A sex difference in the pattern of substance P-like immunoreactivity in the bed nucleus of the stria terminalis

The neurophysiological basis of stress and anxiety - comparing neuronal diversity in the bed nucleus of the stria terminalis (BNST) across species

The bed nucleus of the stria terminalis (BNST), as part of the extended amygdala, has become a region of increasing interest regarding its role in numerous human stress-related psychiatric diseases, including post-traumatic stress disorder and generalized anxiety disorder amongst others. The BNST is a sexually dimorphic and highly complex structure as already evident by its anatomy consisting of 11 to 18 distinct sub-nuclei in rodents. Located in the ventral forebrain, the BNST is anatomically and functionally connected to many other limbic structures, including the amygdala, hypothalamic nuclei, basal ganglia, and hippocampus. Given this extensive connectivity, the BNST is thought to play a central and critical role in the integration of information on hedonic-valence, mood, arousal states, processing emotional information, and in general shape motivated and stress/anxiety-related behavior. Regarding its role in regulating stress and anxiety behavior the anterolateral group of the BNST (BNSTALG) has been extensively studied and contains a wide variety of neurons that differ in their electrophysiological properties, morphology, spatial organization, neuropeptidergic content and input and output synaptic organization which shape their activity and function. In addition to this great diversity, further species-specific differences are evident on multiple levels. For example, classic studies performed in adult rat brain identified three distinct neuron types (Type I-III) based on their electrophysiological properties and ion channel expression. Whilst similar neurons have been identified in other animal species, such as mice and non-human primates such as macaques, cross-species comparisons have revealed intriguing differences such as their comparative prevalence in the BNSTALG as well as their electrophysiological and morphological properties, amongst other differences. Given this tremendous complexity on multiple levels, the comprehensive elucidation of the BNSTALG circuitry and its role in regulating stress/anxiety-related behavior is a major challenge. In the present Review we bring together and highlight the key differences in BNSTALG structure, functional connectivity, the electrophysiological and morphological properties, and neuropeptidergic profiles of BNSTALG neurons between species with the aim to facilitate future studies of this important nucleus in relation to human disease.

Cell-type diversity in the bed nucleus of the stria terminalis to regulate motivated behaviors

Over the past few decades, the bed nucleus of the stria terminalis (BNST) gained popularity as a unique brain region involved in regulating motivated behaviors related to neuropsychiatric disorders. The BNST, a component of the extended amygdala, consists of a variety of subnuclei and neuronal ensembles. Multiple studies have highlighted the BNST as playing a fundamental role in integrating information by interfacing with other brain regions to regulate distinct aspects of motivated behaviors associated with stress, anxiety, depression, and decision-making. However, due to the high molecular heterogeneity found within BNST neurons, the precise mechanisms by which this region regulates distinct motivational states remains largely unclear. Single-cell RNA sequencing data have revealed that the BNST consists of multiple genetically identifiable cell-type clusters. Contemporary tools can therefore be leveraged to target and study such cell-types and elucidate their precise functional role. In this review, we discuss the different subsets of neurons found in the BNST, their anatomical distribution, and what is currently known about BNST cell-types in regulating motivated behaviors.

Extended Amygdala Neuropeptide Circuitry of Emotional Arousal: Waking Up on the Wrong Side of the Bed Nuclei of Stria Terminalis

Sleep is fundamental to life, and poor sleep quality is linked to the suboptimal function of the neural circuits that process and respond to emotional stimuli. Wakefulness ("arousal") is chiefly regulated by circadian and homeostatic forces, but affective mood states also strongly impact the balance between sleep and wake. Considering the bidirectional relationships between sleep/wake changes and emotional dynamics, we use the term "emotional arousal" as a representative characteristic of the profound overlap between brain pathways that: (1) modulate wakefulness; (2) interpret emotional information; and (3) calibrate motivated behaviors. Interestingly, many emotional arousal circuits communicate using specialized signaling molecules called neuropeptides to broadly modify neural network activities. One major neuropeptide-enriched brain region that is critical for emotional processing and has been recently implicated in sleep regulation is the bed nuclei of stria terminalis (BNST), a core component of the extended amygdala (an anatomical term that also includes the central and medial amygdalae, nucleus accumbens shell, and transition zones betwixt). The BNST encompasses an astonishing diversity of cell types that differ across many features including spatial organization, molecular signature, biological sex and hormonal milieu, synaptic input, axonal output, neurophysiological communication mode, and functional role. Given this tremendous complexity, comprehensive elucidation of the BNST neuropeptide circuit mechanisms underlying emotional arousal presents an ambitious set of challenges. In this review, we describe how rigorous investigation of these unresolved questions may reveal key insights to enhancing psychiatric treatments and global psychological wellbeing.

Sex-associated differences in excitability within the bed nucleus of the stria terminalis are reflective of cell-type

The bed nucleus of the stria terminalis (BNST) is a sexually dimorphic brain region which plays a key role in stress, anxiety, and anxiety-related disorders. Human females have an increased susceptibility to anxiety-related disorders, however the physiological basis of this is not fully understood. Here we examined the effect of the oestrous cycle and sex on the electrophysiological properties of Type I and Type II cells in the anterolateral area of the BNST (BNST^ALG) in unstressed animals. There was no significant effect of oestrous cycle on any of the parameters examined in either cell type. Compared to males, the female cohort had lower capacitance in Type I cells while having a higher capacitance in Type II cells. Type II cells also displayed decreased excitability in the female cohort. In order to confirm the effect of these populations on stress and anxiety, a correlation with behaviour on the elevated zero maze was carried out. We observed that increased excitability in Type II neurons correlated with a decrease in anxiety-like behaviour. These sex-specific differences in excitability may contribute to altered susceptibility to anxiety-related disorders.

Involvement of the oxytocin system in the bed nucleus of the stria terminalis in the sex-specific regulation of social recognition

Sex differences in the oxytocin (OT) system in the brain may explain why OT often regulates social behaviors in sex-specific ways. However, a link between sex differences in the OT system and sex-specific regulation of social behavior has not been tested. Here, we determined whether sex differences in the OT receptor (OTR) or in OT release in the posterior bed nucleus of the stria terminalis (pBNST) mediates sex-specific regulation of social recognition in rats. We recently showed that, compared to female rats, male rats have a three-fold higher OTR binding density in the pBNST, a sexually dimorphic area implicated in the regulation of social behaviors. We now demonstrate that OTR antagonist (5 ng/0.5 μl/side) administration into the pBNST impairs social recognition in both sexes, while OT (100 pg/0.5 μl/side) administration into the pBNST prolongs the duration of social recognition in males only. These effects seem specific to social recognition, as neither treatment altered total social investigation time in either sex. Moreover, baseline OT release in the pBNST, as measured with in vivo microdialysis, did not differ between the sexes. However, males showed higher OT release in the pBNST during social recognition compared to females. These findings suggest a sex-specific role of the OT system in the pBNST in the regulation of social recognition.

