Neurogenesis of the sexually dimorphic vasopressin cells of the bed nucleus of the stria terminalis and amygdala of rats

The bed nucleus of the stria terminalis (BNST) and centromedial amygdala share many neuroanatomical and neurochemical characteristics, suggesting similarities in their development. Here we compare the neurogenesis of a group of cells for which already several common characteristics have been documented, that is, the sexually dimorphic arginine vasopressin-immunoreactive (AVP-ir) cells of the BNST and amygdala. To determine when these cells are born, pregnant rats received intraperitoneal injections of the thymidine analogue bromo-2-deoxy-5-uridine (BrdU) on one of nine embryonic days, E10 to E18; E1 being the day that a copulatory plug was found. At 3 months of age, the offsprings of these females were killed and their brains stained immunocytochemically for BrdU and AVP. Most AVP-ir cells were labeled with BrdU by injections on E12 and E13. Although BrdU labeling of AVP-ir cells did not differ between the BNST and amygdala, it differed between males and females. From E12 to E13, the percentage of BrdU-labeled AVP-ir cells decreased more in males than in females. AVP-ir cells appeared to be born earlier than most other cells in the same area, the majority of which were labeled with BrdU by injections on E14, E15, and E16. The similarities in the birthdates of AVP-ir cells in the BNST and amygdala may help to explain why these cells take on so many similar characteristics. The sex difference in birthdates of AVP-ir cells may help to explain which cellular processes underlie the sexual differentiation of these cells. © 1996 John Wiley & Sons, Inc.     

Apoptosis during sexual differentiation of the bed nucleus of the stria terminalis in the rat brain

The bed nucleus of the stria terminalis (BST) in the rat forebrain differs between males and females. To test whether apoptosis may contribute to the development of sex differences in the BST, the incidence of apoptosis was determined in sham-treated males and sham-treated females sacrificed on postnatal days (PN) 2, 4, 6, 8, 10, and 12 (PN 1 being day of birth). More apoptotic nuclei were found in the principal nucleus of the BST (BSTpr) in females than in males, whereas the reverse was true for the lateral division of the BST (BSTl). Moreover, the volume of the BSTpr was larger in males than in females, whereas there was no sex difference in the volume of the BSTl. Our results also confirmed earlier reports indicating that the incidence of apoptosis in the central part of the medial preoptic nucleus (MPNc) is higher in females than in males. No sex difference in apoptosis was found in the ventromedial hypothalamus (VMH) and paraventricular nucleus (PVN). The volume of the MPNc and VMH was larger in males than in females, whereas the PVN volume did not differ between males and females. To test whether sex differences in neonatal levels of gonadal steroids may cause sex differences in the incidence of apoptosis in the BSTpr, the incidence of apoptosis was compared between castrated males and females that were treated with testosterone propionate or vehicle on the day of birth. In the BSTpr of gonadal steroid-treated animals, the incidence of apoptosis was lower when compared to animals treated with vehicle, which was also true for the MPNc. These results are consistent with the hypothesis that gonadal steroids contribute to the sexually dimorphic differentiation of the BST by controlling the incidence of apoptosis.     

Interactions of norepinephrine and galanin in the central amygdala and lateral bed nucleus of the stria terminalis modulate the behavioral response to acute stress

Many aspects of drug abuse and addiction share neurobiological substrates with the modulatory processes underlying the response and adaptation to acute stress. In particular, the ascending noradrenergic system has been implicated in facilitating the response to stress, and in stress-induced reinstatement of drug seeking behavior. Thus, to better understand the link between stress and addictive behaviors, it would be informative to understand better the modulatory function of the ascending noradrenergic system, and its interaction with other neurotransmitters with which it is closely associated or co-localized, such as the neuropeptide galanin. In this paper, we review a series of studies investigating the functional interactions of norepinephrine and galanin in modulating the behavioral response to acute stress in two components of the extended amygdala, the central nucleus of the amygdala and the lateral bed nucleus of the stria terminalis. We showed that norepinephrine facilitates behavioral reactivity to stress on the elevated plus-maze and social interaction tests. However, when stress-induced activation of the noradrenergic system was enhanced by blocking inhibitory adrenergic autoreceptors, galanin release was recruited in the central amygdala, acting to attenuate the behavioral response to stress. By contrast, stress-induced galanin release in the lateral bed nucleus appeared to be independent of enhanced noradrenergic activation, and unlike the central amygdala, both galanin and norepinephrine facilitated behavioral stress reactivity in the bed nucleus. The different modes of interaction and differential region- and response-specificity of galanin and norepinephrine suggest that a complex neural circuit interconnecting these two regions is involved in the modulatory effects of norepinephrine and galanin on the behavioral response to stress. Such complexity may allow for flexibility and plasticity in stress adaptation, and may also contribute to behavioral changes induced by chronic drug administration. Thus, the interaction of galanin and norepinephrine may be a viable target for the future development of novel therapeutic strategies for treating behavioral disorders related to stress or drug abuse.     

