Greater task difficulty amplifies the facilitatory effect of des-glycinamide arginine vasopressin on appetitively motivated learning.

Rats were trained in a discrete-trial forward autoshaping paradigm to touch an extended lever to earn food pellets. Reinforcement was delivered either simultaneously with or 6 s after lever retraction which occurred either non-contingently after 15 s or when the animal touched the lever. Treatment with des-glycinamide arginine vasopressin (DGAVP; 15 micrograms/kg, sc) 1 hr before sessions increased the rate of acquisition of the extended-lever-touch response and also facilitated development of intertrial (adjunctive) nose poking. Effects of the peptide were more robust in the more difficult, delayed reinforcement task. DGAVP lacks the classical peripheral activity of vasopressin. In both experiments, peptide treatment was terminated before asymptotic levels of performance were attained; the continued facilitation of acquisition in treated groups suggests a specific enhancement of learning and/or enhanced memory retrieval.