Turning behaviour as an index of the action of amphetamines and ephedrines on central dopamine-containing neurones.

1. Rats lesioned unilaterally in the substantia nigra show no obvious abnormalities after recovery from the operation but rotate towards the lesioned side after administration of drugs of the amphetamine and ephedrine groups.2. (+)-Amphetamine and (-)-amphetamine are equally potent in producing turning behaviour but (+)-methylamphetamine is considerably more effective.3. (-)-Ephedrine (with a beta-OH group on the ethylamine side chain) induces turning but only in doses approximately 20 times greater than (+)-methylamphetamine.4. (+)-Norpseudoephedrine was the most effective of the ephedrine isomers tested followed by (-)-ephedrine and (+)-pseudoephedrine.5. Turning produced by (-)-ephedrine and (+)-methylamphetamine is not reduced by FLA63 (50 mg/kg) 4 h previously, but is almost completely inhibited by alpha-methyl-p-tyrosine (150 mg/kg) 12 h previously.6. Reserpine pretreatment potentiates turning produced by (-)-ephedrine.7. Chlorpromazine (5 mg/kg) completely blocks turning induced by (+)-methylamphetamine although it concurrently increases exploratory activity. The level of exploratory activity after the (+)-methylamphetamine-chlorpromazine combination is more than 3 times that attained after saline alone.