Dose-dependent and time-dependent action of oxytocin on chick memory

Experiments were conducted to investigate the dose-related and time-dependent effects of oxytocin on memory for a one-trial conditioned taste aversion task using two-day old chicks. Oxytocin was administered intracerebrally 1 min posttraining to 5 groups of chicks in dose levels differing by a factor of 10 and ranging from 5.0 pg to 50 ng. A second experiment tested the time-dependent nature of the neuropeptide's action. In this experiment the oxytocin (5.0 ng) was administered at either 1 min, 9 min or 59 min posttraining. In both experiments saline-injected control groups were included. The taste aversion training for all experiments consisted of presenting an attractive lure, coated with an aversive liquid (EtOH), to each chick for a 10-s training trial. Most chicks pecked 1 or 2 times at the lure before inhibiting any further response. The retention testing took place 24 h after the training and consisted of presenting the dry, uncoated lure to each chick for an additional 10 s. Chicks that avoided pecking at the lure were considered to have exhibited enhanced retention. The groups of chicks receiving 50 pg to 50 ng of oxytocin exhibited enhancement of retention, as did the 1 min group of the time-dependent experiment. These results are compared to the effects on memory consolidation in chicks induced by vasopressin and L-prolyl-L-leucyl-glycineamide. The apparent conflict between these results and those obtained in mammalian studies with oxytocin are discussed.