Dorsal BNST α_2A-Adrenergic Receptors Produce HCN-Dependent Excitatory Actions That Initiate Anxiogenic Behaviors

Abstract

Stress is a precipitating agent in neuropsychiatric disease and initiates relapse to drug-seeking behavior in addicted patients. Targeting the stress system in protracted abstinence from drugs of abuse with anxiolytics may be an effective treatment modality for substance use disorders. α-adrenergic receptors (α-ARs) in extended amygdala structures play key roles in dampening stress responses. Contrary to early thinking, α-ARs are expressed at non-noradrenergic sites in the brain. These non-noradrenergic α-ARs play important roles in stress responses, but their cellular mechanisms of action are unclear. In humans, the α-AR agonist guanfacine reduces overall craving and uncouples craving from stress, yet minimally affects relapse, potentially due to competing actions in the brain. Here, we show that heteroceptor α-ARs postsynaptically enhance dorsal bed nucleus of the stria terminalis (dBNST) neuronal activity in mice of both sexes. This effect is mediated by hyperpolarization-activated cyclic nucleotide-gated cation channels because inhibition of these channels is necessary and sufficient for excitatory actions. Finally, this excitatory action is mimicked by clozapine--oxide activation of the G-coupled DREADD hM4Di in dBNST neurons and its activation elicits anxiety-like behavior in the elevated plus maze. Together, these data provide a framework for elucidating cell-specific actions of GPCR signaling and provide a potential mechanism whereby competing anxiogenic and anxiolytic actions of guanfacine may affect its clinical utility in the treatment of addiction. Stress affects the development of neuropsychiatric disorders including anxiety and addiction. Guanfacine is an α2A-adrenergic receptor (α2A-AR) agonist with actions in the bed nucleus of the stria terminalis (BNST) that produces antidepressant actions and uncouples stress from reward-related behaviors. Here, we show that guanfacine increases dorsal BNST neuronal activity through actions at postsynaptic α2A-ARs via a mechanism that involves hyperpolarization-activated cyclic nucleotide gated cation channels. This action is mimicked by activation of the designer receptor hM4Di expressed in the BNST, which also induces anxiety-like behaviors. Together, these data suggest that postsynaptic α2A-ARs in BNST have excitatory actions on BNST neurons and that these actions can be phenocopied by the so-called "inhibitory" DREADDs, suggesting that care must be taken regarding interpretation of data obtained with these tools.

Galanin Neurons Unite Sleep Homeostasis and α2-Adrenergic Sedation

“…Although it is commonly thought that dexmedetomidine induces sedation by inhibiting noradrenaline release from neurons in the locus ceruleus [55, 56, 57], there is evidence that this is not the case [15, 18, 58]: VLPO lesions in rats blunt the ability of dexmedetomidine to induce sedation [16]; dexmedetomidine induces cFOS expression in the PO [15, 16], and can induce sedation even when noradrenaline release from the locus ceruleus is genetically removed [58]; and reactivating ensembles of PO neuron activity tagged during dexmedetomidine-induced is sufficient to induce NREM sleep and hypothermia [15]. Dexmedetomidine is expected to directly excite PO neurons by influencing hyperpolarization-activated cyclic nucleotide-gated cation channels [59].…”

Galanin neurons in the hypothalamus link sleep homeostasis, body temperature and actions of the α2 adrenergic agonist dexmedetomidine

“…Conceptually, making LPO galanin neurons selectively sensitive to the excitatory effects of hM3Dq CNO receptors ( Fig. S1 & S3) mimics the actions of dexmedetomidine which can directly excite neurons by Gi-mediated inhibition of hyperpolarization-activated cyclic nucleotide-gated cation channels (62). Both CNO and dexmedetomidine induce NREM-like sedation with enhanced delta power and hypothermia, with the exception that the hM3Dq receptors are confined to LPO galanin neurons, whereas a2a receptors are widespread.…”

The first identification of nesfatin-1-expressing neurons in the human bed nucleus of the stria terminalis

“…The bed nucleus of the stria terminalis (BNST), a part of the so-called “extended amygdala”, is a minor gray matter aggregation located in the medial basal forebrain of vertebrate species. Accumulating evidence prove that this intriguing structure plays a crucial role in the integration of stress and reward signaling, generation of anxiety responses, and regulation of fear learning (Harris et al 2018 ; Pelrine et al 2016 ; Rodriguez-Sierra et al 2016 ). This maybe highly involved in the neuromechanism of addiction and feeding behavior (Ch’ng et al 2018 ; Avery et al 2016 ; Pleil et al 2016 ).…”