Choline acetyltransferase expression during periods of behavioral activityand across natural sleep-wake states in the basal forebrain

The present study examined whether the expression of the messenger RNA enco ding the protein responsible for acetylcholine synthesis is associated with sleep-wakefulness. Choline acetyltransferase messenger RNA levels were ana lysed using a semi-quantitative assay in which reverse transcription was co upled to complementary DNA amplification using the polymerase chain reactio n. To examine the relationship between steady-state messenger RNA and behav ioral activity, rats were killed during the day (4.00 p.m.) or night (4.00 a.m.), and tissue from the vertical and horizontal limbs of the diagonal ba nds of Broca was analysed. Choline acetyltransferase messenger RNA levels w ere higher during the day than during the night. The second study examined more closely the association between choline acetyltransferase messenger RN A levels and individual bouts of wakefulness, slow-wave sleep or rapid eye movement sleep. Choline acetyltransferase messenger RNA levels were low dur ing wakefulness, intermediate in slow-wave sleep and high during rapid eye movement sleep. In contrast, protein activity, measured at a projection sit e of cholinergic neurons of the basal forebrain, was higher during wakefuln ess than during sleep. These findings suggest that choline acetyltransferase protein and messenger RNA levels exhibit an inverse relationship during sleep and wakefulness. T he increased messenger RNA expression during sleep is consistent with a res torative function of sleep.