BST Neurons Research Articles

Sex differences in the Role of Basolateral Amygdala Projections to the Bed Nucleus of the Stria Terminalis in Anticipatory Anxiety

Sustained anxiety in the absence of a threat can lead to pathological manifestations like post traumatic stress disorder (PTSD) and anxiety disorders. Recent data suggest that the bed nucleus of the stria terminalis (BST) is implicated in the shift from a phasic to sustained anxiety state, but the specific mechanisms by which this occurs remains unknown. We developed a model for sustained fear conditioning to a long duration cue (8 min) paired with intermittent foot shocks in order to better understand the neurocircuitry of anticipatory anxiety. Sex differences in the prevalence of anxiety disorders exist and a secondary goal of this work was to examine if sex differences exist in anticipatory anxiety during prolonged cues and the circuitry that contributes to this behavior. One of the major inputs to the BST activated during sustained fear learning is the basolateral amygdala (BLA), which also differs in activity between sexes. To determine a role for BLA projecting BST neurons (BLA-BST) in this sustained anxiety paradigm, we examined DREADD-induced suppression of the BLA-BST pathway during prolonged cued fear conditioning in both male and female rats. In males, inhibition of BLA-BST during extinction hastened the extinction of freezing compared to male controls, but had no effect on freezing behavior in females. Inhibition of BLA-BST did not alter exploration of the central area in the open field task, a test of general anxiety-like behavior, in either sex. Since the BLA-BST pathway also mediates social anxiety-like behavior in humans and animals, we assessed potential sex differences in social interaction (SI) following suppression of this pathway. Inhibition of the BLA-BST pathway increased SI time and reduced the latency to interact in male, but not female rats. Together, these results suggest that the BLA-BST projection does not modulate generalized anxiety-like behavior, but is specific to anticipatory anxiety induced by prolonged cued fear or an unpredictable social environment and differs between sexes. To examine potential sex differences in BLA-BST neurons, we implemented in vivo and in vitro electrophysiological approaches to determine the activity of these neurons. While spontaneous general BLA neuronal activity was augmented in females compared to males, sex differences were noted in the activity of BLA-BST projections. In males, the BLA-BST projection neurons were more active and excitable which coincided with a smaller after hyperpolarization (AHP) amplitude compared to other non-BST-projecting BLA neurons whereas in females, BLA-BST neurons were less excitable and had larger AHP amplitudes compared to non-BST-projecting BLA neurons. These physiological data support our behavioral experiment findings in which increased activity of BLA-BST neurons mediates anticipatory anxiety-like behavior in males, but not females. These novel findings suggest BLA-BST neurons contribute to anticipatory anxiety in male rats, but not females. Moreover, these sex differences in neurocircuitry may explain the sex disparity in anxiety disorders.

Sexually differentiated and neuroanatomically specific co-expression of aromatase neurons and GAD67 in the male and female quail brain.

Testosterone aromatization into estrogens in the preoptic area (POA) is critical for the activation of male sexual behavior in many vertebrates. Yet, the cellular mechanisms mediating actions of neuroestrogens on sexual behavior remain largely unknown. We investigated in male and female Japanese quail by dual-label fluorescent in situ hybridization (FISH) whether aromatase-positive (ARO) neurons express glutamic acid decarboxylase 67 (GAD67), the rate-limiting enzyme in GABA biosynthesis. ARO cells and ARO cells double labeled with GAD67 (ARO-GAD67) were counted at standardized locations in the medial preoptic nucleus (POM) and the medial bed nucleus of the stria terminalis (BST) to produce three-dimensional distribution maps. Overall, males had more ARO cells than females in POM and BST. The number of double-labeled ARO-GAD67 cells was also higher in males than in females and greatly varied as a function of the specific position in these nuclei. Significant sex differences were however present only in the most caudal part of POM. Although both ARO and GAD67 were expressed in the VMN, no colocalization between these markers was detected. Together, these data show that a high proportion of estrogen-synthesizing neurons in POM and BST are inhibitory and the colocalization of GAD67 with ARO exhibits a high degree of anatomical specificity as well as localized sex differences. The fact that many preoptic ARO neurons project to the periaqueductal gray in male quail suggests possible mechanisms through which locally produced estrogens could activate male sexual behavior.

