Abstract
Abstract: :
Purpose: To identify the contribution of retinal ganglion cells (RGCs) to the multifocal electroretinogram (MF-ERG) in pigs. Methods: MF-ERGs were investigated by comparing waveforms from control vs. axotomized eyes (57 21 days post-axotomy) of ketamine-anesthetized pigs (n=4), control eyes of ketamine- vs. isoflurane (2.5%)-anesthetized pigs (n=10), and control vs. TTX-injected eyes (5 µM) of ketamine-anesthetized pigs (n=4). The MF-ERG stimulus consisted of an array of 103 unscaled hexagons covering approximately 95 degrees of visual field. Amplitudes and implicit times of the 1st order MF-ERG (213) components N1, P1, N2, P2, and P3 (averaged across all locations) were compared using unpaired t-tests. Results: Late MF-ERG components were affected in axotomized eyes as N2 (p<0.05), P2 (p<0.01), and P3 (p<0.01) were significantly reduced in amplitude. Under isoflurane anesthesia, P3 amplitude was decreased (p<0.05) whereas N1, P1, and N2 (p<0.01) were delayed. TTX completely modified the wave morphology, which became oscillatory. Both the effects of isoflurane and TTX were reversible. Conclusion: A late non-induced wave component (P3) of the MF-ERG signal was associated with RGC loss following axotomy. P3 seems to be the main component correlated with RGC activity. This component was severely attenuated as early as two weeks post-axotomy; a time point at which a large proportion of RGCs remain in the retina, thereby suggesting that loss of function precedes actual cell loss. MF-ERG recordings obtained under isoflurane anesthesia were very similar to the ones acquired in axotomized eyes, suggesting that this anesthetic has an effect on inner retinal activity. Finally, intravitreal injection of TTX produced profound changes in MF-ERG responses, thereby indicating that this particular model has a greater effect on retinal activity than that observed in either the axotomy or isoflurane studies.
Keywords: 396 electroretinography: non-clinical • 415 ganglion cells • 316 animal model