Interneurones are probably not involved in the presynaptic dopaminergic control of dopamine release in rabbit caudate nucleus.

Slices of rabbit caudate nucleus were preincubated with 3H-dopamine and then superfused. The influence of apomorphine and haloperidol on the overflow of tritium evoked by 20 mmol/l potassium was investigated in the presence and in the absence of tetrodotoxin. The potassium-evoked overflow was largely calcium-dependent and consisted mainly of 3H-dopamine. The dopamine receptor agonist apomorphine 0.01-1.0 mumol/l reduced, whereas the antagonist haloperidol 0.1 mumol/l enhanced the potassium-evoked overflow of tritium. The effects of apomorphine and haloperidol were as pronounced in the presence as in the absence of tetrodotoxin 0.3 mumol/l. It is concluded that the presynaptic dopaminergic modulation of dopamine release is not mediated by a tetrodotoxin-sensitive interneuronal pathway.