The central effects of mu-opioid receptor agonist DALDA (ICV 0.00, 0.1, or 1.0 mu g) were investigated in rats for 120 min on activity monitors. The durations in seconds of horizontal. movement time, rearing time, and stereotypy time were measured during 12 consecutive 10-min time blocks. DALDA (ICV, 0.1 and 1.0 mu g) resulted in biphasic effects, inhibition followed by activation for horizontal movement, rearing, and stereotypy times.