Figure 2.
a, NGF induced sprouting in apoE KO mice. Sprouting was measured by the progressive expansion of DCN-T13 pinch fields in mice after their isolation. Expansions are indicated on the ordinate as the “sprouting ratios” (the isolated field areas measured at “F,” the later specified time, relative to the initial field areas, I, measured immediately after the isolation procedure, and normalized to 1.0; the ratio value 1 equals absence of sprouting). In this and subsequent figures, WT are wild-type mice, and KO are apoE KO mice. In one young adult group of each genotype, NGF (1 μg/g, s.c.) was administered on the day of field isolation and continued daily for 19 d. By 21 d, no significant sprouting had occurred in the untreated apoE KO mice, but NGF treatment induced sprouting to the same level as that in untreated WT mice. NGF treatment did not significantly increase the sprouting in the WT mice. The data were analyzed using one-way ANOVA, with Bonferroni's multiple comparison test to show where significances reside (overall, p < 0.0001; ANOVA; F(3,28) = 16.48). The untreated apoE KO results are significantly different from any of the other groups (p < 0.01); the untreated and treated wild-type groups and the NGF-treated apoE KO group are not significantly different from each other (p > 0.05). In a number of places, the SE bars are concealed within the symbols used in these graphs. b, NGF induces sprouting in unoperated mice. Daily NGF injections for 19 d into unoperated mice resulted in an expansion of pinch field areas caused by sprouting of the resident nociceptive fibers; the areas, shown on the ordinate, were measured once only, immediately after completion of the 19 d injection protocol. There was no significant difference in the field expansions between apoE KO and WT mice. (ANOVA; F(3,42) = 1.143; p < 0.0006). c, NGF fails to evoke sprouting in aged animals. Daily administration of NGF into aged (18 months) WT mice (1 μg · g−1 · d−1 for 19 d), performed as in a, failed to evoke sprouting of pinch and heat fibers. This is indicated as in a by the sprouting ratios; here the isolated field areas were measured only initially and at 20 d after field isolation, and the ratios = 1 (i.e., absence of sprouting) (Wilcoxon's signed rank test, p > 0.5 for pinch, p > 0.25 for heat).