Alpha1-adrenergic receptor-induced heterosynaptic long-term depression in the bed nucleus of the stria terminalis is disrupted in mouse models of affective disorders

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.

The impact of psychosocial defeat stress on the bed nucleus of the stria terminalis transcriptome in adult male mice

The bed nucleus of the stria terminalis (BNST) is a focal point for the convergence of inputs from canonical stress-sensitive structures to fine-tune the response to stress. However, its role in mediating phenotypes of stress resilience or susceptibility is yet to be fully defined. In this study, we carried out unbiased RNA-sequencing to analyse the BNST transcriptomes of adult male mice, which were classified as resilient or susceptible following a 10-day chronic psychosocial defeat stress paradigm. Pairwise comparisons revealed 20 differentially expressed genes in resilience (6) and susceptible (14) mice compared with controls. An in silico validation of our data against an earlier study revealed significant concordance in gene expression profiles associated with resilience to chronic stress. Enrichment analysis revealed that resilience is linked to functions including retinoic acid hydrolase activity, phospholipase inhibitor and tumour necrosis factor (TNF)-receptor activities, whereas susceptibility is linked to alterations in amino acid transporter activity. We also identified differential usage of 134 exons across 103 genes associated with resilience and susceptibility; enrichment analysis for genes with differential exon usage in resilient mice was linked to functions including adrenergic receptor binding mice and oxysterol binding in susceptible mice. Our findings highlight the important and underappreciated role of the BNST in stress resilience and susceptibility and reveal research avenues for follow-up investigations.

Somatostatin neurons control an alcohol binge drinking prelimbic microcircuit in mice

Somatostatin (SST) neurons have been implicated in a variety of neuropsychiatric disorders such as depression and anxiety, but their role in substance use disorders, including alcohol use disorder (AUD), is not fully characterized. Here, we found that repeated cycles of alcohol binge drinking via the Drinking-in-the-Dark (DID) model led to hypoactivity of SST neurons in the prelimbic (PL) cortex by diminishing their action potential firing capacity and excitatory/inhibitory transmission dynamic. We examined their role in regulating alcohol consumption via bidirectional chemogenetic manipulation. Both hM3Dq-induced excitation and KORD-induced silencing of PL SST neurons reduced alcohol binge drinking in males and females, with no effect on sucrose consumption. Alcohol binge drinking disinhibited pyramidal neurons by augmenting SST neurons-mediated GABA release and synaptic strength onto other GABAergic populations and reducing spontaneous inhibitory transmission onto pyramidal neurons. Pyramidal neurons additionally displayed increased intrinsic excitability. Direct inhibition of PL pyramidal neurons via hM4Di was sufficient to reduce alcohol binge drinking. Together these data revealed an SST-mediated microcircuit in the PL that modulates the inhibitory dynamics of pyramidal neurons, a major source of output to subcortical targets to drive reward-seeking behaviors and emotional response.

The role of α adrenergic receptors in mediating the inhibitory effect of electrical brain stimulation on epileptiform activity in rat hippocampal slices

The Inhibitory effect of electrical low-frequency stimulation (LFS) on neuronal excitability and seizure occurrence has been indicated in experimental models, but the precise mechanism has not established. This investigation was intended to figure out the role of α₁ and α₂ adrenergic receptors in LFS' inhibitory effect on neuronal excitability. Epileptiform activity induced in an in vitro rat hippocampal slice preparation by high K⁺ ACSF and LFS (900 square wave pulses at 1 Hz) was administered at the beginning of epileptiform activity to the Schaffer collaterals. In CA1 pyramidal neurons, the electrophysiological properties were measured at the baseline, before high K⁺ ACSF washout, and at 15 min after high K⁺ ACSF washout using whole-cell, patch-clamp recording. Results indicated that after high K⁺ ACSF washout, prazosine (10 µM; α₁ adrenergic receptor antagonist) and yohimbine (5 µM; α₂ adrenergic receptor antagonist) suppressed the LFS' effect of reducing rheobase current and utilization time following depolarizing ramp current, the latency to the first spike following a depolarizing current and latency to the first rebound action potential following hyperpolarizing current pulses. Thus, it may be proposed that LFS' inhibitory action on the neuronal hyperexcitability, in some way, is mediated by α₁ and α₂ adrenergic receptors.

α1-Adrenergic Receptors in Neurotransmission, Synaptic Plasticity, and Cognition

α₁-adrenergic receptors are G-Protein Coupled Receptors that are involved in neurotransmission and regulate the sympathetic nervous system through binding and activating the neurotransmitter, norepinephrine, and the neurohormone, epinephrine. There are three α₁-adrenergic receptor subtypes (α_1A, α_1B, α_1D) that are known to play various roles in neurotransmission and cognition. They are related to two other adrenergic receptor families that also bind norepinephrine and epinephrine, the β- and α₂-, each with three subtypes (β₁, β₂, β₃, α_2A, α_2B, α_2C). Previous studies assessing the roles of α₁-adrenergic receptors in neurotransmission and cognition have been inconsistent. This was due to the use of poorly-selective ligands and many of these studies were published before the characterization of the cloned receptor subtypes and the subsequent development of animal models. With the availability of more-selective ligands and the development of animal models, a clearer picture of their role in cognition and neurotransmission can be assessed. In this review, we highlight the significant role that the α₁-adrenergic receptor plays in regulating synaptic efficacy, both short and long-term synaptic plasticity, and its regulation of different types of memory. We will also present evidence that the α₁-adrenergic receptors, and particularly the α_1A-adrenergic receptor subtype, are a potentially good target to treat a wide variety of neurological conditions with diminished cognition.

Repeated norepinephrine receptor stimulation in the BNST induces sensorimotor gating deficits via corticotropin releasing factor

Intense stress precipitates symptoms in disorders such as post-traumatic stress (PTSD) and schizophrenia. Patients with these disorders have dysfunctional sensorimotor gating as indexed by disrupted prepulse inhibition of the startle response (PPI), which refers to decreased startle response when a weak pre-stimulus precedes a startling stimulus. Stress promotes release of norepinephrine (NE) and corticotrophin releasing factor (CRF) within the brain, neurotransmitters that also modulate PPI. We have shown that repeated stress causes sensitization of NE receptors within the basolateral amygdala (BLA) via CRF receptors and promotes long-lasting PPI disruptions and startle abnormalities. The bed nucleus of the stria terminalis (BNST) is another crucial brain region that could be involved in stress-induced alterations in NE and CRF functions to promote PPI changes as this anatomical structure is enriched in CRF and NE receptors that have been shown to regulate each other. We hypothesized that repeated infusions of NE into the BNST would cross-sensitize CRF receptors or vice versa to alter PPI. Separate groups of male Sprague Dawley rats received, CRF (200ng/0.5 μl), NE (20μg/0.5 μl), or vehicle into the BNST, once/day for 3 days and PPI was tested after each infusion. Repeated CRF-or vehicle-treated rats were then challenged with a subthreshold dose of NE (0.3μg/0.5 μl) while repeated NE-treated rats were challenged with CRF (200ng/0.5 μl), and PPI was measured. Surprisingly, initial/repeated CRF or vehicle in the BNST had no effects on PPI. In contrast, initial and repeated NE disrupted PPI. Sub-threshold NE challenge in rats that previously received repeated CRF had no effect on PPI. Interestingly though, intra-BNST challenge dose of CRF significantly disrupted PPI in rats that previously had received repeated NE infusions. Taken together, these results indicate that repeated stress-induced NE release could alter the activity of CRF receptors in the BNST to modulate sensorimotor gating as measured through PPI.

Chronic Intermittent Ethanol and Acute Stress Similarly Modulate BNST CRF Neuron Activity via Noradrenergic Signaling

BACKGROUND

Relapse is a critical barrier to effective long-term treatment of alcoholism, and stress is often cited as a key trigger to relapse. Numerous studies suggest that stress-induced reinstatement to drug-seeking behaviors is mediated by norepinephrine (NE) and corticotropin-releasing factor (CRF) signaling interactions in the bed nucleus of the stria terminalis (BNST), a brain region critical to many behavioral and physiologic responses to stressors. Here, we sought to directly examine the effects of NE on BNST CRF neuron activity and determine whether these effects may be modulated by chronic intermittent EtOH (CIE) exposure or a single restraint stress.