The Proinflammatory Cytokine Interleukin 18 Regulates Feeding by Acting on the Bed Nucleus of the Stria Terminalis.

The proinflammatory cytokine IL-18 has central anorexigenic effects and was proposed to contribute to loss of appetite observed during sickness. Here we tested in the mouse the hypothesis that IL-18 can decrease food intake by acting on neurons of the bed nucleus of the stria terminalis (BST), a component of extended amygdala recently shown to influence feeding via its projections to the lateral hypothalamus (LH). We found that both subunits of the heterodimeric IL-18 receptor are highly expressed in the BST and that local injection of recombinant IL-18 (50 ng/ml) significantly reduced c-fos activation and food intake for at least 6 h. Electrophysiological experiments performed in BST brain slices demonstrated that IL-18 strongly reduces the excitatory input on BST neurons through a presynaptic mechanism. The effects of IL-18 are cell-specific and were observed in Type III but not in Type I/II neurons. Interestingly, IL-18-sensitve Type III neurons were recorded in the juxtacapsular BST, a region that contains BST-LH projecting neurons. Reducing the excitatory input on Type III GABAergic neurons, IL-18 can increase the firing of glutamatergic LH neurons through a disinhibitory mechanism. Imbalance between excitatory and inhibitory activity in the LH can induce changes in food intake. Effects of IL-18 were mediated by the IL-18R because they were absent in neurons from animals null for IL-18Rα (Il18ra(-/-)), which lack functional IL-18 receptors. In conclusion, our data show that IL-18 may inhibit feeding by inhibiting the activity of BST Type III GABAergic neurons. Loss of appetite during sickness is a common and often debilitating phenomenon. Although proinflammatory cytokines are recognized as mediators of these anorexigenic effects, their mechanism and sites of action remain poorly understood. Here we show that interleukin 18, an anorexigenic cytokine, can act on neurons of the bed nucleus of the stria terminalis to reduce food intake via the IL-18 receptor. The findings identify a site and a mode of action that indicate targets for the treatment of cachexia or other eating disorders.

GABAergic neurons in the ventral tegmental area receive dual GABA/enkephalin‐mediated inhibitory inputs from the bed nucleus of the stria terminalis

Activation of mu-opioid receptor (MOR) disinhibits dopaminergic neurons in the ventral tegmental area (VTA) through inhibition of γ-aminobutyric acid (GABA)ergic neurons. This mechanism is thought to play a pivotal role in mediating reward behaviors. Here, we characterised VTA-projecting enkephalinergic neurons in the anterior division of the bed nucleus of the stria terminalis (BST) and investigated their targets by examining MOR expression in the VTA. In the BST, neurons expressing preproenkephalin mRNA were exclusively GABAergic, and constituted 37.2% of the total GABAergic neurons. Using retrograde tracer injected into the VTA, 21.6% of VTA-projecting BST neurons were shown to express preproenkephalin mRNA. Enkephalinergic projections from the BST exclusively formed symmetrical synapses onto the dendrites of VTA neurons. In the VTA, 74.1% of MOR mRNA-expressing neurons were GABAergic, with the rest being glutamatergic neurons expressing type-2 vesicular glutamate transporter mRNA. However, MOR mRNA was below the detection threshold in dopaminergic neurons. By immunohistochemistry, MOR was highly expressed on the extrasynaptic membranes of dendrites in GABAergic VTA neurons, including dendrites innervated by BST-VTA projection terminals. MOR was also expressed weakly on GABAergic and glutamatergic terminals in the VTA. Given that GABAA α1 is expressed at GABAergic BST-VTA synapses on dendrites of GABAergic neurons [T. Kudo etal. (2012) J. Neurosci., 32, 18035-18046], our results collectively indicate that the BST sends dual inhibitory outputs targeting GABAergic VTA neurons; GABAergic inhibition via 'wired' transmission, and enkephalinergic inhibition via 'volume' transmission. This dual inhibitory system provides the neural substrate underlying the potent disinhibitory control over dopaminergic VTA neurons exerted by the BST.

