Demonstration of peptidergic afferents to the bed nucleus of the stria terminalis using local injections of colchicine. A combined immunohistochemical and retrograde tracing study

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.

Sex-related differences in endogenous pituitary adenylate cyclase-activating polypeptide (PACAP) in the thalamic paraventricular nucleus: Implications for addiction neuroscience

Males and females exhibit differences in motivated and affective behavior; however, the neural substrates underlying these differences remain poorly understood. In the paraventricular nucleus of the thalamus (PVT), sex-related differences in neuronal activity have been identified in response to motivated behavior tasks and affective challenges. Within the PVT, the neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), is highly expressed and is also involved in motivated and affective behavior. The purpose of this study was to compare the expression of PACAP mRNA and peptide in the PVT of males and females. Analysis with quantitative real-time PCR in mice revealed that females had significantly higher levels of PACAP mRNA than males in the whole PVT, but no differences in the neuropeptides enkephalin or corticotropin releasing factor (CRF) in this brain region. While in rats, females demonstrated a trend for greater gene expression than males in the anterior/middle and middle/posterior PVT, they again showed no differences in enkephalin or CRF. Analysis with immunofluorescent histochemistry revealed that female mice had significantly more PACAP-containing cells than males as a function of area throughout the PVT, and that female rats had significantly more PACAP-27 and PACAP-38-containing cells than males, both as a percentage of total cells and as a function of PVT area. For PACAP-27, this specifically occurred in the anterior PVT, and for PACAP-38, it occurred throughout the anterior, middle, and posterior PVT. These results suggest that sex-related differences in PVT PACAP may underly some of the established sex-related differences in motivated and affective behavior.

Neural circuit control of innate behaviors

All animals possess a plethora of innate behaviors that do not require extensive learning and are fundamental for their survival and propagation. With the advent of newly-developed techniques such as viral tracing and optogenetic and chemogenetic tools, recent studies are gradually unraveling neural circuits underlying different innate behaviors. Here, we summarize current development in our understanding of the neural circuits controlling predation, feeding, male-typical mating, and urination, highlighting the role of genetically defined neurons and their connections in sensory triggering, sensory to motor/motivation transformation, motor/motivation encoding during these different behaviors. Along the way, we discuss possible mechanisms underlying binge-eating disorder and the pro-social effects of the neuropeptide oxytocin, elucidating the clinical relevance of studying neural circuits underlying essential innate functions. Finally, we discuss some exciting brain structures recurrently appearing in the regulation of different behaviors, which suggests both divergence and convergence in the neural encoding of specific innate behaviors. Going forward, we emphasize the importance of multi-angle and cross-species dissections in delineating neural circuits that control innate behaviors.

Expression and Distribution of Neuropeptide-Expressing Cells Throughout the Rodent Paraventricular Nucleus of the Thalamus

The paraventricular nucleus of the thalamus (PVT) has been shown to make significant contributions to affective and motivated behavior, but a comprehensive description of the neurochemicals expressed in the cells of this brain region has never been presented. While the PVT is believed to be composed of projection neurons that primarily use as their neurotransmitter the excitatory amino acid, glutamate, several neuropeptides have also been described in this brain region. In this review article, we combine published literature with our observations from the Allen Brain Atlas to describe in detail the expression and distribution of neuropeptides in cells throughout the mouse and rat PVT, with a special focus on neuropeptides known to be involved in behavior. Several themes emerge from this investigation. First, while the majority of neuropeptides are expressed across the antero-posterior axis of the PVT, they generally exist in a gradient, in which expression is most dense but not exclusive in either the anterior or posterior PVT, although other neuropeptides display somewhat more equal expression in the anterior and posterior PVT but have reduced expression in the middle PVT. Second, we find overall that neuropeptides involved in arousal are more highly expressed in the anterior PVT, those involved in depression-like behavior are more highly expressed in the posterior PVT, and those involved in reward are more highly expressed in the medial PVT, while those involved in the intake of food and drugs of abuse are distributed throughout the PVT. Third, the pattern and content of neuropeptide expression in mice and rats appear not to be identical, and many neuropeptides found in the mouse PVT have not yet been demonstrated in the rat. Thus, while significantly more work is required to uncover the expression patterns and specific roles of individual neuropeptides in the PVT, the evidence thus far supports the existence of a diverse yet highly organized system of neuropeptides in this nucleus. Determined in part by their location within the PVT and their network of projections, the function of the neuropeptides in this system likely involves intricate coordination to influence both affective and motivated behavior.

The Paraventricular Nucleus of the Thalamus Is an Important Node in the Emotional Processing Network

The paraventricular nucleus of the thalamus (PVT) has for decades been acknowledged to be an important node in the limbic system, but studies of emotional processing generally fail to incorporate it into their investigational framework. Here, we propose that the PVT should be considered as an integral part of the emotional processing network. Through its distinct subregions, cell populations, and connections with other limbic nuclei, the PVT participates in both major features of emotion: arousal and valence. The PVT, particularly the anterior PVT, can through its neuronal activity promote arousal, both as part of the sleep-wake cycle and in response to novel stimuli. It is also involved in reward, being both responsive to rewarding stimuli and itself affecting behavior reflecting reward, likely via specific populations of cells distributed throughout its subregions. Similarly, neuronal activity in the PVT contributes to depression-like behavior, through yet undefined subregions. The posterior PVT in particular demonstrates a role in anxiety-like behavior, generally promoting but also inhibiting this behavior. This subregion is also especially responsive to stressors, and it functions to suppress the stress response following chronic stress exposure. In addition to participating in unconditioned or primary emotional responses, the PVT also makes major contributions to conditioned emotional behavior. Neuronal activity in response to a reward-predictive cue can be detected throughout the PVT, and endogenous activity in the posterior PVT strongly predicts approach or seeking behavior. Similarly, neuronal activity during conditioned fear retrieval is detected in the posterior PVT and its activation facilitates the expression of conditioned fear. Much of this involvement of the PVT in arousal and valence has been shown to occur through the same general afferents and efferents, including connections with the hypothalamus, prelimbic and infralimbic cortices, nucleus accumbens, and amygdala, although a detailed functional map of the PVT circuits that control emotional responses remains to be delineated. Thus, while caveats exist and more work is required, the PVT, through its extensive connections with other prominent nuclei in the limbic system, appears to be an integral part of the emotional processing network.

