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

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