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L.S. Theogarajan, R.J. Jensen, J.F. Rizzo; Stimulation of Rabbit Retinal Ganglion Cells by altering K+ Ion Gradients: Dose–Response Curve . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4215.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Current neural prosthetic devices use electrical stimulation to excite the neural tissue of interest. Electrical stimulation, though easy to implement is not the most effective method of neural stimulation. Common issues with electrical stimulation method are lack of focal stimulation, bio–toxicity and high power requirements. We are investigating the use of small focal application of increased extracellular concentration of potassium as an alternative to electrical stimulation. Methods: Single–cell recordings were made from the axons of ganglion cells with an in vitro rabbit retinal preparation. The ganglion cells were stimulated over the optical receptive field with a multibarrel micropipette which contained various concentrations of KCl (0–40mM) in an osmotically balanced NaCl solution (∼300 mOsm). The micropipette solutions were ejected by using a mulitchannel pressure ejector (PM8000, MDI Systems). All solutions contained Azure B to enable visualations of the solution being ejected. Pulse durations of 30–100msecs were used. Results: The following results were obtained from various cell types of ganglion cells that were located in the inferior, mid–peripheral retina. The control solution which contained 0mM KCl and 150mM NaCl produced no response. Solutions that contained 10–40mM produced appreciable responses, with response strength increasing with K+ concentration. Typical response latencies were 30–60msecs after application of K+. Application of micromolar concentrations of barium (Ba2+) to the bathing solution reversibly abolished the K+–evoked responses. Receptive fields for the K+ responses were about 500 µm in radius. Conclusions: The results indicate a dose–response behaviour with the the threshold for activation at approximately 10mM. The responses to K+ are similar in nature in regards to responses and latencies to the light–evoked responses. Blocking the K+ evoked responses by Ba2+ indicates that the response may not be purely due to a Nernstian behavior but complemented by the potassium siphoning effect of the Müller cells. Additionally, it may also be due to the reversal of the glutamate pumps. The results indicate that the use of potassium is a viable alternative to electrical stimulation for the development of a retinal prosthesis.
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