Abstract
Abstract: :
Purpose: To determine whether one or both types of horizontal cell (HC) in the cat retina give rise to the neurite outgrowths previously described after experimental retinal detachment (IOVS 39: 424–434, 1998). Methods: Sections as well as wholemounts of retinas detached for 7 and 28 days together with control retinas were labeled with antibodies to calretinin, calbindin, and neurofilament protein. Digital immunofluorescence images were collected with a BioRad 1024 confocal microscope. Results:Cats have two types of HC, an axon–bearing (B) and an axonless (A) type. The latter has been shown to be rich in neurofilaments (Proc. Roy. Soc. Lond. B. 186: 317–331, 1974). In control retina, both HC types label intensely with antibodies to calretinin and calbindin. Only the A–type also prominently labels with the neurofilament protein antibody. After 7 and 28 days of detachment, these staining patterns persist, but there is a moderate upregulation of neurofilament protein in the B–type cell. In the detached retina, HC processes sprout neurites that extend to varying depths into the outer nuclear layer (ONL). These neurites appear most commonly as a thatch of fine, beaded processes rising together in a loose array, or, especially at 28 days, as a single, often thick, unbranching process that rises vertically through the ONL, often extending to the subretinal space. These processes sometimes expand at their tips, or display a thick varicosity within the ONL. Both types of outgrowth are strongly calretinin positive and faintly label with antibodies to calbindin and neurofilament protein. Moreover, both arise from similarly labeled processes in the distal–most domain of the outer plexiform layer where the narrowly stratified axon terminals of the B–type HC each innervates numerous rod spherules. Outgrowths were never seen arising from the dendrites of either HC type. Conclusions: Only the axon terminal of the B–type HC innervates rod spherules in the cat; dendrites of both HC types exclusively synapse with cones (J. Comp. Neurol. 155: 1–14, l974). Rods respond to detachment by withdrawing synaptic terminals from the OPL while cones do not (Molec. Neurobiol. 28: 159–175, 2003). Our data is consistent with a very specific remodeling of only the rod–connected axon terminals of the B–type cell. This neuronal remodeling is accompanied by an increase in the expression of neurofilament protein in the axons of these cells.
Keywords: retinal detachment • horizontal cells • plasticity