Organization of multisynaptic circuits within and between the medial and the central extended amygdala

The central and medial extended amygdala comprises the central (CEA) and medial nuclei of the amygdala (MEA), respectively, together with anatomically connected regions of the bed nucleus of the stria terminalis (BST). To reveal direct and multisynaptic connections within the central and medial extended amygdala, monosynaptic and transneuronal viral tracing experiments were performed in adult male rats. In the first set of experiments, a cocktail of anterograde and retrograde tracers was iontophoretically delivered into the medial CEA (CEAm), anterodorsal MEA (MEAad), or posterodorsal MEA (MEApd), revealing direct, topographically organized projections between distinct amygdalar and BST subnuclei. In the second set of experiments, the retrograde transneuronal tracer pseudorabies virus (PRV) was microinjected into the CEAm or MEAad. After 48 hours of survival, there were no significant differences between monosynaptic and PRV cases in the subnuclear distribution or proportions of retrogradely labeled BST neurons. However, after 60 hours of survival, CEAm-injected cases displayed an increased proportion of labeled neurons within the anteromedial group of BST subnuclei (amgBST) and within the posterior BST, which do not directly innervate the CEA. MEApd-injected 60-hour cases displayed a significantly increased proportion of retrograde labeling in the amgBST compared with monosynaptic and 48-hour cases, whereas MEAad-injected cases displayed no proportional changes over time. Thus, multisynaptic circuits within the medial extended amygdala overlap the direct connections making up this anatomical unit, whereas the multisynaptic boundaries of the central extended amygdala extend into BST subnuclei previously identified as part of the medial extended amygdala.

Androgen receptors in the posterior bed nucleus of the stria terminalis increase neuropeptide expression and the stress-induced activation of the paraventricular nucleus of the hypothalamus

The posterior bed nuclei of the stria terminalis (BST) are important neural substrate for relaying limbic influences to the paraventricular nucleus (PVN) of the hypothalamus to inhibit hypothalamic-pituitary-adrenal (HPA) axis responses to emotional stress. Androgen receptor-expressing cells within the posterior BST have been identified as projecting to the PVN region. To test a role for androgen receptors in the posterior BST to inhibit PVN motor neurons, we compared the effects of the non-aromatizable androgen dihydrotestosterone (DHT), the androgen receptor antagonist hydroxyflutamide (HF), or a combination of both drugs implanted unilaterally within the posterior BST. Rats bearing unilateral implants were analyzed for PVN Fos induction in response to acute-restraint stress and relative levels of corticotrophin-releasing hormone and arginine vasopressin (AVP) mRNA. Glutamic acid decarboxylase (GAD) 65 and GAD 67 mRNA were analyzed in the posterior BST to test a local involvement of GABA. There were no changes in GAD expression to support a GABA-related mechanism in the BST. For PVN neuropeptide expression and Fos responses, basic effects were lateralized to the sides of the PVN ipsilateral to the implants. However, opposite to our expectations of an inhibitory influence of androgen receptors in the posterior BST, PVN AVP mRNA and stress-induced Fos were augmented in response to DHT and attenuated in response to HF. These results suggest that a subset of androgen receptor-expressing cells within the posterior BST region may be responsible for increasing the biosynthetic capacity and stress-induced drive of PVN motor neurons.

Modulation of glutamatergic synaptic transmission in the bed nucleus of the stria terminalis

Glutamate, catecholamine and neuropeptide signaling within the bed nucleus of the stria terminalis (BNST) have all been identified as key participants in anxiety-like behaviors and behaviors related to withdrawal from exposure to substances of abuse. The BNST is thought to serve as a key relay between limbic cognitive centers and reward, stress and anxiety nuclei. Human studies and animal models have demonstrated that stressors and drugs of abuse can result in long term behavioral modifications that can culminate in psychological diseases such as addiction and post-traumatic stress disorder. The ability of catecholamines and neuropeptides to influence synaptic glutamatergic transmission (stemming from cognitive centers) within the BNST may have profound consequences over these behaviors. In this review we highlight studies examining synaptic plasticity and modulation of excitatory transmission within the BNST, emphasizing how such modulation may result in alterations in anxiety and reward related behavior.

Sex differences in NeuN- and androgen receptor-positive cells in the bed nucleus of the stria terminalis are due to Bax-dependent cell death

The principal nucleus of the bed nucleus of the stria terminalis (BNSTp) is larger in males than in females of several species. We previously demonstrated that in mice lacking the pro-death gene, bax, total BNSTp cell number is increased and sex differences in cell number are eliminated. This suggests that Bax-dependent cell death underlies sexual differentiation of the BNSTp. However, it is not known what cells in the BNSTp are affected by bax deletion. Here we used immunohistochemistry and stereological techniques to quantify phenotypically-identified cells in the BNSTp of adult male and female bax -/- and bax +/+ mice. Sections were thionin-stained, or double-labeled for antigen expressed in neuronal nuclei (NeuN) and glial fibrillary acidic protein (GFAP) to identify mature neurons and astrocytes, respectively; an additional series was labeled for androgen receptor (AR). As previously demonstrated, sex differences in BNSTp area and overall cell number were seen in wild-type mice, but absent in bax -/- animals. In addition, sex differences (favoring males) were present in the number of NeuN+ and AR+ cells in wild-type mice. Bax gene deletion significantly increased the number of NeuN+ and AR+ cells and reduced or eliminated the sex differences in these cell types. The number of astrocytes in the BNSTp was not sexually dimorphic, nor significantly affected by bax gene status, although there was a trend for more GFAP+ cells in bax -/- mice. Overall brain weight was also greater in bax -/- animals compared with controls. We conclude that the sex differences in neuron and AR+ cell number are due at least in part to Bax-mediated cell death. Increased NeuN+ and AR+ cell number in bax -/- mice suggests that supernumerary cells in bax knockouts differentiate similarly to those in wild-type mice, and retain the capacity to respond to androgens.

Effects of BNST lesions in female rats on forced swimming and navigational learning

The bed nucleus of the stria terminalis (BNST) in the forebrain shows sexual dimorphism in its neuroanatomical connectivity and neurochemical characteristics. The structure is involved in many behavioral and motivational phenomena particularly related to coping with stress. Female rats differ from males in responding to stressful situations such as forced swimming and navigational learning in the water maze. It was previously shown that bilateral damage to the BNST in male Wistar rats aggravated depression as measured by forced swim tests, but did not impair navigational learning in the water maze. The present study extended the findings to female rats demonstrating that bilateral electrolytic lesions of the BNST increased immobility and decreased climbing compared to sham-operated controls, but failed to affect performance in the water maze. Additionally, lesions did not alter behavior in the open field and the elevated plus-maze tests suggesting not only that the modulation of depression by BNST lesions is specific, but also providing support for the view that the BNST may not necessarily be critically involved in anxiety.

