Vasopressin retards the acquisition of positively reinforced lever pressing in homozygous Brattleboro rats.

Previous studies have indicated that vasopressin treatment improves the poor performance of congenitally vasopressin deficient (Brattleboro) rats on shock avoidance paradigms, an effect thought to relate to the peptide's enhancement of mnemonic processing. In the present study, a food rewarded autoshaping task was used to study the acquisition, retention, extinction and subsequent re-acquisition of lever pressing. Vasopressin (1 microgram/rat, subcutaneous) was found to impair acquisition in these animals. The possibility that this deleterious effect was due to a transient suppression of motor capability was tested in a second experiment. Vasopressin increased overall locomotor activity levels, but there was an indication that rates immediately following injection were lower than usual. An explanation for the effects of vasopressin based on arousal enhancement is discussed, and it is suggested that the neuropeptide may be concerned with the regulation of arousal and hence performance.