EXCITATORY AMINO-ACID RECEPTOR ANTAGONIST KYNURENIC ACID ATTENUATES REWARDING POTENTIAL OF MORPHINE

The effect of the non-selective antagonist of excitatory amino acid re ceptors kynurenic acid (50, 100 and 150 mg/kg, i.p.) on morphine-deriv ed reward was studied in rats. Kynurenic acid dose dependently blocked the acquisition of morphine conditioned place preference when injecte d before conditioning. The expression of the previously established co nditioned behavior was also blocked by the pretreatment with kynurenic acid (at the doses which do not reduce spontaneous locomotor activity ) before testing. In the control experiments we failed to find that ky nurenic acid alone exerts positive place preference conditioning or av ersion. Kynurenic acid also attenuated the morphine-induced facilitati on of responding in the intracranial self-stimulation test, causing a decrease in response rate and an increase in threshold current intensi ty. This effect was observed with doses at which kynurenic acid does n ot affect responding in the self-stimulation test by itself.