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Sunil Gandhi, Michael Stryker; Imaging the functional plasticity of identified cell types in visual cortex. Journal of Vision 2007;7(15):42. doi: 10.1167/7.15.42.
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In the visual cortex, the activity of inhibitory cells plays a key role in experience-dependent plasticity. Little is known, however, about how inhibitory neurons respond to perturbations of visual experience. We recorded visually evoked responses from identified excitatory and inhibitory cortical cells using a recently developed method for deep tissue imaging of calcium indicator fluorescence. The indicator is loaded in bulk into the visual cortex of a transgenic mouse in which inhibitory cells express a fluorescent marker. Action potentials in cells that take up and metabolize the indicator produce transient fluorescence in the soma that we measure using 2-photon microscopy. From these calcium recordings, we observed that both excitatory and inhibitory cells in binocular cortex of normal animals respond predominantly to visual stimulation through the contralateral eye. Occluding the dominant, contralateral eye by eyelid suture during the critical period at 4 weeks of age induced a dramatic rearrangement of inhibitory and excitatory cell response strengths. At peak, the combined magnitude of visual responses to both eyes increased ∼50%. After 2 days of eyelid suture, preliminary results indicate that the increase in response to the deprived eye was greater in inhibitory than in excitatory cells, leading to a brief mismatch in the ocular preference of inhibition and excitation. With 4 days of eyelid suture, the boost seen in responses to the non-deprived eye exceeded the response increase for the deprived eye, leading to an overall shift in ocular preference towards the non-deprived eye. After 7–10 days of eyelid suture, responses returned to a level similar to the initial state while maintaining the new balance of eye preference in favor of the non-deprived eye.
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