Riluzole anesthesia: Use-dependent block of presynaptic glutamate fibers

Background: Riluzole (RP 54274) is an experimental benzothiazole with anesthetic properties, but little is known about its synaptic or cellular actions. Methods: The authors investigated riluzole effects on synaptic response of CA 1 pyramidal neurons in rat hippocampal brain slices. Electrophysiologic recordings of population spikes (PS), excitatory postsynaptic potentials (EPSP), and fiber volleys were studied. Paired pulse stimulation (120 ms interpulse interval) was used to measure effects on gamma-amino butyric acid (GABA)-mediated synaptic inhibition, and stimulus trains (33 Hz) were used to test for use-dependent effects. Results: Synaptically evoked PS discharge was blocked in a concentration-dependent manner by riluzole (2.0-20 mu M), similar to effects produced by other anesthetics. Paired pulse inhibition was not altered by riluzole. In contrast, 20 mu M thiopental produced a marked increase in paired pulse inhibition. Riluzole (5.0 mu M) produced a 46.6 +/- 19.8% depression of glutamate-mediated EPSPs, which could account for most of the depression of PS discharge (54.2 +/- 12.6%) produced by this concentration. Riluzole produced a 36 +/- 17% depression of fiver volley amplitudes, which, based on input/output analysis, could completely account for the depression of EPSPs, The depression of fiber volley amplitudes showed a marked use-dependence; the second and subsequent action potentials in a train were progressively depressed by riluzole to a greater extent than the first action potential. Conclusions: Riluzole produced a potent block of excitatory synaptic transmission via depression of presynaptic conduction in glutamatergic nerve fibers. The use-dependent depression observed resembled that produced by some local anestheties on nerve conduction and sodium channels. The presynaptic action, together with a lack of effect on gamma-amino butyric acid-mediated inhibition, provides a unique mechanism of action for a general anesthestic.