Goα labels ON bipolar cells in the tiger salamander retina

Abstract

By using double-label immunocytochemistry and confocal microscopy, we studied rod and cone synaptic contacts, photoreceptor-bipolar cell convergence, and patterns of axon terminal ramification of ON bipolar cells in the tiger salamander retina. An antibody to recoverin, a calcium-binding protein found in photoreceptors and other retinal neurons in various vertebrates, differentially labeled rods and cones by lightly staining rod cell bodies, axons, and synaptic pedicles and heavily staining cone cell bodies and pedicles. An antibody to G_oα labeled most ON bipolar cells, with axon terminals ramified mainly in strata 6–9 and a minor band in stratum 3 of the inner plexiform layer (IPL). Stratum 10 of the IPL was G_oα negative, and previous studies showed that axon terminals of rod-dominated ON bipolar cells are monostratified in that stratum. The axonal morphology of G_oα-positive cells resembled that of the cone-dominated (DBC_C) or mixed rod and cone ON (DBC_M) bipolar cells. The G_oα-positive dendritic processes made close contact with all cone pedicles and superficial contact with some rod pedicles, consistent with the idea that G_oα subunits are present in DBC_Cs and DBC_Ms. The size and density of these cells were analyzed, and their spatial distributions were determined. To our knowledge, this is the first study to characterize photoreceptor inputs and axon terminal morphology of a population of ON bipolar cell with the use of a G_oα antibody as an immunomarker in the salamander retina. J. Comp. Neurol. 461:276–289, 2003.