Effects of the testicular feminization mutation (tfm) of the androgen receptor gene on BSTMPM volume and morphology in rats

The posteromedial bed nucleus of the stria terminalis (BSTMPM) is an important component of the extended amygdala that is sexually dimorphic in rats. We examined the effect of the testicular feminization mutation (tfm), which renders the androgen receptor (AR) dysfunctional, on BSTMPM volume and average somal area. As expected, we found a significant sex difference in the volume of the BSTMPM, with females having a smaller BSTMPM than wild type males. Size of the BSTMPM in tfm males was also significantly smaller than that of wildtype males, although this difference was significant only on the left side. We found no sex difference in BSTMPM somal areas. These findings support the role of androgen receptors in the sexual differentiation of this nucleus.

Ontogeny of bidirectional connections between the medial nucleus of the amygdala and the principal bed nucleus of the stria terminalis in the rat

Nuclei in the amygdala and bed nuclei of the stria terminalis (BST) form functionally organized units that are linked by topographically organized connections. The posterodorsal part of the medial nucleus of the amygdala (MEApd) and the principal nucleus of the BST (BSTpr) share strong birectional connections that project primarily through the stria terminalis. The presence of structural and neurochemical sexual dimorphisms in both the MEApd and BSTpr suggests that connections between the nuclei may develop during the postnatal critical period for sexual differentiation. In this study, 1,1'dioctadecyl-3,3,3'-tetramethylindocarbocyanine perchlorate (DiI) axonal labeling was used to define the ontogeny of this bidirectional pathway. Placement of DiI crystals into the MEApd of rats perfused on embryonic day (E) 20 resulted in DiI-labeled fibers with axonal morphology in the BSTpr, but similar labeling was not evident in the MEApd until after birth. However, as early as E14, tracer implants into the caudal MEA (the presumptive MEApd) labeled elongated cellular processes in the region of the stria terminalis that extended into the presumptive BSTpr. Based on the correspondence of these DiI-labeled processes with immunostaining for vimentin, these cellular processes are probably derived from glial cells. Implants of DiI into the posterior BST also labeled cellular processes that extended through the medial part of the stria terminalis, but they remained confined to the molecular layer of the MEApd from E14 through P1. Labeled axons derived from the BSTpr were not observed in the MEApd until P5, demonstrating that the bidirectional connections that exist between the MEApd and BSTpr in mature rats do not develop simultaneously. The density of connections between the BSTpr and MEApd increased during the postnatal period and was similar to that of adults by P15. These findings suggest that projections from the MEApd through the stria terminalis to the BSTpr may be specified initially by a glial substrate and that return projections to the amygdala from the BSTpr develop secondary to its innervation by the MEApd.

Sex-specific patterns of galanin, cholecystokinin, and substance P expression in neurons of the principal bed nucleus of the stria terminalis are differentially reflected within three efferent preoptic pathways in the juvenile rat

Neurons in the principal bed nucleus of the stria terminalis (BSTp) integrate hormonal and sensory information associated with reproduction and transmit this information to hypothalamic nuclei that regulate neuroendocrine and behavioral functions. The neuropeptides galanin (GAL), cholecystokinin (CCK), and substance P (SP) are highly expressed in BSTp neurons and are differentially regulated by sex steroids. The current experiments investigated whether developmental or peripubertal hormone-mediated changes in GAL, CCK, and SP expression are reflected within efferent pathways to the preoptic structures that regulate gonadotropin secretion and sexual behavior. Anterograde labeling of projections from the BSTp of male and female juvenile rats combined with immunohistochemical labeling of GAL-, CCK-, and SP-containing fibers in the anteroventral periventricular preoptic nucleus (AVPV) and the central and medial divisions of the medial preoptic nucleus (MPNc, MPNm, respectively) revealed unique sex differences in each region. In the AVPV, Phaseolus vulgaris leucoagglutinin-labeled fibers were seen at a greater density in males than in females, and higher percentages of these fibers contained GAL in males than in females. In contrast, fibers projecting from the BSTp to the MPNc were more likely to contain SP in females than in males. Treatment of gonadectomized, peripubertal males and females with exogenous testosterone and estradiol did not alter the densities of GAL-, CCK-, or SP-containing fibers in any of the three brain areas examined. Collectively, these results suggest that patterns of neuropeptide expression in BSTp projections are established during development, resulting in a distinct, stable, and sex-specific chemoarchitectural profile for each projection pathway.

Galanin immunoreactivity in mouse basal forebrain: sex differences and discrete projections of galanin-containing cells beyond the blood-brain barrier

The distribution of galanin-immunoreactive (GAL-IR) cell bodies in the basal forebrain of mice was investigated. The overall pattern of staining for GAL in the area of brain analyzed was similar to that reported in other species with noticeable variations. Distinctive groups of GAL-IR cells were present in the bed nucleus of stria terminalis (BNST), supraoptic nucleus, retrochiasmatic supraoptic nucleus (SOR), magnocellular paraventricular nucleus, arcuate nucleus (ARC) and the nucleus circularis which is one of the cell groups belonging to the accessory magnocellular system. Comparison of the number of GAL-IR cells between the sexes indicated sexual dimorphism in the BNST, SOR and the ARC. As compared with female mice, the mean number of GAL-IR cells/section in the BNST and the SOR was higher and that in the ARC was lower in the males. Unlike in rats, the preoptic area contained mostly scattered GAL-IR cell bodies. Intraperitoneal injection of the retrograde tracer fluoro-gold in male mice resulted in uptake of fluoro-gold by selective GAL-IR cell groups in the basal forebrain suggesting that only some of these cell groups may project outside the blood-brain barrier whereas others may be involved in intracerebral neural transmission.

The medial extended amygdala in male reproductive behavior. A node in the mammalian social behavior network

Hormonal and chemosensory signals regulate social behaviors in a wide variety of mammals. In the male Syrian hamster, these signals are integrated in nuclei of the medial extended amygdala, where olfactory and vomeronasal system transmission is modulated by populations of androgen- and estrogen-sensitive neurons. Evidence from behavioral changes following lesions and from immediate early gene expression supports the hypothesis that the medial extended amygdala and medial preoptic area belong to a circuit that functions selectively in male sexual behavior. However, accumulated behavioral, neuroanatomical, and neuroendocrine data in hamsters, other rodents, and other mammals indicate that this circuit is embedded in a larger integrated network that controls not only male mating behavior, but female sexual behavior, parental behavior, and various forms of aggression. In this context, perhaps an individual animal's social responses can be more easily understood as a repertoire of closely interrelated, hormone-regulated behaviors, shaped by development and experience and modulated acutely by the environmental signals and the hormonal milieu of the brain.