Effects of hypocretin and norepinephrine interaction in bed nucleus of the stria terminalis on arterial pressure

Forebrain neuronal circuits containing hypocretin-1 (hcrt-1) and norepinephrine (NE) are important components of central arousal-related processes. Recently, these two systems have been shown to have an overlapping distribution within the bed nucleus of the stria terminalis (BST), a limbic structure activated by stressful challenges, and which functions to adjust arterial pressure (AP) and heart rate (HR) to the stressor. However, whether hcrt-1 and NE interact in BST to alter cardiovascular function is unknown. Experiments were done in urethane-α-chloralose anesthetized, paralyzed, and artificially ventilated male Wistar rats to investigate the effect of hcrt-1 and NE on the cardiovascular responses elicited by l-glutamate (Glu) stimulation of BST neurons. Microinjections of hcrt-1, NE or tyramine into BST attenuated the decrease in AP and HR to Glu stimulation of BST. Additionally, combined injections of hcrt-1 with NE or tyramine did not elicit a greater attenuation than either compound alone. Furthermore, injections into BST of the α2-adrenergic receptor (α2-AR) antagonist yohimbine, but not the α1-AR antagonist 2-{[β-(4-hydroxyphenyl)ethyl]aminomethyl}-1-tetralone hydrochloride, blocked both the hcrt-1 and NE-induced inhibition of the BST cardiovascular depressors responses. Finally, injections into BST of the GABAA receptor antagonist bicuculline, but not the GABAB receptor antagonist phaclofen, blocked the hcrt-1 and NE attenuation of the BST Glu-induced depressor and bradycardia responses. These data suggest that hcrt-1 effects in BST are mediated by NE neurons, and hcrt-1 likely acts to facilitate the synaptic release of NE. NE neurons, acting through α2-AR may activate Gabaergic neurons in BST, which in turn through the activation of GABAA receptors inhibit a BST sympathoinhibitory pathway. Taken together, these data suggest that hcrt-1 pathways to BST through their interaction with NE and Gabaergic neurons may function in the coordination of cardiovascular responses associated with different behavioral states.

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.

Renal effects produced by microinjection of kappa opioid agonist into the bed nuclei of the stria terminalis (BST)

Intracerebroventricular (ICV) injection of the kappa opioid agonist, U‐50448H (U50), produces a marked diuresis, antinatriuresis, and an increase in renal sympathetic nerve activity (RSNA). The dorsomedial BST has been show to express kappa opioid receptors (KOR) that project to the hypothalamic areas involved in water homeostasis, therefore we examined if injection of U50 into the BST would produce similar effects on renal function.MethodsRats anesthetized with urethane‐chloralose were instrumented to record arterial blood pressure (ABP), heart rate (HR) and RSNA. Catheters were placed in a femoral vein for drug delivery and infusion of isotonic saline (25 μl/min) and in the urinary bladder for urine collection. Urine was sampled during two 10 min control and six 10 min periods starting 10 min after injection of U50 or vehicle to the BST.ResultsU50 significantly increased urine excretion (n=8, P<0.05) without changing HR, mean ABP, urinary sodium excretion or RSNA. Injections of saline (n=8) were without affect.ConclusionThe ability of U50 to increase urine outflow without effecting sodium excretion and RSNA raises the possibility that BST neurons could be an important substrate through which drugs targeting Kappa opioid receptors could selectively facilitate water excretion in sodium retaining diseases such as salt‐sensitive hypertension. This work was supported by 5SC2 HL104639.

