Opiate control of spontaneous locomotor activity in a urodele amphibian

An intraperitoneal injection of the preferential opiate receptor agonist (+/-) bremazocine HCl given to male rough-skinned newts acutely and dose-dependently reduced their spontaneous locomotor activity. Inversely, and contrary to the situation generally observed in other vertebrates, administration of the opiate receptor antagonist naloxone HCl dose-dependently and acutely stimulated locomotion. Given at a behaviorally active dosage, naloxone counteracted the inhibitory effect of bremazocine on locomotion. The behavioral influence of the two substances was observed using two different sampling techniques (continuous recording for 3 minutes: repeated instantaneous sampling for 60 minutes). These data are discussed in view of our current knowledge on the opiate regulation of locomotor activity in vertebrates.