Neurotensin in reward processes

Neurotensin (NTS) is a neuropeptide neurotransmitter expressed in the central and peripheral nervous systems. Many studies over the years have revealed a number of roles for this neuropeptide in body temperature regulation, feeding, analgesia, ethanol sensitivity, psychosis, substance use, and pain. This review provides a general survey of the role of neurotensin with a focus on modalities that we believe to be particularly relevant to the study of reward. We focus on NTS signaling in the ventral tegmental area, nucleus accumbens, lateral hypothalamus, bed nucleus of the stria terminalis, and central amygdala. Studies on the role of NTS outside of the ventral tegmental area are still in their relative infancy, yet they reveal a complex role for neurotensinergic signaling in reward-related behaviors that merits further study. This article is part of the special issue on 'Neuropeptides'.

Timing of Morphine Administration Differentially Alters Paraventricular Thalamic Neuron Activity

The paraventricular thalamic nucleus (PVT) is a brain region involved in regulating arousal, goal-oriented behaviors, and drug seeking, all key factors playing a role in substance use disorder. Given this, we investigated the temporal effects of administering morphine, an opioid with strongly addictive properties, on PVT neuronal function in mice using acute brain slices. Here, we show that morphine administration and electrophysiological recordings that occur during periods of animal inactivity (light cycle) elicit increases in PVT neuronal function during a 24-h abstinence time point. Furthermore, we show that morphine-induced increases in PVT neuronal activity at 24-h abstinence are occluded when morphine administration and recordings are performed during an animals' active state (dark cycle). Based on our electrophysiological results combined with previous findings demonstrating that PVT neuronal activity regulates drug-seeking behaviors, we investigated whether timing morphine administration with periods of vigilance (dark cycle) would decrease drug-seeking behaviors in an animal model of substance use disorder. We found that context-induced morphine-seeking behaviors were intact regardless of the time morphine was administered (e.g., light cycle or dark cycle). Our electrophysiological results suggest that timing morphine with various states of arousal may impact the firing of PVT neurons during abstinence. Although, this may not impact context-induced drug-seeking behaviors.

Neurotensin in the posterior thalamic paraventricular nucleus: inhibitor of pharmacologically relevant ethanol drinking

Individuals prone to ethanol overconsumption may have preexisting neurochemical disturbances that contribute to their vulnerability. This study examined the paraventricular nucleus of the thalamus (PVT), a limbic structure recently shown to participate in ethanol intake. To identify individuals prone to ethanol overconsumption, we tested Long-Evans rats in behavioral paradigms and found high levels of vertical time (rearing behavior) in a novel activity chamber to be a consistent predictor of subsequent excessive 20 percent ethanol drinking under the intermittent access model. Examining neurochemicals in the PVT, we found before ethanol exposure that prone rats with high rearing, compared with non-prone rats, had significantly lower levels of neurotensin (NTS) mRNA and peptide in the posterior (pPVT) but not anterior (aPVT) subregion of the PVT. Our additional finding that ethanol intake has no significant impact on either rearing or NTS levels indicates that these measures, which are different in prone rats before ethanol consumption, remain stable after ethanol consumption. The possibility that NTS directly controls ethanol drinking is supported by our finding that NTS administration specifically suppresses ethanol drinking when injected into the pPVT but not aPVT, with this effect occurring exclusively in higher drinkers that presumably have lower endogenous levels of NTS. Further, an NTS antagonist in the pPVT augments intake in lower drinkers with presumably more endogenous NTS, while NTS in the pPVT inhibits novelty-induced rearing that predicts excessive drinking. Together, these results provide strong evidence that low endogenous levels of NTS in the pPVT contribute to an increased propensity toward excessive ethanol drinking.

The intersection of stress and reward: BNST modulation of aversive and appetitive states

The bed nucleus of the stria terminalis (BNST) is widely acknowledged as a brain structure that regulates stress and anxiety states, as well as aversive and appetitive behaviours. The diverse roles of the BNST are afforded by its highly modular organisation, neurochemical heterogeneity, and complex intrinsic and extrinsic circuitry. There has been growing interest in the BNST in relation to psychopathologies such as anxiety and addiction. Although research on the human BNST is still in its infancy, there have been extensive preclinical studies examining the molecular signature and hodology of the BNST and their involvement in stress and reward seeking behaviour. This review examines the neurochemical phenotype and connectivity of the BNST, as well as electrophysiological correlates of plasticity in the BNST mediated by stress and/or drugs of abuse.

Pituitary Adenylate Cyclase-Activating Polypeptide-27 (PACAP-27) in the Thalamic Paraventricular Nucleus Is Stimulated by Ethanol Drinking

BACKGROUND

The paraventricular nucleus of the thalamus (PVT) is a limbic brain structure that affects ethanol (EtOH) drinking, but the neurochemicals transcribed in this nucleus that may participate in this behavior have yet to be fully characterized. The neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), is known to be transcribed in other limbic areas and to be involved in many of the same behaviors as the PVT itself, possibly including EtOH drinking. It exists in 2 isoforms, PACAP-38 and PACAP-27, with the former expressed at higher levels in most brain regions. The purpose of this study was to characterize PACAP in the PVT and to assess its response to EtOH drinking.

