The electroretinogram of Mongolian gerbil (Meriones unguiculatus): comparison to mouse.

The Mongolian gerbil (Meriones unguiculatus) is a diurnal rodent whose retinal photoreceptors comprise 13% cones in contrast to 1-3% in nocturnal mice and rats. Moreover, it displays a retinal structure more analogous to that of human than of mouse. However, the electroretinogram (ERG) recordings of gerbils have not yet been well studied. Thus, here we compared the ERGs of gerbils and C57 mice. We recorded responses to full-field flashes of increasing intensities under both dark and light adaptation. We also investigated responses to flickers of increasing frequencies and to long-duration flashes under photopic conditions. In scotopic, the amplitudes of the gerbil a- and b-waves are slightly smaller than those of the mouse waves. However, in photopic, the gerbil wave amplitudes are 2-fold larger than those of mice. Gerbils also exhibit larger flicker responses and higher flicker fusion frequencies than mice. Furthermore, unlike mice, gerbils show a positive OFF response (d-wave) and a post b-wave positive potential (i-wave), features commonly observed in human photopic ERGs. Our results suggest that gerbils may complement rod-dominant mice as models for studying retinal cone function and pathologies.