Amacrine cells of the cat retina

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INTRODUCTION Amacrine cells, the interneurons of the inner plexiform layer of the vertebrate retina, form both lateral and radial pathways amongst the bipolar and ganglion cells (Cajal, 1933). In fact, certain amacrine cells are elemental to the rod system of the mammalian retina (Kolb and Famiglietti, 1974). Physiological studies indicate that amacrine cells of the cat retina have distinct response. characteristics suggestive of diverse functions in the rod and cone systems or the on-centre or 0%centre pathways (Nelson et 01.. 1976; Nelson and Kolb, 1978). In addition, pharmacological evidence is now accumulating that specific neurotransmitters are present in specific varieties of amacrines (Pourcho, 1979; Pourcho, 198Oa, 1980b; Tork and Stone, 1979; Nakamura et al., 1980). It thus seems timely to enquire, in greater detail, of the morphology and synaptic connections of the amacrine cells of the cat retina, and attempt to link such findings to the physiology and chemistry of such cells. In our quest to understand amacrine cells of the cat retina, we have used four different experimental procedures. Firstly, we have used the venerated Golgi technique for studying the morphology of the amacrine cells and classifying them by characteristics such as dendritic field size, morphology, branching pattern and stratification within the inner plexiform layer (IPL). Secondly, we have made reconstructions of portions of amacrine cells studied by ultra-thin serial sections in the electron microscope. Such reconstructed three-dimensional profiles can oft-times be identified with specific Golgi-impregnated cell types. Thirdly, intracellular recordings and stainings of amacrine cells have been possible in cat retina and identification of the physiologically recorded units can be made with their Go&impregnated counterparts. Lastly and more recently, we have been using the powerful tool of intracellular injection of horseradish peroxidase (HRP). By this means, a physiologically identified amacrine cell can be visualized and compared to a Golgi-impregnated cell, and, furthermore, examined by electron microscopy for synaptic relationships in the neuropil of the IPL. Although Cajal (1933) left us an encompassing description of the neurons of the vertebrate retina, he did not specifically study the cat retina. Therefore, we Auyusr 1981)