title: Blue-cone horizontal cells in the retinae of horses and other equidae.
abstract: The morphology of horizontal cells chiefly of the horse, but also of asses, mules, and a zebra, has been examined by Lucifer yellow injections into lightly fixed retinae and by immunocytochemistry. In common with other mammals, equids have a B-type horizontal cell, i.e., a cell with dendrites synapsing with cones and possessing a single axon synapsing with rods. Most mammalian retinae have a further type of horizontal cell, the A-type, also synapsing with cones but without an axon. The second type of horizontal cell in equids also has no axon; otherwise, it is most unusual. Compared with other mammalian A-type cells, it has a vary large dendritic field, both absolutely and relative to the dendritic fields of B-type cells. The dendrites are fine and sparsely branching. Their most striking feature is that they bear a low density of irregularly spaced synaptic terminal aggregates, suggesting their cone contacts are selective. Immunolabelling of S (blue)-cones in horse retina showed that they comprise, depending on retinal location, 10-25% of the cone population. For a single horse A-type cell, it is shown that 44 of its 45 terminal aggregates are congruent with the pedicles of S-cones. Immunostaining with a calbindin antibody demonstrated that each type of horizontal cell forms an independent regular mosaic. The density ratio of B- to A-type cells varied between 5 and 10. This is the first demonstration in a mammalian retina of a horizontal cell type with a direct input exclusively from S-cones.
authors.affiliation: Max Planck Institut fũr Hirnforschung, Frankfurt, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Sandmann
authors.forename: B B
authors.initials: BB
authors.lastname: Boycott
authors.forename: L
authors.initials: L
authors.lastname: Peichl
mesh_terms: D000818:Animals; D018397:Equidae; D005260:Female; D006736:Horses; D007150:Immunohistochemistry; D007395:Interneurons / Q000276:immunology / Q000502:physiology*; D008297:Male; D010786:Photoreceptor Cells / Q000502:physiology*; D012160:Retina / Q000033:anatomy & histology* / Q000276:immunology