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S. Kjellstrom, R.A. Bush, R.J. L. Haywood–Watson, II, Z.M. Ahmed, Y. Takada, T.B. Friedman, P.A. Sieving; Reduced ERG Amplitudes in the Absence of Retinal Degeneration in Deaf Ames Waltzer Mice . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1420.
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Mutations in the human gene encoding protocadherin–15 (PCDH15) cause Usher syndrome type 1F (USH1F). Individuals with USH1 have profound congenital deafness, vestibular areflexia and usually begin to exhibit signs of RP in early adolescence. Two different mutant mice, Pcdh15av–5J (5J) and Pcdh15av–Jfb (Jfb) exhibit the typical structural and functional USH1 auditory pathology. This study was to determine whether these mice are good animal models for the USH1 retinal phenotype.
Scotopic and photopic Ganzfeld ERGs were recorded from homozygous 5J and Jfb mice at 2–3 different ages between 5 weeks and 11 months (n=3–5/age) with heterozygous littermates as controls. Outer nuclear layer (ONL) width and rod outer segment (ROS) length was measured in sagittal retinal sections through the optic nerve(n=3).
Compared to heterozygous littermates, homozygous 5J and Jfb mice at every age had scotopic ERG amplitudes approximately 40% lower across all intensities. There was a significant reduction in Vmax in Naka–Rushton fits to the b–wave data (p<0.0005) and maximum intensity (0.6 log cd–s /m2) a–waves (p<0.002). The b/a–wave ratio confirmed that the a–waves and b–waves were reduced proportionally. Homozygous 5J mice had significantly decreased b–wave sensitivity (p<0.02). All mice had significant age related declines a– and b–wave amplitude, but no age–dependence in sensitivity or in the amplitude difference between heterozygous and homozygous mice. ONL width, cell number, and ROS length were not different in heterozygous and homozygous mice.
Pcdh15av5j and Pcdh15avJfb homozygous mice have significantly attenuated ERGs, but do not mimic the other aspects of RP found in USH1. The cause of this decline with preserved b/a wave ratios is not known, but it is not typical of most animal models of photoreceptor disease or RP and warrants further study.
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