Differential impact of pavlovian drug conditioned stimuli on in vivo dopamine transmission in the rat accumbens shell and core and in the prefrontal cortex.

Rationale: Conditioned stimuli (CSs) by pavlovian association with reinforcing drugs (US) are thought to play an important role in the acquisition, maintenance and relapse of drug dependence.
Objective: The aim of this study was to investigate by microdialysis the impact of pavlovian drug CSs on behaviour and on basal and drug-stimulated dopamine (DA) in three terminal DA areas: nucleus accumbens shell, core and prefrontal cortex (PFCX).
Methods: Conditioned rats were trained once a day for 3 days by presentation of Fonzies filled box (FFB, CS) for 10 min followed by administration of morphine (1 mg/kg), nicotine (0.4 mg/kg) or saline, respectively. Pseudo-conditioned rats were presented with the FFB 10 h after drug or saline administration. Rats were implanted with microdialysis probes in the shell, core and PFCX. The effect of stimuli conditioned with morphine and nicotine on DA and on DA response to drugs was studied.
Results: Drug CSs elicited incentive reactions and released DA in the shell and PFCX but not in the core. Pre-exposure to morphine CS potentiated DA release to morphine challenge in the shell but not in the core and PFCX. This effect was related to the challenge dose of morphine and was stimulus-specific since a food CS did not potentiate the shell DA response to morphine. Pre-exposure to nicotine CS potentiated DA release in the shell and PFCX.
Conclusion: The results show that drug CSs stimulate DA release in the shell and medial PFCX and specifically potentiate the primary stimulant drug effects on DA transmission.