Testosterone increases the number of substance P-like immunoreactive neurons in a specific sub-division of the lateral hypothalamus of the weakly electric, brown ghost knifefish, Apteronotus leptorhynchus

During spawning, male and female brown ghost knife fish modulate their electric organ discharge to produce discrete courtship signals known as chirps. However, non-spawning fish show clear sex differences in chirp responsiveness to electrosensory stimuli; males consistently chirp, whereas females do not. This behavioral dimorphism is paralleled by sex differences in substance P-like immunoreactivity (SPl-ir) in the prepacemaker nucleus (PPn) which regulates chirping. The PPn is densely innervated by SPl-ir fibers in males, but not in females. However, we have shown that both female chirping behavior and the expression of SPl-ir in the PPn are enhanced following adult testosterone treatment [J.G. Dulka, L. Maler, W. Ellis, Androgen-induced changes in electrocommunicatory behavior are correlated with changes in substance P-like immunoreactivity in the brain of the electric fish, Apteronotus leptorhynchus, J. Neurosci. 15 (1995) 1879-1890]. Thus, testosterone-induced changes in SPl-ir input to the PPn may modulate female chirping during spawning. Recent evidence suggests that SPl-ir projections to the PPn may originate from SPl-ir neurons in the lateral hypothalamus (Hl). If so, one might expect to see a greater number of SPl-ir neurons in the Hl of testosterone-implanted females compared to Blank-implanted controls. In making this comparison, we found that both groups of females had similar numbers of SPl-ir neurons in the anterior Hl, but that testosterone-implanted females had significantly (p<0.01) more SPl-ir neurons in a distinct part of the posterior Hl. This sub-population of testosterone-sensitive, SPl-ir neurons may contribute to the regulation of chirping, since an increase in their number is positively correlated with the appearance of SPl-ir fibers in the PPn [J.G. Dulka, L. Maler, W. Ellis, Androgen-induced changes in electrocommunicatory behavior are correlated with changes in substance P-like immunoreactivity in the brain of the electric fish, Apteronotus leptorhynchus, J. Neurosci. 15 (1995) 1879-1890].

Effects of gonadal hormones on the morphology of neurons from the medial amygdaloid nucleus of rats

The medial amygdala (MeA) has receptors for gonadal hormones and is a sexually dimorphic area in rats. The aims of the present work were (1) to look at sex differences and the effect of gonadal hormone withdrawal in males castrated as offspring or at adulthood on neuronal soma area in the anterior and posterior MeA and (2) to study the dendritic branching and the density of dendritic spines in neurons from the MeA of intact males and females. Animals were adult rats, for which the single-section Golgi method was used. Stellate and bitufted cells were found in the MeA. Comparing data among groups, no significant difference in cell body area was found. Dendrites divide sparingly and have very different lengths, and a statistical difference (p < 0.001, males higher than females) in the spine density in the anterior MeA, but not in the posterior MeA, was found. These results suggest that castration does not alter the somal area in males submitted to gonadectomy during the early postnatal period or at adulthood. In addition, the already described sex difference in this nucleus may be more related to the neuropil than the neuronal somal area, which may be relevant for the function of the MeA.

Androgen receptor-like immunoreactivity in the Brazilian opossum brain and pituitary: distribution and effects of castration and testosterone replacement in the adult male

Androgens are involved in a variety of centrally mediated functions after binding to their intracellular receptors. In the present report, we have employed the androgen receptor antibody, PG-21, and indirect immunohistochemistry to examine the distribution of cells containing androgen receptor-like immunoreactivity (AR-IR) in the intact adult male Brazilian opossum brain and pituitary. Additional adult males were castrated to examine the effects of withdrawal of circulating androgens and testosterone replacement on AR-IR. Immunoblots and immunohistochemical controls demonstrated that the androgen receptor in the opossum brain and peripheral tissues are of a similar molecular mass as to has been reported for the rat. Cells containing AR-IR were widely distributed throughout the brain of intact adult males. The highest number of immunoreactive cells were present in the dorsal and ventral nuclei of the lateral septum, medial division of the bed nucleus of the stria terminalis, medial preoptic area, median preoptic nucleus, nucleus of the lateral olfactory tubercle, central amygdaloid nucleus, anterior cortical amygdaloid nucleus, posterior amygdaloid nucleus, subiculum, ventromedial hypothalamic nucleus, arcuate-median eminence region, and ventral premammillary nucleus. The anterior pituitary gland also contained a high number of cells containing AR-IR. The general distribution of AR-IR both in the brain and anterior pituitary gland resembled that reported for other mammalian species. Castration of the adult males four days prior to perfusion eliminated androgen receptor immunostaining throughout the brain except for a few lightly immunostained cells in the ventral nucleus of the lateral septum and stria terminalis. Androgen receptor immunostaining was decreased in the anterior pituitary gland following castration and became cytoplasmic. Testosterone administration 2 h before perfusion restored AR-IR both in the brain and anterior pituitary gland. These data suggested that immunohistochemical detection of bound (nuclear) androgen receptors as seen with PG-21 antibody in the brain and anterior pituitary gland of the opossum is dependent upon circulating androgens. Further, the wide distribution and similarity in localization of androgen receptors in the opossum brain and anterior pituitary gland to that of other species suggests that androgen receptors might be involved in similar functions in the opossum as has been reported for other species.

Mapping of neurochemical markers in quail central nervous system: VIP- and SP-like immunoreactivity

The distribution of cells and fibres containing vasoactive intestinal polypeptide (VIP) and substance P (SP) was investigated in the brain of Japanese quail focussing on the centers involved in reproductive activities. SP-immunoreactive (ir) structures were chiefly present within the ventral telencephalic regions, the periventricular hypothalamus and the dorsal aspects of thalamus. VIP immunopositive structures were rarely associated with recognizable nuclei and they were observed in the organum septi laterale (LSO), the lobus paraolfactorius (LPO), the eminentia mediana (ME), the nucleus striae terminalis (nST) and the area ventralis of Tsai (AVT). SP- and VIP-ir structures were both associated with regions implicated in the control of reproduction. SP was mainly distributed within regions that control male copulatory behavior (the preoptic region, the anterior hypothalamus and the central gray), whereas VIP was prevalently located in the mediobasal hypothalamus that is implicated in the control of female reproductive activities.

