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Eric Gustafson, Amy Silberschmidt, Manuel Esguerra, Robert Miller; Recording and Manipulation of the Pattern Electroretinogram in a Mouse Eyecup Preparation. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6132.
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Recently, increased attention has been paid to developing non-invasive ways to measure neuronal activity. Simple eye recordings offer the opportunity to directly access neuronal activity and could potentially act as biomarkers for disease states. We are interested in examining the glutamate receptor inputs onto retinal ganglion cells and have started to examine the pattern electroretinogram (PERG) in both mice and humans. The PERG represents inner retinal activity but the contributions of NMDA and AMPA receptors to this response have not been established. We have developed a mouse eyecup preparation suitable for recording a PERG similar to that measured in intact animals, but with the ability to easily alter the pharmacological and stimulus conditions.
Extracellular recordings were made in everted mouse eyecup preparations. Ringer-filled, beveled glass microelectrodes were lowered into the inner retina and light-evoked responses were recorded. Light stimuli were generated by a computer running customized Vision Egg software and projected through a microscope onto the retina using a multimedia projector. Intensity levels were adjusted using neutral density filters placed in the light path. A gravity fed profusion system was used to maintain retina viability and to deliver pharmacological agents.
The PERG can be reliable elicited using an alternating pattern stimulus in the mouse eyecup preparation. Temperature proved to be essential in acquiring a response that resembled that seen in intact animals—below 37°, the typical positive and negative peaks of the PERG were not distinguishable. These PERG recordings proved to be stable over extended recording times allowing us to tease out the components of the response driven by different receptor types as well as to differentiate the role of the ON versus OFF pathways to the PERG. Of particular importance to us, we determined that the early positive component of the PERG results from glutamate receptor activation—a combination of both NMDA and AMPA receptor responses.
Long-term, stable recordings of the PERG can be measured in the excised retina eyecup of the mouse. This allows for pharmacological manipulations that are not possible in the intact animal. Our findings have established that NMDA and AMPA receptors make substantial contributions to the PERG observed under our stimulus and recording conditions.
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