Orexin neurons of the hypothalamus express adenosine A1 receptors.

Adenosine is a putative sleep factor with effects mainly mediated by the A1 receptor. Recent studies have implicated the hypothalamic orexin/hypocretin-containing neurons in the control of sleep-wakefulness. To help determine if adenosine might play a role in the control of orexin neurons, immunohistochemistry was used to characterize the distribution of adenosine A1 receptor protein on the orexinergic neurons. About 30% of orexin-containing neurons were labeled. The data supports the presence of adenosine A1 receptors on orexinergic neurons and suggests a possible substrate for a functional role of adenosine in the regulation of orexinergic activity.