Suppression of play fighting by amphetamine does not depend upon peripheral catecholaminergic influences

Abstract

As reported earlier, d-amphetamine (0.25–1.0 mg/kg) produced a dose-dependent depression of play fighting as indexed by the frequency of pins and the total duration of play fighting. Amphetamine reduced both the frequency of play bouts and the duration of those bouts that occurred. At the highest dose, play fighting was virtually eliminated. In contrast, 4-OH-amphetamine, which crosses the blood-brain barrier less readily than does d-amphetamine, did not depress play fighting at doses from 0.25 to 2 mg/kg. At 4 mg/kg, this drug reduced pinning, total play duration, and the frequency of play bouts, but did not affect bout duration. In a second experiment, the effects of d-amphetamine on play fighting were studied in animals that had been adrenal demedullated, subjected to chemical sympathectomy with 6-hydroxydopamine, or given a combination of both treatments. Amphetamine produced comparable suppression of play fighting regardless of the functional state of the sympathetic nervous system. Apparently, the effects of psychomotor stimulants on play fighting by juvenile rats are mediated by the central actions of these drugs.