Behavioral activating effects of opiates and opioid peptides.
Locomotor activity of rats and mice was monitored following administration of the opiates, morphine, methadone, and etonitazene, or the opioid peptides, beta-endorphin, D-Ala2-Met5-enkephalinamide, and D-Met2-Pro5-enkephalinamide. In rats these agents produced dose-related biphasic patterns of activity consisting of an initial depression in locomotion followed by a period of hyperactivity. Intravenous administration of morphine, methadone, or etonitazene in mice produced dose-related increases in stereotyped locomotor activity. The metabolically resistant enkephalin analog, D-Met2-Pro5-enkephalinamide induced a similar pattern of effects. However, doses of beta-endorphin up to 20 mg/kg, iv, failed to elicit locomotor stimulation in mice. The similarity in the naloxone-reversible responses induced by opiates and certain opioid peptides suggests that the same underlying mechanisms may subserve their behavioral effects.
D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology; D005106:Exploratory Behavior / Q000187:drug effects; D008297:Male; D008691:Methadone / Q000494:pharmacology; D051379:Mice; D009020:Morphine / Q000494:pharmacology; D009043:Motor Activity / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D051381:Rats
D001562:Benzimidazoles; D004723:Endorphins; D004745:Enkephalins; D009294:Narcotics; D009270:Naloxone; D009020:Morphine; D008691:Methadone