The effect of chlorpromazine and d-amphetamine mixtures on spontaneous behaviour

In two tests of spontaneous activity, rats given d-amphetamine in doses of 1.0, 2.0 and 4.0 mg/kg became hyperactive. Chlorpromazine in doses of 0.5 and 1.0 mg/kg blocked this hyperactivity by increasing the periods of immobility, ambulation and grooming, as measured in an observation box and increasing the number of alleys entered in a Y-maze. In addition, the phenothiazine reduced head lifting, sniffing, head turning and rearing, which appeared in amphetamine treated rats. The most pronounced counter-effects on behaviour induced by 4 mg/kg d-amphetamine, were brought about by 1.0 mg/kg chlorpromazine, but the same ratio of 4: 1 at half these doses was less effective. The possible source of this behavioural antagonism of the two drugs, at a neuronal and a non-neuronal level, is discussed.