Adenosine 2A Receptors Link Astrocytic Alpha-1 Adrenergic Signaling to Wake-Promoting Dopamine Neurons

Abstract

BACKGROUNDSleep and arousal disorders are common, but the underlying physiology of wakefulness is not fully understood. The locus coeruleus promotes arousal via alpha-1 adrenergic receptor (α1AR) driven recruitment of wake-promoting dopamine (DA) neurons in the ventral periaqueductal gray (vPAGDA neurons). α1AR expression is enriched on vPAG astrocytes, and chemogenetic activation of astrocytic Gq signaling promotes wakefulness. Astrocytes can release extracellular "gliotransmitters," such as ATP and adenosine, but the mechanism underlying how vPAG astrocytic α1ARs influence sleep/wake behavior and vPAGDA neuron physiology is unknown. METHODSIn this study, we utilized genetic manipulations with ex vivo calcium imaging in vPAGDA neurons and astrocytes, patch-clamp electrophysiology, and behavioral experiments in mice to probe our hypothesis that astrocytic α1ARs mediate noradrenergic modulation of wake-promoting vPAGDA neurons via adenosine signaling. RESULTSActivation of α1ARs with phenylephrine increased calcium transients in vPAGDA neurons and vPAG astrocytes, and increased vPAGDA neuron excitability ex vivo. Chemogenetic Gq-DREADD activation of vPAG astrocytes similarly increased vPAGDA neuron calcium activity and intrinsic excitability. Conversely, shRNA knockdown of vPAG astrocytic α1ARs reduced the excitatory effect of phenylephrine on vPAGDA neurons and blunted arousal during the wake phase. Pharmacological blockade of adenosine 2A (A2A) receptors precludes the α1AR-induced increase in vPAGDA calcium activity and excitability in brain slices, as well as the wake-promoting effects of vPAG α1AR activation in vivo. CONCLUSIONSWe have identified a crucial role for vPAG astrocytic α1AR receptors in sustaining arousal through heightened excitability and activity of vPAGDA neurons mediated by local A2A receptors.