and in the middle of the light period, but not at the end of the light period. SCN-AVP cell number and immunostaining decreased significantly across the light period in wild-type hamsters, but not in tau mutants. The in vitro study revealed a significantly higher rate of AVP release per 24 h from the tau mutant SCN compared to the wild-type SCN. Robust circadian oscillations in AVP release were not found in either type of hamster. These results may suggest that the SCN-AVP system of hamsters, irrespective of genotype, is relatively weak compared to other species. Moreover, the tau mutation seems to influence the SCN-AVP system by enhancing the rate of AVP release and by reducing AVP content and its daily fluctuation.

Social behavior functions and related anatomical characteristics of vasotocin/vasopressin systems in vertebrates

The neuropeptide arginine vasotocin (AVT; non-mammals) and its mammalian homologue, arginine vasopressin (AVP) influence a variety of sex-typical and species-specific behaviors, and provide an integrational neural substrate for the dynamic modulation of those behaviors by endocrine and sensory stimuli. Although AVT/AVP behavioral functions and related anatomical features are increasingly well-known for individual species, ubiquitous species-specificity presents ever increasing challenges for identifying consistent structure-function patterns that are broadly meaningful. Towards this end, we provide a comprehensive review of the available literature on social behavior functions of AVT/AVP and related anatomical characteristics, inclusive of seasonal plasticity, sexual dimorphism, and steroid sensitivity. Based on this foundation, we then advance three major questions which are fundamental to a broad conceptualization of AVT/AVP social behavior functions: (1) Are there sufficient data to suggest that certain peptide functions or anatomical characteristics (neuron, fiber, and receptor distributions) are conserved across the vertebrate classes? (2) Are independently-evolved but similar behavior patterns (e.g. similar social structures) supported by convergent modifications of neuropeptide mechanisms, and if so, what mechanisms? (3) How does AVT/AVP influence behavior - by modulation of sensorimotor processes, motivational processes, or both? Hypotheses based upon these questions, rather than those based on individual organisms, should generate comparative data that will foster cross-class comparisons which are at present underrepresented in the available literature.

Modulation of rat medial vestibular nucleus neurone activity by vasopressin and noradrenaline in vitro

In the present study, we examined the effects of bath application of vasopressin and noradrenaline on the spontaneous tonic discharge of medial vestibular nucleus (MVN) neurones and investigated if there is an interaction between the two drugs in an in vitro slice preparation of the rat brainstem containing the MVN. The results showed that vasopressin did not affect the spontaneous discharge rate of MVN neurones when applied either as a 60 s pulse or when the drug continuously perfused the slice for a period of 10 min. In contrast, noradrenaline affected the spontaneous discharge rate of the majority of cells tested (53/60, 88%). Noradrenaline excited the majority (46/53, 87%) of MVN neurones through both alpha1 and beta noradrenergic receptor-linked mechanisms. The remaining cells (7/53, 13%) were inhibited by noradrenaline through an alpha2 noradrenergic receptor-linked mechanism. Neither the excitatory nor inhibitory effects of noradrenaline were modified by vasopressin when the two drugs were applied together.

Catecholaminergic enzymes, vasopressin and oxytocin distribution in Siberian hamster brain

Siberian hamsters exhibit marked seasonal changes in physiology and behavior that are triggered by the daylength and that can be mimicked in the laboratory by changing the photoperiod, making them a convenient and popular species for the study of regulatory biology. Because no atlas of neurotransmitter distribution exists for this species, the purpose of the present study was to map the distribution of cell bodies containing catecholaminergic synthetic enzymes (tyrosine hydroxylase and dopamine-beta-hydroxylase) and several neurotransmitters (arginine vasopressin and oxytocin) in Siberian hamster brain using immunocytochemistry. The distributions of these catecholaminergic synthetic enzymes and neurotransmitters largely were similar to those for Syrian hamsters with some notable differences. There were novel groups of neurotransmitter- or synthetic enzyme-immunoreactive neurons such as tyrosine hydroxylase-immunoreactive cells in the bed nucleus of the stria terminalis, dopamine-beta-hydroxylase-immunoreactive cells in the motor trigeminal, hypoglossal, and paraabducens nuclei, and arginine vasopressin- and oxytocin-immunoreactive cells within the nucleus of the diagonal band, dorsal hypothalamic area, and arcuate nucleus compared with Syrian hamsters. This is the first description of the distribution of cell bodies for some commonly studied catecholaminergic synthetic enzymes and peptides in Siberian hamsters.

