[The contribution of glycine and GABA(A) receptors to generation of the inhibitory postsynaptic potentials in the frog spinal cord motoneurones].

The contribution of glycine and GABA(A) receptors to generation of the inhibitory postsynaptic potentials (IPSPs) evoked by microstimulation of the inhibitory fibers was studied intracellularly in the motoneurones of the isolated frog spinal cord. IPSPs were isolated by bloking EPSPs with kynurenate or CNQX and AP-5. The reversion under the small depolarising current (1-10) nA was used for the identification of IPSPs. The selective GlyR antagonist strychnine (1-5 microM) reduced the amplitude of IPSPs by a factor of 4.7 on the average in all studied motoneurones, while the selective GABA(A)R antagonist bicuculline (50-70 microM)--only by a factor of 1.6 and had no effect in 44% of motoneurones. Sequential applications of strychnine and bicuculline completely blocked the IPSPs. The results suggest that postsynaptic inhibition in the frog motoneurones is mediated by glycine (predominantly) and GABA(A) (to a smaller extent) receptors. It is possible the GABA(A) receptors are partly extrasynaptic.