Abstract
Abstract: :
Purpose:Previous studies from our laboratory have demonstrated that changes in dendritic morphology represent the earliest signs of ganglion cell degeneration in the glaucomatous primate eye. Since ganglion cells receive all of their synaptic input via their dendrites, these data imply early changes in ganglion cell function. The purpose of these studies was to examine the structure-function relations of ganglion cells in normal and glaucomatous eyes. Methods:An isolated, living retina, preparation was used to record and label single ganglion cells. Intrinsic membrane properties were examined by injecting depolarizing or hyperpolarizing pulses of current. Visual responses were obtained by presenting either drifting or counter-phased squarewave gratings of varied spatial and temporal frequency. Morphological comparisons were made by injecting the cells with Neurobiotin and reconstructing them using a Neurolucida system. Results:Very little difference was found with respect to the intrinsic membrane properties of parasol cells in the normal and glaucomatous eyes. Mean values of resting membrane potential, input resistance, membrane time constant, and threshold to response for cells from the normal and glaucomatous eyes were: -52 vs -51mV; 21 vs 18Mohm; 2.7 vs 2.2msec., and 0.3 vs 0.4nA, respectively. While both groups of cells preferred low spatial frequency stimuli (0.2c/cm), normal cells responded better to high temporal frequency stimuli (peak TF: 17Hz vs 11Hz). In general, ganglion cells in glaucomatous eyes were less stable to record from, more difficult to label, and often could be driven only by very bright, full field, visual stimuli. Anatomically, ganglion cells from glaucomatous eyes contained 43% less dendritic length, 54% less dendritic surface area, and 65% less dendritic volume. Conclusion:Ganglion cells in the glaucomatous eye retain their intrinsic electrical properties, but become less responsive to visual stimulation. This reduction most likely is due to significant changes in dendritic morphology.
Keywords: 415 ganglion cells • 394 electrophysiology: non-clinical • 444 intraocular pressure