Visual Response Properties of Y Cells in the Detached Feline Retina Visual Neurophysiology

Abstract

PURPOSE. To evaluate early changes in the visual response properties of Y cells in the detached feline retina. METHODS. The retinas of young adult cats were detached by injection, with a glass micropipette, of a solution of 0.004% sodium hyaluronate in a balanced salt solution between the neural retina and the retinal pigment epithelium. At 1, 3, and 7 days after detachment, the eyes were removed. The eyecup was prepared as a flat mount in a recording chamber and superfused with medium. Extracellular single-unit responses from Y cells in the retinas were recorded. RESULTS. One, 3, and 7 days after retinal detachment surgery, Y cells showed clear signs of functional deterioration. At each time point, more ON center cells than OFF cells were encountered. Y cells in the detached retinas showed a statistically significant elevation in the average threshold irradiance after 1-, 3-, and 7-day detachment, respectively. The average contrast threshold recorded from cells in the normal retina was 3.6%, but it increased to 14.5%, 21.8%, and 47.5% after 1-, 3-, and 7-day detachment, respectively. Furthermore, at each time point, the capability of Y cells to process contrast information decreased significantly more because of detachment than because of luminance task performance. CONCLUSIONS. Retinal detachment induced rapid functional remodeling that resulted in degenerated Y-cell function, including an elevated luminance threshold and a deteriorated contrast threshold. Detachment had a greater impact on the latter. These physiological changes after retinal detachment could be used as objective indicators of early deterioration of visual function in future studies of retinal remodeling. (Invest Ophthalmol Vis Sci. 2010;51:1208 -1215 This is partly attributed to the intrinsic nature of photoreceptor cells, in that outer segments are able to regenerate after reattachment and that most of them achieve near-normal morphologies. Nevertheless, visual deficits are common after successful reattachment surgery. 7-9 Regardless of the initial insult, stressed photoreceptors can remodel their synaptic terminals and their relationship to second-order neurons. These changes are proposed to progress through three phases: photoreceptor stress, photoreceptor death, and complex neural remodeling. 10 Although the cells are in detachment, neural remodeling occurs early-within a few days-and, therefore, before massive photoreceptor cell death. Substantial evidence suggests that diagnosis and intervention at the early stages of retinal remodeling, especially during the stress phase, when there is significant photoreceptor terminal modifications, are critical for the successful rescue of injured cells and the restoration of visual function. Over the years, molecular and morphologic changes during this stage have been explicitly addressed in experimental retinal detachment, 3 whereas objective neurophysiological observations correlating these early structural changes have been reported only in data from electroretinography. 11 Electroretinographic (ERG) testing provides one objective measurement of the electrical activity of detached and reattached retinas. 12-16 However, current ERG technology is not sensitive enough to detect alterations at the single-cell level. RGCs play the crucial role in collecting appropriate input from second-order neurons and transmitting visual information to higher visual centers, but little is known about the functional consequence of these neurons after RD and subsequent reattachment. Y cells have been studied for more than 40 years, From th