Analytical study of acquisition on free-operant avoidance response for evaluation of psychotropic drugs in rats

Systematic research was performed on the acquisition of free-operant (Sidman-type) avoidance response, which is widely used for the study of psychotropic drugs, with the following results: When the training session was fixed at 2 hours once daily, shock-shock (S-S) interval at 5 seconds, and response-shock (R-S) interval variable-20, 30 and 60 seconds, the acquisition speed of the response was almost constant independent of the R-S interval, about 6 sessions being always required. When the S-S and R-S intervals were constantly 5 and 30 seconds, respectively and the length of one session was varying-1, 2 and 4 hours, the behavioral baseline was established after about 6 sessions independently of the length of the session. Thus the cumulative time for the acquisition was shortest when one session was 1 hour long, and longest when it was 4 hours long. There was a linear relation with negative inclination between the logarithm of mean numbers of shock delivered per sessions and the number of sessions. In rapid and exact training of animals for the evaluation of drug effects, one session of an hour per day is adequate. In the evaluation of drug effects on the acquisition process, observation of the shift in logarithmic value of shocks delivered is recommended.