Glial Modulation of Electrical Synapses in the Retina

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PROJECT SUMMARY Many neuronal cell types communicate with one another via electrical synapses, which allow the flow of current and ions through channels called gap junctions. Electrical synapses play an integral role in fast communication within sensorimotor processes, and in synchronous communication in many brain areas. Though fast and synchronous communication is necessary for many central and peripheral brain functions, the mechanisms behind gap junction modulation remain understudied. Studies in the retina have explored neuromodulators and signaling cascades that lead to phosphorylation or dephosphorylation of gap junction proteins, which alters the open probability of these channels. However, the role of glial cells in the modulation of electrical synapse communication has not been previously addressed. Modulation of chemical synapse communication by gliotransmission, or the release of molecules by glia, is well studied in the field of glial biology. This project aims to determine if gliotransmission affects electrical synapse plasticity within the retina. Neurons of the light adaptation circuitry in the retina have mechanisms to facilitate the activation of either the rod or cone pathways depending on ambient light levels. One such neuron, the AII amacrine cell, facilitates this mechanism through the opening and closing of gap junctions at electrical synapses between other AII cells and ON cone bipolar cells. The goal of this project is to determine if Müller glial cells play a role in this transient plasticity. Müller glia are the principal astroglia of the retina which release gliotransmitters in response to retinal activity. Aim 1 will determine if the gliotransmitter adenosine modulates gap junctions at AII electrical synapses. Adenosine is a target of interest because adenosine levels increase in darkness. Aim 2 will determine if stimulation or inhibition of Müller glia modulate gap junctions at AII electrical synapses. Müller cell gliotransmission will be stimulated by CNO activation of Gq DREADDs, which will be targeted to Müller cells with a viral vector under control of the GLAST promoter. The effect of Müller cell inhibition on AII electrical synapses will be assessed using an IP3R2KO mouse model. Pharmacological antagonism of adenosine receptors will reveal if adenosine mediates Müller glial modulation of these electrical synapses. The degree of modulation will be determined using conductance measurements with dual whole-cell patch clamp electrophysiology and neurobiotin tracing. The understanding of glial modulation of electrical synapses is essential for clarifying electrical synapse function in the retina, as well as other systems, in health and disease.