THE RELATION BETWEEN DOPAMINE OXIDATION CURRENTS IN THE NUCLEUS-ACCUMBENS AND CONDITIONED INCREASES IN MOTOR-ACTIVITY IN RATS FOLLOWING REPEATED ADMINISTRATION OF D-AMPHETAMINE OR COCAINE

Chronoamperometric recording techniques were used to monitor extracell ular dopamine efflux in the nucleus accumbens associated with uncondit ioned and conditioned increases in motor activity in rats, following t he intravenous administration of either d-amphetamine (0.63 mg/kg) or cocaine (3 mg/kg), or the presentation of a conditioned stimulus paire d repeatedly with one of these psychostimulants. Each drug was adminis tered daily for 7 days, either in the home cage or an environment in w hich a compound stimulus (light offset, odour) was presented. Rats in control groups received saline instead of drug in the distinctive test environment. On day 7 of training, significant increases in unconditi oned motor activity were observed in the 30 min session following infu sions of either d-amphetamine or cocaine. Associated dopamine oxidatio n currents in the nucleus accumbens increased immediately following ad ministration of either drug and remained significantly elevated above baseline during the entire 30 min recording period. On the test day, p resentation of the conditioned stimulus with vehicle infusions, in the distinct environment, was accompanied by an increase in dopamine oxid ation currents and a conditioned increase in motor activity, only in t he groups in which these stimuli had been paired with d-amphetamine or cocaine. Neither the magnitude or duration of the conditioned motor a ctivity matched the corresponding change in extracellular dopamine eff lux in the nucleus accumbens. Accordingly, it is argued that the incre ase in dopamine concentration serves as a neurochemical correlate of t he unconditioned and conditioned stimuli. The change in motor activity constitutes the unconditioned and conditioned responses that are subs erved by the neural systems activated by the initial rise in extracell ullar dopamine.