Abstract
The relative contributions of glutamate and dopamine within the nucleus accumbens to cocaine-induced reinstatement of drug-seeking behavior were assessed. When extinguished cocaine self-administration behavior was reinstated by a cocaine-priming injection, extracellular levels of both dopamine and glutamate were elevated in the nucleus accumbens. However, when yoked cocaine or saline control subjects were administered a cocaine prime, only dopamine levels were elevated. Thus, glutamate increased only when animals reinstated lever pressing, whereas dopamine increased regardless of behavior. The increase in glutamate was not accounted for simply by the act of lever pressing itself, because the cocaine self-administration group still demonstrated elevated glutamate when the levers were withdrawn from the operant chamber. Moreover, reinstatement of lever pressing for food did not elevate extracellular glutamate, indicating that increased glutamate initiated responding selectively for a drug reinforcement. The source of glutamate was shown to be glutamatergic afferents from the prefrontal cortex because inhibiting prefrontal cortical glutamatergic neurons that project to the accumbens prevented the rise in glutamate. Together, these data demonstrate that activation of a glutamatergic projection from the prefrontal cortex to the nucleus accumbens underlies cocaine-primed reinstatement of drug-seeking behavior.