Lesions in the medial posterior region of the BST impair sexual behavior in sexually experienced and inexperienced male rats

Previous studies have showed that lesions in the bed nucleus of the stria terminalis of experienced male rats impair some parameters of sexual behavior. The aim of this study was to examine the contribution of the medial posterior region of the bed nucleus of the stria terminalis (BSTMP), a sexually dimorphic region of this nucleus that pertains to the vomeronasal system, to the modulation of sexual behavior of the male rat. Small electrolytic bilateral lesions in the BSTMP were made in male heterosexual experienced and inexperienced rats. Sham lesioned animals were also tested as a control of the effects of the general surgical procedures. Behavioral tests were then performed to obtain standard measures of masculine sexual behavior. Our results indicate that the sexually experienced male rats with lesioned BSTMPs showed increases in the number of mounts and the number of intromissions and, consequently, in ejaculation latency. In contrast, the sexually naive male rats showed increases in first mount and intromission latencies and in ejaculation latency, but the latter occurred due to increases in the interintromission intervals. This group also showed low correlations between olfactory investigation of the anogenital area of the female and initiation and maintenance of copulatory behavior. The results suggest that sexual experience obtained in the very artificial conditions of laboratory tests could supply some of the cues provided by the BSTMP in the process of sensorial integration, which we hypothesize modulates the initiation and pacing of copulation. However, sexual experience does not apparently supply any other kinds of cues provided or processed in the BSTMP that are involved in modulating the elicitation of intromissions and ejaculations.

Projections from ventrolateral hypothalamic neurons containing progestin receptor- and substance P-immunoreactivity to specific forebrain and midbrain areas in female guinea pigs

Many neurons within the ventrolateral hypothalamus in guinea pigs contain estrogen-induced progestin receptors as well as substance P. Retrograde tracing combined with immunocytochemistry was used to determine the specific projections of this subset of steroid-sensitive cells. Unilateral Fluoro-Gold injections into the dorsal midbrain, including the central gray, labeled a large proportion of the ventrolateral hypothalamic neurons immunoreactive for both progestin receptors and substance P (approximately 30%); substantially fewer of these neurons were labeled by unilateral Fluoro-Gold injections into the preoptic area (approximately 6%), medial amygdala (approximately 10%), or the bed nucleus of the stria terminalis (approximately 11%). The projections of progestin receptor-immunoreactive neurons in the ventrolateral hypothalamus were similar to those of progestin receptor/substance P double-labeled neurons, while a slightly lower percentage of the ventrolateral hypothalamic, substance P-immunoreactive neurons tended to project to each of these areas. These pathways may prove to be components of the neural circuitry underlying a variety of functions influenced by gonadal steroid hormones and substance P, such as female sexual behavior, salt intake, nociception and aggression.

Neurotrophic effects of testosterone on the medial nucleus of the amygdala in adult male rats

Our previous reports of major sex differences in the substance P-immunoreactive (SPir) innervation of the medial posterior divisions of the bed nucleus of the stria terminalis (BST) and medial nucleus of the amygdala in rats raised the question of the hormonal regulation of this innervation. We now report the results of two experiments which examined the effects of castration of adult males on the SPir innervation of these regions. In experiment 2 we asked whether castration might also alter the cytoarchitecture of these regions. In experiment 1 three groups; sham operated (Sham), castrated (C) and castrated plus testosterone (C+T) were examined at each of the three survival periods (2, 4 and 8 weeks) post castration. Animals of the C+T groups each received a 45 mm silastic implant of testosterone sc at the time of castration to maintain testosterone levels postoperatively. Castration produced a consistent and highly significant decrease in the area of dense SPir fiber staining in the posterior medial amygdala which became greater with increasing survival. By 8 weeks the area of staining was 42% smaller in group C as compared to the matched sham-operated group. Smaller decreases were seen in the size of the dense field of SPir fibers in the posterior part of the dorsomedial BST. Testosterone implants maintained the size of the SPir fields of fibers in both the medial amygdala and BST, as the areas of staining in the C+T groups were not significantly different from those in the Sham groups at any of the 3 survival times. In experiment 2 we measured the area and optical density of SPir fiber staining in the medial amygdala and medial BST at 8 weeks post-castration. In addition, we measured the size of the cell groups within these regions using cresyl-stained sections. As in experiment 1, at 8 wks following castration there was a marked decrease in the area of dense SPir staining in both the BST and medial amygdala. The sizes of the dense fields of fibers were reduced by approximately 23% in the BST and by 40% in the posterior medial amygdala. Castration also significantly reduced the optical density of staining within the medial amygdala. The major finding of experiment 2 is that castration affects the cytoarchitecture as well as the SPir staining in these areas. In the BST, the cell group BSTMPM receives most of the dense SPir innervation.(ABSTRACT TRUNCATED AT 400 WORDS)

Connections of the olfactory bulb in the gymnotiform fish, Apteronotus leptorhynchus

This work examines the connectivity of the olfactory bulb in the gynmotiform fish Apteronotus leptorhynchus. Wheat germ agglutinin conjugated horseradish peroxidase was iontophoresed in different areas and depths of the bulb in order to define its efferent and afferent connections. The olfactory bulb projects bilaterally via the medial (medial and centromedial fascicles) and lateral olfactory (lateral and centrolateral fascicles) tracts. The nervus terminalis courses through the ventromedial aspect of the bulb to terminate in parts of the medial subpallium and hypothalamus. Its telencephalic component could be identified by a nonpreadsorbable substance P-like immunoreactivity. Fibers within the medial olfactory tract form four telencephalic terminal fields: peduncular, medial, intermediate and posterior fields. The diencephalic terminal fields in the habenula, preoptic, and hypothalamic areas appear to correspond to some of the nervus terminalis fibers (von Bartheld and Meyer [1986] Cell Tissue Res. 245:143-158, Krishna et al. [1992] Gen. Comp. Endocrinol. 85:111-117), and to axons of telencephalic bulbopetal cells of area dorsalis posterior. The terminal fields of the medial olfactory tract and nervus terminalis partially overlap in the ventral telencephalic areas partes ventralis, supracommissuralis, and rostral preoptic region. The lateral olfactory tract forms a lateral terminal field and contributes to the intermediate and posterior terminal fields. Olfactory fibers cross in the interbulbar, anterior, and habenular commissures and tuberal decussation. Consistent differences were noted between the medial and lateral olfactory bulb, with respect to their cytoarchitectonics, immunohistochemistry, and connections. In addition to the olfactory nerve, bulbar afferents are predominantly ipsilateral, with minor inputs originating from the contralateral bulb and telencephalic area dorsalis posterior, nucleus raphe centralis, and locus ceruleus.

