Interpretation of Length Constants in Retinal Horizontal Cell Layers

Abstract

Introduction Horizontal Cells (HC's) of the vertebrate retina are second order neurons receiving excitatory synaptic input from photoreceptors (PR). Through gap junctions they form homological electrical syncytia, sampling and distributing signals over large areas. Through a feedback mechanism onto PRs and feedforward synapses onto bipolar cells they are thought to play an important role in spatial and color organization of retinal receptive fields and in adaptation processes. Figure 1: A H1 network in the turtle retina stained with neuro-biotin. The bar represents 50 ¯m. Effects of background light or drugs (e.g. dopamine) on the coupling strength or the receptive field size of HC's were quantified by determining directly or indirectly a length constant (whatever it is) from the membrane potential. Because of the interpretation of 2 as the ratio of the membrane resistance<F52