Three Types of Neurochemical Projection from the Bed Nucleus of the Stria Terminalis to the Ventral Tegmental Area in Adult Mice

Dopaminergic (DAergic) neurons in the ventral tegmental area (VTA) play crucial roles in motivational control of behaviors, and their activity is regulated directly or indirectly via GABAergic neurons by extrinsic afferents from various sources, including the bed nucleus of the stria terminalis (BST). Here, the neurochemical composition of VTA-projecting BST neurons and their outputs to the VTA were studied in adult mouse brains. By combining retrograde tracing with fluorescence in situ hybridization for 67 kDa glutamate decarboxylase (GAD67) and vesicular glutamate transporters (VGluTs), VTA-targeting BST neurons were classified into GAD67-positive (GAD67(+))/VGluT3-negative (VGluT3(-)), GAD67(+)/VGluT3(+), and VGluT2(+) neurons, of which GAD67(+)/VGluT3(-) neurons constituted the majority (∼90%) of VTA-projecting BST neurons. GABAergic efferents from the BST formed symmetrical synapses on VTA neurons, which were mostly GABAergic neurons, and expressed GABA(A) receptor α1 subunit on their synaptic and extrasynaptic membranes. In the VTA, VGluT3 was detected in terminals expressing vesicular inhibitory amino acid transporter (VIAAT), plasmalemmal serotonin transporter, or neither. Of these, VIAAT(+)/VGluT3(+) terminals, which should include those from GAD67(+)/VGluT3(+) BST neurons, formed symmetrical synapses. When single axons from VGluT3(+) BST neurons were examined, almost all terminals were labeled for VIAAT, whereas VGluT3 was often absent from terminals with high VIAAT loads. VGluT2(+) terminals in the VTA exclusively formed asymmetrical synapses, which expressed AMPA receptors on postsynaptic membrane. Therefore, the major mode of the BST-VTA projection is GABAergic, and its activation is predicted to disinhibit VTA DAergic neurons. VGluT2(+) and VGluT3(+) BST neurons further supply additional projections, which may principally convey excitatory or inhibitory inputs, respectively, to the VTA.

Neuronal activity in the bed nucleus of the stria terminalis in a rat model for obsessive–compulsive disorder

In search of a new potential target for deep brain stimulation in patients with obsessive–compulsive disorder (OCD), we evaluated the single-cell activity of neurons in the bed nucleus of the stria terminalis (BST) in urethane-anesthetized rats in an animal model for OCD, the schedule-induced polydipsia (SIP) model, and compared this to the BST activity in control rats and to a third group of rats which were introduced in the model but did not develop the SIP, and thus were considered resistant. We compared the firing rate and firing pattern of BST neurons between these groups, between hemispheres and made a correlation of the firing rate and firing pattern to the position in the BST. The variability of BST neurons in SIP rats was lower and the randomness higher than BST neurons in control rats or resistant rats. The firing rate of BST neurons in SIP rats was significantly higher and the burst index lower than BST neurons in resistant rats but not in control rats. Also, neurons from the right hemisphere in the SIP group had a higher burst index than neurons from the left hemisphere. However, this is opposite in the resistant and control group. Third, we found a higher bursting index with increasing (more ventral) depth of recording. These findings suggest that schedule-induced polydipsia, which models compulsive behavior in humans, induces a change in firing behavior of BST neurons.

Role of the bed nucleus of the stria terminalis in the control of ventral tegmental area dopamine neurons

Projections from neurons of the bed nucleus of the stria terminalis (BST) to the ventral tegmental area (VTA) are crucial to behaviors related to reward and motivation. Over the past few years, we have undertaken a series of studies to understand: 1) how excitatory inputs regulate in vivo excitable properties of BST neurons, and 2) how BST inputs in turn modulate neuronal activity of dopamine neurons in VTA. Using in vivo extracellular recording techniques in anesthetized rats and tract-tracing approaches, we have demonstrated that inputs from the infralimbic cortex and the ventral subiculum exert a strong excitatory influence on BST neurons projecting to the VTA. Thus, the BST is uniquely positioned to receive emotional and learning-associated informations and to integrate these into the reward/motivation circuitry. We will discuss how changes in the activity of BST neurons projecting to the VTA could participate in the development or exacerbation of psychiatric conditions such as drug addiction.

Convergent effects of oxytocin and a δ-opioid agonist in the bed nuclei of the stria terminalis of the peripartum rat

In the bed nuclei of the stria terminalis (BST), opioids may suppress the facilitatory effect of oxytocin on its own release pre-partum. In vitro electrophysiological recording showed that in virgin, late-pregnant, and lactating rats, a δ-opioid agonist inhibited a high proportion of BST neurons, many of which were also oxytocin responsive. Response magnitude did not differ significantly between groups, suggesting that the postulated pre-partum increase in opioid tone does not involve postsynaptic changes in neuronal sensitivity.

