LDS-25 as a discriminative stimulus for response selection by pigeons.

Pigeons (N=4) were trained to discriminate between the effects induced by intramuscular (IM) injections of d-LSD and saline using a discrete-trial discrimination paradigm (choice between left and right hand key) in a conventional operant box. The solutions were administered IM 15 min prior to the sessions. A FR 15 schedule was in operation to produce food. Which of the two keys was correct on a given training session depended upon whether LSD or saline had been given. Three of the birds were trained and maintained with a dose of 40 microgram/kg of LSD and the fourth pigeon finally was maintained on 50 microgram/kg of LSD. The dose resulting in 50% LSD appropriate responding (ED50) was 18 microgram/kg and the median time-interval for the decay of the LSD stimulus (40 microgram/kg) was 84 min. Tests with psilocybin (ED50=0.55 mg/kg) and N,N-dimethyltryptamine (ED50=5.7 mg/kg) resulted in responding appropriate for the LSD training condition. Mescaline injections above 10 mg/kg severely suppressed responding. The few responses emitted after tests with 15 and 20 mg/kg of mescaline were directed to the LSD associated key. Tests with BOL (0.1 to 3 mg/kg) as well as three other psychotropic drugs (delta 9-tetrahydrocannabinol, morphine and, pentobarbital) did not result in responding above 50%) LSD appropriate responses. As a possible antidote, methergoline, a pubetative antagonist of post-synaptic serotonin receptor sites, was administered 75 min prior to testing the cueing properties of LSD. No definitive role for a blocking effect of the LSD-cue is provided by the present data.