Androgen concentration by a sexually dimorphic population of tachykinin-immunoreactive neurons in the rat ventral premammillary nucleus

Strong connections with sexually dimorphic nuclei suggest that the ventral premammillary nucleus (PMv) may be involved in the mediation of reproductive behavior. Steroid autoradiography and immunohistochemistry were used to show that: (1) there is a sex difference in the numbers of PMv neurons that contain tachykinin peptides, (ii) dihydrotestosterone concentrating cells are densely distribution in the PMv and about a quarter of these also contain immunoreactive tachykinin and, (iii) size of the immunoreactive tachykinin population does not respond to alterations in levels of gonadal steroids in adulthood. Thus the PMv appears to make a contribution to the regulation of sexual behavior through androgen-concentrating, tachykinin-containing pathways that are anatomically distinct from estrogen receptive circuitry.

Central tachykinin injection potently suppresses the need-free salt intake of the female rat

Repeated sodium depletions produce a persistent, enhanced need-free salt intake in the rat, particularly in the female. The neurochemical mechanisms underlying the phenomenon are still unknown. The present studies evaluated the effect on the enhanced need-free salt intake of the female rat (1) of pharmacological interference with the natriorexigenic hormones angiotensin II and aldosterone and (2) of the central injection of the tachykinin peptides, which are endowed with antinatriorexic activity. The need-free salt intake of the female rat is not modified by treatment with the angiotensin-converting enzyme inhibitor captopril or by the aldosterone receptor antagonist RU-28318. On the other hand, the behavior is highly sensitive to the inhibitory effect of central tachykinins, suggesting the possibility that need-free salt intake might be linked to modification (down-regulation) of the inhibitory tachykininergic system.

Sex differences in subregions of the medial nucleus of the amygdala and the bed nucleus of the stria terminalis of the rat

Sex differences are described in subregions of two nuclei of the rat brain: the medical nucleus of the amygdala (MA) and the bed nucleus of the stria terminalis (BNST). The volume of the posterodorsal region of the medial nucleus of the amygdala (MApd) is approximately 85% greater and the volume of the encapsulated region of the bed nucleus of the stria terminalis (BNSTenc) is approximately 97% greater in males than in females. The MApd and BNSTenc are distinct subregions of the MA and BNST. They exhibit intense uptake of gonadal hormones and are anatomically connected to each other and to other sexually dimorphic nuclei. The MA and BNST in general are involved in regulation of several sexually dimorphic functions, including aggression, sexual behavior, gonadotropin secretion and integration of olfactory information. Precise localization of sex differences in subregions of the MA and BNST, such as the MApd and BNSTenc, may facilitate understanding of the neural basis of such functions.

Lesions of the medial amygdala produce severe impairment of copulatory behavior in sexually inexperienced male rats

The effects of amygdaloid lesions on masculine copulatory behavior were examined in male rats. Sexually inexperienced male rats were castrated and subjected to bilateral lesions in one of the following areas: the medial amygdala, the cortical amygdala, or the basolateral amygdala. Three weeks later, all rats received implantation of silastic capsules containing testosterone. Then, four observations of copulatory behavior were carried out every 5 days following the implantation of testosterone. Rats with medial amygdala lesions showed a severe deficit of copulatory behavior, whereas rats with basolateral amygdala lesions showed no change in the performance of copulation. As for rats with cortical amygdala lesions, although their copulatory behavior was impaired, the effect was confined to a deficit in intromission and ejaculation responses. These findings suggest that the medial amygdala plays a critical role in regulating masculine sexual behavior in the rat.

Substance P-like immunoreactivity in the brain of the gymnotiform fish Apteronotus leptorhynchus: presence of sex differences

The distribution of substance P-like immunoreactivity (SPli) was charted in the brain of the gymnotiform fish Apteronotus leptorhynchus, and correlated with the circuitry underlying intraspecific electrocommunication. Cell bodies were found predominantly in the lateral hypothalamus and in certain paraventricular organs: nucleus preopticus periventricularis, anterior subdivision; anterior hypothalamus; nucleus posterioris periventricularis; nucleus recessus lateralis, medial subdivision 2; nucleus recessus posterioris and nucleus recessus lateralis, lateral subdivision. Cell bodies were also found in the rostral olfactory nucleus, ventral telencephalon (ventral and central subdivisions), the habenula, the vagal sensory and motor nuclei and in the subtrigeminal nucleus. The distribution of SPli fibers was similar in some respects to that reported for other vertebrates. SPli was found in the rhombencephalon associated with vagal afferent fibers and in the funicular nucleus (possibly related to nociception). In the diencephalon and midbrain SPli fibers were found in the habenular-interpeduncular tract, in the hypothalamus and pituitary. SPli fibers were also found in preoptic and forebrain areas. The most striking result was the sexually dimorphic SPli innervation of certain hypothalamic and septal nuclei, and of the prepacemaker nucleus (PPn), a diencephalic cell group which controls communication ('chirping') in gymnotiforms. The PPn and septal/hypothalamic nuclei were densely innervated by SPli in males but devoid of SPli in females.

Bed nucleus of the stria terminalis: site for the antinatriorexic action of tachykinins in the rat

The present study investigated the sensitivity of the posterior part of the medial division of the bed nucleus of the stria terminalis (BNST) to the antinatriorexic action of the tachykinin eledoisin in the rat. Salt appetite was evoked by sodium depletion following furosemide-induced natriuresis. The results obtained show that bilateral injection of eledoisin into the BNST evokes a very potent antinatriorexic effect, a statistically significant inhibition being observed even at the dose of 3.1 ng/BNST. On the other hand, when eledoisin was injected into the lateral ventricle, just above the BNST, much larger doses were required to elicit comparable inhibition of salt appetite. The antinatriorexic effect of eledoisin into the BNST is apparently behaviorally selective, since the same doses, which inhibited salt appetite, did not significantly affect the intake of 10% sucrose solution in the sodium-depleted animal. Present results suggest that the BNST is a site of action for the effect of tachykinins on salt appetite.

Differential and sex-specific effects of kainic acid and domoic acid lesions in the lateral septal area of rats on immune function and body weight regulation

