Screening mouse vision with intrinsic signal optical imaging

The introduction of forward genetic screens in the mouse asks for techniques that make rapid screening of visual function possible. Transcranial imaging of intrinsic signal is suitable for this purpose and could detect the effects of retinal degeneration, and the increased predominance of the contralateral eye in albino animals. We quantified visual response properties of the cortex by introducing a normalization method to reduce the impact of biological noise. In addition, the presentation of a 'reset'-stimulus shortly after the probing stimulus at a different visual location could reduce the interstimulus time necessary for the decay of the response. Applying these novel methods, we found that acuity of C57Bl/6J mice rises from 0.35 cycles per degree (cpd) at postnatal day 25 to 0.56 cpd in adults. Temporal resolution was lower in adults than in juvenile animals. There was no patchy organization of spatial or temporal frequency preference at the intrinsic signal resolution. Monocular deprivation, a model for amblyopia and critical period plasticity, led to a loss in acuity and a shift towards the nondeprived eye in juvenile animals. Short deprivation did not lead to increased acuity of the nondeprived eye. In adults, a small ocular dominance shift was detectable with urethane anaesthesia. This was not observed when the combination of the opiate fentanyl, fluanisone with a benzodiazepine was used, adding evidence to the hypothesis that enhancing GABA(A)-receptor function masks an adult shift. Together, these novel applications confirm that noninvasive screening of many functional properties of the visual cortex is possible.