METHODS

Adult male CRF-tomato reporter mice were treatment-naïve, or either exposed to CIE for 2 weeks or to a single 1-hour restraint stress. Effects of application of exogenous NE on BNST CRF neuron activity were assessed via whole-cell patch-clamp electrophysiological techniques.

RESULTS

We found that NE depolarized BNST CRF neurons in naïve mice in a β-adrenergic receptor (AR)-dependent mechanism. CRF neurons from CIE- or stress-exposed mice had significantly elevated basal resting membrane potential compared to naïve mice. Furthermore, CIE and stress individually disrupted the ability of NE to depolarize CRF neurons, suggesting that both stress and CIE utilize β-AR signaling to modulate BNST CRF neurons. Neither stress nor CIE altered the ability of exogenous NE to inhibit evoked glutamatergic transmission onto BNST CRF neurons as shown in naïve mice, a mechanism previously shown to be α-AR-dependent.

CONCLUSIONS

Altogether, these findings suggest that stress and CIE interact with β-AR signaling to modulate BNST CRF neuron activity, potentially disrupting the α/β-AR balance of BNST CRF neuronal excitability. Restoration of α/β-AR balance may lead to novel therapies for the alleviation of many stress-related disorders.

Genetic identification of a population of noradrenergic neurons implicated in attenuation of stress-related responses

Noradrenergic signaling plays a well-established role in promoting the stress response. Here we identify a subpopulation of noradrenergic neurons, defined by developmental expression of Hoxb1, that has a unique role in modulating stress-related behavior. Using an intersectional chemogenetic strategy, in combination with behavioral and physiological analyses, we show that activation of Hoxb1-noradrenergic (Hoxb1-NE) neurons decreases anxiety-like behavior and promotes an active coping strategy in response to acute stressors. In addition, we use cerebral blood volume-weighted functional magnetic resonance imaging to show that chemoactivation of Hoxb1-NE neurons results in reduced activity in stress-related brain regions, including the bed nucleus of the stria terminalis, amygdala, and locus coeruleus. Thus, the actions of Hoxb1-NE neurons are distinct from the well-documented functions of the locus coeruleus in promoting the stress response, demonstrating that the noradrenergic system contains multiple functionally distinct subpopulations.

Low-Frequency Electrical Stimulation Reduces the Impairment in Synaptic Plasticity Following Epileptiform Activity in Rat Hippocampal Slices through α1, But Not α2, Adrenergic Receptors

Low frequency stimulation (LFS) has anticonvulsant effect and may restore the ability of long-term potentiation (LTP) to the epileptic brain. The mechanisms of LFS have not been completely determined. Here, we showed that LTP induction was impaired following in vitro epileptiform activity (EA) in hippocampal slices, but application of LFS prevented this impairment. Then, we investigated the involvement of α-adrenergic receptors in this effect of LFS. EA was induced by increasing the extracellular K⁺ concentration to 12 mM and EPSPs were recorded from CA1 neurons in whole cell configuration. EA increased EPSP amplitude from 6.9 ± 0.7 mV to 9.6 ± 0.6 mV. For LTP induction, the Schaffer collaterals were stimulated by high frequency stimulation (HFS; two trains of 100 pulses, 100 Hz at the interval of 20 s). The application of HFS resulted in 40.9 ± 2.3% increase in the amplitude of EPSPs. However, following EA, HFS could not produce any significant changes in EPSP amplitude. Administration of LFS (1 Hz, 900 pulses) to Schaffer collaterals at the beginning of EA restored LTP induction to the hippocampal slices and HFS increased the EPSPs amplitude up to 41.7 ± 3.1% of baseline. When slices were perfused by prazosin (α₁-adrenergic receptor antagonist; 10 μM) before and during LFS application, LFS improvement on LTP induction was reduced significantly. Perfusion of slices by yohimbine (α₂-adrenergic receptor antagonist; 5 μM) had no effect on LFS action. Therefore, it may be concluded that following epileptiform activity, LFS can improve the impairment of LTP generation through α₁, but not α₂, adrenergic receptor activity.

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.

Synaptic Plasticity in the Bed Nucleus of the Stria Terminalis: Underlying Mechanisms and Potential Ramifications for Reinstatement of Drug- and Alcohol-Seeking Behaviors

The bed nucleus of the stria terminalis (BNST) is a component of the extended amygdala that shows significant changes in activity and plasticity through chronic exposure to drugs and stress. The region is critical for stress- and cue-induced reinstatement of drug-seeking behaviors and is thus a candidate region for the plastic changes that occur in abstinence that prime addicted patients for reinstatement behaviors. Here, we discuss the various forms of long-term potentiation (LTP) and long-term depression (LTD) in the rodent BNST and highlight the way that these changes in excitatory transmission interact with exposure to alcohol and other drugs of abuse, as well as other stressors. In addition, we highlight potential areas for future research in this area, including investigating input- and cell-specific bidirectional changes in activity. As we continue to accrue foundational knowledge in the mechanisms and effects of plasticity in the BNST, molecular targets and treatment strategies that are relevant to reinstatement behaviors will also begin to emerge. Here, we briefly discuss the effects of catecholamine receptor modulators on synaptic plasticity in the BNST due to the role of norepinephrine in LTD and dopamine on the short-term component of LTP as well as the role that signaling at these receptors plays in reinstatement of drug- and alcohol-seeking behaviors. We hope that insights gained on the specific changes in plasticity that occur within the BNST during abstinence from alcohol and other drugs of abuse will provide insight into the biological underpinnings of relapse behavior in human addicts and inform future treatment modalities for addiction that tackle this complex biological problem.

Glutamatergic and gabaergic ventral BNST neurons differ in their physiological properties and responsiveness to noradrenaline

The bed nucleus of the stria terminalis (BNST) regulates defensive responses to threats and its anteroventral portion (BNST-AV) is involved. BNST-AV contains a minority of glutamatergic neurons scattered among a dominant population of GABAergic cells. There is evidence that these two cell types might exert opposite influences, the former promoting and the latter reducing anxiety. Although GABAergic cells greatly outnumber glutamatergic neurons in BNST-AV, in some circumstances the influence of glutamatergic cells appears to predominate. Related to this, BNST-AV receives a very strong noradrenaline (NA) input and negative emotional states are associated with a marked rise of NA concentration in BNST-AV. However, it is currently unclear whether NA differentially alters the excitability of glutamatergic and GABAergic BNST-AV neurons. Thus, to shed light on how BNST-AV regulates negative emotional states, the present study compared the physiological properties and NA responsiveness of glutamatergic and GABAergic BNST-AV neurons using whole-cell recordings in transgenic mice that express a fluorescent reporter in either cell group. We found that glutamatergic cells had a slightly more complex morphology than the GABAergic cells, a higher intrinsic excitability, and a different responsiveness to NA. Indeed, while NA inhibited EPSPs in both cell types through α1 and α2 adrenoreceptors, the EPSP reduction seen in glutamatergic cells had a lower amplitude and a shorter duration than in GABAergic cells. These differences were due to the presence of a β-receptor-mediated EPSP enhancement in the glutamatergic cells. Together, our results suggest that multiple properties contribute to the disproportionate influence of glutamatergic BNST-AV neurons.

Acute engagement of Gq-mediated signaling in the bed nucleus of the stria terminalis induces anxiety-like behavior

The bed nucleus of the stria terminalis (BNST) is a brain region important for regulating anxiety-related behavior in both humans and rodents. Here we used a chemogenetic strategy to investigate how engagement of G protein-coupled receptor (GPCR) signaling cascades in genetically defined GABAergic BNST neurons modulates anxiety-related behavior and downstream circuit function. We saw that stimulation of vesicular γ-aminobutyric acid (GABA) transporter (VGAT)-expressing BNST neurons using hM3Dq, but neither hM4Di nor rM3Ds designer receptors exclusively activated by a designer drug (DREADD), promotes anxiety-like behavior. Further, we identified that activation of hM3Dq receptors in BNST VGAT neurons can induce a long-term depression-like state of glutamatergic synaptic transmission, indicating DREADD-induced changes in synaptic plasticity. Further, we used DREADD-assisted metabolic mapping to profile brain-wide network activity following activation of Gq-mediated signaling in BNST VGAT neurons and saw increased activity within ventral midbrain structures, including the ventral tegmental area and hindbrain structures such as the locus coeruleus and parabrachial nucleus. These results highlight that Gq-mediated signaling in BNST VGAT neurons can drive downstream network activity that correlates with anxiety-like behavior and points to the importance of identifying endogenous GPCRs within genetically defined cell populations. We next used a microfluidics approach to profile the receptorome of single BNST VGAT neurons. This approach yielded multiple Gq-coupled receptors that are associated with anxiety-like behavior and several potential novel candidates for regulation of anxiety-like behavior. From this, we identified that stimulation of the Gq-coupled receptor 5-HT2CR in the BNST is sufficient to elevate anxiety-like behavior in an acoustic startle task. Together, these results provide a novel profile of receptors within genetically defined BNST VGAT neurons that may serve as therapeutic targets for regulating anxiety states and provide a blueprint for examining how G-protein-mediated signaling in a genetically defined cell type can be used to assess behavior and brain-wide circuit function.

