Presynaptic modulation of the release of dopamine from the rabbit caudate nucleus: differences between electrical stimulation, amphetamine and tyramine
Kamal, L.A.; Arbilla, S.; Langer, S.Z.
Journal of Pharmacology and Experimental Therapeutics 216(3): 592-598
1981
ISSN/ISBN: 0022-3565 PMID: 6259324 Document Number: 174665
The release of recently taken up [3H]dopamine ([3H]DA) from slices of the rabbit caudate nucleus was elicited by exposure to amphetamine (10 .mu.M), tyramine (5 .mu.M) or by electrical stimulation (3 Hz, 2 ms, 24 mA). When expressed as fractional release, the overflow of the labeled transmitter was nearly of the same magnitude for amphetamine, tyramine or electrical stimulation. Qualitative differences were observed in relationship to the Ca dependence and the effects of apomorphine, haloperidol and sulpiride on the stimulation-evoked release of [3H]DA. Although the electrically stimulated release of [3H]DA was completely abolished by removing Ca from the external superfusion medium, the amphetamine and tyramine-induced release remained unaffected. Apomorphine inhibited in a concentration-dependent manner the release of [3H]DA evoked by electrical stimulation, while it had only slight effects on the amphetamine- or tyramine-induced release of [3H]DA which were not concentration-dependent. Haloperidol was able to enhance in a concentration-dependent manner the electrically induced release of [3H]DA without increasing the spontaneous outflow of radioactivity. Haloperidol was considerably less effective in enhancing the amphetamine- or tyramine-induced release of [3H]DA. Sulpiride only enhanced the release of [3H]DA induced by electrical stimulation without affecting the release induced by amphetamine or tyramine. The differences in Ca requirement and the effects of apomorphine, sulpiride and haloperidol in strongly modifying the electrical stimulation and only slightly the amphetamine- and tyramine-evoked release of [3H]DA indicate that presynaptic inhibitory DA autoreceptors modulate the Ca-dependent stimulation-evoked release of [3H]DA elicited by electrical stimulation but do not modulate the Ca-independent amphetamine- or tyramine-evoked release of [3H]DA in the rabbit caudate nucleus.