The effects of nicotine on glutamate-induced cytotoxicity were examined using primary cultures of rat cortical neurons. The cell viability was significantly reduced when cultures were briefly exposed to glutamate or N-methyl-D-aspartate (NMDA) then incubated with normal medium for 1 h. A 1-h exposure of the cultures to kainate or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) reduced cell viability. Incubating cultures with nicotine for 1-24 h protected cortical neurons against glutamate cytotoxicity. Maximum protection against glutamate cytotoxicity was induced with a 2-h nicotine incubation. Exposure to nicotine for up to 2 h did not affect cell viability by itself although cell viability was reduced in a time-dependent manner when the exposure exceeded 4 h. Neuroprotection by nicotine was dependent on both the concentration and incubation period. Nicotine reduced the NMDA cytotoxicity but did not attenuate that of kainate and AMPA. The neuroprotective effects of nicotine against glutamate cytotoxicity were antagonized by mecamylamine and hexamethonium but not by atropine. These results indicate that nicotinic receptor stimulation induces neuroprotection against glutamate cytotoxicity mediated by NMDA receptors.