The role of hippocampal theta activity in sensory gating in the rat

Sensory gating is defined as a decreased reaction on the second click, meas ured as evoked potentials (EP) within a double-click paradigm. Recently, it was established that gating in rats was decreased during REM sleep compare d to wakefulness and non-REM sleep. REM sleep in the rat is characterized b y hippocampal theta rhythm. Therefore, it was investigated whether sensory gating would also be diminished during other states with hippocampal theta. Twelve Wistar rats were implanted with hippocampal electrodes and exposed to double clicks during passive wakefulness, REM sleep, and activity (volun tary movements and walking on a moving belt). Gating was examined by use of the amplitudes of the EPs in reaction to the first conditioned amplitude ( CAMP) and second click test amplitude (TAMP), as well as two gating paramet ers (C - T score and TIC ratio). Except passive wakefulness, all behavioral conditions were accompanied by hippocampal theta. Normal gating was always found, except during REM sleep. The CAMP was then lower than during passiv e wakefulness. Gating was less disturbed during behavioral activity. Negati ve correlations were found between the percentage theta power on the one si de, and the CAMP and the C - T score on the other. The correlation between the percentage theta power and the T/C ratio was also significant. It is co ncluded that the presence of hippocampal. theta is not a sufficient conditi on to cause disturbances in auditory sensory gating. Behavioral states that accompany theta activity, however, tend to affect the CAMP. The decrease i n gating found during REM sleep cannot be easily related to well-known neur ochemical and pharmacological data. (C) 2001 Elsevier Science Inc. All righ ts reserved.