Cinanserin was used to differentiate the effects of d-amphetamine and 2,5-dimethoxy-4-methyl-amphetamine (STP) on blood pressure and spontaneous locomotor activity in rats and mice. Cinanserin itself produced a decrease of blood pressure and spontaneous locomotor activity in the animals. A dose of 2 mg/kg of cinanserin blocked the increase of blood pressure caused by STP; however, it failed to affect the pressor action of d-amphetamine even when the dose was increased to 25 mg/kg. The increase of spontaneous locomotor activity induced by d-amphetamine was counteracted by cinanserin (10 mg/kg) but cinanserin (10 and 25 mg/kg) did not modify spontaneous locomotor activity produced by STP. The results showed that the pressor actions of STP and d-amphetamine, and most likely also their effects on spontaneous locomotor activity, were involved in different mechanisms.
