MODULATION OF COCAINE INTRAVENOUS SELF-ADMINISTRATION IN DRUG-NAIVE ANIMALS BY DIHYDROPYRIDINE CA2+ CHANNEL MODULATORS

The dihydropyridine Ca2+ channel blocker nimodipine and the dihydropyr idine Ca2+ channel activator BayK 8644 -(2-trifluoromethylphenyl)-pyri dine-5-carboxylate) were administered to drug-naive mice and rats that were tested for intravenous cocaine self-administration. A range of c ocaine doses was tested to investigate the nature of the effect. The r esults indicate that nimodipine and BayK 8644 shifted the dose-respons e curve for cocaine's reinforcing action to the right and left, respec tively. Thus, the Ca2+ channel blocker nimodipine decreases the sensit ivity of mice and rats to the reinforcing effects of cocaine while the Ca2+ channel activator BayK 8644 makes the animals more sensitive to cocaine reward. The results suggest that a dihydropyridine-sensitive m echanism is implicated in the initiation of cocaine self-administratio n.