Effects of chronic cocaine administration on [3H]dopamine uptake in the nucleus accumbens, striatum and frontal cortex of rats.

The uptake of [3H]dopamine into synaptosomes obtained from the nucleus accumbens, striatum and frontal cortex was evaluated after chronic treatment with cocaine. Cocaine was administered in a concentration of 10 mg/kg, twice a day for 7 days. Fourteen days after the last injection, locomotor activity and [3H] dopamine uptake were evaluated. Base-line locomotor activity was significantly lower (29%) in rats treated chronically with cocaine compared with saline-treated rats. A challenge dose of cocaine (2.5 mg/kg or 5.0 mg/kg) or d-amphetamine (1 mg/kg) produced similar increases in locomotor activity above the corresponding base-line values in both saline- and cocaine-treated rats, indicating that behavioral sensitization had not occurred. Chronic cocaine administration produced a significant decrease in the uptake of [3H]dopamine into the frontal cortex (49%) with no significant differences in the nucleus accumbens or striatum. The decrease in [3H]dopamine uptake in the frontal cortex was due to a decrease in the Vmax with no change in the affinity of [3H]dopamine for the dopamine transporter. No differences were produced in the IC50 values of GBR 12909 or cocaine for [3H] dopamine uptake after chronic cocaine treatment. However, in all three brain regions, the IC50 values for cocaine were significantly greater than the values for GBR 12909. In addition, the IC50 values for GBR 12909 and cocaine in the frontal cortex were significantly greater than values for either compound in the nucleus accumbens or striatum. The administration of methamphetamine, using a similar treatment schedule, produced no changes in [3H]dopamine uptake in any of the three brain areas. These data indicate an inhibition effect of repeated cocaine administration on [3H]dopamine uptake in the frontal cortex of rats.