Effect of intra-core MK 801 administration in the development of stress-induced reinstatement in extinguished cocaine conditioned animals and its influence on a subsequent cocaine- induced reinstatement.
Previous results from our lab showed that MK 801 blocked the stress-induced reinstatement in extinguished cocaine-conditioned rats evaluated in a conditioned place preference (CPP) test. In the present experiment, our goal was to determine if the nucleus accumbens core is implied in this blockade. Male Wistar rats (220-300 g) were conditioned with cocaine (10 mg/kg i.p.) during four alternated drug/vehicle sessions and later extinguished with successive vehicle associations. On the reinstatement day animals were intra-core administered with MK 801 (0.75 ul/side) or vehicle, and subsequently assigned to two groups according to the following treatments: 1) Stressed animals (SA): 30 min-restraint exposure, and 2) Control animals (CA): left undisturbed in their home cages. All rats were immediately tested in a CPP apparatus for stress-induced reinstatement. Three days after the animals were submitted to a vehicle test and the following day administered with a priming injection of cocaine (5.0 mg/kg i.p.) and evaluated for drug-induced reinstatement. The results demonstrate that intra-core MK 801 administration prevented the stress-induced reinstatement in the SA animals and the cocaine-induced reinstatement in SA and CA animals, suggesting that the nucleus accumbens core may be a target of common glutamatergic mechanisms for both, the stress and cocaine-induced reinstatement.
