Figure 8.

arg^-/- neurites have reduced dynamics and accumulate branches slower than wild-type neurites. A, Camera lucida drawings of representative arg^-/- and wild-type neurons cultured on laminin-1-coated glass and imaged at 40 min intervals for 6 h at 1 DIV. Imaging times are indicated on the left. Branches that have been retracted before the subsequent imaging time are indicated with a red star. Branches that have been added since the previous imaging time are indicated with a green asterisk. Note that more stars and asterisks are associated with wild-type neurites than arg^-/- neurites, indicating that their behavior is more dynamic than arg^-/- neurites. B, C, Quantitation of dynamic behavior of wild-type and arg^-/- neurites cultured on either polyornithine (ornithine) or polyornithine plus laminin-1 (laminin). Gray bars indicate the initial or final average number of branchpoints per neurite (B) or average neurite length (C) at the start of the imaging session. Green and red bars indicate the average cumulative number of branchpoints per neurite added or retracted (B) or cumulative neurite length extended or retracted (C) over the initial amount for the 6 h imaging session. Wild type on ornithine, n = 10 cells, 47 neurites; wild type on laminin, n = 15 cells, 63 neurites; arg^-/- on ornithine, n = 9 cells, 43 neurites; arg^-/- on laminin, n = 14 cells, 58 neurites. p values represent statistical significance by Student's t test of the difference between wild-type and arg^-/- neurons cultured on laminin, ^*p = 0.08. D, E, Wild-type (n = 14) or arg^-/- (n = 12) neurons cultured on laminin-1 were imaged at 7 and 17 h intervals from 18 to 96 h in vitro (1-4 DIV). The average number of branchpoints per cell (D) or total neurite length per cell (E) is plotted versus time in culture. Dashed lines are best-fit linear trendlines showing the decreased growth rate of arg^-/- neurite arbors.