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.

Chronic anabolic-androgenic steroid treatment during adolescence increases anterior hypothalamic vasopressin and aggression in intact hamsters

The present study examines the hypothesis that exposure to anabolic-androgenic steroids (AAS) during adolescent development predisposes hamsters to heightened levels of aggressive behavior by influencing the anterior hypothalamic-arginine vasopressin (AH-AVP) neural system. To test this, adolescent male hamsters (Mesocricetus auratus) were treated with high doses of AAS, tested for offensive aggression in the absence or presence of AH-AVP receptor antagonists, and then examined for changes in AH-AVP expression and neural organization. AAS exposure during adolescence significantly increased aggression intensity (number of attacks and bites) and initiation (latency to the first bite). Yet, only increases in aggression intensity were inhibited by AH-AVP receptor antagonism. Adolescent AAS-treated hamsters showed significant increases in AH-AVP fiber density and peptide content. However, no alterations in AH-AVP neuronal organization or mRNA expression were found. Together, these data suggest that adolescent AAS exposure increase aggression intensity by altering AH-AVP expression and activity, providing direct evidence for a causal role of AH-AVP expression and function in early onset AAS-stimulated aggression.

Neuronal projections to the lateral retrochiasmatic area of sheep with special reference to catecholaminergic afferents: immunohistochemical and retrograde tract-tracing studies

The retrochiasmatic area contains the A15 catecholaminergic group and numerous monoaminergic afferents whose discrete cell origins are unknown in sheep. Using tract-tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the retrochiasmatic area in sheep. The retrogradely labeled cells were seen by observation of the tracer by direct fluorescence or by immunohistochemistry with specific antibodies raised in rabbits or horses. Among the retrogradely labeled neurons, double immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, and serotonin were used to characterize catecholamine and serotonin FG labeled neurons. The retrochiasmatic area, which included the A15 dopaminergic group and the accessory supraoptic nucleus (SON), received major inputs from the lateral septum (LS), the bed nucleus of the stria terminalis (BNST), the thalamic paraventricular nucleus, hypothalamic paraventricular and supraoptic nuclei, the perimamillary area, the amygdala, the ventral part of the hippocampus and the parabrachial nucleus (PBN). Further, numerous scattered retrogradely labeled neurons were observed in the preoptic area, the ventromedial part of the hypothalamus. the periventricular area, the periaqueductal central gray (CG), the ventrolateral medulla and the dorsal vagal complex. Most of the noradrenergic afferents came from the ventro-lateral medulla (Al group), and only a few from the locus coeruleus complex (A6/A7 groups). A few dopaminergic neurons retrogradely labeled with flurogold were observed in the periventricular area of the hypothalamus. Rare serotoninergic fluorogold labeled neurons belonged to the dorsal raphe nucleus. Most of these afferents came from both sides of the brain, except for hypothalamic supraoptic and paraventricular nuclei. In the light of these anatomical data, we compared our results with data obtained from rats, and we discussed the putative role of these afferents in sheep in the regulation of several specific functions in which the retrochiasmatic area may be involved, such as reproduction.

