Different behavioral mechanisms underlie tolerance to the anorectic effects of fenfluramine and quipazine.

Chronic administration of fenfluramine or quipazine before scheduled daily feeding sessions led to rapid and complete tolerance to the initial anorexia. Rats that received daily injections of fenfluramine after the daily meal also developed full tolerance. In contrast, quipazine administration after meals led to the development of little tolerance, indicating that quipazine tolerance appears to be learned or contingent. The implications of these data for neurochemical mechanisms of satiety are discussed.