Abstract

The novel competitive N-methyl-D-aspartate (NMDA) receptor antagonist DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (CGP 37849) was found to produce a phencyclidine (PCP)-like behavioral syndrome (ataxia, locomotion, stereotypies) in amygdala-kindled rats, whereas the amphetamine-like behavioral alterations of the syndrome (locomotion, stereotypies) were only infrequently seen in nonkindled rats. In dose-response experiments in kindled and nonkindled rats, behavioral effects were scored using a ranked intensity scale, and the behaviors and behavioural scores determined after CGP 37849 were compared with those determined after i.p. administration of the noncompetitive NMDA receptor antagonist dizocilpine maleate (MK-801). In kindled rats, 20 mg/kg of CGP 37849 produced about the same scores for hyperlocomotion and head weaving as 0.1 mg/kg of MK-801. Kindled rats exhibited higher behavioral scores than nonkindled rats, especially in the case of CGP 37849. The behavioral effects produced by CGP 37849 in kindled rats were almost indistinguishable from the PCP-like behavioral effects induced by MK-801, indicating that CGP 37849 indeed produces a PCP-like pattern of behavior in kindled rats. Hyperlocomotion and head weaving induced by CGP 37849 in kindled rats could be attenuated or totally prevented by pretreatment with ipsapirone, a partial agonist/antagonist at postsynaptic 5-hydroxytryptamine (5-HT) receptors of the 5-HT1A subtype. Furthermore, these behavioural effects were attenuated or blocked by the dopamine antagonist haloperidol and the alpha-1 adrenoceptor antagonist, prazosin. The data demonstrate that kindling induces a hypersensitivity to PCP-like behavioral effects of competitive and noncompetitive NMDA receptor antagonists, which could relate to the recent finding of increased function of NMDA receptors following kindling.(ABSTRACT TRUNCATED AT 250 WORDS)