Role of medial prefrontal, entorhinal, and occipital 5-HT in cocaine-induced place preference and hyperlocomotion: evidence for multiple dissociations

Abstract

Rationale: Application of cocaine or exposure to cocaine-related stimuli induces widespread activation of the cortex in neuroimaging studies with human subjects. In accordance to these findings, it was reported in previous microdialysis experiments that cocaine increased serotonin (5-HT) and dopamine in various cortical brain areas. The present series of studies set out to investigate the functional role of the observed increases in 5-HT in the medial prefrontal cortex (mPFC), the entorhinal cortex (EC), and the occipital cortex (OccC) in the mediation of cocaine-induced conditioned place preference (CPP) and hyperactivity.

Materials and methods: To reduce 5-HTergic neurotransmission in circumscribed brain areas, bilateral local infusions of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), were made into the mPFC, EC, or OccC. Two weeks following surgery, cocaine-induced (10 mg/kg; i.p.) CPP was measured in an unbiased design.

Results: The 90% depletion of 5-HT in the mPFC significantly attenuated the preference for the cocaine-associated environment and the hyperlocomotor response to cocaine. A 61% depletion of 5-HT in the EC reduced conditioned place preference without modulation of hyperactivity, while a 78% 5-HT depletion of the OccC cortex had no effect on cocaine-induced CPP and hyperactivity. No lesion affected general activity, habituation learning, or visual stimulation-induced behavioral activation.

Conclusion: These results indicate an important role of cortical 5-HT in the mediation of cocaine-induced CPP and specify the region-dependent contribution of a neurochemical response to cocaine-mediated behavior.