Blood supply of the bed nucleus of the stria terminalis in rat

Summary The topographical distribution of the blood vessels in the bed nucleus of the stria terminalis (NIST) has been mapped in rats. Arteries and veins were visualized in red and blue by using a double-ink perfusion technique. Arteries supplying the NIST arise from the anterior cerebral artery directly or through the anterior communicating and interhemispheric arteries. Only a few, dorsal branches derive from the medial cerebral artery through thalamostriatal arteries. According to their terminal branches, NIST arteries can be divided into five groups: medial, ventral, lateral, septal and dorsal, which have only a relatively small overlap in their territories. About 90% of veins from the NIST drain into the major basal veins. Medial branches run into the perioptic and interhemispheric veins, while the ventral branches and the large lateral vein drain directly into the anterior cerebral vein. A small proportion of NIST veins run dorsalward into the vena cerebri magna via thalamostriatal veins.     

Allopregnanolone induces state-dependent fear via the bed nucleus of the stria terminalis

Gonadal steroids and their metabolites have been shown to be important modulators of emotional behavior. Allopregnanolone (ALLO), for example, is a metabolite of progesterone that has been linked to anxiety-related disorders such as posttraumatic stress disorder. In rodents, it has been shown to reduce anxiety in a number of behavioral paradigms including Pavlovian fear conditioning. We have recently found that expression of conditioned contextual (but not auditory) freezing in rats can be suppressed by infusion of ALLO into the bed nucleus of the stria terminalis (BNST). To further explore the nature of this effect, we infused ALLO into the BNST of male rats prior to both conditioning and testing. We found that suppression of contextual fear occurred when the hormone was present during either conditioning or testing but not during both procedures, suggesting that ALLO acts in a state-dependent manner within the BNST. A shift in interoceptive context during testing for animals conditioned under ALLO provided further support for this mechanism of hormonal action on contextual fear. Interestingly, infusions of ALLO into the basolateral amygdala produced a state-independent suppression of both conditioned contextual and auditory freezing. Altogether, these results suggest that ALLO can influence the acquisition and expression of fear memories by both state-dependent and state-independent mechanisms.     

Vasopressin-immunoreactive cell bodies in the bed nucleus of the stria terminalis of the rat

In the dorsal and ventral portions of the bed nucleus of the stria terminalis of the rat numerous cell bodies immunoreactive for vasopressin and neurophysin II were found after colchicin pretreatment. These cells are predominantly multipolar but sometimes also bipolar, and have a width and length of approximately 9 and 16 microns, respectively. In the homozygous Brattleboro rat, which is deficient in vasopressin, no immunoreactive vasopressin was found in these cells. Following incubation with anti-oxytocin and anti-bovine neurophysin I, only magnocellular immunoreactive cell bodies were found in the septal region. The consequences of these results concerning the vasopressin fiber pathways in the brain are discussed.     

Medullary taste responses are modulated by the bed nucleus of the stria terminalis

Previous studies have shown a modulatory influence of limbic forebrain areas, such as the central nucleus of the amygdala and lateral hypothalamus, on the activity of taste-responsive cells in the nucleus of the solitary tract (NST). The bed nucleus of the stria terminalis (BST), which receives gustatory afferent information, also sends descending axons to the NST. The present studies were designed to investigate the role of the BST in the modulation of NST gustatory activity. Extracellular action potentials were recorded from 101 taste-responsive cells in the NST of urethane-anesthetized hamsters and analyzed for a change in excitability following bilateral electrical stimulation of the BST. The response of NST taste cells to stimulation of the BST was predominately inhibitory. Orthodromic inhibitory responses were observed in 29 of 101 (28.7%) NST taste-responsive cells, with four cells inhibited bilaterally. An increase in excitability was observed in seven of the 101 (6.9%) NST taste cells. Of the 34 cells showing these responses, 25 were modulated by the ipsilateral BST and 15 by the contralateral; four were inhibited bilaterally and two inhibited ipsilaterally and excited contralaterally. The duration of inhibitory responses (mean = 177.9 ms) was significantly longer than that of excitatory responses (35.4 ms). Application of subthreshold electrical stimulation to the BST during taste trials inhibited or excited the taste responses of every BST-responsive NST cell tested with this protocol. NST neurons that were most responsive to sucrose, NaCl, citric acid or quinine hydrochloride were all affected by BST stimulation, although citric acid-best cells were significantly more often modulated and NaCl-best less often modulated than expected by chance. These results combine with excitatory and inhibitory modulation of NST neurons by the insular cortex, lateral hypothalamus and central nucleus of the amygdala to demonstrate extensive centrifugal modulation of brainstem gustatory neurons.     