METHODS

First, EtOH-naïve, Sprague Dawley rats were examined using quantitative real-time polymerase chain reaction (qPCR) and immunohistochemistry, to characterize PACAP mRNA and peptide throughout the rostrocaudal axis of the PVT. Next, EtOH-naïve, vGLUT2-GFP transgenic mice were examined using immunohistochemistry, to identify the neurochemical phenotype of the PACAPergic cells in the PVT. Finally, Long Evans rats were trained to drink 20% EtOH under the intermittent-access paradigm and then examined with PCR and immunohistochemistry, to determine the effects of EtOH on endogenous PACAP in the PVT.

RESULTS

Gene expression of PACAP was detected across the entire PVT, denser in the posterior than the anterior portion of this nucleus. The protein isoform, PACAP-27, was present in a high percentage of cell bodies in the PVT, again particularly in the posterior portion, while PACAP-38 was instead dense in fibers. All PACAP-27⁺ cells colabeled with glutamate, which itself was identified in the majority of PVT cells. EtOH drinking led to an increase in PACAP gene expression and in levels of PACAP-27 in individual cells of the PVT.

CONCLUSIONS

This study characterizes the PVT neuropeptide, PACAP, and its understudied protein isoform, PACAP-27, and demonstrates that it is involved in pharmacologically relevant EtOH drinking. This indicates that PACAP-27 should be further investigated for its possible role in EtOH drinking.

A retrograde adeno-associated virus for collecting ribosome-bound mRNA from anatomically defined projection neurons

The brain contains a large variety of projection neurons with different functional properties. The functional properties of projection neurons arise from their connectivity with other neurons and their molecular composition. We describe a novel tool for obtaining the gene expression profiles of projection neurons that are anatomically defined by the location of their soma and axon terminals. Our tool utilizes adeno-associated virus serotype 9 (AAV9), which we found to retrogradely transduce projection neurons after injection at the site of the axon terminals. We used AAV9 to express Enhanced Green Fluorescent Protein (EGFP)-tagged ribosomal protein L10a (EGFP-L10a), which enables the immunoprecipitation of EGFP-tagged ribosomes and associated mRNA with a method known as Translating Ribosome Affinity Purification (TRAP). To achieve high expression of the EGFP-L10a protein in projection neurons, we placed its expression under control of a 1.3 kb alpha-calcium/calmodulin-dependent protein kinase II (Camk2a) promoter. We injected the AAV9-Camk2a-TRAP virus in either the hippocampus or the bed nucleus of the stria terminalis (BNST) of the mouse brain. In both brain regions the 1.3 kb Camk2a promoter did not confer complete cell-type specificity around the site of injection, as EGFP-L10a expression was observed in Camk2a-expressing neurons as well as in neuronal and non-neuronal cells that did not express Camk2a. In contrast, cell-type specific expression was observed in Camk2a-positive projection neurons that were retrogradely transduced by AAV9-Camk2a-TRAP. Injection of AAV9-Camk2a-TRAP into the BNST enabled the use of TRAP to collect ribosome-bound mRNA from basal amygdala projection neurons that innervate the BNST. AAV9-Camk2a-TRAP provides a single-virus system that can be used for the molecular profiling of anatomically defined projection neurons in mice and other mammalian model organisms. In addition, AAV9-Camk2a-TRAP may enable the discovery of protein synthesis events that support information storage in projection neurons.

Optogenetic strategies to investigate neural circuitry engaged by stress

Optogenetic techniques have given researchers unprecedented access to the function of discrete neural circuit elements and have been instrumental in the identification of novel brain pathways that become dysregulated in neuropsychiatric diseases. For example, stress is integrally linked to the manifestation and pathophysiology of neuropsychiatric illness, including anxiety, addiction and depression. Due to the heterogeneous populations of genetically and neurochemically distinct neurons in areas such as the bed nucleus of the stria terminalis (BNST), as well as their substantial number of projections, our understanding of how neural circuits become disturbed after stress has been limited. Using optogenetic tools, we are now able to selectively isolate distinct neural circuits that contribute to these disorders and perturb these circuits in vivo, which in turn may lead to the normalization of maladaptive behavior. This review will focus on current optogenetic strategies to identify, manipulate, and record from discrete neural circuit elements in vivo as well as highlight recent optogenetic studies that have been utilized to parcel out BNST function.

Role of bed nucleus of the stria terminalis and amygdala AMPA receptors in the development and expression of context conditioning and sensitization of startle by prior shock

A core symptom of post-traumatic stress disorder is hyper-arousal-manifest in part by increases in the amplitude of the acoustic startle reflex. Gewirtz et al. (Prog Neuropsychopharmacol Biol Psychiatry 22:625-648, 1998) found that, in rats, persistent shock-induced startle increases were prevented by pre-test electrolytic lesions of the bed nucleus of the stria terminalis (BNST). We used reversible inactivation to determine if similar effects reflect actions on (a) BNST neurons themselves versus fibers-of-passage, (b) the development versus expression of such increases, and (c) associative fear versus non-associative sensitization. Twenty-four hours after the last of three shock sessions, startle was markedly enhanced when rats were tested in a non-shock context. These increases decayed over the course of several days. Decay was unaffected by context exposure, and elevated startle was restored when rats were tested for the first time in the original shock context. Thus, both associative and non-associative components could be measured under different conditions. Pre-test intra-BNST infusions of the AMPA receptor antagonist NBQX (3 μg/side) blocked the non-associative (as did infusions into the basolateral amygdala) but not the associative component, whereas pre-shock infusions disrupted both. NBQX did not affect baseline startle or shock reactivity. These results indicate that AMPA receptors in or very near to the BNST are critical for the expression and development of non-associative shock-induced startle sensitization, and also for context fear conditioning, but not context fear expression. More generally, they suggest that treatments targeting the BNST may be clinically useful for treating trauma-related hyper-arousal and perhaps for retarding its development.

