EEG change in the conscious rat during immobility induced by psychological stress

EEG changes in the conscious rat under conditions of stress were quantitatively analyzed. After conditioning the rat to expect an electroshock when placed in the test box, the rat assumed a catatonia-like immobility when placed in the box even though the electroshock was not applied. While in this state relative brain-wave activity over the range 7.5--13.0 Hz significantly increased in the cortex and the hippocampus, but not in the amygdaloid and the caudate nuclei. The immobility accompanied by changes in the EEG disappeared when the animal was returned to the home cage and immediately reappeared after the rat was retransferred to the test box. Diazepam (10 mg/kg, PO), CS-386 (5 mg/kg, PO), nicotinamide (1 mg/kg, IP), and chlorpromazine (10 mg/kg, PO) significantly suppressed the augmented activity under the same stress condition. The difference between drug-induced catatonia or catalepsy and the catatonia-like immobility under the stress condition was discussed.