Multifocal Electroretinogram in Rhodopsin P347L Transgenic Pigs

¹ School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Hong Kong
² School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China.
³ College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, United States
⁴ Department of Animal Science, North Carolina State University, Raleigh, North Carolina, United States
⁵ Departments of Ophthalmology and Neurobiology, Duke University, School of Medicine, Durham, North Carolina, United States

^* To whom correspondence should be addressed. E-mail: forrest.ng{at}polyu.edu.hk.

	Abstract

Purpose: Neural ectopic re-wiring in retinal degeneration such as retinitis pigmentosa (RP) may form functional synapses between cones and rod bipolar cells which cause atypical signal processing. In this study, the multifocal electroretinograms (mfERG) of a large animal model of RP, the rhodopsin P347L transgenic pig (Tg), were measured to examine the sources and nature of altered signal processing. Methods: MfERG responses from 6-week old Tg were recorded before and after sequential application of TTX, NMDA, APB and PDA to identify contributions to the retinal signal from inner retinal neurons, the ON-pathway, the OFF-pathway and photoreceptors. The mfERG response contributions from different retinal components of Tg were estimated and compared with control data from age-matched wild-type (WT) pigs. Results: There was a prominent difference in the estimates of inner retinal response and ON-bipolar cell pathway contribution between the Tg and WT mfERG responses. In particular, the early components of the inner retinal contribution were obviously altered in Tg mfERG; the inner retinal components at about 24 and 40ms appeared to be inverted. Differences in the estimates of OFF-bipolar cell pathway contributions were minimal. There was no change of cone cell responses in Tg mfERG. Conclusions: In Tg pigs, ectopic synapses formed between cones and rod bipolar cells probably altered signal processing of the ON-bipolar cell pathway. In response to the altered visual signal input from outer retina, signal processing in inner retinal neurons was also modified.

Key Words: retinitis pigmentosa, transgenic, multifocal electroretinogram, signal processing, pig, retina

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