Corticotropin-releasing factor modulation of forebrain GABAergic transmission has a pivotal role in the expression of anabolic steroid-induced anxiety in the female mouse

Increased anxiety is commonly observed in individuals who illicitly administer anabolic androgenic steroids (AAS). Behavioral effects of steroid abuse have become an increasing concern in adults and adolescents of both sexes. The dorsolateral bed nucleus of the stria terminalis (dlBnST) has a critical role in the expression of diffuse anxiety and is a key site of action for the anxiogenic neuromodulator, corticotropin releasing factor (CRF). Here we demonstrate that chronic, but not acute, exposure of female mice during adolescence to AAS augments anxiety-like behaviors; effects that were blocked by central infusion of the CRF receptor type 1 antagonist, antalarmin. AAS treatment selectively increased action potential (AP) firing in neurons of the central amygdala (CeA) that project to the dlBnST, increased the frequency of GABA(A) receptor-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) in dlBnST target neurons, and decreased both c-FOS immunoreactivity (IR) and AP frequency in these postsynaptic cells. Acute application of antalarmin abrogated the enhancement of GABAergic inhibition induced by chronic AAS exposure whereas application of CRF to brain slices of naïve mice mimicked the actions of this treatment. These results, in concert with previous data demonstrating that chronic AAS treatment results in enhanced levels of CRF mRNA in the CeA and increased CRF-IR in the dlBnST neuropil, are consistent with a mechanism in which the enhanced anxiety elicited by chronic AAS exposure involves augmented inhibitory activity of CeA afferents to the dlBnST and CRF-dependent enhancement of GABAergic inhibition in this brain region.

Characterization of the bed nucleus of the stria terminalis in the forebrain of anuran amphibians

Major common features have been reported for the organization of the basal telencephalon in amniotes, and most characteristics were thought to be acquired in the transition from anamniotes to amniotes. However, gene expression, neurochemical, and hodological data obtained for the basal ganglia and septal and amygdaloid complexes in amphibians (anamniotic tetrapods) have strengthened the idea of a conserved organization in tetrapods. A poorly characterized region in the forebrain of amniotes has been the bed nucleus of the stria terminalis (BST), but numerous recent investigations have characterized it as a member of the extended amygdala. Our study analyzes the main features of the BST in anuran amphibians to establish putative homologies with amniotes. Gene expression patterns during development identified the anuran BST as a subpallial, nonstriatal territory. The BST shows Nkx2.1 and Lhx7 expression and contains an Islet1-positive cell subpopulation derived from the lateral ganglionic eminence. Immunohistochemistry for diverse peptides and neurotransmitters revealed that the distinct chemoarchitecture of the BST is strongly conserved among tetrapods. In vitro tracing techniques with dextran amines revealed important connections between the BST and the central and medial amygdala, septal territories, medial pallium, preoptic area, lateral hypothalamus, thalamus, and prethalamus. The BST receives dopaminergic projections from the ventral tegmental area and is connected with the laterodorsal tegmental nucleus and the rostral raphe in the brainstem. All these data suggest that the anuran BST shares many features with its counterpart in amniotes and belongs to a basal continuum, likely controlling similar reflexes, reponses, and behaviors in tetrapods.

Phasic and sustained fear are pharmacologically dissociable in rats

Previous findings suggest differences in the neuroanatomical substrates of short- (seconds) vs longer-duration (minutes) fear responses. We now report that phasic and sustained fear can also be differentiated pharmacologically, based on their response to several treatments that either are or are not clinically effective anxiolytics. For these experiments, short- or long-duration clicker stimuli were paired with footshock. Acoustic startle amplitude was later measured in the absence of the clicker, or within seconds (phasic fear) or minutes (sustained fear) of its onset. Before testing, rats received a single injection of vehicle, the benzodiazepine chlordiazepoxide, the 5HT(1A) agonist and dopamine D2 antagonist buspirone, the selective serotonin reuptake inhibitor fluoxetine, or a 3-week treatment with either vehicle or fluoxetine. Chlordiazepoxide blocked sustained, but not phasic startle increases. Acute buspirone, which is not anxiolytic in human beings, did not affect sustained startle increases, but did disrupt phasic increases. Chronic fluoxetine blocked sustained startle increases and unreliably reduced phasic increases; acute fluoxetine affected neither. The results indicate that phasic and sustained fear responses can be pharmacologically dissociated, further validating this distinction, and suggest that sustained startle increases may be especially useful as anxiety models and anxiolytic screens.

