[Acquisition of a lever press behavior by mice in a water reinforcement situation].

An operant chamber for mice, consisting of two adjacent compartments of W 130 X L 120 X H 150 mm, with a liquid dispenser which is operated by lever press was prepared. Using the apparatus, the applicability of mice for the study of learning of lever press behavior in a water reinforcement situation was investigated. Animals were deprived of water in the home cage and water was only supplied in the operant chamber by the lever press. A session of 15 min training was performed daily. By continuous reinforcement schedule, animals learned the lever pressing by 3 sessions. With these trained animals which attained more than 150 responses further experiments with a fixed ratio (FR) schedule was made, from FR 1 to FR 20. The best increase in responses was observed when the FR was regularly and gradually stepped up from 1 to 20 by every 5 sessions. Scopolamine, 1 mg/kg ip, significantly suppressed the lever press at FR 1 sessions, and the latency time until the first lever press was also prolonged significantly in these sessions. Thus, the applicability of mice for the study of learning of lever press behavior and the experimental schedules were established.