Short-Term Plasticity of Glutamatergic and GABA-Ergic Synaptic Transmission between Co-Cultured Retinal Ganglion Cells and Superior Colliculus Neurons

Abstract

Received 21 November, 2013. We studied changes in the efficacy of synaptic transmission via glutamatergic and GABA-ergic synaptic connections between co-cultured retinal ganglion cells (RGCs) and neurons of the superior colliculus (SC) at paired stimulation of RGCs (as a form of short-term synaptic plasticity). In a parallel manner, we recorded transmembrane currents and potentials in synaptically connected pairs of RGCs and SC neurons using the paired whole-cell patch-clamp technique. When glutamatergic synaptic action was mediated by activation of exclusively NMDA or non-NMDA receptor channel complexes on the postsynaptic membrane of SC neurons, depression of synaptic transmission after the second AP was observed. In the case of GABA-ergic transmission mediated by activation of GABA А receptor-channel complexes, analogous paired stimulation resulted in facilitation of synaptic action on an SC neuron after the second AP generated by an RGC. The use of basic and complete quantal analyses allowed us to find a significant decrease (Р < 0.05) in the binomial parameter n in the case of depression of NMDA-mediated evoked postsynaptic currents (ePSCs) and a significant drop in both quantal parameter q and binomial parameters n and p at depression of non-NMDA-mediated ePSCs. In the former case the estimate was indicative of possible presynaptic localization of the mechanisms of depression resulting from a decrease in the number of released synaptic vesicles containing the transmitter, while in the latter case not only pre- but also post-synaptic mechanisms (decrease in the number of released synaptic vesicles and desensitization of postsynaptic receptors) are probably involved. Estimation of normalized alterations of the quantal and binomial parameters at facilitation of GABA А -mediated ePSCs demonstrated a significant increase (Р < 0.05) in the presynaptic factors n and p and, correspondingly, in the quantal content m. Therefore, the effect of facilitation can be due to the processes realized in a presynaptic terminal (enhancement of the number of synaptic vesicles).