Effects of body weight levels on cannabis self-injection.

Previous findings have shown that naive rats self-inject IV delta 9-THC 12.5 microgram/kg/infusion in the presence of a FT-1 non contingent food delivery schedule. In the present study the effects of three different body weight levels, 80%, 90% and 100%, with and without a FT-1 food delivery schedule, were examined on the THC self-injection behavior. Results confirmed that 80% body weight plus the FT-1 schedule condition leads to the highest intake of THC. In a further experiment, naive rats acquired THC self-injection at 80% body weight with a FT-1 schedule. Rats were then allowed to regain body weight to their free feeding level and were tested again in the same basic paradigm. Animals recovering body weight did not maintain the self-injection rates. The data indicate that the environmental conditions necessary in the acquisition phase are also required to maintain intake of THC 12.5 microgram/kg/infusion.