A Key Role for Neurotensin in Chronic-Stress-Induced Anxiety-Like Behavior in Rats

Chronic stress is a major cause of anxiety disorders that can be reliably modeled preclinically, providing insight into alternative therapeutic targets for this mental health illness. Neuropeptides have been targeted in the past to no avail possibly due to our lack of understanding of their role in pathological models. In this study we use a rat model of chronic stress-induced anxiety-like behaviors and hypothesized that neuropeptidergic modulation of synaptic transmission would be altered in the bed nucleus of the stria terminalis (BNST), a brain region suspected to contribute to anxiety disorders. We use brain slice neurophysiology and behavioral pharmacology to compare the role of locally released endogenous neuropeptides on synaptic transmission in the oval (ov) BNST of non-stressed (NS) or chronic unpredictably stressed (CUS) rats. We found that in NS rats, post-synaptic depolarization induced the release of vesicular neurotensin (NT) and corticotropin-releasing factor (CRF) that co-acted to increase ovBNST inhibitory synaptic transmission in 59% of recorded neurons. CUS bolstered this potentiation (100% of recorded neurons) through an enhanced contribution of NT over CRF. In contrast, locally released opioid neuropeptides decreased ovBNST excitatory synaptic transmission in all recorded neurons, regardless of stress. Consistent with CUS-induced enhanced modulatory effects of NT, blockade of ovBNST NT receptors completely abolished stress-induced anxiety-like behaviors in the elevated plus maze paradigm. The role of NT has been largely unexplored in stress and our findings highlight its potential contribution to an important behavioral consequence of chronic stress, that is, exaggerated avoidance of open space in rats.

Acute and chronic effects of noradrenergic enhancement on transcranial direct current stimulation-induced neuroplasticity in humans

KEY POINTS

Chronic administration of the selective noradrenaline reuptake inhibitor (NRI) reboxetine (RBX) increased and prolonged the long-term potentiation-like plasticity induced by anodal transcranial direct current stimulation (tDCS) for over 24 h. Chronic administration of RBX converted cathodal tDCS-induced long-term depression-like plasticity into facilitation for 120 min. Chronic noradrenergic activity enhancement on plasticity of the human brain might partially explain the delayed therapeutic impact of selective NRIs in depression and other neuropsychiatric diseases.

ABSTRACT

Noradrenaline affects cognition and motor learning processes via its impact on long-term potentiation (LTP) and depression (LTD). We aimed to explore the impact of single dose and chronic administration of the selective noradrenaline reuptake inhibitor (NRI) reboxetine (RBX) on plasticity induced by transcranial direct current stimulation (tDCS) in healthy humans via a double-blinded, placebo-controlled, randomized crossover study. Sixteen healthy volunteers received placebo or single dose RBX (8 mg) before anodal or cathodal tDCS of the primary motor cortex. Afterwards, the same subjects took RBX (8 mg day-1 ) consecutively for 21 days. During this period, two additional interventions were performed (RBX with anodal or cathodal tDCS), to explore the impact of chronic RBX treatment on plasticity. Plasticity was monitored by motor-evoked potential amplitudes elicited by transcranial magnetic stimulation. Chronic administration of RBX increased and prolonged the LTP-like plasticity induced by anodal tDCS for over 24 h. Chronic RBX significantly converted cathodal tDCS-induced LTD-like plasticity into facilitation, as compared to the single dose condition, for 120 min after stimulation. The results show a prominent impact of chronic noradrenergic enhancement on plasticity of the human brain that might partially explain the delayed therapeutic impact of selective NRIs in depression and other neuropsychiatric diseases.

Locus Ceruleus Norepinephrine Release: A Central Regulator of CNS Spatio-Temporal Activation?

Norepinephrine (NE) is synthesized in the Locus Coeruleus (LC) of the brainstem, from where it is released by axonal varicosities throughout the brain via volume transmission. A wealth of data from clinics and from animal models indicates that this catecholamine coordinates the activity of the central nervous system (CNS) and of the whole organism by modulating cell function in a vast number of brain areas in a coordinated manner. The ubiquity of NE receptors, the daunting number of cerebral areas regulated by the catecholamine, as well as the variety of cellular effects and of their timescales have contributed so far to defeat the attempts to integrate central adrenergic function into a unitary and coherent framework. Since three main families of NE receptors are represented-in order of decreasing affinity for the catecholamine-by: α2 adrenoceptors (α2Rs, high affinity), α1 adrenoceptors (α1Rs, intermediate affinity), and β adrenoceptors (βRs, low affinity), on a pharmacological basis, and on the ground of recent studies on cellular and systemic central noradrenergic effects, we propose that an increase in LC tonic activity promotes the emergence of four global states covering the whole spectrum of brain activation: (1) sleep: virtual absence of NE, (2) quiet wake: activation of α2Rs, (3) active wake/physiological stress: activation of α2- and α1-Rs, (4) distress: activation of α2-, α1-, and β-Rs. We postulate that excess intensity and/or duration of states (3) and (4) may lead to maladaptive plasticity, causing-in turn-a variety of neuropsychiatric illnesses including depression, schizophrenic psychoses, anxiety disorders, and attention deficit. The interplay between tonic and phasic LC activity identified in the LC in relationship with behavioral response is of critical importance in defining the short- and long-term biological mechanisms associated with the basic states postulated for the CNS. While the model has the potential to explain a large number of experimental and clinical findings, a major challenge will be to adapt this hypothesis to integrate the role of other neurotransmitters released during stress in a centralized fashion, like serotonin, acetylcholine, and histamine, as well as those released in a non-centralized fashion, like purines and cytokines.

Dynorphin Controls the Gain of an Amygdalar Anxiety Circuit

Kappa opioid receptors (KORs) are involved in a variety of aversive behavioral states, including anxiety. To date, a circuit-based mechanism for KOR-driven anxiety has not been described. Here, we show that activation of KORs inhibits glutamate release from basolateral amygdala (BLA) inputs to the bed nucleus of the stria terminalis (BNST) and occludes the anxiolytic phenotype seen with optogenetic activation of BLA-BNST projections. In addition, deletion of KORs from amygdala neurons results in an anxiolytic phenotype. Furthermore, we identify a frequency-dependent, optically evoked local dynorphin-induced heterosynaptic plasticity of glutamate inputs in the BNST. We also find that there is cell type specificity to the KOR modulation of the BLA-BNST input with greater KOR-mediated inhibition of BLA dynorphin-expressing neurons. Collectively, these results provide support for a model in which local dynorphin release can inhibit an anxiolytic pathway, providing a discrete therapeutic target for the treatment of anxiety disorders.

Anxiety-like responses induced by nitric oxide within the BNST in mice: Role of CRF1 and NMDA receptors

It has been shown that the bed nucleus of the stria terminalis (BNST) of rats contains nitrergic neurons, which are activated during animal exposure to aversive stimuli. The BNST is also populated by glutamatergic and corticotrophin releasing factor (CRFergic) neurons, which in turn are activated under stressful situations. Here we investigated the anxiogenic-like effects of intra-BNST injections of a nitric oxide (NO) donor, NOC-9 in mice. The role of CRFergic and glutamatergic systems on defensive behavior induced by NOC-9 was investigated with previous intra-BNST infusion of different doses of CP376395, a CRF type 1 receptor antagonist (CRF1), or AP-7, an NMDA (N-methyl-D-aspartate) receptor antagonist. Anxiety-like behavior was assessed immediately and 5 min after intra-BNST drug injection, exposing mice to a novel arena and to the elevated plus-maze (EPM; an anxiogenic situation). Results showed that NOC-9 provoked a short period (≈ 150 s) of freezing behavior in the novel arena and increased anxiety in the EPM. Both CP and AP-7 attenuated the anxiogenic-like effects of NOC-9 in the EPM without changing freezing behavior in the novel arena. When given alone (i.e. without prior intra-BNST injection of NOC-9), AP-7 (0.20 nmol), but not CP (0.75, 1.50, or 3.00 nmol), attenuated anxiety in mice exposed to the EPM. These results suggest that CRF1 and NMDA receptors located within the BNST differentially modulate aversive effects induced by NO production in this limbic forebrain structure.

