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. 2008 Jul 30;28(31):7891–7899. doi: 10.1523/JNEUROSCI.1461-08.2008

Figure 1.

Figure 1.

Collateral sprouting into adjacent denervated skin fails in apoE KO mice and in aged mice, but axonal regeneration occurs normally. a, Sprouting of mechano-nociceptive (pinch) and heat-nociceptive (heat) fibers in DCN-T13, 21 d after isolation of the nerve field by denervation of surrounding skin was measured as percentage increase, final field area relative to initial field area. The animal groups studied were young adult (2–3 months) and aged (18 months) wild-type (C57BL/6) mice (WT) and young adult apoE KO mice. Aged mice were measured only initially and at 21 d after isolation. The inset sketches show typical fields (not to scale) at 0 and 21 d; the innermost (dashed) outline is that of the low-threshold mechano-sensitive (“touch”) fibers, which do not undergo collateral sprouting. The intermediate outline is the field of the heat-nociceptive fibers, and the outermost one the field of the pinch (mechanical)-nociceptive fibers. The extent of sprouting at 21 d was assessed using ANOVA (F(2,20) = 19.55). There was significant nociceptive nerve sprouting in the young adult WT group (p < 0.0047), but not in the aged WT and the apoE KO groups. b, Axonal regeneration was measured by the restoration and progressive expansion of the two nociceptive and the touch field areas after their disappearance after nerve crush. The first measurements were made at 11 d after nerve crush for the nociceptive fibers and at 21 d (the only measurement) for the touch fibers. In the aged mice, the last nociceptive field measurements were made at 25 d and not at 21 d. Regeneration rates of both nociceptive fiber types were not significantly different (ANOVA; F(2,25) = 0.578; p > 0.56) for the three animal groups (young adult WT, aged WT, and apoE KO), nor was regeneration of touch fibers at 21 d significantly different in young adult WT mice and in apoE KO mice. The inset sketches show typical young adult WT nociceptive fields (not to scale) at 10, 15, and 21 d; the outer perimeter is the pinch field, and the inner is the heat. At 21 d, the touch field coincided with the heat field. In aged WT mice, touch fiber regeneration occurred but was not studied quantitatively. In this and subsequent figures, the numbers above histograms and alongside inset legends show numbers of animals used. Error bars indicate SEM.