Electrophysiology and density of retinal neurons in mice with a mutation that includes the Pax2 locus.

Purpose: The Krd mouse has a deletion in chromosome 19 that includes the Pax2 gene locus. The aim of this study was to characterize in detail how these retinas differ from normal.

Methods: Both electroretinographic and anatomic methods were used to assess visual function. Full-field flash electroretinograms (ERGs) and planimetric densities were obtained from Krd and control animals.

Results: Measurements of the ERG show that in the Krd mice, both a- and b-wave amplitudes are attenuated relative to control by amounts that vary from animal to animal. The b-wave of the ERG generally is affected more severely than the a-wave. However, there is little or no shift of the curves relating the b-wave and a-wave amplitude to the intensity of the stimulus. Also, no change in the response kinetics seems to be associated with the attenuated responses. Estimates of planimetric cell density in the outer nuclear, inner nuclear, and ganglion cell layers show significant cell losses in affected animals that are more pronounced proportionally in the inner layers. Comparisons between electrophysiological and histologic measurements made on each eye show good correlation between the reduction in the ERG components and the magnitude of cell losses.

Conclusions: These experiments show that the eyes of Krd mice have reduced ERGs and reduced cellular density. There is a loss of cells in all layers of the retina, but the inner layers are affected more severely. Consistent with this, the b-wave is reduced more than the a-wave. The normal functional dependency of the ERG on stimulus intensity and the normal response kinetics suggest the cellular losses are not associated with changes in cellular function.