Decreased basal levels of extracellular glutamate have been observed in the nucleus accumbens following withdrawal from cocaine self-administration. Cocaine-primed relapse to cocaine-seeking in the animal model of reinstatement is associated with enhanced glutamate release relative to drug-naive animals. System xC-,which exchanges one extracellular cystine molecule for one intracellular glutamate molecule, has been found to account for the majority of basal extracellular glutamate levels in the nucleus accumbens and its activity is significantly down-regulated after chronic cocaine, as is that of the major glial glutamate transporter, GLT-1. The beta-lactam antibiotic ceftriaxone has been found to increase the expression and function of both GLT-1 and system xC-. I have previously reported that ceftriaxone prevents relapse to cocaine seeking in the extinction-reinstatement animal model of relapse. Here I propose to assess the relative importance of increasing expression of GLT-1 and xCT (the catalytic subunit of system xC-) in mediating the therapeutic effects of ceftriaxone. Completion of the experiments proposed here will further our knowledge regarding the relative importance of GLT-1 and system xC- in mediating reinstatement probability and maintaining glutamate homeostasis in the nucleus accumbens core.