Adenosine A2A receptors in the olfactory bulb suppress rapid eye movement sleep in rodents

Rapid eye movement (REM) sleep behavior disorder in humans is often accompanied by a reduced ability to smell and detect odors, and olfactory bulbectomized rats exhibit increased REM sleep, suggesting that the olfactory bulb (OB) is involved in REM-sleep regulation. However, the molecular mechanism of REM-sleep regulation by the OB is unknown. Adenosine promotes sleep and its A(2A) receptors (A(2A)R) are expressed in the OB. We hypothesized that A(2A)R in the OB regulate REM sleep. Bilateral microinjections of the A(2A)R antagonist SCH58261 into the rat OB increased REM sleep, whereas microinjections of the A(2A)R agonist CGS21680 decreased REM sleep. Similar to the A(2A)R antagonist, selective A(2A)R knockdown by adeno-associated virus carrying short-hairpin RNA for A(2A)R in the rat OB increased REM sleep. Using chemogenetics on the basis of designer receptors exclusively activated by designer drugs, we demonstrated that the inhibition of A(2A)R neurons increased REM sleep, whereas the activation of these neurons decreased REM sleep. Moreover, using a conditional anterograde axonal tract-tracing approach, we found that OB A(2A)R neurons innervate the piriform cortex and olfactory tubercle. These novel findings indicate that adenosine suppresses REM sleep via A(2A)R in the OB of rodents.