Electrical coupling, receptive fields, and relative rod/cone inputs of horizontal cells in the tiger salamander retina

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas 77030ABSTRACTLight responses, dendritic/axonal morphology, receptive field diameters, patterns of dyecoupling, and relative rod/cone inputs of various types of horizontal cells (HCs) were studiedusing intracellular recording and Lucifer yellow/neurobiotin dye injection methods in theflatmount tiger salamander retina. Three physiologically and morphologically distinct typesof HC entities were identified. 1) The A-type HCs are somas that do not bear axons, withaverage ( SE) soma diameters of 20.01 0.59 m, relatively sparse and thick dendrites, andthey resemble the A-type HC in mammals. The average receptive field diameter of these cellsis 529.6 10.87 m and they receive inputs predominantly from cones. 2) The B-type HCsare broad-field somas that bear thin and long axons, with average soma diameters of 17.67 0.38 m, thinner dendrites of higher density, and they resemble the B-type HC in mammals.The average receptive field diameter of these cells is 1,633.55 37.34 m and they receivemixed inputs from rods and cones. 3) The B-type HC axon terminals are broad-field, coarseaxon terminal processes and they resemble the B-type HC axon terminal in rabbits. Theaverage receptive field diameter of these axon terminals is 1,291.67 24.02 m and theyreceivemixedinputsfromrodsandcones.AllthesetypesofHCaredye-coupledwithadjacentHCs of the same type. Additionally, B-type HCs and axon terminals are dye-coupled withsubpopulations of bipolar cells whose axon terminals ramify in the proximal half of the innerplexiform layer, raising the possibility that these HCs may send feedforward antagonisticsurround responses to depolarizing bipolar cells through electrical synapses. J. Comp. Neu-rol. 499:422–431, 2006.