Golgi-impregnated amacrine cells and GABAergic retinal neurons: a comparison of dendritic, immunocytochemical and histochemical stratification in the inner plexiform layer of rat retina.

This paper concerns the banding pattern produced in the inner plexiform layer of rat retina by glutamic acid decarboxylase (GAD) immunocytochemistry. It presents a comparison of this pattern with the dendritic stratification of neurons that are reasonable candidates for GABAergic amacrine cells in Golgi preparations, and also with the banding patterns produced by other histochemical techniques. First, the spacing of five dense GAD-positive bands and four intervening less dense bands in central retina is quantitatively described. Second, examples of a particular, morphologically homogenous group of Golgi-impregnated amacrine cells are examined in the details of their structure, especially with regard to their dendritic stratification. Computer reconstructions of the dendritic trees of some of these narrow-field, multistratified amacrines are compared with the GAD-positive banding pattern. This group of amacrines is judged to represent many of the GABAergic neurons in rat retina, accounting for the form and distribution of GAD-positive synaptic terminals by their dendritic morphology and stratification. Third, a general schema for the laminar subdivision (stratification) of the inner plexiform layer in rat retina is derived from a comparison of the results of several histochemical procedures. Finally, similarities and differences in the distribution of GAD-positive amacrine cell dendrites are noted among mammals and the functional implications of their broad distribution are discussed. A conspicuous difference is cited between mammals and certain nonmammalian vertebrates in which GAD-positive dendrites are restricted to sublamina beta (ON-center cells) of the inner plexiform layer.