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JL Duncan, H Yang, AV Chappelow, D Yasumura, MT Matthes, HS Earp, GK Matsushima, D Vollrath, MM LaVail; Functional Correlates of Photoreceptor Loss in Mer Knockout Mice . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2710.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To describe the functional correlates of photoreceptor (PR) loss in mice with a targeted disruption (merkd) of the Mer receptor tyrosine kinase gene, mutation of which causes retinal dystrophy in RCS rats. Methods: Scotopic and photopic Ganzfeld electroretinograms were recorded from merkd and C57BL/6 wild-type (WT) mice at ages ranging from postnatal day (P) 20 to P253. The extent of PR cell loss was determined histologically. Results: At the youngest ages examined, amplitudes of scotopic b-waves and a-waves were lower than age-matched WT responses and declined with age in parallel with PR loss. Photopic amplitudes were normal until P25, then declined rapidly. None of the amplitudes was measurable beyond P58, an age at which nearly all PRs were lost. Photopic b-wave thresholds remained normal until P36, while scotopic b-wave thresholds were above WT levels at the youngest ages examined. Both scotopic and photopic b-wave thresholds rapidly increased until no measurable b-wave responses were elicited by a bright stimulus (+2.4 log cds/m2) in merkd mice older than P58. The scotopic threshold response (STR), an inner retinal response that reflects residual PR function in degenerating retinas, remained normal until P33 in merkd mice, then increased as additional PRs were lost. However, a small amplitude STR was still elicited at P253, when only scattered PR nuclei remained. Conclusion: Loss of retinal function progressed rapidly and correlated with PR loss in the merkd mouse. The STR persisted at advanced stages of retinal degeneration. Support: Grants from the NIH, the Foundation Fighting Blindness, the Ruth and Milton Steinbach Fund, the Karl Kirchgessner Foundation, That Man May See, Inc., Macula Vision Research Foundation and Research to Prevent Blindness.
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