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Sarah Davis, Christopher L Passaglia; Light-evoked properties of compound action potentials of the rat optic nerve. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5864.
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© ARVO (1962-2015); The Authors (2016-present)
The health of the eye is commonly assessed via the electroretinogram (ERG), a noninvasively recorded signal that reflects the summed electrical response of retinal neurons to a light stimulus. The aim of this study was to isolate the subcomponent of the signal produced by action potentials fired by retinal ganglion cells and to characterize how the compound action potential (CAP) waveform depends on the light stimulus.
Long Evans and Brown Norway rats (male, 300-400g, 6-8 months old) were anesthetized with ketamine and xylazine. The optic nerve was exposed via an incision along the supraorbital ridge or a craniotomy at Bregma, and a bipolar electrode was inserted into the dura of the nerve. Electrodes were placed on the cornea to record the ERG and in the posterior skull to record the visual evoked potential (VEP). Animals were placed in darkness for 15 minutes, and a series of full-field LED flashes were then delivered to the eye under dark and light-adapted conditions. The flashes were 10ms in duration, spaced 3s apart, and varied logarithmically in intensity (0.0001 to 1.25 log cd s/m2).
The full-field flash CAP recorded from the rat optic nerve differed noticeably in waveform from the ERG and VEP, consisting of several positive waves that decreased in latency, increased in amplitude, and increased number with stimulus intensity. For the brightest flashes tested, the CAP had 8 ± 2 peaks on average, which correlated in time with oscillatory potentials in the ERG. The mean amplitude and latency of the first peak had a mean latency of 37±7 ms and mean amplitude of 22±11 μV. No change in CAP waveform was detected under dark- and light-adapted conditions.
Light-evoked CAPs can be recorded from the optic nerve of rats. The signal has multiple peaks that presumably reflect the synchronous firing of populations of nerve fibers. As such. the light-evoked CAP offers a direct measure of optic nerve health in animal models of ocular disease.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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