Identification of sleep-promoting neurons in vitro

The neurons responsible for the onset of sleep are thought to be located in the preoptic area(1-3) and more specifically, in the ventrolateral preopti c nucleus (VLPO)(4-6). Here we identify sleep-promoting neurons in vitro an d show that they represent an homogeneous population of cells that must be inhibited by systems of arousal during the waking state. We rnd that two-th irds of the VLPO neurons are multipolar triangular cells that show a low-th reshold spike. This proportion matches that of cells active during sleep in the same region(6). We then show, using single-cell reverse transcriptase followed by polymerase chain reaction, that these neurons probably contain g-aminobutyric acid (GABA). We also show that these neurons are inhibited b y noradrenaline and acetylcholine, both of which are transmitters of wakefu lness(3,7,8). As most of these cells are also inhibited by serotonin but un affected by histamine, their overall inhibition by transmitters of wakefuln ess is in agreement with their relative inactivity during waking with respe ct to sleep(6). We propose that the reciprocal inhibitory interaction of su ch VLPO neurons with the noradrenergic, serotoninergic and cholinergic waki ng systems to which they project(5,9,10) is a key factor for promoting slee p.