Fig. 4. Axon lesion leads to axon formation at the opposite pole. (A) A polarized neuron (0'; axon: arrowheads), the axon of which was cut (5', arrow), develops a new axon opposite to the transected one (24 hours, arrowheads). Axonal identity was confirmed by tau-1 immunoreactivity (right panel). (B) Frequency distribution representing the site of axon regeneration after axotomy (n=187). 0° is the position of the original axon. Bin size 20°. (C) Double axotomy: after the first transection (5', arrow) the new axon formed opposite (24 hours, arrowheads) to the first one (0'). 24 hours after cutting this new axon (24 hours, arrow), axonal regrowth occurred again from the site of the initial axon (48 hours, arrowheads). Axonal identity was confirmed by tau-1 immunoreactivity (right lower panel). In eight out of the 16 cells that survived the double axotomy, the new axon formed from the original pole (from the stump of the original axon) in four cells or from a neurite that was close to the original axon in the other four cells. In four of the remaining cells the new axon grew from the `second' pole and in the last four cells a new axon grew from a random position. Bars, 10 µm.