Exposure of dissociated cultures from fetal rat brainstem to glutamate for upto 6 h decreased cellular contents of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in a concentration- and time-dependent manner. In addition, glutamate induced lactate dehydrogenase leakage. Tetrodotoxin did not block the effects induced by glutamate. MK-801 (1μM), an N-methyl-D-aspartate (NMDA) channel blocker, but not 6-cyano-2,3-dihydroxy-7-nitro-quinoxazoline (CNQX; 3μM), a non-NMDA receptor antagonist, blocked glutamate-induced effects, indicating that these glutamate-induced responses are mediated through NMDA receptors.