Neuronal networks formed by retinal electrical synapses, or gap junctions, are of physiological importance for visual information processing. Horizontal cells (HCs), second-order interneurons, are electrically coupled through gap junctions to form a dense neuronal network that mediates the antagonistic center-surround organization of bipolar and ganglion cell receptive fields. Modulation of HC gap junctions underlies adaptive changes in the function of retinal neuronal networks to different levels of illumination. Dopamine is one of the gap junction neuromodulators that significantly alters HC networks during light adaptation. Overall, HCs are an excellent model system to study the functional aspects of electrical coupling and neuronal network plasticity. The long-term goal of my research is to understand the role of HC electrical synapses in retinal plasticity and visual information processing. The retinal degeneration (rd) mouse that lacks rods and cones is an advantageous model for investigation of electrophysiological properties of mammalian HC electrical synapses. The use of flat-mount rd retinas permits HCs to be readily approached for recording. I have combined this technique with the dual whole-cell patch-clamp technique to demonstrate the feasibility of obtaining electrophysiological recordings of currents through HC gap junctions. These techniques can be utilized to achieve the following specific aims:
Specific Aim 1 : Characterization of electrophysiological properties of HC electrical synapses. Specifically, I will (1) measure gap junction conductance and coupling coefficient of HC electrical coupling; (2) determine whether carbenoxolone and intracellular H+ affect HC electrical synapses; (3) test whether HC electrical synapses function as a low-pass filter.
Specific Aim 2 : Modulation of HC electrical synapses by dopamine. Specifically, I will (1) characterize regulation of HC gap junctions by exogenous and endogenous dopamine; (2) determine the cellular mechanism of dopamine on HC electrical, synapses. These studies will greatly advance our understanding of the function and plasticity of retinal neuronal networks during light/dark adaptation and our understanding of retinal functional modification during photoreceptor degeneration. ? ?
