Effects of histamine on thermosensitive neurons in rat preoptic slice preparations

Single neuronal activities were recorded extracellularly from slice preparations of the rat preoptic area and effects of histamine (0.01 10 microM) on the activities were examined with regard to thermosensitivies of the neurons. Superfusion of histamine increased the firing rate in 52 of 75 warm-sensitive neurons and in 22 of 41 thermally insensitive neurons in a dose-dependent manner. Ten (3%) warm-sensitive neurons and 6 (15%) thermally insensitive neurons were inhibited by histamine. Mepyramine (10 microM) (H1-antagonist), but not famotidine (H2-antagonist), blocked the histamine (10 microM) induced excitation in 19 (76%) of 25 warm-sensitive neurons and in 6 (75%) of 8 thermally insensitive neurons. These results suggest that histamine excites both warm-sensitive and thermally insensitive neurons in the preoptic area mainly via the H1-receptor.