Abstract
Abstract: :
Purpose:The objective is to determine similarities and differences in receptive field properties of various types of bipolar cells (BCs) in the tiger salamander retina, and the contributions of electrical coupling, horizontal cell–cone feedback, horizontal cell–bipolar cell feedforward and amacrine cell–bipolar cell feedback synapses to center and surround responses of various types of bipolar cells. Methods: BCs were impaled with microelectrodes filled with Neurobiotin and Lucifer yellow in the superfused flatmount retinas of the tiger salamander, and voltage responses to light spots or annuli of various diameters were recorded. Results: All BCs in the salamander retina exhibit CSARF, and the relative surround/center response strength of the rod–dominated BCs is weaker than that of the cone–dominated BCs. The receptive field center diameter (RFCD) correlates with the degree of dye coupling: HBCRs are strongly dye coupled to each other and their RFCDs are 500–650µm whereas DBCRs are weakly coupled and their RFCDs are less than 350 µm. A subpopulation of DBCs are dye coupled with broad field HCs. Conductance changes associated with the center and surround responses of various BCs were measured by current injection through a bridge circuit, and in most BCs the conductance change of the surround response is of the opposite sign to the conductance change of the center response. Application of GABA reduced the surround responses of a subpopulation of HBCs and exerted no effect on surround response of other BCs, while application of gap–junction blockers (e.g. octonol, carbenoxolone or quinine) suppressed (and sometimes reversed) the surround responses of HBCs. Conclusions: The CSARFs of the four major types of BCs (HBCR, HBCC, DBCC and DBCR) differ in the relative surround/center response strength, receptive field center diameter, degree of electrical coupling and interneuron synaptic pathways for the surround responses.
Keywords: bipolar cells • gap junctions/coupling • receptive fields