Abstract
Abstract: :
Purpose:Determine the depth of retinal neurons that respond to various electrical stimuli by utilizing a mathematical model for the charge arriving at the cell. Methods:Extracellular single cell recordings of action potentials of individual off–brisk transient ganglion cell axons were made in superfused adult New Zealand White rabbit retinas in a dimly lit room. Ganglion cells were stimulated electrically by a (5, 25, 125, and 500 um diameter) electrode, positioned on the inner retinal surface over the receptive field. The electrical stimulus was a 2 msec current pulse. The return electrode was an Ag/AgCl surface located underneath the sclera (transretinal stimulation). Stimulations were applied at different locations by varying the elevation above the retina or the location relative to the center of a ganglion cell receptive field, at a direction perpendicular to the estimated axon path. The measured results were applied to a mathematical model in order to get an estimate for the depth of the activated cell in the retina. Results:Ganglion cells responses to electrical stimulation included a short–latency (3–5 msec) single action potential, followed by a burst of action potentials (n=4–8) that occurred 11–50 msec following stimulus onset. The two types of responses were inserted into the mathematical model respectively, and the location (depth) of the activated cell was evaluated. The short–latency results show a median cell depth of 67–85 um below the surface of the retina, while the longer latency results show a cell depth of 180–190 um beneath the inner limiting membrane. Conclusions:The results confirm our previous work that demonstrated that the long latency responses were pre–synaptic to ganglion cells which is consistent with results of the mathematical model. Since the actual thickness of the retina and sclera were not measured for each cell, and since the collected threshold data is not perfect, the model can not identify precisely the type of cell that produced the delayed response, or its actual location (inner or outer nuclear layer). The ranges only suggest that the origin of the delayed response is pre–synaptic to ganglion cells.
Keywords: ganglion cells • retina • retinal connections, networks, circuitry