Gabaergic neurons with alpha2-adrenergic receptors in basal forebrain and preoptic area express c-Fos during sleep.

The basal forebrain (BF) contains cholinergic neurons that stimulate cortical activation during waking. In addition, both the BF and adjacent preoptic area (POA) contain neurons that promote sleep. We examined c-Fos expression in cholinergic and GABAergic neurons in the BF and POA to determine whether they are differentially active following sleep deprivation versus recovery and whether the GABAergic neurons are active during sleep. Whereas the numbers of c-Fos+ cells and proportions of c-Fos+ cells that were cholinergic were decreased, the proportions that were GABAergic were increased following sleep recovery across BF and POA nuclei. Moreover, the sleep-active GABAergic neurons were immunostained for alpha2A-adrenergic receptors. We conclude that GABAergic neurons that commonly bear alpha2-adrenergic receptors comprise sleep-active cells of the BF and POA. These GABAergic cells would be inhibited by noradrenaline (NA) released from locus coeruleus neurons during waking; they would be disinhibited through diminished NA release during drowsiness and thus become active to promote sleep by inhibiting in turn wake-promoting neurons.