The Journal of Neurophysiology Vol. 78 No. 5 November 1997, pp. 2662-2673
Copyright ©1997 The American Physiological Society

Response Sensitivity and Voltage Gain of the Rod- and Cone-Bipolar Cell Synapses in Dark-Adapted Tiger Salamander Retina

Xiong-Li Yang and Samuel M. Wu

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas 77030

Yang, Xiong-Li and Samuel M. Wu. Response sensitivity and voltage gain of the rod- and cone-bipolar cell synapses in dark-adapted tiger salamander retina. J. Neurophysiol. 78: 2662-2673, 1997. Rods, cones, and bipolar cells were recorded in superfused, flat-mounted isolated retinas of the larval tiger salamander, Ambystoma tigrinum, under dark-adapted conditions. Voltage responses of 24 rods, 15 cones, and 41 bipolar cells in dark-adapted retinas to 500 nm light steps of various intensities were listed and fitted with hyperbolic functions, and their step sensitivities and relative sensitivities (log ) were estimated. In the linear response-intensity ranges, the step sensitivity of rods, S_S(rod), is 1.0 mV photon¹ µm² s or 0.034 mV Rh*¹ s rod and that of the cones, S_S(cone), is ~0.00146 mV photon¹ µm² s or 0.000048 mV Rh*¹ s rod. The rod and cone responses were relatively homogenous with little variations in response amplitude and sensitivity. In contrast, bipolar cell responses were heterogenous with large variations in response amplitude and sensitivity. The maximum response amplitude of bipolar cells varied from 5 to 25 mV, and the relative response sensitivity (log ) varied >6 log units (8.11 to 2.32). The step sensitivity of bipolar cells in the linear response-intensity range varied from 0.0000438 to 51.82 mV photon¹ µm² s. Bipolar cells in dark-adapted tiger salamander retinas fell into two groups according to their relative sensitivities with very few cells falling in the intermediate light intensity region. The mixed bipolar cells (DBC_M and HBC_M) exhibited relative response sensitivity ranged from 8.11 to 5.54, and step sensitivity ranged from 1.22 to 51.82 mV photon¹ µm² s. The cone-driven bipolar cells (DBC_C and HBC_C) exhibited relative response sensitivity ranged from 3.45 to 2.32, and step sensitivity ranged from 0.0000438 to 0.00201 mV photon^-1 µm² sec. The chord voltage gain of the rod-DBC_M or rod-HBC_M synapses near the rod dark membrane potential ranged from 1.14 to 48.43 and that of the cone-DBC_C or cone-HBC_C synaptic gain near the cone dark membrane potential ranged from 0.03 to 1.38. The highest voltage gains were found near the rod or cone dark membrane potentials. By the use of linear subtraction method, we studied the synaptic inputs from cones to five mixed bipolar cells, and the voltage gains of the cone synapses in each of the bipolar cells were very close to the voltage gain of the rod synapses. This result suggests that although the responses of mixed bipolar cells are mediated mainly by rods when lights of short and medium wavelengths are used, their responses to long wavelength lights (>650 nm) are mediated by both rods and cones with comparable synaptic gains. Functional roles of the mixed and cone-driven bipolar cells in information processing in dark-adapted retinas are discussed.

This article has been cited by other articles:

				J. W. Xu, M. Hou, and M. M. Slaughter Photoreceptor encoding of supersaturating light stimuli in salamander retina J. Physiol., December 1, 2005; 569(2): 575 - 585. [Abstract] [Full Text] [PDF]

				T. Ichinose and P. D. Lukasiewicz Inner and outer retinal pathways both contribute to surround inhibition of salamander ganglion cells J. Physiol., June 1, 2005; 565(2): 517 - 535. [Abstract] [Full Text] [PDF]

				J. Zhang and S. M. Wu Physiological properties of rod photoreceptor electrical coupling in the tiger salamander retina J. Physiol., May 1, 2005; 564(3): 849 - 862. [Abstract] [Full Text] [PDF]

				N. Hosoi, I. Arai, and M. Tachibana Group III Metabotropic Glutamate Receptors and Exocytosed Protons Inhibit L-Type Calcium Currents in Cones But Not in Rods J. Neurosci., April 20, 2005; 25(16): 4062 - 4072. [Abstract] [Full Text] [PDF]

				T. Ichinose, C. R. Shields, and P. D. Lukasiewicz Sodium Channels in Transient Retinal Bipolar Cells Enhance Visual Responses in Ganglion Cells J. Neurosci., February 16, 2005; 25(7): 1856 - 1865. [Abstract] [Full Text] [PDF]

				J.-J. Pang, F. Gao, and S. M. Wu Segregation and Integration of Visual Channels: Layer-by-Layer Computation of ON-OFF Signals by Amacrine Cell Dendrites J. Neurosci., June 1, 2002; 22(11): 4693 - 4701. [Abstract] [Full Text] [PDF]

				X.-L. Yang, F. Gao, and S. M Wu Non-linear, high-gain and sustained-to-transient signal transmission from rods to amacrine cells in dark-adapted retina of Ambystoma J. Physiol., February 15, 2002; 539(1): 239 - 251. [Abstract] [Full Text] [PDF]

				S. M. Wu, F. Gao, and B. R. Maple Functional Architecture of Synapses in the Inner Retina: Segregation of Visual Signals by Stratification of Bipolar Cell Axon Terminals J. Neurosci., June 15, 2000; 20(12): 4462 - 4470. [Abstract] [Full Text] [PDF]

				F. Gao, B. R. Maple, and S. M. Wu I4AA-Sensitive Chloride Current Contributes to the Center Light Responses of Bipolar Cells in the Tiger Salamander Retina J Neurophysiol, June 1, 2000; 83(6): 3473 - 3482. [Abstract] [Full Text] [PDF]

				D. A. Burkhardt and P. K. Fahey Contrast Enhancement and Distributed Encoding by Bipolar Cells in the Retina J Neurophysiol, September 1, 1998; 80(3): 1070 - 1081. [Abstract] [Full Text] [PDF]