Several evidences indicate that cocaine in able to induce behavioural and molecular sensitization in both, the dopaminergic (DA) and glutamatergic (Glu) mesocorticolimbic systems. The aum of this work was to study if the basal concentration of extracellular Glu as well as the AMPA receptor expression (AMPAR) participates in th long-term cross-sensitization between stress and cocaine. Wistar rats were restrained for two hours, while control animals were left undisturbed in their cages. Twenty-one days after this stress episode: I) Microdialysis: basal extracellular and saline- and cocaine (15mg/kg i.p) induced Glu levels were determinated by HPLC in NAcc Core and Shell. II) AMPAR in Core after i.p. injection of saline or cocaine. Our results demostrate that pre- stressed animals have raised basal extracellular concentrations of glutamate in the Core, but not Shell, and this could be related with the decrease in the cocaine-induced glutamate release in the core as compared with control values. We propose that the increase observed in the AMPAR in pre- stressed animals could be associated with the decrease in glutamate release after stimulus. These results are discussed in the context of disrupted glutamate homeostasis induced by acute stress 21 days before the cocaine challenge.