LOCAL PREOPTIC-ANTERIOR HYPOTHALAMIC WARMING ALTERS SPONTANEOUS AND EVOKED NEURONAL-ACTIVITY IN THE MAGNO-CELLULAR BASAL FOREBRAIN

Local warming of the medial preoptic/anterior hypothalamus (POAH) prom otes sleep, enhances EEG slow-wave activity during sleep, and suppress es arousal-related discharge in neurons of the midbrain reticular form ation (MRF) and the posterior lateral hypothalamic area (PLHa). Anothe r important site of sleep and arousal regulation, and a potential site of POAH thermal modulation, is the magnocellular basal forebrain (BF) . We examined the ability of local POAH warming during wakefulness to influence the spontaneous and evoked discharge of neurons recorded in the BF of unanesthetized, unrestrained cats. Seventy of 174 BF neurons responded to 60-90 s periods of POAH warming with either increases or decreases in discharge rate. Forty-one of the 70 responsive cells dis played suppression of waking discharge during warming. Discharge rate in these cells declined by an average of 26.04 +/- 2.76%/degrees C of POAH temperature increase. The majority of warming-suppressed BF cells (73%) displayed higher rates of discharge during periods of wakefulne ss compared to periods of sleep. Twenty-nine of 70 responsive cells re sponded to POAH warming with an average increase in discharge rate of 43.81 +/- 6.26%/degrees C. A majority of these neurons (62%) exhibited higher spontaneous discharge rates during sleep compared to waking. O rthodromic excitatory responses were evoked in 29 BF cells by electric al stimulation of the MRF or PLHa. Thirteen of 29 cells displayed a wa king-related discharge pattern, and responded to POAH warming with a s ignificant suppression of evoked excitation. For a group of 15 behavio ral state-indifferent cells (i.e., cells displaying no modulation of s pontaneous discharge rate across the sleep-waking cycle), POAH warming had no effect on evoked excitatory responses. These results support t he hypothesis that thermosensitive neurons of the POAH exert control o f sleep-waking state, in part, via modulation of arousal- and sleep-re gulating cell types within the magnocellular BF.