Résumé : Using quantitative in situ hybridization, a significant decrease in expression of proenkephalin (27.1%) and of protachykinin (27.1%) and of protachykinin mRNAs (20.0%) is observed in the rat caudate-putamen 14 days after daily intraperitoneal administration of N-methyl-D-aspartate receptor antagonist MK-801, 2 mg/kg.