Contingent suppression of tolerance to the "anorexigenic" effect of haloperidol

Two experiments were performed to determine whether tolerance to the "anorexigenic" effect of haloperidol is contingent on access to food in the drugged state. In the first experiment groups of rats were given injections of haloperidol (2.5 or 5 mg/kg) either before or after a 30-min drinking session for 53 days. Control groups were given saline injections. On Day 54 all groups were given the drug before milk access to determine the level of tolerance. Rats which had received the drug after milk were found to be more tolerant than rats given the drug chronically before milk on Day 54. In the second experiment the length of drug administration was shortened to 14 days. Findings suggested that rats which received chronic post-test injections of haloperidol continued to develop tolerance with repeated injections of the drug, while the development of such tolerance was suppressed after Day 15 in rats given repeated pre-test injections of the drug. (Abstract shortened with permission of author.)