Corticotropin-releasing factor enhances inhibitory synaptic transmission to type III neurons in the bed nucleus of the stria terminalis

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

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

Corticotropin releasing factor and norepinephrine related circuitry changes in the bed nucleus of the stria terminalis in stress and alcohol and substance use disorders

Alcohol Use Disorder (AUD) affects around 14.5 million individuals in the United States, with Substance Use Disorder (SUD) affecting an additional 8.3 million individuals. Relapse is a major barrier to effective long-term treatment of this illness with stress often described as a key trigger for a person with AUD or SUD to relapse during a period of abstinence. Two signaling molecules, norepinephrine (NE) and corticotropin releasing factor (CRF), are released during the stress response, and also play important roles in reward behaviors and the addiction process. Within the addiction literature, one brain region in which there has been increasing research focus in recent years is the bed nucleus of the stria terminalis (BNST). The BNST is a limbic structure with numerous cytoarchitecturally and functionally different subregions that has been implicated in drug-seeking behaviors and stress responses. This review focuses on drug and stress-related neurocircuitry changes in the BNST, particularly within the CRF and NE systems, with an emphasis on differences and similarities between the major dorsal and ventral BNST subregions.

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

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

Inhibitory synaptic transmissions to the bed nucleus of the stria terminalis neurons projecting to the ventral tegmental area are enhanced in rats exposed to chronic mild stress

The comorbidities of depression and chronic pain have long been recognized in the clinic, and several preclinical studies have demonstrated depression-like behaviors in animal models of chronic pain. These findings suggest a common neuronal basis for depression and chronic pain. Recently, we reported that the mesolimbic dopaminergic system was tonically suppressed during chronic pain by enhanced inhibitory synaptic inputs to neurons projecting from the dorsolateral bed nucleus of the stria terminalis (dlBNST) to the ventral tegmental area (VTA), suggesting that tonic suppression of the mesolimbic dopaminergic system by this neuroplastic change may be involved in chronic pain-induced depression-like behaviors. In this study, we hypothesized that inhibitory synaptic inputs to VTA-projecting dlBNST neurons are also enhanced in animal models of depression, thereby suppressing the mesolimbic dopaminergic system. To test this hypothesis, we performed whole-cell patch-clamp electrophysiology using brain slices prepared from rats exposed to chronic mild stress (CMS), a widely used animal model of depression. The results showed a significant enhancement in the frequency of spontaneous inhibitory postsynaptic currents in VTA-projecting dlBNST neurons in the CMS group compared with the no stress group. The findings revealed enhanced inhibitory synaptic inputs to VTA-projecting dlBNST neurons in this rat model of depression, suggesting that this neuroplastic change is a neuronal mechanism common to depression and chronic pain that causes dysfunction of the mesolimbic dopaminergic system, thereby inducing depression-like behaviors.

Tonic Suppression of the Mesolimbic Dopaminergic System by Enhanced Corticotropin-Releasing Factor Signaling Within the Bed Nucleus of the Stria Terminalis in Chronic Pain Model Rats

Although dysfunction of the mesolimbic dopaminergic system has been implicated in chronic pain, the underlying mechanisms remain to be elucidated. We hypothesized that increased inhibitory inputs to the neuronal pathway from the dorsolateral bed nucleus of the stria terminalis (dlBNST) to the ventral tegmental area (VTA) during chronic pain may induce tonic suppression of the mesolimbic dopaminergic system. To test this hypothesis, male Sprague Dawley rats were subjected to spinal nerve ligation to induce neuropathic pain and then spontaneous IPSCs (sIPSCs) were measured in this neuronal pathway. Whole-cell patch-clamp electrophysiology of brain slices containing the dlBNST revealed that the frequency of sIPSCs significantly increased in VTA-projecting dlBNST neurons 4 weeks after surgery. Next, the role of corticotropin-releasing factor (CRF) signaling within the dlBNST in the increased sIPSCs was examined. CRF increased the frequency of sIPSCs in VTA-projecting dlBNST neurons in sham-operated controls, but not in chronic pain rats. By contrast, NBI27914, a CRF type 1 receptor antagonist, decreased the frequency of sIPSCs in VTA-projecting dlBNST neurons in the chronic pain rats, but not in the control animals. In addition, histological analyses revealed the increased expression of CRF mRNA in the dlBNST. Finally, bilateral injections of NBI27914 into the dlBNST of chronic pain rats activated mesolimbic dopaminergic neurons and induced conditioned place preference. Together, these results suggest that the mesolimbic dopaminergic system is tonically suppressed during chronic pain by enhanced CRF signaling within the dlBNST via increased inhibitory inputs to VTA-projecting dlBNST neurons.SIGNIFICANCE STATEMENT The comorbidity of chronic pain and depression has long been recognized. Although dysfunction of the mesolimbic dopaminergic system has been implicated in both chronic pain and depression, the underlying mechanisms remain to be elucidated. Here, we show that the inhibitory inputs to the neuronal pathway from the dorsolateral bed nucleus of the stria terminalis (dlBNST) to the ventral tegmental area increase during chronic pain. This neuroplastic change is mediated by enhanced corticotropin-releasing factor signaling within the dlBNST that leads to tonic suppression of the mesolimbic dopaminergic system, which may be involved in the depressive mood and anhedonia under the chronic pain condition.

