Abstract

An increasing body of evidence points to the role of N-methyl-D-aspartate (NMDA) receptors in the limbic system in the mechanism of drug dependence. We studied the influence of acute and repeated morphine (20 mg/kg i.p. or increasing dose for 10 days) and cocaine (3x20 mg/kg i.p. per day at hourly intervals, for 1 or 5 days) administration on the expression of glutamate NMDA receptor subunit 1 (NMDAR1) in the central and basolateral nuclei of the rat amygdala and hippocampal formation. Acute or chronic morphine and cocaine administration increased NMDAR1 mRNA level in the central and basolateral nuclei of the amygdala; morphine did so 3 h after the last dose and 48 h after withdrawal, cocaine 3 h after acute and last chronic dose. Morphine did not change the NMDAR1 mRNA level in the hippocampal formation, but chronic cocaine did decrease it in the dentate gyrus only. Our study suggests a possible link between the expression of NMDAR1 and changes in limbic system neuronal activity and behaviour after administration of morphine and cocaine. In summary, the present study demonstrated that morphine and cocaine influenced the expression of NMDAR1 in the structure of the limbic system which could be involved in dependence phenomena.