Catecholamine-CRF synaptic interaction in a septal bed nucleus: Afferents of neurons in the bed nucleus of the stria terminalis

Projections of catecholamine neurons to the bed nucleus of the stria terminalis (BST), especially its corticotropin releasing factor (CRF)-producing neurons, are implicated as being major contributors to the neurochemically mediated central regulation of the stress response. The purpose of the present study was to examine in the BST of the rat brain the morphological characteristics of interactions between two neuron populations of the brain, catecholaminergic and CRF neurons. A double-label immunocytochemical, light and electron microscopic technique allowed the demonstration of the synaptic interaction between dopamine (DA i.e, tyrosine hydroxylase-containing) and norepinephrine (NE i.e., dopamine-beta-hydroxylase-containing) axons and CRF neurons in the BST. DA terminals formed synapses with dendrites and soma of CRF neurons in the dorsolateral BST. NE terminals formed synapses with dendrites of CRF neurons in the ventrolateral BST. In conclusion, catecholamine afferents can directly affect the contribution of CRF neurons of the BST to an animals response to stress.

Effect of glutamate stimulation of bed nucleus of the stria terminalis on arterial pressure and heart rate

Experiments were done in the chloralose-anesthetized, paralyzed, and artificially ventilated rat to determine the cardiovascular responses elicited during chemical stimulation of bed nucleus of the stria terminalis (BST) and to investigate the components of the peripheral autonomic nervous system that mediate these responses. Neurons in BST were selectively stimulated by the microinjection (10-20 nl) of the excitatory amino acid L-glutamate (1 M). Stimulation of BST elicited decreases in mean arterial pressure (n = 105) of -6 to -55 mmHg. These depressor responses were on occasion (n = 60) accompanied by decreases in heart rate ranging between -10 and -40 beats/min. The largest depressor responses were consistently elicited from a crescent-shaped region of BST around the dorsolateral, lateral, and ventrolateral surfaces of the anterior commissure. Intravenous administration of the muscarinic receptor blocker, atropine methylbromide, had no affect on the magnitude of the mean arterial pressure and heart rate responses. On the other hand, administration (intravenous) of the nicotinic receptor blocker, hexamethonium bromide or arfonad, abolished both the depressor response and cardiac slowing during stimulation of BST. These data suggest that the BST depressor and the bradycardia responses are mediated by inhibition of both sympathetic vasoconstrictor fibers to the vasculature and cardioacceleratory fibers to the heart, respectively.

Interleukin-1β has excitatory effects on neurons of the bed nucleus of the stria terminalis

Arginine vasopressin (AVP) is an endogenous antipyretic which acts in the ventral septal area (VSA) of the brain following its release from terminals of neurons from the bed nucleus of the stria terminalis (BST). The neurochemical mechanisms involved in the activation of these BST neurons are unknown. The present study was conducted to determine whether a naturally occurring brain cytokine (interleukin-1β, IL-1) selectively activates the population of BST neurons projecting to the VSA or another locus known to receive vasopressinergic input from the BST, the habenular nuclei (HAB). Single unit extracellular recordings were made from identified BST neurons in urethane-anesthetized rats. Human recombinant IL-1 applied iontophoretically or by micropressure, evoked marked excitations of long duration in 24% of all BST cells observed ( n = 102 cells). Iontophoresis of sodium salicylate attenuated or reversed the effects of the cytokine in all cases tested. The selective and long-lasting excitatory actions of IL-1 on BST neurons are consistent with a direct CNS function for this cytokine. In addition, these results are compatible with a role for IL-1 in evoking AVP release from BST neurons during fever.