Functional sex differences ('sexual diergism') of central nervous system cholinergic systems, vasopressin, and hypothalamic-pituitary-adrenal axis activity in mammals: a selective review

Sexual dimorphism of the mammalian central nervous system (CNS) has been widely documented. Morphological sex differences in brain areas underlie sex differences in function. To distinguish sex differences in physiological function from underlying sexual dimorphisms, we use the term, sexual diergism, to encompass differences in function between males and females. Whereas the influence of sex hormones on CNS morphological characteristics and function of the hypothalamic-pituitary-gonadal axis has been well-documented, little is known about sexual diergism of CNS control of the hypothalamic-pituitary-adrenal (HPA) axis. Many studies have been conducted on both men and women but have not reported comparisons between them, and many animal studies have used males or females, but not both. From a diergic standpoint, the CNS cholinergic system appears to be more responsive to stress and other stimuli in female than in male mammals; but from a dimorphic standpoint, it is anatomically larger, higher in cell density, and more stable with age in males than in females. Dimorphism often produces diergism, but age, hormones, environment and genetics contribute differentially. This review focuses on the sexual diergism of CNS cholinergic and vasopressinergic systems and their relationship to the HPA axis, with resulting implications for the study of behavior, disease, and therapeutics.

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 and oxytocin in the control of social behavior in Syrian hamsters (Mesocricetus auratus)

Vasopressin (VP) and oxytocin (OT) play an important role in regulating social behavior in a variety of species as a result of their actions in the central nervous system. The following paper reviews the actions of VP and OT in controlling a range of social behaviors involved in communication, aggression and reproduction in the Syrian hamster. These data suggest that social and hormonal stimuli alter the expression of specific social behaviors by altering the release of, or the response to, VP and OT within key elements of the neural circuits controlling these behaviors.

Vasopressin binding sites in the central nervous system: distribution and regulation

High affinity binding sites for vasopressin (VP) are widely distributed within the rat brain and spinal cord. Since their presence is associated with neuronal sensitivity to VP application, their anatomical distribution maps structures which could be activated by endogenous VP. Interestingly, marked species-related differences of the VP receptor distribution have been revealed. Some evidence has also been provided that mechanisms of receptor regulation may vary among species. In the rat, the expression of VP binding sites in some motor nuclei shows remarkable plasticity, in particular up-regulation after axotomy. These data suggest that VP may, in addition to affecting motoneuronal excitability, act as a trophic factor onto motoneurones.

Historadioautographic localisation of oxytocin and vasopressin binding sites in the central nervous system of the merione (Meriones shawi)

The distribution of vasopressin and oxytocin binding sites in the central nervous system of the merione (Meriones shawi), a rodent adapted to desert life, was studied by means of conventional film radioautography at macroscopic scale and historadioautography at cellular level using radioiodinated ligands highly selective for either oxytocin or type V1 a vasopressin receptors. Both types of binding sites exhibited the same selectivity for endogenous peptides as in the rat. Distribution of oxytocin binding sites was similar in some structures (limbic system, spinal cord) to that described in the rat and in other rodents. Vasopressin binding sites were much more widely distributed in the merione than in the rat brain. In addition to locations common to most rodents (lateral septum and suprachiasmatic nucleus), in merione vasopressin binding sites occurred in several areas known to express oxytocin binding sites in the rat (olfactory system, hypothalamus). Colocalisation of vasopressin and oxytocin binding sites, which occurred in the CA1 and CA2 fields of Ammon's horns of the hippocampus, the caudate-putamen and the fundus striati of the merione, has so far not been reported in any other rodent.

Vasopressin in the forebrain of common marmosets (Callithrix jacchus): studies with in situ hybridization, immunocytochemistry and receptor autoradiography

The distribution of vasopressin (AVP) producing cells, their projections and AVP receptors was examined in the brain of common marmosets (Callithrix jacchus) using in situ hybridization, immunocytochemistry and receptor autoradiography. Clusters of cells labeled for AVP mRNA or stained for AVP immunoreactivity (AVP-ir) were found in the paraventricular (PVN), supraoptic (SON) and suprachiasmatic nuclei (SCN) of the hypothalamus. Scattered AVP producing cells were also found in the lateral hypothalamus and the bed nucleus of the stria terminalis (BST). Neither AVP mRNA-labeled nor AVP-ir cells were detected in the amygdala. Although AVP-ir fibers were evident outside of the hypothalamic-neurohypophyseal tract, a plexus of fibers in the lateral septum, as observed in the rat brain, was not detected. Receptor autoradiography using 125I-linear-AVP revealed specific binding for AVP receptors in the nucleus accumbens, diagonal band, lateral septum, the BST, SCN, PVN, amygdala, anterodorsal and ventromedial nucleus of the hypothalamus, indicating sites for central AVP action in the marmoset brain. Together, these data provide a comprehensive picture of AVP pathways in the marmoset brain, demonstrating differences from rodents in the distribution of cell bodies, fibers and receptors.