Stress Modulation of Opposing Circuits in the Bed Nucleus of the Stria Terminalis

The anterior bed nucleus of the stria terminalis (BNST) has been recognized as a critical structure in regulating trait anxiety, contextual fear memory, and appetitive behavior, and is known to be sensitive to stress manipulations. As one of the most complex structures in the central nervous system, the intrinsic circuitry of the BNST is largely unknown; however, recent technological developments have allowed researchers to begin to untangle the internal connections of the nucleus. This research has revealed the possibility of two opposing circuits, one anxiolytic and one anxiogenic, within the BNST, the relative strength of which determines the behavioral outcome. The balance of these pathways is critical in maintaining a normal physiological and behavioral state; however, stress and drugs of abuse can differentially affect the opposing circuitry within the nucleus to shift the balance to a pathological state. In this review, we will examine how stress interacts with the neuromodulators, corticotropin-releasing factor, norepinephrine, dopamine, and serotonin to affect the circuitry of the BNST as well as how synaptic plasticity in the BNST is modulated by stress, resulting in long-lasting changes in the circuit and behavioral state.

Chronic stress impairs α1-adrenoceptor-induced endocannabinoid-dependent synaptic plasticity in the dorsal raphe nucleus

Alpha 1-adrenergic receptors (α1-ARs) control the activity of dorsal raphe nucleus (DRn) serotonin (5-HT) neurons and play crucial role in the regulation of arousal and stress homoeostasis. However, the precise role of these receptors in regulating glutamate synapses of rat DRn 5-HT neurons and whether chronic stress exposure alters such regulation remain unknown. In the present study, we examined the impact of chronic restraint stress on α1-AR-mediated regulation of glutamate synapses onto DRn 5-HT neurons. We found that, in the control condition, activation of α1-ARs induced an inward current and long-term depression (LTD) of glutamate synapses of DRn 5-HT neurons. The α1-AR LTD was initiated by postsynaptic α1-ARs but mediated by a decrease in glutamate release. The presynaptic expression of the α1-AR LTD was signaled by retrograde endocannabinoids (eCBs). Importantly, we found that chronic exposure to restraint stress profoundly reduced the magnitude of α1-AR LTD but had no effect on the amplitude of α1-AR-induced inward current. Chronic restraint stress also reduced the CB1 receptor-mediated inhibition of EPSC and the eCB-mediated depolarization-induced suppression of excitation. Collectively, these results indicate that chronic restraint stress impairs the α1-AR LTD by reducing the function of presynaptic CB1 receptors and reveal a novel mechanism by which noradrenaline controls synaptic strength and plasticity in the DRn. They also provide evidence that chronic stress impairs eCB signaling in the DRn, which may contribute, at least in part, to the dysregulation of the stress homeostasis.

Mechanisms of Neuroplasticity and Ethanol's Effects on Plasticity in the Striatum and Bed Nucleus of the Stria Terminalis

Long-lasting changes in synaptic function (i.e., synaptic plasticity) have long been thought to contribute to information storage in the nervous system. Although synaptic plasticity mainly has adaptive functions that allow the organism to function in complex environments, it is now clear that certain events or exposure to various substances can produce plasticity that has negative consequences for organisms. Exposure to drugs of abuse, in particular ethanol, is a life experience that can activate or alter synaptic plasticity, often resulting in increased drug seeking and taking and in many cases addiction.Two brain regions subject to alcohol's effects on synaptic plasticity are the striatum and bed nucleus of the stria terminalis (BNST), both of which have key roles in alcohol's actions and control of intake. The specific effects depend on both the brain region analyzed (e.g., specific subregions of the striatum and BNST) and the duration of ethanol exposure (i.e., acute vs. chronic). Plastic changes in synaptic transmission in these two brain regions following prolonged ethanol exposure are thought to contribute to excessive alcohol drinking and relapse to drinking. Understanding the mechanisms underlying this plasticity may lead to new therapies for treatment of these and other aspects of alcohol use disorder.

Impaired adrenergic-mediated plasticity of prefrontal cortical glutamate synapses in rats with developmental disruption of the ventral hippocampus

Neonatal ventral hippocampus (nVH) lesion in rats is a useful model to study developmental origins of adult cognitive deficits and certain features of schizophrenia. nVH lesion-induced reorganization of excitatory and inhibitory neurotransmissions within prefrontal cortical (PFC) circuits is widely believed to be responsible for many of the behavioral abnormalities in these animals. Here we provide evidence that development of an aberrant medial PFC (mPFC) α-1 adrenergic receptor (α-1AR) function following neonatal lesion markedly affects glutamatergic synaptic plasticity within PFC microcircuits and contributes to PFC-related behavior abnormalities. Using whole-cell patch-clamp recording, we report that norepinephrine-induced α-1AR-dependent long-term depression (LTD) in a subset of cortico-cortical glutamatergic inputs is strikingly diminished in mPFC slices from nVH-lesioned rats. The LTD impairment occurs in conjunction with completely blunted α-1AR signaling through extracellular signal-regulated kinase 1/2. These α-1AR abnormalities have functional significance in a mPFC-related function, that is, extinction of conditioned fear memory. Post-pubertal animals with nVH lesion show significant resistance to extinction of fear by repeated presentations of the conditioned tone stimulus. mPFC infusion of an α-1AR antagonist (benoxathian) or LTD blocking peptide (Tat-GluR23Y) impaired fear extinction in sham controls, but had no significant effect in the lesioned animals. The data suggest that impaired α-1 adrenergic regulation of cortical glutamatergic synaptic plasticity may be an important mechanism in cognitive dysfunctions reported in neurodevelopmental psychiatric disorders.

α(2A)-adrenergic receptors filter parabrachial inputs to the bed nucleus of the stria terminalis

α2-adrenergic receptors (AR) within the bed nucleus of the stria terminalis (BNST) reduce stress-reward interactions in rodent models. In addition to their roles as autoreceptors, BNST α(2A)-ARs suppress glutamatergic transmission. One prominent glutamatergic input to the BNST originates from the parabrachial nucleus (PBN) and consists of asymmetric axosomatic synapses containing calcitonin gene-related peptide (CGRP) and vGluT2. Here we provide immunoelectron microscopic data showing that many asymmetric axosomatic synapses in the BNST contain α(2A)-ARs. Further, we examined optically evoked glutamate release ex vivo in BNST from mice with virally delivered channelrhodopsin2 (ChR2) expression in PBN. In BNST from these animals, ChR2 partially colocalized with CGRP, and activation generated EPSCs in dorsal anterolateral BNST neurons that elicited two cell-type-specific outcomes: (1) feedforward inhibition or (2) an EPSP that elicited firing. We found that the α(2A)-AR agonist guanfacine selectively inhibited this PBN input to the BNST, preferentially reducing the excitatory response in ex vivo mouse brain slices. To begin to assess the overall impact of α(2A)-AR control of this PBN input on BNST excitatory transmission, we used a Thy1-COP4 mouse line with little postsynaptic ChR2 expression nor colocalization of ChR2 with CGRP in the BNST. In slices from these mice, we found that guanfacine enhanced, rather than suppressed, optogenetically initiated excitatory drive in BNST. Thus, our study reveals distinct actions of PBN afferents within the BNST and suggests that α(2A)-AR agonists may filter excitatory transmission in the BNST by inhibiting a component of the PBN input while enhancing the actions of other inputs.