Cardiovascular functions of central corticotropin-releasing factor related peptides system

The corticotropin-releasing factor (CRF) related peptides system has widespread distributions in central nervous system, to perform many physiological and pathophysiological functions, including cardiovascular functions. A complex connection exists between the central CRF related peptides system and cardiovascular system. There are multiple pathways and mechanisms through which the central CRF related peptides system influences cardiovascular functions. A dysfunction in the central CRF related peptides system may lead to a wide range of alterations in cardiovascular functions. Though there are difficulties or limitations in establishing exact modulatory roles of the central CRF related peptides system in cardiovascular functions. The central CRF related peptides system as target to prevent cardiovascular diseases is being pursued with increasing interest. In this review, we summarize recent understanding on cardiovascular functions of the CRF related peptides system in limbic forebrain, hypothalamus and brain stem structures, discuss mechanisms of the central CRF related peptides system in control of cardiovascular functions, and suggest that the central CRF related peptides system may be a potent candidate for prevention of cardiovascular diseases.

Characterization of the relaxin family peptide receptor 3 system in the mouse bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BNST) is a critical node involved in stress and reward-related behaviors. Relaxin family peptide receptor 3 (RXFP3) signaling in the BNST has been implicated in stress-induced alcohol seeking behavior. However, the neurochemical phenotype and connectivity of BNST RXFP3-expressing (RXFP3+) cells have yet to be elucidated. We interrogated the molecular signature and electrophysiological properties of BNST RXFP3+ neurons using a RXFP3-Cre reporter mouse line. BNST RXFP3+ cells are circumscribed to the dorsal BNST (dBNST) and are neurochemically heterogeneous, comprising a mix of inhibitory and excitatory neurons. Immunohistochemistry revealed that ~48% of BNST RXFP3+ neurons are GABAergic, and a quarter of these co-express the calcium-binding protein, calbindin. A subset of BNST RXFP3+ cells (~41%) co-express CaMKIIα, suggesting this subpopulation of BNST RXFP3+ neurons are excitatory. Corroborating this, RNAscope® revealed that ~35% of BNST RXFP3+ cells express vVGluT2 mRNA, indicating a subpopulation of RXFP3+ neurons are glutamatergic. RXFP3+ neurons show direct hyperpolarization to bath application of a selective RXFP3 agonist, RXFP3-A2, while around 50% of cells were depolarised by exogenous corticotrophin releasing factor. In behaviorally naive mice the majority of RXFP3+ neurons were Type II cells exhibiting I_h and T type calcium mediated currents. However, chronic swim stress caused persistent plasticity, decreasing the proportion of neurons that express these channels. These studies are the first to characterize the BNST RXFP3 system in mouse and lay the foundation for future functional studies appraising the role of the murine BNST RXFP3 system in more complex behaviors.

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.

Activation of the neural pathway from the dorsolateral bed nucleus of the stria terminalis to the central amygdala induces anxiety-like behaviors

The bed nucleus of the stria terminalis (BNST) and the central amygdala (CeA) comprise a forebrain unit that has been described as the "extended amygdala". These two nuclei send dense projections to each other and have been implicated in the regulation of negative emotional states, including anxiety and fear. The present study employed an optogenetic technique to examine whether stimulation of CeA-projecting dorsolateral BNST (dlBNST) neuron terminals would influence anxiety-like behaviors in male Sprague-Dawley rats. Photostimulation of CeA-projecting dlBNST neuron terminals produced anxiogenic effects in an elevated plus maze test. This finding is inconsistent with previous reports showing that optogenetic stimulation of BNST neurons projecting to the lateral hypothalamus (LH) and ventral tegmental area (VTA) produces anxiolytic rather than anxiogenic effects. To address this issue, electrophysiological analyses were conducted to characterize dlBNST neurons projecting to the CeA, LH, and VTA. dlBNST neurons can be electrophysiologically classified into three distinct cell types (types I-III) according to their responses to depolarizing and hyperpolarizing current injections. Whole-cell patch-clamp recordings revealed that more than 60% of the CeA-projecting dlBNST neurons were type II, whereas approximately 80% of the LH- and VTA-projecting dlBNST neurons were type III. These electrophysiological results will help elucidate the mechanisms underlying the heterogeneity of BNST neurons during the regulation of anxiety-like behaviors.

