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A quantitative ultrastructural study of the inner plexiform layer of the rat retina
Author(s) -
Sosula Leo,
Glow Peter H.
Publication year - 1970
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.901400405
Subject(s) - inner plexiform layer , amacrine cell , retina , neuroscience , biology , synapse , postsynaptic potential , outer plexiform layer , ganglion , synaptic vesicle , vesicle , biochemistry , receptor , genetics , membrane
The inner plexiform layer (IPL) and adjacent regions of the rat retina were studied by electron microscopy. The IPL contains neural processes of amacrine, bipolar, and ganglion cells, and glial (Müller) processes. Type 1 amacrine processes (maximum diameter 3.1 μ) traced from their somata structurally resemble amacrine perikarya. These processes rarely form synapses. Type 2 amacrine processes (maximum diameter 0. 7 μ) are radially oriented, forming synaptic expansions en passant , giving origin to collaterals, also with expansions. The type 2 amacrine processes form conventional synapses onto bipolar, ganglionic and other amacrin processes, onto amacrine and ganglionic somata, and onto dendritic spines. Amacrine perikarya in rare cases contain synaptic vesicles and form somatic synapses onto surrounding processes. Bipolar processes traverse the IPL, forming terminal expansions up to 6 μ in diameter near the ganglion somata, which they contact without synaptic vesicle clustering. Bipolar processes form synapses onto dyads. In 73% of dyads, both processes are vesiculated. One process of the dyad pair could usually be identified as an amacrine by its reciprocal synapse back onto the presynaptic bipolar process. The other dyad process, when vesiculated, contains vesicles which are significantly larger and less concentrated than in the adjacent amacrine, and is presumably a ganglion cell dendrite. The ratio of the incidence of amacrine synapses: bipolar synapses is about 8:1. A subdivision of the IPL into thirds shows that the highest incidence of amacrine synapses is in the middle third. Amacrine somata are significantly larger than bipolar somata. Synaptic vesicles in receptor terminals of the outer plexiform layer are significantly larger and more concentrated than those in axonal processes of the IPL. The functional aspects of these findings are discussed in relation to physiological investigations and interspecies differences described in the literature.