THE CORRELATION OF ELECTRORETINOGRAPHIC AND HISTOPATHOLOGICAL FINDINGS IN THE EYES OF MICE INFECTED WITH THE 79A STRAIN OF SCRAPIE

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Abstract
Retinal degeneration was produced using the 79A strain of scrapie injected intracerebrally into mice of the MM inbred strain, and studied by electroretinography and light and electron microscopy during the preclinical and clinical phases of the disease. The changes in the electroretinogram (ERG), detectable in some mice at 118 days post-injection (d.p.i.), appeared to coincide with the earliest morphological evidence of photoreceptor damage. In the early stages there was a progressive reduction of b-wave amplitude without marked loss of retinal sensitivity or significant change in a- and b-wave peak implicit times. Extinction of the ERG, observed in half the mice examined at 144 d.p.i., approximated to a stage of the retinopathy in which the outer nuclear layer was reduced to about four rows of nuclei. Early morphological changes suggested that the primary lesion involved the integrity of the photoreceptor as a whole, the electrophysiological findings reflecting a primary loss of light sensitive tissue rather than impairment of the transduction mechanism or neurotransmission.