Suppressive effects of morphine injected into the ventral bed nucleus of the stria terminalis on the affective, but not sensory, component of pain in rats

Pain is a complex experience with both sensory and affective components. Clinical and preclinical studies have shown that the affective component of pain can be reduced by doses of morphine lower than those necessary to reduce the sensory component. Although the neural mechanisms underlying the effects of morphine on the sensory component of pain have been investigated extensively, those influencing the affective component remain to be elucidated. The bed nucleus of the stria terminalis (BNST) has been implicated in the regulation of various negative emotional states, including aversion, anxiety and fear. Thus, this study aimed to clarify the role of the ventral part of the BNST (vBNST) in the actions of morphine on the affective and sensory components of pain. First, the effects of intra-vBNST injections of morphine on intraplantar formalin-induced conditioned place aversion (CPA) and nociceptive behaviors were investigated. Intra-vBNST injections of morphine reduced CPA without affecting nociceptive behaviors, which suggests that intra-vBNST morphine alters the affective, but not sensory, component of pain. Next, to examine the effects of morphine on neuronal excitability in type II vBNST neurons, whole-cell patch-clamp recordings were performed in brain slices. Bath application of morphine hyperpolarized type II vBNST neurons. Thus, the suppressive effects of intra-vBNST morphine on pain-induced aversion may be due to its inhibitory effects on neuronal excitability in type II vBNST neurons. These results suggest that the vBNST is a key brain region involved in the suppressive effects of morphine on the affective component of pain.

Functional Heterogeneity in the Bed Nucleus of the Stria Terminalis

Early work stressed the differing involvement of the central amygdala (CeA) and bed nucleus of the stria terminalis (BNST) in the genesis of fear versus anxiety, respectively. In 2009, Walker, Miles, and Davis proposed a model of amygdala-BNST interactions to explain these functional differences. This model became extremely influential and now guides a new wave of studies on the role of BNST in humans. Here, we consider evidence for and against this model, in the process highlighting central principles of BNST organization. This analysis leads us to conclude that BNST's influence is not limited to the generation of anxiety-like responses to diffuse threats, but that it also shapes the impact of discrete threatening stimuli. It is likely that BNST-CeA interactions are involved in modulating responses to such threats. In addition, whereas current views emphasize the contributions of the anterolateral BNST region in anxiety, accumulating data indicate that the anteromedial and anteroventral regions also play a critical role. The presence of multiple functional subregions within the small volume of BNST raises significant technical obstacles for functional imaging studies in humans.

Activation of adenylate cyclase-cyclic AMP-protein kinase A signaling by corticotropin-releasing factor within the dorsolateral bed nucleus of the stria terminalis is involved in pain-induced aversion

Pain is a complex experience involving sensory and affective components. Although the neuronal mechanisms underlying the sensory component of pain have been extensively studied, those underlying its affective component have yet to be elucidated. Recently, we reported that corticotrophin-releasing factor (CRF)-induced depolarization in type II neurons within the dorsolateral bed nucleus of the stria terminalis (dlBNST) is critical for pain-induced aversive responses in rats. However, the intracellular signaling underlying the excitatory effects of CRF and the contribution of such signaling to the induction of pain-induced aversion remain unclear. In the present study, we addressed these issues by conducting whole-cell patch-clamp recordings in rat brain slices and by undertaking behavioral pharmacological analyses. Intracellular perfusion of protein kinase A (PKA) inhibitor Rp-cyclic adenosine monophosphorothioate (Rp-cAMPS) or KT5720 suppressed the excitatory effects of CRF in type II dlBNST neurons, and bath application of Rp-cAMPS also suppressed it. In addition, bath application of forskolin, an adenylate cyclase (AC) activator, mimicked the effects of CRF, and pretreatment with forskolin diminished the excitatory effects of CRF. Furthermore, a conditioned place aversion (CPA) test showed that co-administration of Rp-cAMPS with CRF into the dlBNST suppressed CRF-induced CPA. Intra-dlBNST injection of Rp-cAMPS also suppressed pain-induced CPA. These results suggest that CRF increases excitability of type II dlBNST neurons through activation of the AC-cAMP-PKA pathway, thereby causing pain-induced aversive responses. The present findings shed light on the neuronal mechanisms underlying the negative affective component of pain and may provide therapeutic targets for treating intractable pain accompanied by psychological factors.