Abstract
Abstract: :
Purpose: As part of our develoment effort toward a neurotransmitter–based visual prosthesis, we have examined the neurotoxicological profiles of a number of phototriggered stimulatory molecules. Our previous work has demonstrated that ‘caged’ forms of L–glutamate are often less excitotoxic than L–glutamate, alone. The purpose of this study was to elucidate the neurotoxicologic profiles of MNI and MCNI cages independent of L–glutamate by employing glutamate receptor antagonists (GlutRa’s). 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 (MNI or MCNI), 50 uM photoactivated caged glutamate (MNI or MCNI) with and without a glutamate receptor antagonist cocktail (25uM MK–801, 50uM DNQX and 1uM NBQX). Neuronal viability was assessed after 24 hours 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). Cultures treated with GlutRa’s and MNI–glutamate did not demonstrate an increase in neuronal viability compared to cultures treated with MNI–glutamate alone (p=0.589). However, cultures treated with photoactivated MNI–glutamate also did not demonstrate a significant increase in viability with the addition of GlutRa’s (p=0.914). The addition of GlutRa’s did not affect the viability of MCNI–treated cultures (p=0.324), but did significantly increase the viability of photoactivated MCNI–glutamate treated cultures (p<0.001) when compared to treatment without GlutRa’s. Conclusion: The MNI caged, once liberated from L–glutamate appears to be toxic to neurons, independent of glutamate. However, the liberated MCNI cage was not toxic to our neuronal cultures. These data suggest that while the MNI cage is toxic to neurons, the MCNI cage is relatively non–toxic and has potential for use in a visual prosthetic device.
Keywords: drug toxicity/drug effects • excitatory neurotransmitters • neurotransmitters/neurotransmitter systems