Fig. 2.

Phase-contrast photomicrographs of neurons showing the two typical patterns of neurite regeneration. A, An example of regenerative growth in which the new growth merely extends the cut neurites 4 d after plating growth had ceased and the neurites were cut at the arrowhead. Fifteen minutes later the cell was photographed again (C). One day later (F) several prominent growth cones were visible. In the ensuing days the neurites extended, retracted, and then slowly extended again. Seventeen days later, the cell was still growing (I), and it survived >32 d. The other response (B) is much more complex. The neurites of this cell were cut after 4 d in culture (arrowheads), and the cell was photographed 15 min later (D). During the next 11 d the neurite stumps were resorbed into the soma, and new growth emerged (G). The neurites formed thick fascicles that grew extensively and by 24 d after cutting had formed an arbor very different from the original (J) (see also Fig. 3). This cell survived for 31 d. Scale bar, A, B, 100 μm. A control cell (E) in the dish with the cell in A had stopped growing after 4 d. Varicosities on the neurite began to appear 6 d later (H); by day 17 many of the neurites had disappeared, and the cell began to disintegrate (K). Scale bar, 150 μm.