Basal ganglia organization in amphibians: afferent connections to the striatum and the nucleus accumbens

As part of a research program to determine if the organization of basal ganglia (BG) of amphibians is homologous to that of amniotes, the afferent connections of the BG in the anurans Xenopus laevis and Rana perezi and the urodele Pleurodeles waltl were investigated with sensitive tract-tracing techniques. Hodological evidence is presented that supports a division of the amphibian BG into a nucleus accumbens and a striatum. Both structures have inputs in common from the olfactory bulb, medial pallium, striatopallial transition area, preoptic area, ventral thalamus, ventral hypothalamic nucleus, posterior tubercle, several mesencephalic and rhombencephalic reticular nuclei, locus coeruleus, raphe, and the nucleus of the solitary tract. Several nuclei that project to both subdivisions of the BG, however, show a clear preference for either the striatum (lateral amygdala, parabrachial nucleus) or the nucleus accumbens (medial amygdala, ventral midbrain tegmentum). In addition, the anterior entopeduncular nucleus, central thalamic nucleus, anterior and posteroventral divisions of the lateral thalamic nucleus, and torus semicircularis project exclusively to the striatum, whereas the anterior thalamic nucleus, anteroventral, and anterodorsal tegmental nuclei provide inputs solely to the nucleus accumbens. Apart from this subdivision of the basal forebrain, the results of the present study have revealed more elaborate patterns of afferent projections to the BG of amphibians than previously thought. Moreover, regional differences within the striatum and the nucleus accumbens were demonstrated, suggesting the existence of functional subdivisions. The present study has revealed that the organization of the afferent connections to the BG in amphibians is basically similar to that of amniotes. According to their afferent connections, the striatum and the nucleus accumbens of amphibians may play a key role in processing olfactory, visual, auditory, lateral line, and visceral information. However, contrary to the situation in amniotes, only a minor involvement of pallial structures on the BG functions is present in amphibians.

Substantia innominata: a notion which impedes clinical-anatomical correlations in neuropsychiatric disorders

Comparative neuroanatomical investigations in primates and non-primates have helped disentangle the anatomy of the basal forebrain region known as the substantia innominata. The most striking aspect of this region is its subdivision into two major parts. This reflects the fundamental organizational scheme for this portion of the forebrain. According to this scheme, two major subcortical telencephalic structures, i.e. the striatopallidal complex and extended amygdala, form large diagonally oriented bands. The rostroventral extension of the pallidum accounts for a large part of the rostral subcommissural substantia innominata, while the sublenticular substantia innominata is primarily occupied by elements of the extended amygdala. Also dispersed across this region is the basal nucleus of Meynert, which is part of a more or less continuous collection of cholinergic and non-cholinergic corticopetal and thalamopetal cells, which stretches from the septum diagonal band rostrally to the caudal globus pallidus. The basal nucleus of Meynert is especially prominent in the primate, where it is sometimes inappropriately applied as a synonym for the substantia innominata, thereby tacitly ignoring the remaining components. In most mammals, the extended amygdala presents itself as a ring of neurons encircling the internal capsule and basal ganglia. The extended amygdala may be further subdivided, i.e. into the central extended amygdala (related to the central amygdaloid nucleus) and the medial extended amygdala (related to the medial amygdaloid nucleus), which generally form separate corridors both in the sublenticular region and along the supracapsular course of the stria terminalis. The extended amygdala is directly continuous with the caudomedial shell of the accumbens, and to some extent appears to merge with it. Together the accumbens shell and extended amygdala form an extensive forebrain continuum, which establishes specific neuronal circuits with the medial prefrontal-orbitofrontal cortex and medial temporal lobe. This continuum is particularly characterized by a prominent system of long intrinsic association fibers, and a variety of highly differentiated downstream projections to the hypothalamus and brainstem. The various components of the extended amygdala, together with the shell of the accumbens, are ideally structured to generate endocrine, autonomic and somatomotor aspects of emotional and motivational states. Behavioral observations support this proposition and demonstrate the relevance of these structures to a variety of functions, ranging from the various elements of the reproductive cycle to drug-seeking behavior. The neurochemical and connectional features common to the accumbens shell and the extended amygdala are especially relevant to understanding the etiology and treatment of neuropsychiatric disorders. This is discussed in general terms, and also in specific relation to the neurodevelopmental theory of schizophrenia and to the neurosurgical treatment of neuropsychiatric disorders.

