Adenosine A2A Receptors Link Astrocytic a1-Adrenergic Signaling to Wake-Promoting Dopamine Neurons

BACKGROUND: Sleep and arousal disorders are common, but the underlying physiology of wakefulness is not fully understood. The locus coeruleus promotes arousal via a1-adrenergic receptor (a1AR)-driven recruitment of wakepromoting dopamine neurons in the ventral periaqueductal gray (vPAGDAneurons). a1AR 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 a1ARs influence sleep/wake behavior and vPAGDAneuron physiology is unknown. METHODS: In this study, we utilized genetic manipulations with ex vivo calcium imaging in vPAGDAneurons and astrocytes, patch-clamp electrophysiology, and behavioral experiments in mice to test our hypothesis that astrocytic a1ARs mediate noradrenergic modulation of wake-promoting vPAGDAneurons via adenosine signaling. RESULTS: Activation of a1ARs with phenylephrine increased calcium transients in vPAGDAneurons and vPAG exclusively activated by designer drugs) activation of vPAG astrocytes similarly increased vPAGDAneuron calcium activity and intrinsic excitability. Conversely, short hairpin RNA knockdown of vPAG astrocytic a1ARs reduced the excitatory effect of phenylephrine on vPAGDAneurons and blunted arousal during the wake phase. Pharmacological blockade of adenosine A2A receptors precluded the a1AR-induced increase in vPAGDAcalcium activity and excitability in brain slices, as well as the wake-promoting effects of vPAG a1AR activation in vivo. CONCLUSIONS: We have identified a crucial role for vPAG astrocytic a1ARs in sustaining arousal through heightened excitability and activity of vPAGDAneurons mediated by local A2A receptors.