Riluzole blocks dopamine release evoked by N-methyl-D-aspartate, kainate, and veratridine in the rat striatum

Dopamine (DA) is released in large amounts during cerebral ischemia and may exacerbate tissue damage. Riluzole (54274 RP) is a recently developed agent that depresses glutamate neurotransmission in the central nervous system (CNS) and that may protect against ischemic injury in some animal models. Because glutamate stimulates the release of DA in the striatum, the authors hypothesized that riluzole could antagonize DA release in this structure. Assay for DA release consisted of superfusing 3H-DA preloaded synaptosomes with artificial cerebrospinal fluid (1 ml/min, 37 degrees C) and measuring the radioactivity obtained from 1-min fractions over 22 min, first in the absence of any treatment (spontaneous release, 8 min), then in the presence of depolarizing agents combined with riluzole (0.1-100 microM, 5 min), and finally with no pharmacologic stimulation (9 min). The following depolarizing agents were tested: KCl (9, 15 mM), veratridine (0.01-1 microM), N-methyl-D-aspartate (NMDA, 0.1-1 mM), kainate (0.1-1 mM), and nicotine (0.01-0.5 mM). Assay for DA uptake was performed by measuring the radioactivity incorporated in synaptosomes incubated with 3H-DA (44 nM; 5 min; 37 degrees C). All depolarizing agents produced a significant, concentration-related increase from basal 3H-DA release. Riluzole was found to decrease the release induced by veratridine (1 microM), NMDA (1 mM), and kainate (1 mM) in a significant, concentration-related manner (IC50 = 9.5 microM, 1.6 microM, and 5.8 microM for veratridine, NMDA, and kainate, respectively). In contrast, it did not affect the release elicited by either KCl or nicotine. Riluzole had no significant effect on the specific 3H-DA uptake. Riluzole produced a potent blockade of the release of DA mediated by activation of presynaptic sodium channels, NMDA, and kainate receptors. Depression of glutamate transmission together with blockade of DA release may contribute to the actions of this agent in vivo.