In order to explore further the presynaptic modulation of monoamine release by glutamatergic nerve fibers, we investigated the effects of selective agonists for ionotropic glutamate (GLU) receptors on striatal release of dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT). In the striatum of anesthetized Sprague-Dawley rats, in vivo microdialysis was performed to measure the release of monoamines and metabolites, and also to administer GLU agonists locally in the tissue. l-GLU and its selective agonists (N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) and kainate (KA)) evoked simultaneous release of striatal DA, NA and 5-HT in a dose-dependent manner. Pretreatment with MK-801 (5 mg/kg i.p.), a noncompetitive NMDA receptor antagonist, selectively suppressed NMDA-evoked monoamine release. The rank order of GLU agonist efficacy in releasing monoamines was different among DA, NA, and 5-HTergic terminals: AMPA = KA > NMDA for DA release, AMPA > NMDA = KA for NA release, and NMDA = AMPA = KA for 5-HT release. In conclusion, presynaptic ionotropic GLU receptors exist extensively on monoaminergic terminals including not only catecholaminergic (DA and NA) but also indoleaminergic (5-HT) terminals in the rat striatum. Their subtypes include both NMDA subtype and AMPA/KA subtype, and show a differential distribution among these three monoaminergic terminals and a differential contribution to facilitating monoamine release.
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