Prostaglandin D2-sensitive, sleep-promoting zone defined in the ventral surface of the rostral basal forebrain.

The site of action for the sleep-promoting effect of prostaglandin (PG) D2 was extensively examined in the brain of adult male rats (n = 231). PGD2 was administered at 100 pmol/0.2 microliter per min for 6 hr (2300-0500 hr) through chronically implanted microdialysis probes or infusion cannulae. Among the administrations of PDG2 by dialysis probes (n = 176), only those (n = 8) to a ventro-rostral part of the basal forebrain by the probes implanted on the midline consistently increased slow-wave sleep (SWS), by 51 +/- 6 min (mean +/- SEM) above the baseline value (111 +/- 11 min). Since this area is separated by a cleft into right and left regions, the results were interpreted to mean that, through this cleft, PGD2 diffused in the subarachnoid space over the adjacent ventral surface, where it had the effect of promoting sleep. When PGD2 was directly infused into the subarachnoid space (n = 55), extraordinary increases exceeding 90 min were consistently attained for the SWS at sites located between 0.5 and 2 mm rostral to the bregma and between 0 and 1.2 mm lateral to the midline defined according to the stereotaxic coordinates adopted from the brain atlas of Paxinos and Watson [Paxinos, G. & Watson, C. (1986) The Rat Brain in Stereotaxic Coordinates (Academic, San Diego)]. Thus, we demarcated a "PGD2-sensitive, sleep-promoting zone" within this region in the ventral surface of the rostral basal forebrain. During the bilateral infusion of PGD2 into the subarachnoid space of this zone, the hourly mean SWS level of the nocturnal animals (n = 6) in the night reached the maximum at the second hour of the infusion period; this maximum hourly SWS level, corresponding to the daytime level of the same animals, lasted until the end of PGD2 infusion.