Vasopressin and ACTH analogs affect orienting but not activity in rabbits

Two experiments were conducted in which albino rabbits were tested for cardiac Orienting Reflexes to novel tones and open field locomotor activity in a novel environment. In Experiment I subcutaneous doses of desglycinamide-arginine8-vasopressin (DGAVP; 25 micrograms/kg) and ACTH fragment 4-10 (250 micrograms/kg) altered tonic heart rate but did not affect bradycardiac Orienting Reflexes, activity, habituation or retention of habituation. In Experiment II a lower dose of DGAVP (5 micrograms/kg) enhanced the magnitude of cardiac orienting reflexes when administered 60 min before an initial orienting test. Both DGAVP and a lower dose of ACTH4-10 (50 micrograms/kg) administered before the first orienting test enhanced cardiac orienting and delayed habituation during a second (retention) test conducted following saline treatment; neither peptide had any effect on orienting when administered before the retention test. The lower doses of the peptides also failed to affect activity, habituation of activity or retention of habituation. These data suggest that low doses of DGAVP and ACTH4-10 affect stimulus processing and attention, but not more generalized responses to environmental novelty, in rabbits.