Cardiovascular effects of neuronal activation of the extended amygdala in rats

The bed nucleus of the stria terminalis (BST) and the sublenticular substantia innominata (SI) are considered rostral extensions of the medial and central amygdaloid nuclei. In contrast to amygdaloid nuclei proper, the involvement of BST and SI neurons in cardiovascular control has not been studied. These areas were systematically explored in 35 urethane-anesthetized Wistar rats for sites from which changes in arterial pressure (AP) and heart rate (HR) could be obtained by injection of 20 nl of glutamate solutions (Glu, 0.5 M). Injections into 84 of the 130 histologically verified sites were followed after an8.0±0.7 s latency by depressor responses ranging from −4 to −33 (mean−13.3±0.8) mmHg, accompanied by variable changes in HR. Pressor responses were elicited from only 3 sites; 43 sites were not responsive. An additional group of 10 rats was instrumented for bilateral Glu injections (0.1 M, 200 nl per side) into the ventral division of the lateral BST and ventral BST and for the recording of AP, HR and regional blood flows measured with pulsed Doppler probes in the conscious state. In these rats, decreases in AP (−11.9±1.7mmHg) were accompanied by significant increases in hinquarter conductance (44.2±11.45), while renal and mesenteric vascular conductances remained unchanged. The fall in AP usually preceded the rise in hindquarer flow. These results suggest the existence of a depressor area in regions of the BST and SI, but the contribution of the elicited depressor effects in the overall central control of the circulation remains to be established.

Ventral subicular interaction with the hypothalamic paraventricular nucleus: evidence for a relay in the bed nucleus of the stria terminalis.

The axonal projections of the ventral subiculum to the bed nucleus of the stria terminalis (BST) were examined in the rat with the anterograde neuronal tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). Axons originating in the ventral subiculum coursed to the BST through either the fimbria-fornix, or a pathway involving the stria terminalis via the amygdala. Ventral subicular axons gave rise to dense terminal networks that were preferentially distributed in medial and ventral subregions of the BST. The distribution of subicular fibers and terminals was examined in relation to BST neurons that project to the hypothalamic paraventricular nucleus (PVN). In these cases, discrete iontophoretic injections of the retrograde tracer Fluoro-gold were made in the PVN, with PHA-L delivered to the ipsilateral ventral subiculum. An immunocytochemical double-labeling protocol was then employed for the simultaneous detection of PHA-L and Fluoro-gold, and provided light microscopic evidence for subicular input to PVN-projecting cells located within the BST. In a second series of experiments, the gamma-amino butyric acid (GABA)ergic nature of the BST was examined by in situ hybridization histochemistry for detection of transcripts encoding GAD67 mRNA. The studies revealed that a high proportion of BST neurons express GAD67 transcripts. Also, experiments combining Fluoro-gold tracing with GAD67 in situ hybridization suggested that a proportion of PVN-projecting neurons in the BST are GABAergic. Taken together, the results of these sets of studies suggest that the inhibitory influences of the hippocampus on the PVN might be relayed through specific portions of the BST. These findings may have important implications for our understanding of the neural regulation of the hypothalamic-pituitary-adrenal axis.

Fiber outgrowth from fetal vasopressin neurons of the suprachiasmatic nucleus, bed nucleus of the stria terminalis, and medial amygdaloid nucleus transplanted into adult Brattleboro rats

Outgrowth of fibers from different types of vasopressin (AVP) neurons was compared in the brains of AVP-deficient Brattleboro rats. Fetal grafts of the suprachiasmatic nucleus (SCN), the bed nucleus of the stria terminalis (BST), and the medial amygdaloid nucleus (MA) were implanted into the lateral ventricle. AVP-immunoreactive fibers from all grafts entered the host tissue in the lateral septum. SCN fibers were confined to the lateral margin of the septum. In contrast, MA and BST fibers formed equally dense networks spanning the width of the lateral septum. The data suggest that these transplanted neurons show specific outgrowth, and that the phylogenetically related BST and MA neurons follow similar cues to reach their targets.

