Figure 6

Regeneration of the axolotl telencephalon. (A) Normal forebrain (ablated region marked with red box). (B) 15 weeks later showing complete regeneration. (C) RT97 wholemount showing the medial olfactory tract. (D) 9 weeks after removal of the right anterior third and olfactory bulb showing failure of regeneration and swelling of the regenerating olfactory nerve (arrowhead). (E) After removal of the olfactory bulb (right) the telencephalon heals but does not regenerate until the olfactory nerve regenerates (arrowhead = olfactory nerve swelling). (F-L) Regeneration after removal of the middle third of the telencephalon (as in A). After 3 weeks (F, G) there is no regeneration but an increase in BrdU⁺ cells in the damaged VZ (right). Close-up of the undamaged (H) and damaged (I) VZ shows more BrdU⁺ cells in I. J, BrdU⁺ counts in the VZ from 3-week regenerating (3r), 3-week undamaged (3c), 6-week regenerating (6r), 6-week undamaged (6c) with standard deviations. K, after 6 weeks there is restoration of the damaged side (right) but not full tissue replacement. After overnight BrdU labeling at 6-weeks there is local proliferation at the cut site (L). (M-Q) Regeneration after dorsal pallium removal (red box in M). M, damage site (right) after 8 days. N, after 24 days there is near complete regeneration. O, 40 days after removal the left and right telencephalons are indistinguishable (damage site marked with red star). P, regenerated brain 6 weeks after removal of the right dorsal pallium (as in M) shows complete regeneration. Q, 6 weeks after right dorsal pallium removal and olfactory nerve severing there is wound repair but shrinkage of the right telencephalon while the olfactory nerve regenerates. Red bars show the left/right difference in telencephalon length. Scale bars = 1 mm.