Excitatory drive onto dopaminergic neurons in the rostral linear nucleus is enhanced by norepinephrine in an α1 adrenergic receptor-dependent manner

Dopaminergic innervation of the extended amygdala regulates anxiety-like behavior and stress responsivity. A portion of this dopamine input arises from dopamine neurons located in the ventral lateral periaqueductal gray (vlPAG) and rostral (RLi) and caudal linear nuclei of the raphe (CLi). These neurons receive substantial norepinephrine input, which may prime them for involvement in stress responses. Using a mouse line that expresses eGFP under control of the tyrosine hydroxylase promoter, we explored the physiology and responsiveness to norepinephrine of these neurons. We find that RLi dopamine neurons differ from VTA dopamine neurons with respect to membrane resistance, capacitance and the hyperpolarization-activated current, Ih. Further, we found that norepinephrine increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) on RLi dopamine neurons. This effect was mediated through the α1 adrenergic receptor (AR), as the actions of norepinephrine were mimicked by the α1-AR agonist methoxamine and blocked by the α1-AR antagonist prazosin. This action of norepinephrine on sEPSCs was transient, as it did not persist in the presence of prazosin. Methoxamine also increased the frequency of miniature EPSCs, indicating that the α1-AR action on glutamatergic transmission likely has a presynaptic mechanism. There was also a modest decrease in sEPSC frequency with the application of the α2-AR agonist UK-14,304. These studies illustrate a potential mechanism through which norepinephrine could recruit the activity of this population of dopaminergic neurons.

Noradrenergic neurotransmission within the bed nucleus of the stria terminalis modulates the retention of immobility in the rat forced swimming test

The bed nucleus of the stria terminalis (BNST) is a limbic structure that has a direct influence on the autonomic, neuroendocrine, and behavioral responses to stress. It was recently reported that reversible inactivation of synaptic transmission within this structure causes antidepressant-like effects, indicating that activation of the BNST during stressful situations would facilitate the development of behavioral changes related to the neurobiology of depression. Moreover, noradrenergic neurotransmission is abundant in the BNST and has an important role in the regulation of emotional processes related to the stress response. Thus, this study aimed to test the hypothesis that activation of adrenoceptors within the BNST facilitates the development of behavioral consequences of stress. To investigate this hypothesis, male Wistar rats were stressed (forced swimming, 15 min) and 24 h later received intra-BNST injections of vehicle, WB4101, RX821002, CGP20712, or ICI118,551, which are selective α(1), α(2), β(1), and β(2) adrenoceptor antagonists, respectively, 10 min before a 5-min forced swimming test. It was observed that administration of WB4101 (10 and 15 nmol), CGP20712 (5 and 10 nmol), or ICI118,551 (5 nmol) into the BNST reduced the immobility time of rats subjected to forced swimming test, indicating an antidepressant-like effect. These findings suggest that activation of α(1), β(1), and β(2) adrenoceptors in the BNST could be involved in the development of the behavioral consequences of stress.

Contrasting distribution of physiological cell types in different regions of the bed nucleus of the stria terminalis

We characterized the electroresponsive and morphological properties of neurons in the bed nucleus of the stria terminalis (BNST). Previously, Rainnie and colleagues distinguished three cell types in the anterolateral region of BNST (BNST-AL): low-threshold bursting cells (LTB; type II) and regular spiking neurons that display time-dependent (RS; type I) or fast (fIR; type III) inward rectification in the hyperpolarizing direction (Hammack SE, Mania I, Rainnie DG. J Neurophysiol 98: 638-56, 2007). We report that the same neuronal types exist in the anteromedial (AM) and anteroventral (AV) regions of BNST. In addition, we observed two hitherto unreported cell types: late-firing (LF) cells, only seen in BNST-AL, that display a conspicuous delay to firing, and spontaneously active (SA) neurons, only present in BNST-AV, firing continuously at rest. However, the feature that most clearly distinguished the three BNST regions was the incidence of LTB cells (approximately 40-70%) and the strength of their bursting behavior (both higher in BNST-AM and AV relative to AL). The incidence of RS cells was similar in the three regions (∼25%), whereas that of fIR cells was higher in BNST-AL (∼25%) than AV or AM (≤8%). With the use of biocytin, two dominant morphological cell classes were identified but they were not consistently related to particular physiological phenotypes. One neuronal class had highly branched and spiny dendrites; the second had longer but poorly branched and sparsely spiny dendrites. Both often exhibited dendritic varicosities. Since LTB cells prevail in BNST, it will be important to determine what inputs set their firing mode (tonic vs. bursting) and in what behavioral states.

Noradrenergic synaptic function in the bed nucleus of the stria terminalis varies in animal models of anxiety and addiction

Lewis rats show increased anxiety-like behaviors and drug consumption compared with Sprague-Dawley rats. Prior work suggests norepinephrine (NE) signaling in the bed nucleus of the stria terminalis (BNST) could have a role in mediating these phenotypes. Here, we investigated NE content and dynamics in the ventral BNST (vBNST) using fast-scan cyclic voltammetry in these two rat strains. We found that NE release evoked by electrical stimulus and its subsequent uptake was dysregulated in the more anxious Lewis rats. Because addiction is a multifaceted disease influenced by both genetic and environmental factors, we hypothesized NE dynamics would vary in these strains after the induction of a physical dependence on morphine. Following naloxone-precipitated morphine withdrawal, NE release and uptake dynamics were not changed in Lewis rats but were significantly altered in Sprague-Dawley rats. The alterations in Sprague-Dawley rats were accompanied by an increase in anxiety-like behavior in those animals as measured with the elevated plus maze. These studies suggest novel mechanisms involved in the development of affective disorders, and highlight the noradrenergic system in the vBNST as a common substrate for the manifestation of pathological anxiety and addiction.

Amygdala and bed nucleus of the stria terminalis circuitry: Implications for addiction-related behaviors

Complex motivated behavioral processes, such as those that can go awry following substance abuse and other neuropsychiatric disorders, are mediated by a distributive network of neurons that reside throughout the brain. Neural circuits within the amygdala regions, such as the basolateral amygdala (BLA), and downstream targets such as the bed nucleus of the stria terminalis (BNST), are critical neuroanatomical structures for orchestrating emotional behavioral responses that may influence motivated actions such as the reinstatement of drug seeking behavior. Here, we review the functional neurocircuitry of the BLA and the BNST, and discuss how these circuits may guide maladaptive behavioral processes such as those seen in addiction. Thus, further study of the functional connectivity within these brain regions and others may provide insight for the development of new treatment strategies for substance use disorders. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Noradrenergic control of the bed nucleus of the stria terminalis in stress and reward

The bed nucleus of the stria terminalis (BNST) is a group of inter-connected subnuclei that play critical roles in stress-reward interactions. An interesting feature of this brain region is the massive noradrenergic input that it receives. Important roles for norepinephrine in this region have been documented in a number of stress and reward related behaviors. This work has been paralleled over the last several years by efforts to understand the actions of norepinephrine on neuronal function in the region. In this review, we will summarize the current state of these research areas.

Both α1- and β1-adrenoceptors in the bed nucleus of the stria terminalis are involved in the expression of conditioned contextual fear

BACKGROUND AND PURPOSE

The bed nucleus of the stria terminalis (BNST) is a limbic structure that is involved in the expression of conditioned contextual fear. Among the numerous neural inputs to the BNST, noradrenergic synaptic terminals are prominent and some evidence suggests an activation of this noradrenergic neurotransmission in the BNST during aversive situations. Here, we have investigated the involvement of the BNST noradrenergic system in the modulation of behavioural and autonomic responses induced by conditioned contextual fear in rats.

EXPERIMENTAL APPROACH

Male Wistar rats with cannulae bilaterally implanted into the BNST were submitted to a 10 min conditioning session (6 footshocks, 1.5 ma/ 3 s). Twenty-four hours later freezing and autonomic responses (mean arterial pressure, heart rate and cutaneous temperature) to the conditioning box were measured for 10 min. The adrenoceptor antagonists were administered 10 min before the re-exposure to the aversive context.

KEY RESULTS

L-propranolol, a non-selective β-adrenoceptor antagonist, and phentolamine, a non-selective α-adrenoceptor antagonist, reduced both freezing and autonomic responses induced by aversive context. Similar results were observed with CGP20712, a selective β(1) -adrenoceptor antagonist, and WB4101, a selective α(1) -antagonist, but not with ICI118,551, a selective β(2) -adrenoceptor antagonist or RX821002, a selective α(2) -antagonist.

CONCLUSIONS AND IMPLICATIONS

These findings support the idea that noradrenergic neurotransmission in the BNST via α(1) - and β(1) -adrenoceptors is involved in the expression of conditioned contextual fear.