Distribution and axonal projections of neurons coexpressing thyrotropin-releasing hormone and urocortin 3 in the rat brain

Thyrotropin-releasing hormone (TRH) decreases food intake when administered intracerebroventricularly or into the ventromedial hypothalamus. However, it is unknown which population of TRH neurons exerts this anorexigenic function. In the rostral perifornical area, the pattern of TRH-expressing neurons is reminiscent of the distribution of neurons expressing urocortin3 (Ucn3) that also inhibits feeding when injected into the hypothalamic ventromedial nucleus (VMN). Since colocalization of TRH and Ucn3 may help to identify feeding-related TRH neurons, the putative coexpression of the two peptides was examined using fluorescent in situ hybridization combined with immunofluorescence. Almost all (95.5 +/- 0.2%) Ucn3-immunoreactive neurons in the perifornical area expressed pro-TRH mRNA, while 50.2 +/- 1.6% Ucn3 neurons were double-labeled in the bed nucleus of the stria terminalis (BNST). Only a few Ucn3/pro-TRH neurons were found outside these two areas. The distribution of axons containing both Ucn3 and TRH was examined by dual immunofluorescence. Ucn3/TRH fibers heavily innervated the VMN. In addition, high densities of double-labeled axons were observed in the lateral septal nucleus, posterior division of the BNST, medial amygdaloid nucleus, amygdalohippocampal area, and ventral hippocampus, forebrain areas associated with psychological stress and anxiety. We conclude that Ucn3 and TRH are coexpressed in a discrete, continuous population of neurons in the perifornical area and BNST, making Ucn3 a neurochemical marker to define a distinct subset of TRH neurons. The distribution of their axons suggests that Ucn3/TRH neurons may coordinate feeding and behavioral responses to stressful stimuli.

Mu-opioid and corticotropin-releasing-factor receptors show largely postsynaptic co-expression, and separate presynaptic distributions, in the mouse central amygdala and bed nucleus of the stria terminalis

The anxiolytic effects of opiates active at the mu-opioid receptor (mu-OR) may be ascribed, in part, to suppression of neurons that are responsive to the stress-associated peptide, corticotropin releasing factor (CRF), in the central amygdala (CeA) and bed nucleus of the stria terminalis (BNST). The corticotropin releasing factor receptor (CRFr) and mu-OR are expressed in both the CeA and BNST, but their subcellular relationship to each other is not known in either region. To address this question, we used dual electron microscopic immunolabeling of mu-OR and CRFr in the mouse lateral CeA and anterolateral BNST. Immunolabeling for each receptor was detected in the same as well as in separate somatic, dendritic and axonal profiles of neurons in each region. CRFr had a plasmalemmal or cytoplasmic distribution in many dendrites, including those co-expressing mu-OR. The co-expression of CRFr and mu-OR also was seen near excitatory-type synapses on dendritic spines. In both the CeA and BNST, over 50% of the CRFr-labeled dendritic profiles (dendrites and spines) contained immunoreactivity for the mu-OR. However, less than 25% of the dendritic profiles containing the mu-OR were labeled for CRFr in either region, suggesting that opiate activation of the mu-OR affects many neurons in addition to those responsive to CRF. The dendritic profiles containing CRFr and/or mu-OR received asymmetric, excitatory-type synapses from unlabeled or CRFr-labeled axon terminals. In contrast, the mu-OR was identified in terminals forming symmetric, inhibitory-type synapses. Thus, in both the CeA and BNST, mu-OR and CRFr have strategic locations for mediation of CRF and opioid effects on the postsynaptic excitability of single neurons, and on the respective presynaptic release of excitatory and inhibitory neurotransmitters. The commonalities in the synaptic location of both receptors in the CeA and BNST suggest that this is a fundamental cellular association of relevance to both drug addiction and stress-induced disorders.

Differential Expression of Intrinsic Membrane Currents in Defined Cell Types of the Anterolateral Bed Nucleus of the Stria Terminalis

The anterolateral group of the bed nucleus of the stria terminalis (BNSTALG) plays a critical role in a diverse array of behaviors, although little is known of the physiological properties of neurons in this region. Using whole cell patch-clamp recordings from rat BNSTALG slices in vitro, we describe three distinct physiological cell types. Type I neurons were characterized by the presence of a depolarizing sag in response to hyperpolarizing current injection that resembled activation of the hyperpolarization-activated cation current Ih and a regular firing pattern in response to depolarizing current injection. Type II neurons exhibited the same depolarizing sag in response to hyperpolarizing current injection, but burst-fired in response to depolarizing current injection, which was indicative of the activation of the low-threshold calcium current IT. Type III neurons did not exhibit a depolarizing sag in response to hyperpolarizing current injection, but instead exhibited a fast time-independent rectification that became more pronounced with increased amplitude of hyperpolarizing current injection, and was indicative of activation of the inwardly rectifying potassium current IK(IR). Type III neurons also exhibited a regular firing pattern in response to depolarizing current. Using voltage-clamp analysis we further characterized the primary active currents that shaped the physiological properties of these distinct cell types, including Ih, IT, IK(IR), the voltage-dependent potassium current IA, and the persistent sodium current INaP. The functional relevance of each cell type is discussed in relation to prior anatomical studies, as well as how these currents may interact to modulate neuronal activity within the BNSTALG.

Cocaine pre-exposure produces a sensitized and context-specific c-fos mRNA response to footshock stress in the central nucleus of the AMYGDALA

In recent years, there has been growing interest in the putative relationship between stress and vulnerability to relapse in former drug addicts. In animal studies aimed at exploring this relationship, it has been shown that brief exposure to intermittent footshock stress produces reliable reinstatement of drug seeking after prolonged drug-free periods. Whereas footshock reinstates drug seeking, it does not reinstate behaviors maintained by non-drug reinforcers, suggesting that prior drug experience may produce a form of sensitization within neuronal systems that mediate stress-induced reinstatement. The primary objective of the present experiments was to determine whether pre-exposure to cocaine produces a long-lasting, sensitized neuronal response to footshock stress within two brain regions known to mediate footshock-induced reinstatement; the central nucleus of the amygdala (CeA) and bed nucleus of the stria terminalis (BNST). In experiment 1, animals were injected for 7 days with cocaine (days 1 and 7 in test chambers; days 2-6 in homecages) or saline. After 21 drug-free days, they were exposed to footshock or no footshock. In experiment 2, rats were injected daily for 7 days with cocaine in one of two contexts and saline in the alternate context. After 21 drug-free days, they were given footshock either in the same context that they were given cocaine in or the alternate context. In CeA, footshock produced enhanced expression of c-fos mRNA in cocaine, but not saline, pre-exposed animals. Furthermore, this effect was gated by the environmental context in which cocaine was given; footshock only enhanced c-fos mRNA expression when it was given in a context that had previously been paired with cocaine. Although footshock induced c-fos mRNA expression in the BNST, its effects in this region were not dependent on drug history. The major findings are that a history of cocaine exposure produces sensitization to an acute stressor within CeA, and this effect is gated by environmental context.

