CONDITIONED CHANGES IN DOPAMINE OXIDATION CURRENTS IN THE NUCLEUS-ACCUMBENS OF RATS BY STIMULI PAIRED WITH SELF-ADMINISTRATION OR YOKED-ADMINISTRATION OF D-AMPHETAMINE

In vivo chronoamperometry was used to monitor changes in dopamine oxid ation currents corresponding to dopamine efflux in the nucleus accumbe ns of rats after presentation of a conditioned light stimulus repeated ly paired with either yoked-or self-administered intravenous injection s of the psychostimulant d-amphetamine. Daily conditioning trials bega n with a non-contingent drug injection, paired with a conditioned stim ulus consisting of a 5 s flashing light and 30 s lights out, after whi ch a house light was illuminated during the 3 h session, signalling dr ug availability. Each subsequent injection of d-amphetamine was paired with the conditioned stimulus. Electrochemical measures were taken on conditioning trials 4-7, and on each trial, intravenous d-amphetamine (0.25 mg/kg per injection) self-administration produced a significant maximal increase in mean dopamine oxidation currents of approximate t o 8 nA above baseline. Dopamine oxidation currents in rats receiving y oked d-amphetamine were approximate to 5 nA above baseline by the four th day of drug administration and reached approximate to 8 nA on the s eventh and final day of drug administration. On day 9 the first presen tation of the vehicle injection and conditioned stimulus, in combinati on with illumination of the house lights, induced an immediate increas e in nucleus accumbens dopamine oxidation currents in all rats that ha d previously received d-amphetamine. Subsequent presentations of the c onditioned stimulus at 30 min intervals induced further increases in e xtracellular dopamine oxidation currents in both drug-treated groups. By the end of the 3 h session, both groups had similar maximal conditi oned increases in dopamine oxidation currents of approximate to 6 nA. These data are discussed with relation to the neurochemistry of drug c raving.