Norepinephrine: a neuromodulator that boosts the function of multiple cell types to optimize CNS performance

Norepinephrine (NE) is a neuromodulator that in multiple ways regulates the activity of neuronal and non-neuronal cells. NE participates in the rapid modulation of cortical circuits and cellular energy metabolism, and on a slower time scale in neuroplasticity and inflammation. Of the multiple sources of NE in the brain, the locus coeruleus (LC) plays a major role in noradrenergic signaling. Processes from the LC primarily release NE over widespread brain regions via non-junctional varicosities. We here review the actions of NE in astrocytes, microglial cells, and neurons based on the idea that the overarching effect of signaling from the LC is to maximize brain power, which is accomplished via an orchestrated cellular response involving most, if not all cell types in CNS.

Yohimbine depresses excitatory transmission in BNST and impairs extinction of cocaine place preference through orexin-dependent, norepinephrine-independent processes

The alpha2 adrenergic receptor (α(2)-AR) antagonist yohimbine is a widely used tool for the study of anxiogenesis and stress-induced drug-seeking behavior. We previously demonstrated that yohimbine paradoxically depresses excitatory transmission in the bed nucleus of the stria terminalis (BNST), a region critical to the integration of stress and reward pathways, and produces an impairment of extinction of cocaine-conditioned place preference (cocaine-CPP) independent of α(2)-AR signaling. Recent studies show yohimbine-induced drug-seeking behavior is attenuated by orexin receptor 1 (OX(1)R) antagonists. Moreover, yohimbine-induced cocaine-seeking behavior is BNST-dependent. Here, we investigated yohimbine-orexin interactions. Our results demonstrate yohimbine-induced depression of excitatory transmission in the BNST is unaffected by alpha1-AR and corticotropin-releasing factor receptor-1 (CRFR(1)) antagonists, but is (1) blocked by OxR antagonists and (2) absent in brain slices from orexin knockout mice. Although the actions of yohimbine were not mimicked by the norepinephrine transporter blocker reboxetine, they were by exogenously applied orexin A. We find that, as with yohimbine, orexin A depression of excitatory transmission in BNST is OX(1)R-dependent. Finally, we find these ex vivo effects are paralleled in vivo, as yohimbine-induced impairment of cocaine-CPP extinction is blocked by a systemically administered OX(1)R antagonist. These data highlight a new mechanism for orexin on excitatory anxiety circuits and demonstrate that some of the actions of yohimbine may be directly dependent upon orexin signaling and independent of norepinephrine and CRF in the BNST.

The role of biogenic amine signaling in the bed nucleus of the stria terminals in alcohol abuse

There is a growing body of evidence that suggests that stress and anxiety can influence the development of alcohol use disorders. This influence is believed to be due in part to persistent adaptations in discrete brain regions that underlie stress responsivity. One structure that has been proposed to be a site of important neuroadaptations underlying this behavior is the extended amygdala. The extended amygdala is a series of extensively inter-connected limbic structures including the central nucleus of the amygdala (CeA) and the bed nucleus of the stria terminalis (BNST). These structures are critical regulators of behavioral and physiological activation associated with anxiety. Additionally, numerous reports have suggested that these regions are involved in increased drinking behavior associated with chronic alcohol exposure and withdrawal. The focus of this review will be to discuss the role of the BNST in regulation of behavior, to provide some insight in to the circuitry of the BNST, and to discuss the actions of the biogenic amines, serotonin, dopamine and norepinephrine, in the BNST.

Activation of alpha1-adrenoceptors enhances glutamate release onto ventral tegmental area dopamine cells

The ventral tegmental area (VTA) plays an important role in reward and motivational processes that facilitate the development of drug addiction. Glutamatergic inputs into the VTA contribute to dopamine (DA) neuronal activation related to reward and response-initiating effects in drug abuse. Previous investigations indicate that alpha1-adrenoreceptors (α1-ARs) are primarily localized at presynaptic elements in the ventral midbrain. Studies from several brain regions have shown that presynaptic α1-AR activation enhances glutamate release. Therefore, we hypothesized that glutamate released onto VTA-DA neurons is modulated by pre-synaptic α1-AR. Recordings were obtained from putative VTA-DA cells of male Sprague-Dawley rats (28-50 days postnatal) using voltage clamp techniques. Phenylephrine (10 μM) and methoxamine (80μM), both α1-AR agonists, increased AMPA receptor-mediated excitatory postsynaptic currents' (EPSCs) amplitude evoked by electrical stimulation of afferent fibers (p<0.05). This effect was blocked by the α1-AR antagonist prazosin (1 μM). Phenylephrine decreased the paired-pulse ratio (PPR) and increased spontaneous EPSCs' frequencies but not their amplitudes suggesting a presynaptic locus of action. No changes in miniature EPSCs (0.5μM, tetrodotoxin [TTX]) were observed after phenylephrine's application which suggests that α1-AR effect was action potential dependent. Normal extra- and intracellular Ca(2+) concentration seems necessary for the α1-AR effect since phenylephrine in low Ca(2+) artificial cerebrospinal fluid (ACSF) and depletion of intracellular Ca(2+) stores with thapsigargin (10 μM) failed to increase the AMPA EPSCs' amplitude. Chelerythrine (1μM, protein kinase C (PKC) inhibitor) but not Rp-cAMPS (11 μM, PKA inhibitor) blocked the α1-AR activation effect on AMPA EPSCs, indicating that a PKC intracellular pathway is required. These results demonstrated that presynaptic α1-AR activation modulates glutamatergic inputs that affect VTA-DA neuronal excitability. α1-AR action might be heterosynaptically localized at glutamatergic fibers terminating onto VTA-DA neurons. It is suggested that drug-induced changes in α1-AR could be part of the neuroadaptations occurring in the mesocorticolimbic circuitry during the addiction process.

In vivo voltammetry monitoring of electrically evoked extracellular norepinephrine in subregions of the bed nucleus of the stria terminalis

Norepinephrine (NE) is an easily oxidized neurotransmitter that is found throughout the brain. Considerable evidence suggests that it plays an important role in neurocircuitry related to fear and anxiety responses. In certain subregions of the bed nucleus of the stria terminalis (BNST), NE is found in large amounts. In this work we probed differences in electrically evoked release of NE and its regulation by the norepinephrine transporter (NET) and the α(2)-adrenergic autoreceptor (α(2)-AR) in two regions of the BNST of anesthetized rats. NE was monitored in the dorsomedial BNST (dmBNST) and ventral BNST (vBNST) by fast-scan cyclic voltammetry at carbon fiber microelectrodes. Pharmacological agents were introduced either by systemic application (intraperitoneal injection) or by local application (iontophoresis). The iontophoresis barrels were attached to a carbon fiber microelectrode to allow simultaneous detection of evoked NE release and quantitation of iontophoretic delivery. Desipramine (DMI), an inhibitor of NET, increased evoked release and slowed clearance of released NE in both regions independent of the mode of delivery. However, the effects of DMI were more robust in the vBNST than in the dmBNST. Similarly, the α(2)-AR autoreceptor inhibitor idazoxan (IDA) enhanced NE release in both regions but to a greater extent in the vBNST by both modes of delivery. Since both local application by iontophoresis and systemic application of IDA had similar effects on NE release, our results indicate that terminal autoreceptors play a predominant role in the inhibition of subsequent release.

mGluR8 modulates excitatory transmission in the bed nucleus of the stria terminalis in a stress-dependent manner

Metabotropic glutamate receptors (mGluRs) are important modulators of excitatory transmission, and have been implicated in anxiety and stress-related behaviors. Previously, we showed that group III mGluR agonists could depress excitatory synaptic transmission in the bed nucleus of the stria terminalis (BNST), an integral component of the anxiety circuitry. Here, we provide converging evidence indicating that this effect is mediated primarily by mGluR8, is exerted presynaptically, and is modulated by noradrenergic signaling and stress. The effects of the group III mGluR agonist L-AP4 on excitatory transmission are not potentiated by the mGluR4-selective allosteric potentiator PHCCC, but are mimicked by the mGluR8-selective agonist DCPG. Consistent with these results, mGluR8-like immunoreactivity is seen in the BNST, and the actions of L-AP4 on excitatory transmission are absent in slices from mGluR8 knockout (KO) mice. Application of DCPG is associated with an increase in paired-pulse evoked glutamate synaptic currents, and a decrease in spontaneous glutamate synaptic current frequency, consistent with a primarily presynaptic action. mGluR8-mediated suppression of excitatory transmission is disrupted ex vivo by activation of α1 adrenergic receptors (α1 ARs). BNST mGluR8 function is also disrupted by both acute and chronic in vivo exposure to restraint stress, and in brain slices from α2A AR KO mice. These studies show that mGluR8 is an important regulator of excitatory transmission in the BNST, and suggest that this receptor is selectively disrupted by noradrenergic signaling and by both acute and chronic stress.

