Optogenetic tools for in vivo applications in neonatal mice

Spontaneous neural activities exist early in development and their spatiotemporal patterns play important roles in the development of sensory maps such as maps of retinotopy in the visual system. We summarized different optogenetic tools, including transgenic mouse lines, viral-mediated transfection and electroporation methods to enable the expression of light-gated channelrhodopsin (ChR2) in retinal ganglion cells (RGCs) before the onset of vision. Patch-clamp and extracellular recording experiments verified that activities of ChR2-expressing cells were precisely manipulated by the patterns of optical stimuli. In chronic stimulation experiments, light-emitting diodes controlled the activity patterns of ChR2-expressing RGCs in vivo. Changes in the retinotopic map in Superior Colliculus (SC) were examined by quantifying the relative sizes of fluorescently labeled target zones. Our results revealed that various optogenetic and optical tools can manipulate retinal activities with precise temporal patterns. These techniques can be readily used in studying the development of the central nervous system of neonatal rodents.