Differential effects of dopamine agonists upon stimulated limbic and striatal dopamine release: in vivo voltammetric data.

1. Fast cyclic voltammetry at carbon fibre microelectrodes was used in rats anaesthetized with chloral hydrate to monitor dopamine release in the caudate and nucleus accumbens evoked by electrical stimulation of the median forebrain bundle. Stimulation trains (50 Hz sinusoidal current, 100 +/- 10 microA r.m.s., 2s duration) were repeated every 5 min throughout the experiment. 2. The actions of the dopamine agonists quinpirole, pergolide, SKF 38393, bromocriptine, (+)-3-(3-hydroxyphenyl)-N-n-propylpiperidine ((+)-3PPP) and (-)-3PPP were compared in the two nuclei. 3. Bromocriptine (10 mg kg-1, i.p.) did not affect release in either nucleus while SKF 38393 caused a fleeting decrease in limbic but not striatal dopamine release at a high dose (20 mg kg-1, i.p.). 4. Quinpirole and pergolide (both 1 mg kg-1, i.p.) decreased stimulated dopamine release in the nucleus accumbens while in the caudate the drugs each caused a transient, though not quite significant, elevation of stimulated dopamine release followed by decrease in release of the same magnitude as that seen in the nucleus accumbens. 5. The (-)-enantiomer of 3PPP (20 mg kg-1, i.p.), a partial agonist at the dopamine autoreceptor, increased stimulated dopamine release in both nuclei although the action in the caudate was larger and more prolonged. (+)-3PPP (20 mg kg-1, i.p.), a full agonist, decreased release in the nucleus accumbens. A small, transient and not significant increase in the caudate was followed by decreased release. 6. The results are interpreted as being evidence for differences in the dopamine autoreceptor in the two nuclei, possibly in the affinity state of the receptor in each nucleus.