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Morphology and synaptic connections of HRP‐filled, axon‐bearing horizontal cells in the Xenopus retina
Author(s) -
Witkovsky Paul,
Stone Susan,
MaCdonald E. Douglas
Publication year - 1988
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.902750104
Subject(s) - axon , retina , biology , axon terminal , xenopus , neuroscience , gap junction , synapse , anatomy , biophysics , synaptic cleft , intracellular , microbiology and biotechnology , central nervous system , neurotransmitter , biochemistry , gene
Axon‐bearing horizontal cells of the Xenopus retina were studied by intracellular injection of HRP following physiological characterization. The profile of the cell viewed in whole mount consisted of a round or oval perikaryon about 50 μm in diameter and an axon about 1 mm long which lacked a prominent terminal expansion. The axonal diameter was 0.5‐1.0 μm in its proximal third but 2‐4 μm in its distal portion. Along its course the axon emitted 25‐40 branchlets each 0.2 μm in diameter, up to 10 μm long and terminating in a cluster of two to six synaptic knobs. Electron microscopic examination revealed that both perikaryal dendrites and axon branchlets ended in both rod and cone synaptic bases; cone contacts outnumbered rod contacts by two‐ to threefold. We were unable to document synapses of presumed interplexiform cells onto identified horizontal cells. Horizontal cell axons are joined in their distal portions by numerous, small (0.2 μm long) gap junctions. Other gap junctions were noted between horizontal cell processes within the synaptic endings of photoreceptors. An hypothesis is advanced whereby the cluster of axon branchlet synaptic knobs permits dynamic interaction of rod and cone synaptic inputs to the horizontal cell.