THE ORGANIZATION OF THE INNER NUCLEAR LAYER OF THE RABBIT RETINA

The initial goal of this study was to establish an accounting of the m ajor classes of cells present in the inner nuclear layer (INL) of the rabbit's retina, Series of 80-100 radial sections 1 mu m thick were cu t from retinal blocks dissected at intervals along the vertical meridi an, They were photographed at high magnification in the light microsco pe, By visualizing the initial segments of processes leaving the somat a, we could identify each cell as a bipolar, amacrine, horizontal, or Muller cell, The identifications made by light microscopy were confirm ed by electron microscopy of alternating ultrathin sections, On averag e, bipolar cells made up 41% of the total INL cells, amacrine cells 32 %, horizontal cells 1.5%, and Muller cells 24%, These fractions varied relatively little across the retina or among different animals, We ne xt immunolabeled the rod bipolar cells of whole-mounted retinas with a ntibodies against protein kinase C, using FITC as the visualizing agen t, The same retinas were counterstained with a DNA-binding probe that fluoresces at longer wavelengths, Serial optical horizontal sections o f the double-labeled wholemounts were made by confocal microscopy, On average, rod bipolars accounted for 10% of the total INL cells, By sub traction, the cone bipolars made up 31% of the total cells, We conclud e that cone bipolars substantially outnumber rod bipolars, even in a r etina in which rods outnumber cones by more than 20:1. Using the base of reference created here, a similar analysis can be carried out for o ther subclasses of retinal neuron, Because the analysis does not depen d on absolute cell densities or corrections for shrinkage, data acquir ed by different histochemical techniques may be combined.