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.

Vasopressin binding in the cerebral cortex of the Mongolian gerbil is reduced by transient cerebral ischemia

In Mongolian gerbils, the content of vasopressin in the cerebral cortex, the striatum, and the hypothalamus is increased after induction of acute cerebral ischemia. We used an iodinated vasopressin analogue and light microscopic autoradiography to study the distribution of vasopressin V1 receptors in the brain of adult male gerbils and to evaluate the effects of a transient bilateral cerebral ischemia (6 minutes) on the density of this receptor population. The animals were killed immediately or 10, 30, or 100 hours after transient bilateral occlusion of the common carotid arteries. In control animals, specific [125I]-VPA binding sites were present in various structures of the brain (olfactory bulb, anterior olfactory nucleus, lateral septum, bed nucleus of the stria terminalis, median preoptic area, ventral pallidum, substantia innominata, amygdala, thalamus, hypothalamic mammillary nuclei, superior colliculus, subiculum, central gray, nucleus of the solitary tract, hypoglossal nucleus). The strongest labeling was detected in the cerebral cortex, layers 5-6. After 30-100 hours of survival time following ischemia there was a marked decrease in [125I]-VPA binding site density in these cerebral cortex layers. To a lesser degree, a decrease was also detected in the lateral septal nucleus. In contrast, labeling in other noncortical structures remained unchanged. All animals with 100 hours recovery showed a loss of cells in hippocampus (CA1 layer) and striatum. In addition, ischemia induced concomitant and proliferative changes in cortical and hippocampal astrocytes assessed by glial fibrillary acid protein immunoreactivity. These observations indicate a role for vasopressin in the cerebral cortex either on neurons or on glial cells and the modulation of vasopressin receptor expression by transient cerebral ischemia.

Ontogeny of arginine vasopressin-like immunoreactivity in the Brazilian opossum brain

The neuropeptide arginine vasopressin is involved in many centrally mediated functions and brain development. In this study, we have examined the ontogeny of arginine vasopressin-like immunoreactivity (AVP-IR) in the Brazilian opossum (Monodelphis domestica) brain to further understand the involvement of AVP in the forming central nervous system. Monodelphis is a small pouchless marsupial and its pups are born in an extremely immature state before neurogenesis is completed. In the adult brain, cell bodies containing AVP-IR were found in several nuclear groups and areas, and immunoreactive fibers were found to be widely distributed throughout the brain. The distribution of AVP-IR in the adult opossum brain generally resembled that reported for other species including the rat, however, some differences in localization of immunoreactive cells were observed. In the developing opossum brain, AVP-IR was first seen in the mesencephalon and diencephalon between embryonic days 12 and 13. Subsequently, a distinct group of AVP immunoreactive cells was present in the forming supraoptic nucleus on day 1 of postnatal life (1 PN) and at 3 PN in the paraventricular nucleus. Between 1 and 3 PN, a few cells transiently expressed AVP-IR in the forming thalamus and tegmental area. At these ages a few immunoreactive fibers were also detected in the forming cerebellum. These fibers were not seen at later ages in these areas. By 5 PN, an increased expression of AVP-IR was seen in the forming supraoptic and paraventricular hypothalamic nuclei, median eminence, and posterior pituitary. At 7 PN, immunoreactive cells and fibers were seen in several forebrain areas. The distribution pattern of AVP-IR became adult-like by 60 PN. A sex difference in the amount of AVP-IR in the lateral septum was also observed in the opossum brain at 60 PN. This difference persisted in the adult brain. Due to the early presence of AVP-IR in the Monodelphis brain before neurogenesis and morphogenesis is completed, we suggest that AVP may be involved in morphogenesis of the central nervous system. In addition, AVP may have a significant physiological function in regard to homeostasis before the forebrain contributes to these control mechanisms. Further studies, including physiological and developmental manipulations, will define the significance of the early presence of AVP during the differentiation and maturation of the central nervous system in Monodelphis.

