Abstract

Purified synaptosomes from the rat striatum were superfused continuously with [3H]tyrosine in order to estimate the release of newly synthesized [3H]dopamine. When tested from 10(-6) to 10(-3) M, several excitatory amino acids or their analogues markedly stimulated the release of [3H]dopamine, their apparent rank order of potency being kainate greater than glutamate = D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) greater than homocysteate greater than quisqualate greater than aspartate greater than ibotenate. N-acetyl-aspartyl-glutamate was without effect. In addition, in the range of concentrations of 10(-6) to 10(-3) M, the maximal response of glutamate was higher than that of kainate, AMPA or homocysteate, whereas the effects of quisqualate, aspartate and ibotenate, particularly, were of lower amplitude. In favor of the existence of glutamate receptors of the AMPA type on dopaminergic nerve terminals, the stimulatory effect of AMPA (5 x 10(-5) M) on [3H]dopamine release was antagonized by 6,7-dinitroquinoxaline-2,3-dione, 6-cyano-7-nitro-quinoxaline-2,3-dione, tau-D-glutamyl-amino-methyl-sulphonate and tau-D-glutamyl-glycine tested at 10(-4) M. 6,7-Dinitroquinoxaline-2,3-dione was the most potent, whereas L-glutamate diethylester was without effect. As expected D-2-amino-5-phosphonovalerate did not affect the AMPA-evoked response. Further experiments indicated that kainate and quisqualate stimulate the release of [3H]dopamine by acting on quisqualate/kainate or AMPA receptors. The quisqualate-evoked desensitization of AMPA receptors was prevented by concanavalin A (10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)