MODULATION OF THE TIME COURSE OF FAST EPSCS AND GLUTAMATE CHANNEL KINETICS BY ANIRACETAM

It is generally accepted that glutamate serves as the neurotransmitter at most excitatory synapses in the mammalian central nervous system (CNS). Synaptic release of glutamate may trigger a fast and a slow excitatory postsynaptic current (EPSC). The slow EPSC is mediated by N-methyl-D-aspartate (NMDA) receptor channels, whereas the fast EPSC is mediated by non-NMDA receptor channels. The nootropic agent aniracetam selectively and reversibly slows the desensitization kinetics of non-NMDA channels and lengthens their single-channel open times. Aniracetam also modulates the kinetics of the fast EPSC in a manner that mirrors its action on the kinetics of the non-NMDA channels. These results support the hypothesis that the properties of the non-NMDA glutamate channels rather than the rate of neurotransmitter clearance are the primary determinants of the kinetics of the fast EPSC in the mammalian CNS.