The lateral septal area (LSA) has been implicated in the control of various psychoneuroendocrine processes in the rat. Interactions between the endocrine and immune systems and sex differences in immunity reflect the interdependence of the immune and neuroendocrine systems. Kainic acid (KA) lesions in the lateral septal area not only modify neuroendocrine processes, but also produce a suppression of humoral immunity in female rats. Presently, we have evaluated the effects of neurotoxic lesions in the LSA on the humoral immune response and body weight regulation of male and female rats. Bilateral lesions in the LSA of adult male and female rats were produced by stereotaxically infusing either 0.25 microliters of kainic acid (1.5 micrograms/microliters) or 0.5 microliters of domoic acid (DA; 0.3 micrograms/microliters) into the LSA. In an additional study, LSA lesions using 0.25 microliters of DA (0.6 micrograms/microliters) were produced in female rats only. Sham operations consisted of bilateral injections of 0.9% saline into the LSA. The effects of these lesions on antibody production, following immunization with 100 micrograms ovalbumin in complete Freund's adjuvant, were examined. Blood samples were collected on Days 7 and 14 following immunization. The anti-ovalbumin IgM and IgG antibody titers were measured by an enzyme amplified ELISA assay. As found previously, KA-induced LSA lesions in adult female rats produced an increase in body weight and a suppression of the humoral immune response. However, LSA lesions produced with the neurotoxin DA had a similar effect on body weight but had no effect on humoral immunity. In male rats, neither body weight regulation nor the humoral immune response was affected by KA or DA lesions in the LSA. These results indicate that the effects of neurotoxic LSA lesions on body weight regulation and the humoral immune response are sex specific and further demonstrate that two closely related kainate neurotoxins have differential effects on the humoral immune response, but have similar effects on body weight regulation. Thus, neurons in the LSA of female rats that are involved in the inhibitory control of body weight are susceptible to both KA and DA, whereas neurons in the LSA associated with immunoregulation are differentially affected by KA and DA. Of further interest, a sex difference in DA susceptibility was noted, with male rats showing greater cell loss in the LSA following DA infusions, as compared to female rats.

Differential distribution of immunohistochemical markers in the bed nucleus of the stria terminalis in the human brain

A variety of histochemical findings have contributed to a more differentiated architectonical description of the bed nucleus of the stria terminalis (BNST) in the mammalian brain. However, in the human brain investigations of the chemoarchitecture of this nucleus have been rare. Therefore we chose this region in six human autopsy brains in order to map the distribution patterns of 13 immunohistochemical markers for neurotensin (NT), neuropeptide Y (NPY), somatostatin (SOM), enkephalins (ENK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurophysins (NPH), glial fibrillary acid protein, 3-fucosyl-N-acetyl-lactosamine epitope, myelin basic protein (MBP), calbindin (CAB), synaptophysin (SYN) and chromogranin-A (CHR-A). Three chemoarchitectonically distinct areas could be defined. The lateral subdivision of the BNST contained high amounts of NPY and SP-fibre immunoreactivity and was further characterized by the occurrence of neurons labelled for NPY. The central subdivision of the BNST appeared as a histochemically clearly circumscribed compartment with massive fibre immunoreactivity for SOM, ENK, VIP, SYN, CHR-A, CAB as well as SOM, ENK, NT and CAB positive cells but lacked cytosolic or fibre-like immunolabel for NPY and SP. This structure was also ensheathed by myelinated fibres identified by means of MBP immunohistochemistry. The medial subdivision of the BNST showed moderate to high SP and NPY fibre immunoreactivity but lacked immunolabelled neurons and was only scarcely supplied with varicose or punctiform ENK immunoproduct. In the most posterior levels of our sections a cell group labelled for NPH was located lateral to the fornix columns. The lateral subdivision of the BNST (with NPY, SYN) and mainly the central BNST (with SOM, ENK, VIP, SYN and CHR-A) contributed to ventrolateral extensions of dense patchy fibre immunoreactivity throughout the basal forebrain region.

Sex difference in the bed nucleus of the stria terminalis of the human brain

A quantitative analysis of the volume of the darkly staining region of the posteromedial bed nucleus of the stria terminalis was performed on the brains of 26 age-matched male and female human subjects. We suggest the term "darkly staining posteromedial" component of the bed nucleus of the stria terminalis (BNST-dspm) to describe this sexually dimorphic region of the human brain. The volume of the BNST-dspm was 2.47 times greater in males than in females. This region in humans appears to correspond to an area of the bed nucleus of the stria terminalis in laboratory animals that exhibits volumetric and neurochemical sexual dimorphisms, concentrates gonadal steroids, and is anatomically connected to several other sexually dimorphic nuclei. Furthermore, the bed nucleus of the stria terminalis is involved in sexually dimorphic functions, including aggressive behavior, sexual behavior, and gonadotropin secretion, which are also influenced by gonadal steroids. Therefore, it is possible that in human beings as well, gonadal hormones influence the sexual dimorphism in the BNST-dspm and that this morphological difference, in part, underlies sexually dimorphic function.

Sex differences in hormonal responses of vasopressin pathways in the rat brain

Vasopressin (AVP) immunoreactivity in cells and projections of the bed nucleus of the stria terminalis (BST) and medial amygdaloid nucleus (MA) depends on gonadal steroids. In addition, the AVP projections from the BST show denser fiber staining in males than in females. To study whether these differences depend on different hormone levels in adulthood, male and female rats were gonadectomized and similarly treated with testosterone for 4 weeks prior to sacrifice. Immunocytochemistry showed that males had significantly more AVP-immunoreactive (AVP-IR) cells in the BST and significantly denser AVP-IR projections from this nucleus to the lateral septum, lateral habenular nucleus, and periaqueductal central gray than did females. The number of AVP-IR cells in the MA nucleus was not statistically different, but denser AVP-IR fiber networks were found in the MA and ventral hippocampus, which receives its input from the MA. No differences were found in the anteroventral portion of the periventricular nucleus and the dorsomedial nucleus of the hypothalamus that receive their AVP innervation from the suprachiasmatic nucleus. These results indicate that the sex difference in the steroid-sensitive AVP pathways depends on other factors besides circulating hormone levels in adulthood.

Sex difference in the substance P-immunoreactive innervation of the medial nucleus of the amygdala

Discrete fields of substance P-immunoreactive fibers are present within the posterior dorsal division of the medial nucleus of the amygdala and the posterior medial bed nucleus of the stria terminalis in adult male and female rats. We previously reported a sex difference in the extent of this innervation of the bed nucleus. In the present study, we have replicated our earlier finding and found an equally dramatic sex difference in the amygdala. Morphometry revealed that the areas of dense staining in both the medial amygdala and the medial bed nucleus were more than twice as large in male brains.

Peptidergic control of male rat sexual behavior: the effects of intracerebral injections of substance P and cholecystokinin

Behavioral experiments examined the roles of substance P (SP) and cholecystokinin (CCK) in male rat copulatory behavior. Male copulatory behavior was recorded subsequent to injections of different doses of CCK and SP into the medial preoptic-anterior-hypothalamic area (MPOA-AH), caudate/putamen (CP), or the lateral ventricles (LV) in sexually experienced male rats. In the first experiment, three different doses of SP (10, 100, and 200 ng/cannula) injected bilaterally into the MPOA-AH produced marked changes in several components of male copulatory behavior. Latencies were most affected. All three doses significantly shortened the interval to initiate copulation, and the 10 and 100 ng, but not 200 ng dose also significantly reduced ejaculation latencies. Injections of 10 ng of SP into the CP did not affect sexual behavior, while injections into the LV produced changes different from those of MPOA-AH injections. These data argue for some degree of site specificity of the effects of the MPOA-AH injections. Bilateral injections of 10 ng of SP into the MPOA-AH, were incapable of inducing copulatory behavior in castrated rats deprived of testosterone. Injections of an undiluted SP antiserum (2 microliters/cannula) into the MPOA-AH produced a dramatic impairment of male copulatory behavior. These injections significantly lengthened amount, intromission, and ejaculation latencies, while having no effect on the number of mounts or intromissions prior to ejaculation. In contrast, bilateral injections of CCK-8 (10, 100, and 200 ng/cannula) into the MPOA-AH failed to affect any parameter of male copulatory behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex differences in vasopressin neurons in the bed nucleus of the stria terminalis by in situ hybridization