Neuroplasticity regulation by noradrenaline in mammalian brain

The neuromodulator noradrenaline (NA) is released in almost all brain areas in a highly diffused manner. Its action is slow, as it acts through G protein-coupled receptors, but its wide release in the brain makes NA a crucial regulator for various fundamental brain functions such as arousal, attention and memory processes [102]. To understand how NA acts in the brain to promote such diverse actions, it is necessary to dissect the cellular actions of NA at the level of single neurons as well as at the level of neuronal networks. In the present article, we will provide a compact review of the main literatures concerning the NA actions on neuroplasticity processes. Depending on which subtype of adrenoceptor is activated, NA differently affects intrinsic membrane properties of postsynaptic neurons and synaptic plasticity. For example, beta-adrenoceptor activation is mainly related to the potentiation of synaptic responses and learning and memory processes. alpha2-adrenoceptor activation may contribute to a high-order information processing such as executive function, but currently the direction of synaptic plasticity modification by alpha2-adrenoceptors has not been clearly determined. The activation of alpha1-adrenoceptors appears to mainly induce synaptic depression in the brain. But its physiological roles are still unclear: while its activation has been described as beneficial for cognitive functions, it may also exert detrimental effects in some brain structures such as the prefrontal cortex.

β-Adrenergic receptors enhance excitatory transmission in the bed nucleus of the stria terminalis through a corticotrophin-releasing factor receptor-dependent and cocaine-regulated mechanism

BACKGROUND

Evidence suggests that the noradrenergic and corticotrophin-releasing factor (CRF) systems play critical roles in relapse and stress-related behaviors. In particular, behavioral studies point to a serial signaling process initiated by β-adrenergic receptors that requires CRF receptor (CRFR)-dependent signaling in the bed nucleus of the stria terminalis (BNST) to produce stress-induced relapse to cocaine seeking.

METHODS

We used whole cell patch clamp recordings from acutely prepared mouse brain slices to examine the actions of β-adrenergic receptors and CRFR1 on excitatory transmission in BNST. We examined the effects of agonists of these receptors in slices prepared from naive, sham, and cocaine-conditioned mice.

RESULTS

β(1)-adrenergic receptor activation within the BNST produces an enhancement of excitatory synaptic transmission that requires CRFR1-dependent signaling. We show that chronic cocaine administration transiently disrupts β(1)-adrenergic- and CRFR1-dependent enhancement of glutamatergic transmission, that this disruption wanes with time, and that it can be reintroduced with a cocaine challenge.

CONCLUSIONS

In total, these studies identify a circuit mechanism within the BNST that may play an important role in CRF- and norepinephrine-regulated behaviors.

The role of the central noradrenergic system in behavioral inhibition

Although the central noradrenergic system has been shown to be involved in a number of behavioral and neurophysiological processes, the relation of these to its role in depressive illness has been difficult to define. The present review discusses the hypothesis that one of its chief functions that may be related to affective illness is the inhibition of behavioral activation, a prominent symptom of the disorder. This hypothesis is found to be consistent with most previous neuropsychopharmacological and immunohistochemical experiments on active behavior in rodents in a variety of experimental conditions using manipulation of neurotransmission at both locus coeruleus and forebrain adrenergic receptors. The findings support a mechanism in which high rates of noradrenergic neural activity suppress the neural activity of principal neurons in forebrain regions mediating active behavior. The suppression may be mediated through postsynaptic galaninergic and adrenergic receptors, and via the release of corticotrophin-releasing hormone. The hypothesis is consistent with clinical evidence for central noradrenergic system hyperactivity in depressives and with the view that this hyperactivity is a contributing etiological factor in the disorder. A similar mechanism may underlie the ability of the noradrenergic system to suppress seizure activity suggesting that inhibition of the spread of neural activation may be a unifying function.

Double-dissociation of the catecholaminergic modulation of synaptic transmission in the oval bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BST) is a cluster of nuclei within the extended amygdala, a forebrain macrostructure with extensive projection to motor nuclei of the hindbrain. The subnuclei of the BST coordinate autonomic, neuroendocrine, and somato-motor functions and receive robust neuromodulatory monoaminergic afferents, including 5-HT-, noradrenaline (NA)-, and dopamine (DA)-containing terminals. In contrast to 5-HT and NA, little is known about how DA modulates neuronal activity or synaptic transmission in the BST. DA-containing afferents to the BST originate in the ventral tegmental area, the periaqueducal gray, and the retrorubral field. They form a fairly diffuse input to the dorsolateral BST with dense terminal fields in the oval (ovBST) and juxtacapsular (jxBST) nuclei. The efferent-afferent connectivity of the BST suggests that it may play a key role in motivated behaviors, consistent with recent evidence that the dorsolateral BST is a target for drugs of abuse. This study describes the effects of DA on synaptic transmission in the ovBST. Whole cell voltage clamp recordings were performed on ovBST neurons in brain slices from adult rats in the presence or absence of exogenous DA and receptor-targeted agonists and antagonists. The results showed that DA selectively and exclusively reduced inhibitory synaptic transmission in the ovBST in a dose-dependent and D2-like dopamine receptor-dependent manner. DA also modulated excitatory synaptic transmission in a dose-dependent dependent manner. However, this effect was mediated by α2-noradrenergic receptors. Thus these data reveal a double dissociation in catecholaminergic regulation of excitatory and inhibitory synaptic transmission in the ovBST and may shed light on the mechanisms involved in neuropathological behaviors such as stress-induced relapse to consumption of drugs of abuse.

Distinct forms of Gq-receptor-dependent plasticity of excitatory transmission in the BNST are differentially affected by stress

Long-term depression (LTD) is an important synaptic mechanism for limiting excitatory influence over circuits subserving cognitive and emotional behavior. A major means of LTD induction is through the recruitment of signaling via G(q)-linked receptors activated by norepinephrine (NE), acetylcholine, and glutamate. Receptors from these transmitter families have been proposed to converge on a common postsynaptic LTD maintenance mechanism, such that hetero- and homosynaptic induction produce similar alterations in glutamate synapse efficacy. We report that in the dorsolateral and ventrolateral bed nucleus of the stria terminalis (BNST), recruitment of G(q)-linked receptors by glutamate or NE initiates mechanistically distinct forms of postsynaptically maintained LTD and these LTDs are differentially regulated by stress exposure. In particular, we show that although both mGluR5- and alpha(1)-adrenergic receptor (AR)-dependent LTDs involve postsynaptic endocytosis, the alpha(1)-AR-initiated LTD exclusively involves modulation of signaling through calcium-permeable AMPA receptors. Further, alpha(1)-AR- but not mGluR5- dependent LTD is disrupted by restraint stress. alpha(1)-AR LTD is also impaired in mice chronically exposed to ethanol. These data thus suggest that in the BNST, NE- and glutamate-activated G(q)-linked signaling pathways differentially tune glutamate synapse efficacy in response to stress.

Presynaptic 5-HT(1B) receptor-mediated serotonergic inhibition of glutamate transmission in the bed nucleus of the stria terminalis

Activation of neurons in the bed nucleus of the stria terminalis (BNST) plays a critical role in stress and anxiety-related behaviors. Previously, we have shown that serotonin (5-HT) can directly modulate BNST neuronal excitability by an action at postsynaptic receptors. In this study we built upon that work to examine the effects of 5-HT on excitatory neurotransmission in an in vitro rat BNST slice preparation. Bath application of 5-HT reversibly reduced the amplitude of evoked excitatory postsynaptic currents (eEPSCs). These effects were mimicked by the 5-HT(1B/D) receptor agonist, sumatriptan, and by the 5-HT(1B) receptor selective agonist, CP93129. Conversely, the effects of 5-HT and sumatriptan could be blocked by the 5-HT(1B) receptor-selective antagonist, GR55562. In contrast, the 5-HT(1A) receptor agonist 8-OH DPAT or antagonist WAY 100635 could not mimic or block the effect of 5-HT on eEPSCs. Together, these data suggest that the 5-HT-induced attenuation of eEPSCs was mediated by 5-HT(1B) receptor activation. Moreover, sumatriptan had no effect on the amplitude of the postsynaptic current elicited by pressure applied AMPA, suggesting a possible presynaptic locus for the 5-HT(1B) receptor. Furthermore, 5-HT, sumatriptan and CP93129 all increased the paired pulse ratio of eEPSCs while they concomitantly decreased the amplitude of eEPSCs, suggesting that these agonists act to reduce glutamate release probability at presynaptic locus. Consistent with this observation, sumatriptan decreased the frequency of miniature EPSCs, but had no effect on their amplitude. Taken together, these results suggest that 5-HT suppresses glutamatergic neurotransmission in the BNST by activating presynaptic 5-HT(1B) receptors to decrease glutamate release from presynaptic terminals. This study illustrates a new pathway by which the activity of BNST neurons can be indirectly modulated by 5-HT, and suggests a potential new target for the development of novel treatments for depression and anxiety disorders.