Demonstration of distinct corticotropin releasing factor ? containing neuron populations in the bed nucleus of the stria terminalis. A light and electron microscopic immunocytochemical study in the rat

Immunocytochemical light and electron microscopic studies revealed two distinct populations of corticotropin releasing factor (CRF) - containing neurons, a dorsolateral and ventrolateral group, located in the bed nucleus of the stria terminalis (BST) of the rat brain. CRF neurons of the dorsolateral group had a smaller diameter and more primary dendrites than those of the ventrolateral group. CRF neurons in the dorsolateral BST had both somatic and dendritic spines, smooth contoured nuclei, and many dense and alveolate vesicles in their cytoplasm. Whereas, CRF neurons in the ventrolateral BST had only dendritic spines, irregularly-shaped indented nuclei and contained only alveolate vesicles in their cytoplasm. The only obvious difference in the type of unidentified afferents that synapsed on the CRF neurons of the BST could be attributed to the presence of the somatic spines on the CRF neurons of the dorsolateral population. Otherwise, the CRF neurons of the BST had a profuse innervation that included axosomatic, axospinous and axodendritic synapses. CRF-containing axons were distributed unevenly throughout the BST. The density of CRF axons was greatest in the lateral subdivisions of the BST, but the ventromedial BST contained many more CRF axons than the dorsomedial BST. The presence of these two CRF neuron populations in the BST suggests functional subdivision beyond previous proposals of a medial and lateral separation of function. Now there is additional morphological evidence to support the proposal of a dorsal and ventral separation of function within the BST.

Localization of DARPP-32 immunoreactive neurons in the bed nucleus of the stria terminalis and central nucleus of the amygdala: co-distribution with axons containing tyrosine hydroxylase, vasoactive intestinal polypeptide, and calcitonin gene-related peptide

The distribution and morphology of neurons containing the dopamine- and cyclic AMP-regulated phosphoprotein, DARPP-32, were investigated in the bed nucleus of the stria terminalis (BST) and the central nucleus of the amygdala (CeA). DARPP-32 immunoreactive neurons are numerous in both regions, but are restricted to the lateral dorsal and the lateral juxtacapsular subdivisions of the BST, and the central lateral and lateral capsular subdivisions of the CeA. Immunoreactive neurons in the lateral dorsal BST, and the central lateral and lateral capsular CeA are similar morphologically, while those in the juxtacapsular BST appear to be a subpopulation of striatal medium-sized spiny neurons. The distribution of DARPP-32 immunoreactive neurons in the BST and CeA overlaps considerably with axonal plexuses containing tyrosine hydroxylase (TH), vasoactive intestinal polypeptide (VIP), and calcitonin gene-related peptide (CGRP). These studies provide further evidence of the close relationship between the CeA and BST, and also provide anatomical evidence for possible interactions between neurotransmitters, neuropeptides, and phosphoproteins.

Bed nucleus of the stria terminalis: Cytoarchitecture, immunohistochemistry, and projection to the parabrachial nucleus in the rat

The bed nucleus of the stria terminalis (BST) sends a dense projection to the parabrachial nucleus (PB) in the pons. The BST contains many different types of neuropeptidelike immunoreactive cells and fibers, each of which exhibits its own characteristic distribution within cytoarchitecturally distinct BST subnuclei. Corticotropin releasing factor (CRF)-, neurotensin (NT)-, somatostatin (SS)-, and enkephalin (ENK)-like immunoreactive (ir) neurons are particularly numerous within areas of the BST that project to the PB. In this study, we use the combined retrograde fluorescence-immunofluorescence method to determine whether neurons in the BST that project to the PB contain these immunoreactivities. After Fast Blue injections into PB, retrogradely labeled neurons were numerous throughout the lateral part of the BST, particularly in the dorsal lateral (DL) and posterior lateral subnuclei. Retrogradely labeled neurons were also present in the preoptic, ventral lateral, and supracapsular BST subnuclei and in the parastrial nucleus. Many of the CRF-ir, NT-ir, and SS-ir neurons in DL were retrogradely labeled. A few double-labeled cells of each type were also found in the posterior lateral, ventral lateral and supracapsular BST subnuclei ENK-ir neurons were never retrogradely labeled. Our results show that BST neurons that project to the PB stain for the same neuropeptides as those in the central nucleus of the amygdala (CeA) that project to the PB, demonstrating further the close anatomical relations between these two structures.