Distribution of small vasopressinergic neurons in golden hamsters

In rats, small (diameter: ca. 10 micrograms) vasopressinergic neurons have been localized in the forebrain, including extrahypothalamic sites, such as the bed nucleus of the stria terminalis (BST) and the medial amygdala (MeA). In golden hamsters, no such neurons have ever been described in extrahypothalamic sites, while their presence in some hypothalamic sites, such as the paraventricular nucleus (PVN), remains controversial. The present studies were carried out to confirm the existence of small vasopressinergic neurons in the forebrain of golden hamsters, using rats as a positive control. The presence of small vasopressinergic neurons in these sites was first tested by immunocytochemistry in colchicine-treated animals. The resulting distribution was corroborated by in situ hybridization for vasopressin (AVP) mRNA. While a large number of small AVP-immunoreactive (AVP-ir) neurons was found in the BST and MeA of colchicine-treated rats, none was found in the same locations in hamsters. Interestingly, as a few large (diameter: 20-25 micrograms) AVP-ir neurons were found in the BST just medial to the small neurons in rats, the same area contained a few large and small AVP-ir neurons in hamsters. In the PVN, large and small AVP-ir neurons were found in rats and hamsters. However, three to four times more neurons were counted in rats. These data were confirmed by in situ hybridization. Indeed, in hamsters, no labelling for AVP mRNA was detected in small neurons within the BST and MeA. Furthermore, the PVN of rats contained more labelling for AVP mRNA, as compared to hamsters. These results confirm that the distribution of vasopressinergic neurons in rats cannot be generalized to other species without a detailed analysis.

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.

Sexual differences in vasopressin receptor binding within the ventrolateral hypothalamus in golden hamsters

In the following studies, the presence of a sexual difference in arginine-vasopressin (AVP) receptor binding was tested within the ventrolateral hypothalamus (VLH), an area rich in gonadal steroid receptors. The density of AVP receptor binding was estimated by in vitro quantitative autoradiography within the entire rostro-caudal extent of the VLH. The density of AVP binding was higher in males than in females at all levels of this area. Furthermore, dependency on testosterone treatment was also compared between gonadectomized males and females. While gonadectomy resulted in a near total disappearance of binding in both males and females, testosterone treatment resulted in equally high levels of binding in both sexes. Indeed, a high density of AVP receptor binding was observed at all levels of the VLH in both testosterone-treated males and females. These results show that adult female golden hamsters are equally capable as males of expressing high levels of AVP receptor binding in the VLH in response to high levels of testosterone. Together, our results suggest that, while AVP receptor binding within the VLH is sexually different in gonadally-intact animals, these differences are not related to differential responsiveness to testosterone, but rather to a differential production and availability of the hormone.

The ependyma: a protective barrier between brain and cerebrospinal fluid

This review summarizes the current scientific literature concerning the ependymal lining of the cerebral ventricles of the brain with an emphasis on selective barrier function and protective roles for the common ependymal cell. Topics covered include the development, morphology, protein and enzyme expression including reactive changes, and pathology. Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.