Relation between hippocampal γ waves and behavioral disturbances induced by phencyclidine and methamphetamine

Abstract

The relationship between hippocampal electrical activity and behavioral hyperactivity induced by either phencyclidine (PCP) or methamphetamine (MAP) was examined in freely behaving rats. The EEGs at the hippocampal CA1 region were simultaneously recorded with the animal’s behavior for 2 h after administration of either PCP or MAP. PCP (10 mg/kg, intraperitoneal (i.p.)) significantly increased locomotor activity including rearing, walking, head-weaving and circling. Spectral analysis of the EEG showed that hippocampal γ waves (30–70 Hz), but not other frequency bands, were significantly increased from 5 to 120 min after systemic injection of PCP. Inactivation of the medial septum with muscimol, a γ-aminobutyric acid receptor A agonist, 15 min prior to injection of PCP, suppressed both hippocampal γ waves and locomotor activity. MAP (1.5 mg/kg, i.p.) also increased locomotor activity for longer than 2 h. During the behavioral hyperactivity induced by MAP, hippocampal EEG showed θ and γ rhythms that were not significantly different from those during walking before MAP. However, MAP-induced behavioral activity was suppressed by pre-injection of muscimol in the medial septum, which also decreased hippocampal γ activity. It is suggested that the medial septum plays a role in mediating behavioral disturbances induced by both PCP and MAP through control of the hippocampal electrical activity, and that hippocampal γ waves may play a permissible role in the expression of behaviors.