BRAIN TEMPERATURE-RELATED AND BEHAVIOR-RELATED CHANGES IN THE DENTATEGYRUS FIELD POTENTIAL DURING SLEEP, COLD-WATER IMMERSION, RADIANT HEATING, AND URETHANE ANESTHESIA

The field potential evoked in the dentate gyrus (DG) by stimulation of the perforant path (PP) is known to vary with ongoing behavior and wi th brain temperature. To further study these phenomena chronic stimula ting and recording electrodes were implanted into the PP and DG of rat s, and a thermistor was implanted into the contralateral homotopic DG. Field potentials and brain temperature records were made during (1) s low wave sleep (SWS), (2) radiant heating, (3) immersion in cool water , (4) a control session during which no manipulations were made, and ( 5) under urethane anesthesia. In another group of rats field potential s were recorded during (1) baseline immobile wakefulness, (2) SWS, (3) before SWS or after gentle awakening from SWS (eyes open and presence of intermittent slow waves in the EEG), (4) immobile wakefulness, and (5) 24 h later. Findings were that field EPSP slope decreased and pop ulation spike (PS) amplitude increased by up to 60% of baseline values during conditions in which brain temperature was reduced (SWS, immers ion in cool water, urethane anesthesia). Conversely, EPSP slope increa sed and PS amplitude decreased by up to 100% of baseline values during conditions in which brain temperature increased (awakening from SWS, radiant heating, and warming after immersion in cool water or urethane anesthesia). Product moment correlations between brain temperature an d field potential measures confirmed the statistical reliability of th ese findings and accounted for up to 77% of the variance. These findin gs confirm the robust effect on hippocampal field potentials of brain temperature changes due to exogenous heating and cooling, and extend t his effect to anesthetic- and sleep-induced brain temperature changes. They also identify a state that behaviorally resembles quiet wakefuln ess but resembles SWS in terms of neocortical EEG, brain temperature, and hippocampal field potential measures. The findings indicate the ne ed to control for brain temperature-mediated changes in hippocampal re search that uses the dentate gyrus field potential as a dependent meas ure.