Abstract
Abstract: :
Purpose: To study the synaptic preferences of photoreceptors for bipolar cell types during regeneration of synaptic circuitry. Specifically, do cone and rod cells contact their normal or a novel bipolar cell type when new synapses are made? Methods: Adult, tiger salamander retinas were dissociated and plated, and a single photoreceptor was paired with a bipolar neuron either by random association or by micromanipulation of the photoreceptor using optical tweezers. Bipolar cells were identified morphologically at plating by their distinct Landolt club. Cell pairs were followed for 7 days, fixed and then stained with antibodies against rod opsin to distinguish rods from cones, and against Goα to distinguish cone–dominant and mixed rod–cone ON bipolar cells from other bipolar cells. In randomly plated cells, rod/Goα–positive bipolar cell pairs were studied after 2 weeks of culture. Photoreceptors were classified as attracted to, repelled by, or neutral towards its paired neuron. Results: In the intact salamander retina, all cone cells input to Goα–positive cells, which in turn make up about 40% of all bipolar cells (Zhang and Wu, J. Comp. Neurol., 2003, 461:276). For the 20 cone–bipolar cell pairs formed by micromanipulation, 13 bipolar cells were attractive to cones, and 8 of them stained positive for Goα, suggesting formation of normal contacts. For rod cells in intact retina, only 30% of them input to Goα–positive cells (Zhang and Wu, 2003). In 48 pairs from the 2 week–cultures, 60% of bipolar cells contacted by rods, stained for Goα, an unexpectedly large number. Further, in manipulated pairs, all bipolars which repulsed rods, were Goα–negative. It would have been expected that some Goα–positive cells would have repelled rods. Conclusions: The data indicate that cone cells have predominantly normal interactions, whereas, rod cells seek novel bipolar partners. Previous studies showed that rods also frequently contact inappropriate third–order neurons. It is possible that the attraction of rod cells to novel partners may drive the remodeling of inner retinal synaptic circuitry that occurs in disease.
Keywords: photoreceptors • plasticity • regeneration