The paraventricular thalamus is required for homeostatic sleep regulation by adenosine

Adenosine has been proposed as a prominent mediator of sleep homeostasis. Adenosine accumulation during wakefulness induces transitions to non-rapid eye movement (NREM) sleep. However, the precise neural mechanisms underlying the homeostatic regulation of sleep by adenosine have not been fully elucidated.

All experiments were conducted in male mice. Genetically-encoded adenosine sensors were used to assess the dynamic fluctuations of extracellular adenosine in the paraventricular thalamus (PVT). We performed whole-cell patch-clamp recordings in vitro to investigate the effects of adenosine on PVT neurons, and combined these experiments with fibre photometry and multi-channel electrophysiological recordings in vivo. Electroencephalogram (EEG)/electromyogram (EMG) recordings were used to investigate the role of adenosine in regulating wakefulness and sleep, together with drug administration, sleep deprivation (SD) and RNA interference (RNAi).

In the PVT, extracellular adenosine was significantly elevated during wakefulness compared with NREM sleep. Adenosine caused membrane potential hyperpolarisation and decreased action potential firing in PVT neurons by activating A₁ receptors (A₁Rs). Adenosine also decreased spontaneous calcium activity and spike firing of PVT neurons in vivo. PVT application of adenosine promoted NREM sleep at the beginning of the dark phase, whereas A₁R blockade or selective knockdown of A₁Rs decreased NREM sleep mainly during the light phase. High concentrations of adenosine beyond the physiological range exhibited blunted NREM sleep-promoting effects by activating A_2A receptors (A_2ARs).

These results revealed that homeostatic sleep regulation by adenosine requires the PVT, adding new insights into the homeostatic regulation of sleep.