Downloads & Free Reading Options - Results

A landmark event in the history of behavioral pharmacology was the discovery in the early 1970s of opiate receptors in the mammalian brain. Later research showed that opiate receptors occurred in all vertebrate brains. Two pentapeptides, met- and leu-enkephalin, accounted for most of the opioid activity of the brain extracts. Three experiments were conducted to assess the effects of a met-enkephalin analog (D-Ala2)-methionine enkephalinamide (DAME) on learning and memory of monkeys. Experiment 1 demonstrated that DAME impaired multiple discrimination reversal learning by capuchin monkeys. The DAME effect was not caused by DAME's effect on the monkeys' response to distracting or irrelevant stimuli nor was it caused by increasing production of systematic errors. Experiment 2 revealed DAME enhancement of two-choice spatial delayed response performance by squirrel monkeys at long but not short delays. However, in Experiment 3 low doses (100 micrograms/Kg) of DAME impaired delayed response performance on nine-choice spatial delayed response. DAME did not exert disproportionate effects on systematic as opposed to nonsystematic errors in either Experiment 2 or 3. DAME clearly has differing effects on different types of learning and memory problems in primates. These results strongly indicate that DAME would not be an effective agent for improving human performance.