PSYCHOMOTOR STIMULANT EFFECTS OF D-AMPHETAMINE, MDMA AND PCP - AGGRESSIVE AND SCHEDULE-CONTROLLED BEHAVIOR IN MICE

The objective of the present experiments was to characterize psychomot or stimulant effects of d-amphetamine, methylenedioxymethamphetamine ( MDMA) and phencyclidine (PCP) on conditioned performance and on aggres sive behavior in mice. In a novel protocol with alternating periods of schedule-controlled responding and aggressive behavior toward an intr uder it was possible to assess a range of species-specific agonistic a cts, postures, and motor activities as well as response rates and patt erns engendered by a multiple Fixed Interval (FI) and Fixed Ratio (FR) schedule within the same animal. Initially, it was confirmed that d-a mphetamine and, less reliably, MDMA and PCP, increased FI, but not FR responding in mice. In the next experiment, mice confronted an intrude r at the midpoint of the 1-h daily session; following the display of a ggressive behavior, the rate of FI responding showed an amphetamine-li ke increase, whereas only a transient change occurred after non-aggres sive encounters. Thirdly, using this new protocol, PCP, d-amphetamine and MDMA altered FI and FR responding in a way that was closely simila r to the first experiment. Low PCP and d-amphetamine doses increased a ggressive behavior erratically in certain individuals, but not reliabl y for the group. MDMA dose-dependently decreased aggressive behavior, and all drugs disrupted aggressive behavior at higher doses. The chara cteristic increases in walking and decreases in rearing after higher d oses of PCP and d-amphetamine were greatly attenuated when the intrude r was present. The rate-increasing effects of d-amphetamine, MDMA and PCP occurred in the early portion of the fixed interval when the contr ol rate is typically low; by contrast, low attack rates during the lat er portion of the confrontation with the intruder remained unaffected. The dose-dependent quantitatively and qualitatively differentiated pr ofile of effects on schedule-controlled responding, motor activity and aggressive behavior suggest that the common properties of d-amphetami ne, MDMA and PCP pertain mostly to the disruption of organized behavio r patterns and activation of repetitive motor routines at high doses, but point to different mechanisms for modulating aggressive behavior a nd conditioned performance at lower doses.-