The role of the anteriolateral bed nucleus of the stria terminalis in stress-induced nociception

Activation of the central amygdala (CeA) by corticosterone (CORT) induces somatic and colonic hypersensitivity through corticotrophin-releasing factor (CRF)-dependent mechanisms. However, the importance of the bed nucleus of the stria terminalis (BNST), part of the extended amygdala, on nociception remains unexplored. In the present study, we test the hypothesis that stimulation of the CeA by CORT induces somatic and colonic hypersensitivity through activation of the anteriolateral BNST (BNST(AL)). Animals were implanted with micropellets of CORT or cholesterol (CHOL) onto the CeA or the BNST(AL). Mechanical sensitivity was quantified using electronic von Frey filaments, and colonic nociception was measured by quantifying a visceromotor response to graded colorectal distension. In situ hybridization was used to determine mRNA levels for CRF, CRF(1), and CRF(2) receptors in the BNST(AL). In a second group, animals were implanted bilaterally with 1) CORT or CHOL micropellets onto the CeA; and 2) cannulas localized to the BNST(AL) to administer a CRF(1) receptor antagonist (CP376395). Animals implanted with CORT onto the CeA, but not the BNST(AL), exhibited increased expression of CRF mRNA and increased CRF(1)-to-CRF(2) receptor ratio in the BNST, as well as somatic and colonic hypersensitivity compared with CHOL controls. Infusion of CP376395 into the BNST(AL) inhibited somatic and colonic hypersensitivity in response to elevated amygdala CORT. Somatic and colonic hypersensitivity induced by elevated amygdala CORT is mediated via a CRF(1) receptor-dependent mechanism in the BNST(AL). The CeA through a descending pathway involving the BNST(AL) plays a pivotal role in somatic and colonic nociception.     

Peptide immunoreactive neurons in the amygdala and the bed nucleus of the stria terminalis project to the midbrain central gray in the rat.

The central nucleus of the amygdala, bed nucleus of the stria terminalis, and central gray are important components of the neural circuitry responsible for autonomic and behavioral responses to threatening or stressful stimuli. Neurons of the amygdala and bed nucleus of the stria terminalis that project to the midbrain central gray were tested for the presence of peptide immunoreactivity. To accomplish this aim, a combined immunohistochemical and retrograde tracing technique was used. Maximal retrograde labeling was observed in the amygdala and bed nucleus of the stria terminalis after injections of retrograde tracer into the caudal ventrolateral midbrain central gray. The majority of the retrogradely labeled neurons in the amygdala were located in the medial central nucleus, although many neurons were also observed in the lateral subdivision of the central nucleus. Most of the retrogradely labeled neurons in the BST were located in the ventral and posterior lateral subdivisions, although cells were also observed in most other subdivisions. Retrogradely labeled neurotensin, corticotropin releasing factor (CRF), and somatostatin neurons were mainly observed in the lateral central nucleus and the dorsal lateral BST. Retrogradely labeled substance P-immunoreactive cells were found in the medial central nucleus and the posterior and ventral lateral BST. Enkephalin-immunoreactive retrogradely labeled cells were not observed in the amygdala or bed nucleus of the stria terminalis. A few cells in the hypothalamus (paraventricular and lateral hypothalamic nuclei) that project to the central gray also contained CRF and neurotensin immunoreactivity. The results suggest the amygdala and the bed nucleus of the stria terminalis are a major forebrain source of CRF, neurotensin, somatostatin, and substance P terminals in the midbrain central gray.     

