Interactions between N-Methyl-D-.Aspartate and CGS 19755 Administered Intramuscularly and Intracerebroventricularly in

Behavioral effects of N-methyl-D-aspartate (NMDA) and the corn-petitive NMDA antagonist c/s-4-phosphonornethyl-2-piperidine-carboxylic acid (CGS 1 9755) were studied in pigeons. NMDA decreased responding under a fixed-ratio schedule offood pres-entation and was 8000 times more potent administered intracer-ebroventricularly (i.c.v.) as compared to intramuscularly (i.m.). CGS 1 9755 was 870 times more potent in producing catalepsy when administered i.c.v.; however, the duration of catalepsy was similar by the two routes of administration. Administered i.m. CGS 1 9755 decreased response rates only at doses that also produced catalepsy; administered i.c.v. some doses of CGS 19755 decreased responding without producing other behavioral effects. Rate-decreasing effects of i.m. NMDA were attenuated by i.m. CGS 1 9755; however, when CGS 1 9755 was adminis