Adenosine A(2A) Receptors Link Astrocytic α(1)-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 α(1)-adrenergic receptor (α(1)AR)-driven recruitment of wake-promoting dopamine neurons in the ventral periaqueductal gray (vPAG(DA) neurons). α(1)AR expression is enriched on vPAG astrocytes, and chemogenetic activation of astrocytic G(q) signaling promotes wakefulness. Astrocytes can release extracellular gliotransmitters, such as ATP and adenosine, but the mechanism underlying how vPAG astrocytic α(1)ARs influence sleep/wake behavior and vPAG(DA) neuron physiology is unknown. METHODS: In this study, we utilized genetic manipulations with ex vivo calcium imaging in vPAG(DA) neurons and astrocytes, patch-clamp electrophysiology, and behavioral experiments in mice to test our hypothesis that astrocytic α(1)ARs mediate noradrenergic modulation of wake-promoting vPAG(DA) neurons via adenosine signaling. RESULTS: Activation of α(1)ARs with phenylephrine increased calcium transients in vPAG(DA) neurons and vPAG astrocytes and increased vPAG(DA) neuron excitability ex vivo. Chemogenetic Gq-DREADD (designer receptor exclusively activated by designer drugs) activation of vPAG astrocytes similarly increased vPAG(DA) neuron calcium activity and intrinsic excitability. Conversely, short hairpin RNA knockdown of vPAG astrocytic α(1)ARs reduced the excitatory effect of phenylephrine on vPAG(DA) neurons and blunted arousal during the wake phase. Pharmacological blockade of adenosine A(2A) receptors precluded the α(1)AR-induced increase in vPAG(DA) calcium activity and excitability in brain slices, as well as the wake-promoting effects of vPAG α(1)AR activation in vivo. CONCLUSIONS: We have identified a crucial role for vPAG astrocytic α(1)ARs in sustaining arousal through heightened excitability and activity of vPAG(DA) neurons mediated by local A(2A) receptors.