A critical role for the parabrachial nucleus in generating central nervous system responses elicited by a systemic immune challenge

Using Fos immunolabelling as a marker of neuronal activation, we investigated the role of the parabrachial nucleus in generating central neuronal responses to the systemic administration of the proinflammatory cytokine interleukin-1beta (1 microg/kg, i.a.). Relative to intact animals, parabrachial nucleus lesions significantly reduced the number of Fos-positive cells observed in the central amygdala (CeA), the bed nucleus of the stria terminalis (BNST), and the ventrolateral medulla (VLM) after systemic interleukin-1beta. In a subsequent experiment in which animals received parabrachial-directed deposits of a retrograde tracer, it was found that many neurons located in the nucleus tractus solitarius (NTS) and the VLM neurons were both retrogradely labelled and Fos-positive after interleukin-1beta administration. These results suggest that the parabrachial nucleus plays a critical role in interleukin-1beta-induced Fos expression in CeA, BNST and VLM neurons and that neurons of the NTS and VLM may serve to trigger or at least influence changes in parabrachial nucleus activity that follows systemic interleukin-1beta administration.

Effects of chronic cocaine exposure on corticotropin-releasing hormone binding protein in the central nucleus of the amygdala and bed nucleus of the stria terminalis

The neuropeptide, corticotropin-releasing hormone (CRH), has been shown to play a role in behavioral and neurobiological effects of drugs of abuse. An important modulator of CRH, the CRH binding protein (CRH-BP), has not, on the other hand, been assessed for its role in drug-associated effects. The primary objective of the present experiment was to assess whether prior, chronic exposure to cocaine modulates expression of CRH-BP, and to compare expression of the BP with that of the peptide itself. We assessed CRH-BP and CRH mRNA expression in two brain regions where CRH is known to affect responses to drugs of abuse; namely, the central nucleus of the amygdala (CeA) and bed nucleus of the stria terminalis (BNST). Male Long-Evans rats were given 14 daily injections of cocaine (30 mg/kg, i.p.) or saline. One, 3, 10, 28, or 42 days post-treatment, animals were killed and adjacent brain sections through the CeA and BNST were processed for CRH-BP and CRH by in situ hybridization. In the CeA, cocaine pre-exposure increased both CRH and CRH-BP mRNA expression 1 day post-treatment. In the dorsal BNST, cocaine pre-exposure elevated levels of CRH-BP, but not CRH, mRNA 3 days post-treatment. Taken together, the results suggest that withdrawal-induced changes in the expression of the CRH-BP, and CRH itself, are relatively short-lived and that a dysregulation in basal expression of either gene is not likely responsible for long-lasting behavioral effects noted with cocaine and other drugs of abuse.

Stress-induced relapse to drug seeking in the rat: role of the bed nucleus of the stria terminalis and amygdala

There is growing interest in the role that the bed nucleus of the stria terminalis (BNST) and central nucleus of the amygdala (CeA), components of the extended amygdala, play in drug addiction. Within the BNST and CeA, there is an extensive system of intrinsic, primarily GABAergic, interconnections known to synthesize a variety of neuropeptides, including corticotrophin-releasing factor (CRF). The actions of CRF at extrahypothalamic sites,including the BNST and CeA, have been implicated in stress responses and in the aversive effects of withdrawal from drugs of abuse. Most recently, we have shown a critical role for extrahypothalamic CRF in stress-induced reinstatement of drug seeking in rats. In attempting to determine which brain circuitry mediates the effect of stress on relapse and, more specifically, where in the brain CRF acts to initiate the behaviours involved in relapse, we focused on the BNST and CeA. In the present paper, we summarize studies we have conducted that explore the role of these brain sites in stress-induced relapse to heroin and cocaine seeking, and then consider how our findings can be understood within the more general context of what is known about the role of the BNST and CeA in stress-related and general approach behaviours, such as drug seeking.

The innervation of the human antro-pyloric region: Organization and composition

Although the composition of the gastric innervation has been determined in animal models, relatively little known about the innervation of the human antro-pyloric region. We used immunocytochemical techniques to establish the localization and co-expression of neuropeptides and nitric oxide in the human antrum and upper duodenum. Our results demonstrate the existence of a clearly defined submucosal plexus in the antral region that is absent in rats and guinea pigs. The abundant innervation of the lamina propria contains 3 major nerve populations: VIP- and NOS-, SP- and CGRP-, and GRP-immunoreactive. For the first time, NOS-containing nerve fibers were observed throughout the length of the antral glands. Within the antrum somatostatin was confined to endocrine cells, however, at the pyloric sphincter both enteric plexi contained immunoreactive neurons and nerve fibres. Within the pyloric sphincter CGRP- and SP-immunoreactive fibres were significantly increased, correlating with the presence of large ganglia in the submucosal plexus. In conclusion, the organization and composition of the innervation of human antro-pylorus differed substantially from that reported in other mammals. The presence of an abundant mucosal innervation paralled by a well-defined submucosal plexus indicates that the functional regulation of the gastric–pyloric region will be distinct from that of smaller animal models.Key words: gastric innervation, pyloric sphincter, neuropeptides, nitric oxide, somatostatin.

