Abstract: Excitatory amino acids are involved in acute and chronic neurodegenerativediseases.Little is known about the potential consequences of chronic blockade of NMDA receptors (onesubtype of excitatory amino acid receptors).Receptor function measured as ³H-GABA release inculture media after pretreatment with MK801 was studied in rat cortical neurons in primary cultures.Cultured neurons were exposed to 1μmol·L^-1 MK801 for 4 days since the 14th day.Glutamate( 1 mmol·L^-1 )evoked ³H-GABA release was shown to be significantly increased(control0.2174‰±1.40‰; MK801 treatment 0.763%±0.192%).KCl 40 mmol·L^-1 stimulation showedno such effect.This result suggests that the NMDA receptor function of releasing neurotransmitterschanged after chronic treatment with noncompetitive antagonists.