To determine whether a sex difference exists in the biosynthetic capacity of vasopressingergic (AVP) neurons in the bed nucleus of the stria terminalis (BNST), we have used in situ hybridization and quantitative autoradiography to measure propressophysin messenger RNA levels in these cells from adult male and female rats. We have found that significantly more (p less than 0.01) neurons are labeled in male rats than in female rats and that these labeled cells averaged more grains/cell (p less than 0.05) in males than in females. Therefore, the sexual dimorphism of AVP pathways in the BNST and lateral septum recently shown by immunohistochemistry results from a sex difference in the biosynthetic capacity of these AVP neurons.

Neuropeptides and male sexual behavior

Evidence is rapidly accumulating that a number of neuropeptides are involved in the central control of male sexual behavior. This is consistent with their neuroanatomical distribution, i.e., in CNS loci previously implicated in the control of this behavior such as the medial preoptic area, and with recent findings that the peptide content of some of these regions is regulated by testosterone or its metabolites. Most of the work has been done using rats, but relevant human studies have been included whenever such material has been available. At this point there are relatively few studies which directly demonstrate the involvement of peptides in this behavior. Inhibitory and facilitatory actions, however, have been demonstrated following injections of peptides, peptide antisera, or antagonists into the CNS of male rats. Significant new developments include demonstrations that injections of substance P and A-MSH directly into the medial preoptic area can facilitate this behavior, while ventricular injection of an oxytocin antagonist can produce a powerful inhibition. The emerging picture is that GnRH, oxytocin, A-MSH and substance P stimulate, while CRF, beta-endorphin, prolactin, and neuropeptide Y are inhibitory. The inhibitory peptides CRF, beta-endorphin and prolactin are related, as they are released in response to stress. This may be relevant to the low level of sexual motivation in some depressed men. Questions concerning sites of action and mechanisms of action which mediate the behavioral effects which have been demonstrated remain largely unanswered.

Sex- and hormone-dependent antigen immunoreactivity in developing rat hypothalamus

Morphological sex differences in adults can result from differential gonadal steroid exposure during critical perinatal periods. This study describes the use of a monoclonal antibody we have developed to study mechanisms of sexual differentiation of brain structure and function. Used as a marker in immunocytochemistry, antibody AB-2 revealed subsets of cells, including radial glia, transiently during the perinatal period. Peak reactivity in radial glia was on embryonic day 19 in males and on postnatal day 1 in females. On postnatal day 1, AB-2 immunoreactivity in radial glia was 2-fold greater in females than in males. Greater activity was detected in males on one side of the brain than the other (2- to 4-fold, depending on the region). To test the hormone dependence of this sex difference, pregnant rats were injected with testosterone propionate to expose fetal females to androgen on embryonic day 18. This resulted in lower levels of AB-2 immunoreactivity in radial glia of the treated female offspring on postnatal day 1 relative to control females, and the pattern was bilaterally asymmetric, approaching that of males. Thus the difference between sexes in immunoreactivity with AB-2 as a marker was hormone dependent in a predictable manner. Whether this marker is revealing a sex difference in accessibility of antigen by immunocytochemistry or a sex difference in intrinsic antigen levels is not yet resolved. In either case these results support the hypothesis that certain hormone-dependent molecular events occur transiently during development.

Chemoanatomic compartments in the human bed nucleus of the stria terminalis

Recent studies have indicated that peptidergic inputs to the bed nucleus of the stria terminalis are more developed in man than in rodents. To facilitate interspecies comparisons, the definition of the chemoanatomical subdivisions of the human bed nucleus of the stria terminalis was attempted. The immunocytochemistry of synenkephalin, [Met]enkephalin, somatostatin, and tyrosine hydroxylase was analysed on four verticofrontal levels in five control subjects. Four principal sectors were identified in the bed nucleus of the stria terminalis: (1) lateral, displaying an irregular patchy terminal innervation overlapping for the four markers studied; (2) central, characterized by a high density of somatostatin neurons, by pericellular basket-like formations for all markers, and by a shell of dense somatostatin innervation; (3) medial, characterized by a less dense aminergic and peptidergic innervation; and (4) lateroventral, where peptidergic (somatostatin and enkephalin) peridendritic plexuses were prominent. Double-labeling analyses showed that the somatostatin, enkephalin and tyrosine hydroxylase-like immunoreactive terminals rarely converged on the same soma or dendrite even in areas where they appeared closely interdigitated. The differences and similarities of these sectors with those defined in the rat are discussed; a marked development of the lateral and ventral bed nucleus of the stria terminalis is emphasized in man. Islands with dense peptidergic innervation, similar to the ventral bed nucleus of the stria terminalis, extended into the sublenticular substantia innominata (intercalated between the ventral pallidum and the basal magnocellular nucleus). This supports the existence of an extended amygdaloid complex from the amygdala to the bed nucleus of the stria terminalis in the human brain, as has been proposed in the rat. In relation to the literature, the present findings suggest the increasing importance of the central and lateral amygdaloid-bed nucleus of the stria terminals components and of their cortical connections in man while the medial amygdala-bed nucleus of the stria terminalis nuclei, which are preferentially connected to the olfactory system, appear less developed.

Early effects of gonadal steroids on the neuron number in the medial posterior region and the lateral division of the bed nucleus of the stria terminalis in the rat

This work investigates the possible existence of sex differences in the number of neurons in the medial posterior region (BNSTMp) and the lateral division (BNSTL) of the bed nucleus of the stria terminalis in the rat. These two zones of the bed nucleus of the stria terminalis belong, respectively, to the vomeronasal system (VNS), and to the main olfactory system (MOS). In the BNSTMp, males showed a greater number of neurons than females. Early postnatal (Day 1 after birth) orchidectomy in males, and androgenization in females, eliminated and reversed these differences. In the BNSTL, sexual dimorphism was restricted to its anterior region (BNSTLa). Females showed there a greater number of neurons than males. Male orchidectomy on Day 1 after birth increased the number of neurons, while female androgenization produced the opposite effect. The results obtained in this study support the hypothesis that the VNS is sexodimorphic, and suggest that sex differences exist in MOS, and that these differences are controlled by gonadal steroids during the perinatal period.