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

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

Marked behavioral activation from inhibitory stimulation of locus coeruleus alpha1-adrenoceptors by a full agonist

alpha(1)-Adrenoceptors are concentrated in the locus coeruleus (LC) where they appear to regulate various active behaviors but have been difficult to stimulate effectively. The present study examined the behavioral, pharmacological and neural effects of possible stimulation of these receptors with 6-fluoronorepinephrine (6FNE), the only known selective alpha-agonist that has full efficacy at all brain alpha-receptors. Infusion of this compound in the mouse LC was found to produce extreme activation of diverse motivated behaviors of exploration, wheel-running and operant approach responding in different environments consistent with a global behavioral function of the dorsal noradrenergic system. Infusion of selective antagonists of alpha(1)- (terazosin) or alpha(2)- (atipamezole) receptors or of either the partial alpha(1)-agonist, phenylephrine, or full alpha(2)-agonist, dexmedetomidine, indicated that the behavioral effects of 6FNE were due largely due to activation of LC alpha(1)-receptors consistent with the known greater density of alpha(1)- than alpha(2)-adrenoreceptors in the mouse nucleus. Immunohistochemistry of fos in tyrosine hydroxylase-positive LC neurons following IV ventricular infusions indicated that 6FNE markedly depressed whereas terazosin strongly enhanced the apparent functional activity of the nucleus. The changes in fos expression following 6FNE and terazosin were significantly greater than those following dexmedetomidine and atipamezole. It is hypothesized that the alpha(1)-receptors of the mouse LC are strongly activated by 6FNE and serve to potently inhibit its tonic or stress-induced activity which in turn disinhibits prepotent motivated behaviors.

alpha2A-adrenergic receptors heterosynaptically regulate glutamatergic transmission in the bed nucleus of the stria terminalis

Stress is a major driving force in reinstatement of drug-seeking behavior. The bed nucleus of the stria terminalis (BNST) has been identified as a key brain region in this behavior, and receives a dense input of the stress-neurotransmitter norepinephrine through the ventral noradrenergic bundle. Activation of alpha(2)-adrenergic receptors (alpha(2)-ARs) in the BNST blocks stress-induced reinstatement of drug-seeking, indicating a potentially important role for these receptors. Currently, it is unclear how alpha(2)-AR agonists elicit this behavioral action, or through which alpha(2)-AR subtype. Activation of alpha(2)-ARs decreases glutamatergic transmission in the BNST, an effect which is nearly absent in the alpha(2A)-AR knockout mouse. Here, we take advantage of a knock-in mouse in which a hemagglutinin-tagged alpha(2A)-AR was inserted into the endogenous locus, along with the alpha(2A)-AR selective agonist guanfacine, to further study the role of the alpha(2A)-AR subtype in modulation of neurotransmission in the BNST. Using immunohistochemistry, we find that alpha(2A)-ARs are highly expressed in the BNST, and that this expression is more similar in distribution to the vesicular glutamate transporters than to either norepinephrine transporter or tyrosine hydroxylase positive terminals. Using whole cell patch-clamp recordings, we show that guanfacine causes a depression of evoked excitatory and, to a more limited extent, inhibitory fast synaptic transmission. In total, these data support a prominent heterosynaptic role for alpha(2A)-ARs in modulating fast synaptic transmission in the BNST.

Alpha-1A adrenergic receptor activation increases inhibitory tone in CA1 hippocampus

The endogenous catecholamine norepinephrine (NE) exhibits anti-epileptic properties, however it is not well understood which adrenergic receptor (AR) mediates this effect. The aim of this study was to investigate alpha(1)-adrenergic receptor activation in region CA1 of the hippocampus, a subcortical structure often implicated in temporal lobe epilepsies. Using cell-attached and whole-cell recordings in rat hippocampal slices, we confirmed that selective alpha(1)-AR activation increases action potential firing in a subpopulation of CA1 interneurons. We found that this response is mediated via the alpha(1A)-AR subtype, initiated by sodium influx, and appears independent of second messenger signaling. In CA1 pyramidal cells, alpha(1A)-AR activation decreases activity due to increased pre-synaptic GABA and somatostatin release. Examination of post-synaptic receptor involvement revealed that while GABA(A) receptors mediate the majority of alpha(1A)-adrenergic effects on CA1 pyramidal cells, significant contributions are also made by GABA(B) and somatostatin receptors. Finally, to test whether alpha(1A)-AR activation could have potential therapeutic implications, we performed AR agonist challenges using two in vitro epileptiform models. When GABA(A) receptors were available, alpha(1A)-AR activation significantly decreased epileptiform bursting in CA1. Together, our findings directly link stimulation of the alpha(1A)-AR subtype to release of GABA and somatostatin at the single cell level and suggest that alpha(1A)-AR activation may represent one mechanism by which NE exerts anti-epileptic effects within the hippocampus.

Post-training infusion of glutamate into the bed nucleus of the stria terminalis enhanced inhibitory avoidance memory: an effect involving norepinephrine

This study examined an interaction between glutamate and norepinephrine in the bed nucleus of the stria terminalis (BNST) in modulating affective memory formation. Male Wistar rats with indwelling cannulae in the BNST were trained on a one-trial step-through inhibitory avoidance task and received pre- or post-training intra-BNST infusion of glutamate, norepinephrine or their antagonists. Results of the 1-day test indicated that post-training intra-BNST infusion of DL-2-amino-5-phosphonovaleric acid (APV) impaired retention in a dose- and time-dependent manner, while infusion of glutamate had an opposite effect. Co-infusion of 0.2microg glutamate and 0.02microg norepinephrine resulted in marked retention enhancement by summating non-apparent effects of the two drugs given at a sub-enhancing dose. The amnesic effect of 5.0microg APV was ameliorated by 0.02microg norepinephrine, while the memory enhancing effect of 1.0microg glutamate was attenuated by 5.0microg propranolol. These findings suggest that training on an inhibitory avoidance task may alter glutamate neurotransmission, which by activating NMDA receptors releases norepinephrine to modulate memory formation via beta adrenoceptors in the BNST.

Yohimbine impairs extinction of cocaine-conditioned place preference in an alpha2-adrenergic receptor independent process

Extinction, a form of learning that has the ability to reshape learned behavior based on new experiences, has been heavily studied utilizing fear learning paradigms. Mechanisms underlying extinction of positive-valence associations, such as drug self-administration and place preference, are poorly understood yet may have important relevance to addiction treatment. Data suggest a major role for the noradrenergic system in extinction of fear-based learning. Employing both pharmacological and genetic approaches, we investigated the role of the alpha(2)-adrenergic receptor (alpha(2)-AR) in extinction of cocaine-conditioned place preference (CPP) and glutamatergic transmission in the bed nucleus of the stria terminalis (BNST). We found that pre-extinction systemic treatment with the alpha(2)-AR antagonist yohimbine impaired cocaine CPP extinction in C57BL/6J mice, an effect that was not mimicked by the more selective alpha(2)-AR antagonist, atipamezole. Moreover, alpha(2A)-AR knockout mice exhibited similar cocaine CPP extinction and exacerbated extinction impairing effects of yohimbine. Using acute brain slices and electrophysiological approaches, we found that yohimbine produces a slowly evolving depression of glutamatergic transmission in the BNST that was not mimicked by atipamezole. Further, this action was extant in slices from alpha(2A)-AR knockout mice. Our data strongly suggest that extinction-modifying effects of yohimbine are unlikely to be due to actions at alpha(2A)-ARs.