EEG AROUSAL, SYMPATHETIC ACTIVITY, AND BROWN ADIPOSE-TISSUE THERMOGENESIS AFTER CONDITIONED TASTE-AVERSION

Conditioned taste aversion was induced in rats by pairing saccharin wi th intraperitoneal LiCl injection. Animals injected with NaCl served a s controls. After evaluating the preference levels for saccharin in ra ts of both groups, the animals were anesthetized with urethane and the duration of EEG desynchronization, firing rate of sympathetic nerves innervating interscapular brown adipose tissue (BAT), and temperature of the same tissues were recorded, before and after oral stimulation w ith saccharin or water. The EEG desynchronization was longer in condit ioned rats after stimulation with saccharin. Firing rate of sympatheti c nerves was higher in conditioned rats after presentation of sacchari n. BAT temperature, decreased in conditioned rats after saccharin stim ulus, was unchanged in the three other conditions. In a second experim ent temperature and firing rate of sympathetic nerves of BAT were reco rded after oral presentation of water or saccharin in rats treated as in the first experiment and injected with the alpha(1)-adrenergic bloc ker prazosin. As in the first experiment, saccharin presentation in co nditioned animals enhanced the neural sympathetic activity, whereas di fferently from the first experiment it increased BAT temperature. No c hanges were found in the same measurements in the three other conditio ns. The drop in interscapular BAT temperature found in the first exper iment, an unexpected finding, probably depends on the use of lithium a s unconditioned stimulus, because LiCl interacting with adrenergic rec eptors changes the two-phase response, normally seen in interscapular BAT after increased sympathetic activity, in a single-phase response.