Axon terminals containing CGRP-immunoreactivity form synapses with CRF- and Met-enkephalin-immunopositive neurons in the laterodorsal division of the bed nucleus of the stria terminalis in the rat

The lateral division of the bed nucleus of the stria terminalis (BSTL) is an important forebrain structure that relays information between limbic structures and the hypothalamus. The BSTL displays a very dense calcitonin gene-related peptide-immunoreactive (-ir) fiber terminal network, and contains a substantial number of the corticotropin releasing factor (CRF)-ir neurons. Several Met-enkephalin-ir perikarya have also been observed in the BSTL. The distributions of CRF- and Met-enkephalin-ir neurons and that of the calcitonin gene-related peptide (CGRP)-ir axon terminals overlap within the BSTL, suggesting synaptic connections between CRF- and Met-enkephalin-ir neurons and axon terminals immunoreactive for CGRP. Double staining immunohistochemistry revealed that CGRP-ir axon terminals were within close proximity to dendrites or perikarya of corticotropin releasing factor and Met-enkephalin-ir neurons. When viewed at the electron microscopic level, axodendritic or axosomatic synapses between CGRP-ir fiber terminals and neurons immunoreactive for CRF and Met-enkephalin were detected. Most of the CRF-ir neurons project to brainstem centers, which modulate the physiological changes accompanying stress, whereas the Met-enkephalin-ir perikarya are most likely interneurons that often colocalize with GABA. The parabrachial nucleus, a vital autonomic center, is the primary source of CGRP-ir fiber terminals to the BSTL. The synaptic contacts between the CGRP axon terminals and CRF- and Met-enkephalin-ir neurons underlie the importance of connections between autonomic brainstem centers and BSTL, which can be fundamental in the modulatory control of endocrine, physiological and behavioral responses during stress.

Associative fear conditioning of enkephalin mRNA levels in central amygdalar neurons

The central nucleus of the amygdala (CEA) is required for the expression of learned fear responses. This study used in situ hybridization to show that mRNA levels of the neuropeptide enkephalin are increased in CEA neurons after rats are placed in an environment that they associate with an unpleasant experience. In contrast, mRNA levels of another neuropeptide, corticotropin releasing hormone, do not change under the same conditions in the CEA of the same rats. Conditioned neuropeptide levels in amygdalar circuits may act as a reversible "gain control" for long-term modulation of subsequent fear responses.

The source of origin of PACAP- and VIP-immunoreactive fibers in the laterodorsal division of the bed nucleus of the stria terminalis in the rat

The bed nucleus of the stria terminalis (BSTL), which is known to be involved in the modulation of stress responses, exhibits a dense network of pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) immunoreactive (ir) fibers. The origin of the PACAP-ir fibers is unknown, and the origin of the VIP-ir fibers remains uncertain. The most important brain regions connected to the BSTL are the amygdaloid nuclei, the paraventricular and ventromedial hypothalamic nuclei, mesencephalic periaqueductal grey, the dorsal and linear raphe nuclei, the parabrachial nucleus, and the dorsal vagal complex. After microinjecting cholera toxin B subunit (CTB) in the BSTL as a retrograde tracer, neurons were double labeled for CTB and PACAP or VIP immunohistochemistry and the cells from which the PACAP- and VIP-ir fiber networks in the BSTL originated were identified. Cholera toxin B subunit labeled and VIP-ir cells were found in the mesencephalic periaqueductal grey and the dorsal and linear raphe nuclei, but no double labeled cells were seen in the amygdaloid nuclei or the hypothalamic region. CTB- and PACAP-ir neurons were observed in the paraventricular nucleus and the dorsal vagal complex. No double labeled perikarya were seen in the parabrachial nucleus or in the amygdaloid nuclei.

Patterns of c-fos expression induced by fluvoxamine are different after acute vs. chronic oral administration

Fluvoxamine is a selective serotonin (5-HT) reuptake inhibitor (SSRI) with a broad spectrum of behavioral and therapeutic effects, e.g. in depressive illness. We used the expression of c-fos, after both acute and chronic oral administration of fluvoxamine in the rat, to study its immediate and long-term effects, in relation to the distribution of Galanin (GAL) and Vasoactive Intestinal Polypeptide (VIP). After acute oral administration, most consistent increases were apparent in (parts of); the nucleus of the solitary tract, medial part; the lateral parabrachial nucleus, external part; the bed nucleus of the stria terminalis, dorsolateral part; and the central nucleus of the amygdala, lateral part. After chronic administration, distribution of Fos-IR was similar to acute administration, although numbers of Fos-IR neurons were no longer significantly different from control values. It is concluded that activation of 5-HT3-receptors in the caudal brainstem or gastro-intestinal afferents of the vagal nerve may play a role in the observed pattern of Fos-IR after fluvoxamine administration. The relationship with the antidepressant effects of fluvoxamine needs further investigations.

