Effects of alpha-MSH, TRH and AVP on learning and memory, pain threshold, and motor activity: preliminary results

The effect of daily peripheral administration of various peptides on learning and memory performance was studied in male albino rats. Groups of rats were treated with either TRH (1.0 mg/kg) alpha-MSH (1.0 mg/kg), or saline for three days. Other groups were treated either with vasopressin (1.0 microgram/kg) or saline. All treatments were 30 min before testing in a Morris Water Task apparatus. This type of learning is spatial learning which requires integration of environmental cues. Only alpha-MSH treated rats exhibited improved learning on Day 1 and Day 3 of the training period. One month later all rats were retested with no difference between the experimental groups. Single doses of these peptides caused a nonsignificant increase in pain threshold. The body weight gain of vasopressin-treated rats was significantly reduced as well as their motoric behavior. Therefore, the alpha-MSH effect on learning cannot be explained by nonspecific effects on body weight, pain threshold, or motor activity level.