ACTIVATION OF VENTROLATERAL PREOPTIC NEURONS BY THE SOMNOGEN PROSTAGLANDIN D-2

Prostaglandin D-2 (PGD(2)) is an extensively studied sleep-promoting s ubstance, but the neuroanatomical basis of PGD(2)-induced sleep is onl y partially understood. To determine potential regions involved in thi s response, we used Fos immunohistochemistry to identify neurons activ ated by infusion of PGD(2) into the subarachnoid space below the rostr al basal forebrain, PGD(2) increased nonrapid eye movement sleep and i nduced striking expression of Fos in the ventrolateral preoptic area ( VLPO), a cluster of neurons that may promote sleep by inhibiting the t uberomammillary nucleus, the source of the ascending histaminergic aro usal system, Fos expression in the VLPO was positively correlated with the preceding amount of sleep and negatively correlated with Fos expr ession in the tuberomammillary nucleus. PGD(2) also increased Fos immu noreactivity in the basal leptomeninges and several regions implicated in autonomic regulation, These observations suggest that PGD(2) may i nduce sleep via leptomeningeal PGD(2) receptors with subsequent activa tion of the VLPO.