On the mechanism of amphetamine-induced behavioural changes in the mouse. I. An observational analysis of dexamphetamine.

The effects of dexamphetamine have been studied on 18 separate items of observed behaviour in the mouse. The intensity of dexamphetamine action was assessed by scoring differences in behaviour from control (vehicle injected) mice and by measuring ED50 values for dexamphetamine to cause detectable differences from controls for each individual item. The experiments were performed blind in that the observer had no knowledge of the dose of dexamphetamine given to the test group or even whether these had received dexamphetamine at all. The results show a clear division of behavioural items into two groups according to ED50 values; group 1 with ED50 values greater than 15 mg/kg was associated with falls in whole-brain norepinephrine. Group 1 contained elements of increased motor activity, the stereotypies (except compulsive gnawing) and certain aspects of increased alertness. Group 2 consisted of compulsive gnawing and the remaining aspects of increased alertness. Compulsive gnawing was negatively correlated in intensity with the majority of other behavioural items but no other evidence was found for a smooth replacement of one type of activity by another with increasing dose.