The bed nucleus of the stria terminalis is critical for sexual solicitation,but not for opposite-sex odor preference,in female Syrian hamsters

Successful reproduction in vertebrates depends critically upon a suite of precopulatory behaviors that occur prior to mating. In Syrian hamsters (Mesocricetus auratus), these behaviors include vaginal scent marking and preferential investigation of male odors. The neural regulation of vaginal marking and opposite-sex odor preference likely involves an interconnected set of steroid-sensitive nuclei that includes the medial amygdala (MA), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA). For example, lesions of MA eliminate opposite-sex odor preference and reduce overall levels of vaginal marking, whereas lesions of MPOA decrease vaginal marking in response to male odors. Although BNST is densely interconnected with both MA and MPOA, little is known about the role of BNST in female precopulatory behaviors. To address this question, females received either bilateral, excitotoxic lesions of BNST (BNST-X) or sham lesions (SHAM), and were tested for scent marking and for investigatory responses to male and female odors. Whereas SHAM females vaginal marked more to male odors than female odors on two days of the estrous cycle, BNST-X females marked at equivalent levels to both odors. This deficit is not due to alterations in social odor investigation, as both BNST-X and SHAM females investigated male odors more than female odors. Finally, BNST lesions did not generally disrupt the cyclic changes in reproductive behaviors that occur across the estrous cycle. Taken together, these results demonstrate that BNST is critical for the normal expression of solicitational behaviors by females in response to male odor stimuli.     

The bed nucleus of the stria terminalis is critical for sexual solicitation, but not for opposite-sex odor preference, in female Syrian hamsters

Successful reproduction in vertebrates depends critically upon a suite of precopulatory behaviors that occur prior to mating. In Syrian hamsters (Mesocricetus auratus), these behaviors include vaginal scent marking and preferential investigation of male odors. The neural regulation of vaginal marking and opposite-sex odor preference likely involves an interconnected set of steroid-sensitive nuclei that includes the medial amygdala (MA), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA). For example, lesions of MA eliminate opposite-sex odor preference and reduce overall levels of vaginal marking, whereas lesions of MPOA decrease vaginal marking in response to male odors. Although BNST is densely interconnected with both MA and MPOA, little is known about the role of BNST in female precopulatory behaviors. To address this question, females received either bilateral, excitotoxic lesions of BNST (BNST-X) or sham lesions (SHAM), and were tested for scent marking and for investigatory responses to male and female odors. Whereas SHAM females vaginal marked more to male odors than female odors on two days of the estrous cycle, BNST-X females marked at equivalent levels to both odors. This deficit is not due to alterations in social odor investigation, as both BNST-X and SHAM females investigated male odors more than female odors. Finally, BNST lesions did not generally disrupt the cyclic changes in reproductive behaviors that occur across the estrous cycle. Taken together, these results demonstrate that BNST is critical for the normal expression of solicitational behaviors by females in response to male odor stimuli.     

Neuro-pathophysiologic effects during primary hyperactivation of the bed nucleus of the stria terminalis in the rat brain

Penicillin administration into the bed nucleus of stria terminalis (BNST) in the rat brain caused epileptiform activity (EpA)--the formation of the generator of pathologically enhanced excitation (GPEE) in the nucleus. GPEE was registered during the first 3 days. EpA was also detected in the amygdala during 5-8 days, and in the hippocamp during the whole period of registration (2-3 weeks). There was the generalized enhancement of synchronized EpA in the range of 6-10 oscillations per s., in some cases with high-amplitude spindle (7-8 oscillations per s.). 50% of animals had emotional behavioural disorders, a marked fear reaction was observed for a month and more. Some animals demonstrated psychotic-like paroxysms with the elements of stereotypy accompanied by high-frequency low-amplitude EpA. It is suggested that when a primary GPEE in BNST is formed, the structures of septo-hippocampal system (BNST, amygdala, hippocamp) play a role of pathological determinants under the influence of which the pathological system consisting of a number of limbic and extrapyramidal structures is formed. Its activity is clinically manifested in the complex polymorphic neuropathological syndrome.     

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.     

GABA and NMDA receptors in CRF neurons have opposing effects in fear acquisition and anxiety in central amygdala vs. bed nucleus of the stria terminalis

This article is part of a Special Issue “SBN 2014”.Beginning with Vale and Colleagues in 1981, corticotropin releasing factor (CRF) also called corticotropin releasing hormone (CRH) has repeatedly been identified as an important contributor to fear and anxiety behavior. These findings have proven useful to further our understanding of disorders that have significant fear-dysregulation, such as post-traumatic stress, as well as other stress- and anxiety-related disorders. Unfortunately, the data are not all in agreement. In particular the role of CRF in fear learning is controversial, with studies pointing to contradictory effects from CRF manipulation even within the same brain structure. Further, very few studies address the potentially promising role of CRF manipulation in fear extinction behavior. Here, we briefly review the role of CRF in anxiety, fear learning and extinction, focusing on recent cell-type and neurotransmitter-specific studies in the amygdala and bed nucleus of the stria terminalis (BNST) that may help to synthesize the available data on the role of CRF in fear and anxiety-related behaviors.     

