Interactions of (+)-amphetamine and chlorpromazine on neurones in the lower brain stem of the rat.

1 The ability of chlorpromazine to antagonize the effects of iontophoretic application of (+)-amphetamine to single neurones in the medulla and lower pons of anaesthetized rats has been studied. 2 Chlorpromazine, administered systemically or iontophoretically, consistently and specifically antagonized the excitatory actions of (+)-amphetamine, but not those of noradrenaline on the same neurone. 3 It is concluded that chlorpromazine reduces the effect of (+)-amphetamine by a presynaptic mechanism. 4 (+)-Amphetamine did not mimic the prolonged inhibitory response of some neurones to noradrenaline but often excited these neurones and chlorpromazine blocked these excitatory responses to (+)-amphetamine.