The effect of delta 9-tetrahydrocannabinol and LSD on the acquisition of an active avoidance response in the rat.

The course of active avoidance learning of rats in a symmetrical Y-maze under the influence of 1, 3, and 9 mg/kg of delta 9-THC i.p., and 5, 20, and mug/kg of LSD was investigated. Delta-THC in a dosage of 1 mg/kg had no effect on avoidance learning. Three to a lesser extent 9 mg/kg produced more rapid learning with a significantly better performance. Learning under delta 9-THC proved to be state-dependent. The withdrawal of delta 9-THC caused a decrease in the avoidance rate, which was dependent on the dosage. Upon renewal of the THC doses, the animals reattained their earlier preformance. In the course of the experiment there was rapid tolerance development, especially of the sedative properties of THC. LSD retarded the rate of acquisition of the active avoidance response. Whereas the control animals displayed over 80% successful active avoidance from the 14th session onwards, this was achieved by the LSD groups only after the 20th session. However, in contrast to the control group the LSD animals were able to increase their avoidance rate to over 90%, and this was maintained to the end of the experiment (a total of 24 sessions with LSD). The sudden withdrawal of LSD produced a fall in avoidance rate, which was dependent on the pervious training dosage; as with delta 9-THC state-dependent learning can also be assumed for LSD.