In vivo and in vitro studies with agents that cause quasi-morphine withdrawal syndromes.

Compounds that elicit a "quasi-morphine withdrawal syndrome" (QMWS) after acute administration to rats constitute a new class of behavior-modifying agent. In studying the pharmacological bases of quasi-opiate withdrawal syndromes, we found that the dihydrocodeinone, RX 336-M, a standard QMWS-inducing agent, caused a naloxone-insensitive increase in twitch tension on the field-stimulated rat was deferens preparation. In contrast, IBMX (3-isobutyl-1-methylxanthine), the historical inducer of quasi-abstinence in rats, gave a naloxone-insensitive decrease in twitch tension. Tolerance developed to the "wet-dog" shakes elicited by twice-daily s.c. injections of RX 336-M or IBMX in rats for 5 or 15 days, respectively. The parallel development of tolerance to the in vitro effects of these compounds could not be demonstrated.