Effects of competitive and noncompetitive NMDA receptor antagonists on kindling and LTP

In the present study, comparative studies of the effects of competitive and noncompetitive antagonists of NMDA receptors (CPP, CGS19755 and MK-801) on two models of neuronal plasticity, kindling and long-term potentiation (LTP), were performed in rats. Systemic administration of CPP (5, 10 mg/kg), CGS19755 (5, 10 mg/kg) or MK-801 (1, 2 mg/kg) strongly retarded kindling development from the amygdala (AM), in which the early stage of kindled seizures and the growth of afterdischarges (ADs) recorded from the AM were significantly suppressed. After establishment of kindling, however, these compounds only reduced the previously AM-kindled seizure stage without shortening the AD duration. These NMDA receptor antagonists with the same dose sufficient for suppressing AM kindling almost completely blocked LTP of the synaptic component in the hippocampal dentate gyrus following high-frequency trains of the perforant path in urethane-anesthetized rats. These results further support the hypothesis that neuronal plasticity is induced by activation of the NMDA receptor complex and one of the basic neuronal mechanisms underlying kindling may be a long-lasting increase in synaptic transmission.