Supernormal ERG oscillatory potentials in transgenic rabbit with rhodopsin P347L mutation and retinal degeneration

To determine the properties of the retina of a rhodopsin P347L transgenic (Tg) rabbit model of retinal degeneration by electroretinography (ERG).

Full-field ERGs were recorded in 12- to 48-week-old wild-type (WT) and Tg rabbits. The a-wave was analyzed by the a-wave fitting model of Hood and Birch. The stimulus-response function of the b-wave was analyzed by the Michaelis-Menten equation. Oscillatory potentials (OPs) were extracted by digital filtering after subtracting the a-wave. OPs were also recorded before and after an intravitreal injection of l-2 amino-4-phosphonobutyric acid (APB), cis-2,3 piperidine dicarboxylic acid (PDA), gamma-amino butyric acid (GABA), or tetrodotoxin citrate (TTX).

All the ERG components of Tg rabbits decreased progressively with age with the a-wave more affected than the b-wave, and the OPs were most preserved. Of interest, the summed OP amplitudes of the Tg rabbits were significantly larger than those of WT rabbits when they were 12 weeks of age. The changes in the amplitudes of the OPs after intravitreal injections of APB, PDA, or GABA in Tg rabbits did not differ significantly from those of WT rabbits. However, injection of TTX resulted in a significantly larger amplitude reduction of the OPs in Tg (65.3%) than in WT (28.6%) rabbits.

The significantly larger OPs in Tg rabbits resulted from alterations in the inner retinal neurons. The greater effect of TTX on the OP amplitudes in Tg rabbits suggests that the supernormal OPs in Tg rabbits may be related to secondary changes in the spiking neurons of the inner retina after photoreceptor degeneration.