Projection from the ventral bed nucleus of the stria terminalis to the retrorubral field in rats and the effects of cells in these areas on mating in male rats versus gerbils

This research identified the rat counterpart of the lateral cell group of the sexually dimorphic area (SDA) found in medial preoptic area (MPOA) gerbil of gerbils. The lateral SDA (lSDA) is critical for mating in male gerbils and contains most of the SDA cells projecting to the retrorubral field (RRF), a projection that is also important for mating. Therefore, to locate the counterpart of the lateral SDA, we traced the inputs to the rat RRF, which were dense in the ventral part of the bed nucleus of the stria terminalis (BST). To determine if the ventral BST or its projection to the RRF affects mating in male rats, we disrupted them bilaterally by placing cell-body lesions bilaterally in the ventral BST or unilaterally there and in the contralateral RRF. We also studied the effects of RRF lesions in both rats and gerbils. Bilateral ventral BST lesions, which left the medial preoptic nucleus intact, produced persistent and severe mating deficits. Disconnecting the ventral BST from the RRF also had long-lasting, but less severe, consequences. RRF lesions produced only temporary mating deficits in rats, but virtually eliminated mating in gerbils. The recovery of mating in rats after RRF, but not ventral BST, lesions, and the intermediate effects of disconnecting these areas from each other suggest that the ventral BST may contain mating-related projection neurons other than those projecting to the RRF or that its RRF-projecting cells send collaterals to another site. In either case, the pedunculopontine tegmental nucleus or raphe nuclei may be involved.     

Development of sex differences in the principal nucleus of the bed nucleus of the stria terminalis of mice: role of Bax-dependent cell death

Neuron number in the principal nucleus of the bed nucleus of the stria terminalis (BNSTp) is greater in adult male mice than in females. Deletion of the proapoptotic gene, Bax, increases the number of BNSTp cells in adulthood and eliminates the sex difference in cell number. Here, we map the ontogeny of sex differences in nuclear volume and cell number in the BNSTp of neonatal mice, and evaluate the role of cell death in the development of these differences. We find that BNSTp volume and cell number do not differ between male and female wild-type mice on postnatal days P3, P5, or P7. Sex differences emerge after the first postnatal week and both measures are significantly greater in males than in females on P9 and P11. Cell death, assessed by TUNEL staining, was observed in the BNSTp of both sexes from P1-P8. Females had more TUNEL-positive cells than males from approximately P3-P6, with the maximum number of dying cells observed on P5/P6. To test whether the Bax gene is required for sexually dimorphic cell death in the BNSTp, TUNEL cells were counted on P6 in Bax -/- mice and their Bax +/+ siblings. Bax gene deletion nearly abolished TUNEL-positive cells in the BNSTp of both sexes. Together, these findings support the interpretation that the sex difference in BNSTp cell number seen in adulthood is due to Bax-dependent, sexually dimorphic cell death during the first week of life.     

Chronic morphine treatment and withdrawal increase extracellular levels of norepinephrine in the rat bed nucleus of the stria terminalis

Extracellular levels of norepinephrine (NE) and glutamate (Glu) in the ventral bed nucleus of the stria terminalis (vBNST) of saline- and chronic morphine-treated rats, with or without withdrawal, were studied by means of the in vivo microdialysis technique in anesthetized rats. In addition, the tissue concentration of NE was studied at different rostrocaudal levels of the vBNST. Chronic morphine treatment significantly increased extracellular levels of NE, but not Glu, in vBNST. At 48 h after naloxone-induced morphine withdrawal there was a further significant increase in the extracellular levels of NE, but not Glu, in vBNST. The presence of UK 14304, an alpha(2)-adrenergic agonist, induced a significant decrease in NE extracellular levels in all experimental groups. In contrast, UK 14304 induced a significant decrease in Glu extracellular levels only in saline-treated rats. The results also show that the vBNST presents a rostrocaudal gradient of NE and contains 9.4% of total brain NE. The increase in NE extracellular levels in vBNST induced by chronic morphine treatment and the further increase in NE levels 48 h after naloxone-induced morphine withdrawal suggest that NE in vBNST may be involved in the pharmacological effects of chronic morphine and withdrawal.