Changing pattern of oxytocin-induced excitation of neurons in the bed nuclei of the stria terminalis and ventrolateral septum in the peripartum period

Oxytocin acts within the limbic system (bed nuclei of the stria terminalis and ventrolateral septum) to induce maternal behaviour and to facilitate neuroendocrine activity at specific times during the peripartum period. Studies were undertaken to determine whether the timing of these effects arises from modulation of the oxytocin-induced excitation of limbic neurons. Extracellular activity of single units was recorded on urethane-anaesthetized rats and neurons were tested for responses to intracerebroventricular injection of 1.1 ng oxytocin. In the first part, animals were recorded on days 19 and 22 of pregnancy and on days 3 and 5 of lactation. No significant differences in the basal firing rates or in the proportion of oxytocin-responsive neurons were detected, but responses by neurons on day 22 of pregnancy occurred after a significant delay (10.7 +/- 2.0 min), resulting in a smaller overall response compared to the other groups. These differences in the pattern of response were not due to changes in density of oxytocin binding in the limbic areas studied, since autoradiographic detection of oxytocin binding sites using the iodinated antagonist [125I]d(CH2)5[Tyr(Me)2, Thr4, Orn3, Tyr-NH2(9)]-vasotocin showed no differences between the pregnant and postpartum animals. In the second part, parturient animals (day 22 of pregnancy) received intravenous injection of the long-acting opioid antagonist naltrexone, or unilateral knife-cut lesions to the stria terminalis, a source of inhibitory inputs (including enkephalinergic) to the bed nuclei of the stria terminalis and ventrolateral septum. Both treatments abolished the characteristic delay of oxytocin-induced excitation in non-treated animals on day 22 of pregnancy, and increased the overall excitatory response. Thus, during the peripartum period, a population of limbic neurons sensitive to oxytocin display a dynamically changing pattern of excitatory responses, apparently modulated by an endogenous opioid cone and independent of changes in oxytocin receptor expression. The attenuated neuronal response to central oxytocin seen on the day of parturition could account for the absence of a facilitatory effect of oxytocin on neuroendocrine activity at this time.

Physiological mapping of local inhibitory inputs to the hypothalamic paraventricular nucleus

Local inhibitory synaptic inputs to neurons of the rat hypothalamic paraventricular nucleus (PVN) were studied by using glutamate microstimulation and conventional intracellular and whole-cell patch-clamp recording in coronal, horizontal, and parasagittal slices of rat hypothalamus. PVN cells were classified as magnocellular or parvocellular neurons on the basis of electrophysiological and post hoc immunohistochemical analyses; GABA-producing neurons were localized with in situ hybridization. Glutamate microstimulation of different sites around the PVN evoked volleys of postsynaptic potentials in 43% of the PVN neurons tested. Some responses to stimulation at each site were blocked by bicuculline, suggesting that they were mediated by the activation of presynaptic GABA neurons. In the coronal plane, presynaptic inhibitory sites were located lateral to the PVN and ventral to the fornix, corresponding to the lateral hypothalamic area and the posterior bed nucleus of the stria terminalis (BNST). In the horizontal plane, presynaptic inhibitory sites were found rostral, lateral, and caudal to the nucleus, corresponding to parts of the anterior hypothalamic area, the posterior BNST, the medial preoptic area, and the dorsomedial hypothalamus. In the parasagittal plane, presynaptic inhibitory neurons were revealed at sites rostral and caudal to the nucleus, corresponding to the medial preoptic area and the dorsomedial hypothalamus, and in a site dorsal to the optic chiasm that included the suprachiasmatic nucleus. These presynaptic sites each contained GABA-producing neurons based on in situ hybridization with a glutamic acid decarboxylase riboprobe and together formed a three-dimensional ring around the PVN. Unexpectedly, both magnocellular and parvocellular neurons received inhibitory synaptic inputs from common sites.

Opposite changes in the expression of enkephalin in the amygdala and hypothalamus after lesions of the bed nucleus of the stria terminalis in the rat

The expression of enkephalin in neurons of the rat forebrain was studied by in situ hybridization and immunohistochemistry after unilateral injections of ibotenic acid into the bed nucleus of the stria terminalis. Initially, we observed that the destruction of nerve cell bodies in this nucleus resulted in a prominent bilateral increase in the number of neuronal perikarya immunoreactive for [Met]enkephalin in the lateral/basolateral amygdaloid complex-especially in the anterior division of the latter nucleus-as compared with NaCl-injected rats. In a separate set of experiments, this effect was associated with a significant (two times) enhancement of the number of nerve cell bodies containing preproenkephalin A messenger RNAs in the same amygdaloid nucleus ipsilateral to the injection, as compared with controls. In the hypothalamus of both experimental and control rats, the nerve cell bodies immunoreactive for [Met]enkephalin were few since the animals were not pretreated with colchicine, and the effects of the lesion were difficult to appreciate. However, using in situ hybridization, numerous nerve cell bodies containing preproenkephalin A messenger RNAs were detected bilaterally in the perifornical area, the paraventricular (parvocellular division) and the ventromedial nuclei of the hypothalamus. In the latter nucleus, the lesion of the bed nucleus of the stria terminalis resulted in a strong decrease (about two times) in the number of labelled cell bodies as compared with the controls, whereas no significant changes were found bilaterally in the paraventricular nucleus. In agreement with some data of the literature, our results indicate that the bed nucleus of the stria terminalis plays an important role in the regulation of neuropeptide genes expression in certain regions of the limbic system. Such a role is often exerted by nerve fibres afferents to the nerve cell bodies considered. However, from numerous neuroanatomical data of the literature, it appears more probable that the induction or inhibition of the expression of enkephalin in presynaptic neurons is due to the disappearance of their postsynaptic target in the bed nucleus of the stria terminalis.

A sex difference in the human brain and its relation to transsexuality

Transsexuals have the strong feeling, often from childhood onwards, of having been born the wrong sex. The possible psychogenic or biological aetiology of transsexuality has been the subject of debate for many years. Here we show that the volume of the central subdivision of the bed nucleus of the stria terminals (BSTc), a brain area that is essential for sexual behaviour, is larger in men than in women. A female-sized BSTc was found in male-to-female transsexuals. The size of the BSTc was not influenced by sex hormones in adulthood and was independent of sexual orientation. Our study is the first to show a female brain structure in genetically male transsexuals and supports the hypothesis that gender identity develops as a result of an interaction between the developing brain and sex hormones.