Improved recognition memory in monkeys following naloxone administration.

The effects of naloxone on visual recognition were evaluated in five macaques trained in delayed nonmatching-to-sample with trial-unique objects. In four of the five monkeys, naloxone yielded an inverted U-shaped dose-effect curve. For each of these four animals, as well as for all five animals as a group, at least one dose within a narrow range (0.32-3.2 mg/kg) produced a significant increase in the number of objects correctly recognized. Lower doses had little effect, while the highest dose (10.0 mg/kg) tended to disrupt performance.