Age- and sex-related differences in contrast sensitivity in C57Bl/6 mice
PURPOSE. To measure contrast sensitivity in C57BL/6, the most commonly used mouse in behavioral neuroscience, and to study the effect of sex, age, and miotic drugs on the contrast sensitivity function. In addition, the authors tested a mutant in which plasticity in the cerebellum is impaired by expressing a protein kinase C inhibitor. This inhibitor is also expressed in the retina, possibly affecting vision. METHODS. The gain of the optokinetic reflex (OKR) decreases as stimuli become more difficult to see. Recording OKR gains evoked by moving sine gratings shows whether the stimulus was distinguished from a homogeneous background and how well the stimulus was distinguished. RESULTS. Female mice have lower OKR gains than male mice (both groups: n 10, P 0.001). A similar difference was observed between 4-month-old (n 10) and 9-month-old (n 5) C57Bl/6 mice (P 0.001). These differences could not be detected with earlier dichotomic tests. C57BL/6 mice are able to see contrasts as low as 1%, well below the previously reported 5% threshold. Pilocarpine had no significant effect on contrast sensitivity (both groups: n 10, P 0.89). Vision in L7-PKCi mutants was unaffected (both groups: n 10, P 0.82). CONCLUSIONS. OKR gains decrease as stimuli become more difficult to see, making the OKR a powerful tool to quantify contrast sensitivity. In C57BL/6 these response magnitudes vary greatly between sexes and between mice that differ only a few months in age. Therefore, it is important to match groups according to age and sex in experiments that require unim- paired vision. Otherwise, impaired vision can be misinter- preted as a learning or motor problem.