[Discriminative properties of cycloprolylglycine on the operant behavior in rats].

Discriminative stimulus properties of cycloprolylglycine (Cpg) (0.1 mg/kg, i.p.) have been studied under liquid-reinforced operant drug-discrimination (Dd) paradigm in male outbred rats. It is established that only 33% of rats trained under the FRI regime conditions successfully demonstrated Dd "Cpg versus saline". After 30 training sessions, a high level of stimulus control was obtained in these animals under both non-drug and drug training (appropriate level responses were 80% and above). Under more complicated FR10 scheduling during the subsequent 40 training sessions, the rats failed to demonstrate Dd. Thus, the discriminative stimulus properties of Cpg are established, which allows Cpg to be classified as pure discriminable substance.