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S.S. Kapi, T.L. Walraven, G.W. Abrams, R. Iezzi; "Caged Neurotransmitters for Visual Prosthesis: Toxicological Profiles for the Phototriggerable Cage NPEC." . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4205.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Much of our research focuses on the development of a neurotransmitter–based prosthetic device for retinal and cortical stimulation. Using photoactivated neurotransmitters in our prostheses, we are able to both temporally and spatially control the release of active neurotransmitters, thereby selectively activating neurons. While there are many neurotransmitters and neuromodulators involved in the generation of sight, our work focuses primary on the ‘caged’ form of the excitatory neurotransmitter, L–glutamate. Prior to the implementation of caged neurotransmitters in an in–vivo prosthetic device, the toxicologic profiles of the caging molecules must be elucidated. This is accomplished by using glutamate receptor antagonists (GlutRa’s) in conjunction with both caged glutamate and photoactivated–caged glutamate to isolate the effects of the cages themselves on cultured neurons. Methods: Visual cortical neurons were cultured from embryonic Sprague–Dawley rat pups and incubated for 8 days prior to exposure to either 50 uM L–glutamate, 50 uM caged glutamate (NPEC), 50 uM photoactivated caged glutamate (NPEC) with and without a glutamate receptor antagonist cocktail (25uM MK–801, 50uM DNQX and 1uM NBQX). Neuronal viability was assessed 24 hours following exposure using a 0.4% Trypan Blue dye exclusion assay. Results: GlutRa’s significantly increased the neuronal viability of L–glutamate treated cultures (p<0.001). When combined with caged NPEC–glutamate, GlutRa’s did not affect neuronal viability, compared to NPEC–glutamate treatment without GlutRa’s (p=0.765). The addition of GlutRa’s to photoactivated NPEC glutamate resulted in a significant increase in viability compared to treatment with photoactivated NPEC–glutamate, alone (p<0.001). The viability of neurons treated with both photoactivated NPEC glutamate and GlutRa’s was not significantly different from those cultures treated with L–glutamate and GlutRa’s. Conclusion: When liberated from L–glutamate, the NPEC cage does not appear to be toxic to neurons, independent of glutamate, as examined through the use of GlutRa’s. These data suggest that the NPEC cage does not induce neuronal toxicity and may be useful in a visual prosthetic device. Future work will involve the chronic, intravitreal infusion of this molecule in the rat model.
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