Extracellular dopamine and its metabolites in the nucleus accumbens of Fischer and Lewis rats: basal levels and cocaine-induced changes.

Rats of the Lewis (LEW) strain show a greater preference for drugs of abuse than do Fischer 344 (F344) rats. The in vivo microdialysis procedure was used to examine basal and cocaine-evoked extracellular (EC) levels of dopamine (DA), DOPAC, and HVA in the nucleus accumbens (NAc) of F344 and LEW rats. The basal EC levels of the DA metabolites DOPAC and HVA in the NAc were markedly lower in LEW than in F344 rats. Although the increase in EC DA after 3, 10, or 30 mg/kg, i.p. of cocaine was similar in both strains, LEW rats had a smaller peak DA elevation followed by a slower return to basal DA levels at the 30 mg/kg dose. The neurochemical differences observed may contribute to the strain differences in the behavioral response to cocaine.