Extracellular glutamate levels in prefrontal cortex during the expression of associative responses to cocaine related stimuli.

We conducted studies to examine the potential role of glutamate in the prefrontal cortex (PFC) during conditioned responses to stimuli (flashing light and metronome) previously associated with cocaine administration. During training, PAIRED subjects received cocaine injections (15 mg/kg) during stimuli sessions while UNPAIRED subjects received saline injections (but received cocaine in the home cage an hour later). We showed previously that PAIRED subjects exhibit conditioned locomotion when tested with the stimuli alone. In this study, we further demonstrated that the expression of behavioral sensitization in response to cocaine challenge is under conditioned control in PAIRED subjects. Then, we used microdialysis to examine extracellular levels of glutamate in the PFC in response to presentation of the conditioned stimuli alone and challenge with cocaine in the presence of the conditioned stimuli. Although PAIRED subjects demonstrated conditioned locomotion and conditioned control of sensitization during the microdialysis experiment, PFC glutamate levels were unaltered during the tests and did not differ between the PAIRED and UNPAIRED subjects.