An analysis of synaptic transmission to motoneurones in the cat spinal cord using a new selective receptor blocker.

We have investigated the role of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors on synaptic transmission in vivo between Ia primary afferents and cat spinal motoneurones using a selective non-N-methyl-D-aspartate (non-NMDA) receptor antagonist, GYKI 52466. Both microionophoretic and intravenous application of GYKI 52466 depressed the excitatory post-synaptic potential (Ia EPSP) in a dose-dependent manner, without any apparent effect on membrane conductance or resting potential of the motoneurone. GYKI 52466 reduced selectively alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)- but not N-methyl-D-aspartate (NMDA)-induced depolarizations. Our results suggest that a large part of the Ia EPSP is mediated by AMPA receptors. The participation of other excitatory amino-acid receptors in the Ia EPSP is also discussed.