Methods for longitudinal imaging of cortical circuitry.

(A) Timeline of experimental procedures. The barrel cortex is mapped electrophysiologically in order to guide placement of injections of genetically modified virus. After allowing several weeks for expression of genes carried by the virus, images of fluorescent label are taken to establish baseline connectivity. The cortex is reimaged at various time points following initiation of whisker plucking. (B) Surface view of horizontally projecting axons, imaged with 2-photon microscopy. (C) Cortical representation of mouse whiskers, with barrels arranged in rows (A to E) and arcs (1 to 6). (D) Whisker plucking induced remapping of barrel cortex topography in adult animals. The movement of the representation of C row whiskers into the deprived cortex following plucking of D and E rows is plotted as a function of the number of days of plucking. The original C/D row border corresponds to zero on the y-axis. The horizontal line at 300 micrometers indicates the original boundary between the D and E rows. (E) A reconstruction of the axonal plexus of excitatory neurons labeled by AAV-eYFP injection into C3 barrel column, shown in surface view. The axonal reconstruction is superimposed on the whisker map. The virus injection site was at the center of the C3 barrel column.