July 2019
Volume 60, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2019
Comparison of light-evoked spike trains, compound action potentials, and electroretinograms in rats
Author Affiliations & Notes
  • Youssef Mohamed
    ChBME, University of South Florida, Tampa, Florida, United States
  • Nick Johnson
    Nueroscience, University of South Florida, Tampa, Florida, United States
  • Radouil T Tzekov
    Opthamology, University of South Florida, Tampa, Florida, United States
  • Christopher L Passaglia
    ChBME, University of South Florida, Tampa, Florida, United States
  • Footnotes
    Commercial Relationships   Youssef Mohamed, None; Nick Johnson, None; Radouil Tzekov, None; Christopher Passaglia, None
  • Footnotes
    Support  NIH R01 EY027037
Investigative Ophthalmology & Visual Science July 2019, Vol.60, 5969. doi:
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    • Get Citation

      Youssef Mohamed, Nick Johnson, Radouil T Tzekov, Christopher L Passaglia; Comparison of light-evoked spike trains, compound action potentials, and electroretinograms in rats. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5969.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : A common diagnostic tool used in assessing the health of the retina is the electroretinogram (ERG), a noninvasively-acquired signal that reflects the summed electrical activity of retinal neurons to a flash of light. Of particular interest for certain diseases is the contribution of retinal ganglion cells (RGCs) to the ERG. The aim of this project was to investigate the light-dependent relationship between the ERG and the electrical activity of individual RGCs and populations of RGCs.

Methods : Brown Norway rats were anaesthetized under a mixture of ketamine and xylazine and their head fixed in a stereotaxic device. A circular gold electrode was placed on the cornea to record the ERG. A craniotomy was performed at Bregma, and a tungsten-in-glass electrode was descended into the optic chiasm to record the spike trains of individual RGCs or a bipolar needle electrode was placed in the optic nerve to record the compound action potential (CAP). Animals were placed in darkness for 30 minutes before ganzfeld flashes of 10ms duration and logarithmically-increasing intensity were presented to the eye. Measurements were then repeated with background illumination. ERGs were simultaneously digitized with RGC spike trains or CAPs and analyzed off-line.

Results : At bright flash intensities, the time-average spike activity of individual RGCs and the CAP of the optic nerve were similar in latency, duration, and waveform to the oscillatory potential (OP) component of the ERG. Both exhibited multimodal waveforms like the OP, and the number of peaks increased with flash intensity in the same manner. The latencies of initial peaks (36, 52, 65 ms) were nearly identical for all three waveforms. Later peaks at the brightest intensities could differ slightly in timing. Both spike activity and CAP waveforms ended before the falling phase of the ERG b-wave. No signal was detected at dim flash intensities that elicit a scotopic threshold response in the dark-adapted ERG or during the photopic negative response component of the light-adapted ERG.

Conclusions : Presence of OPs in the ERG correlates to phase-locked spike activity in individual RGCs that is synchronized across the rat optic nerve. Since studies have shown that OPs are minimally affected by spike-channel blockers, retinal signals that underlie OPs likely drive the phasic-spike activity evoked by brighter flashes.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

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