Prepulse inhibition (PPI) is thought to reflect the operation of a sensorimotor gating system in the brain. Sensorimotor gating abnormalities have been identified in schizophrenic patients, and various neural systems are involved in this function. To study the modulation of the sensorimotor gating system by the N-methyl-D-aspartate (NMDA) receptor channel complex, the effects of noncompetitive and competitive NMDA antagonists on PPI were examined in rats. PPI was not disrupted by CGS 19755, a competitive NMDA antagonist, at 30 min after subcutaneous (s.c.) administration. However, CGS 19755 (40 mg/kg s.c.) decreased PPI at 120 min after administration with a marked decrease of startle amplitude. Late onset of the effect of CGS 19755 was also observed in the increase of spontaneous locomotor activity (SLA). On the other hand, phencyclidine, a noncompetitive NMDA antagonist, disrupted PPI at 30 min after administration and increased SLA from 20 min after administration. PPI was also disrupted by bilateral intracerebroventricular administration of 5,7-dichlorokyn urenate (10 and 20 micrograms/side X 2), an antagonist at the strychnine-insensitive glycine receptor, which is an allosteric binding site in the NMDA receptor-channel complex. It is concluded that the NMDA receptor-channel complex plays an important role in regulation of PPI.