Axon regeneration is regulated by eCa²⁺, P38MAPK, ERK, and mTOR signaling cascades. A–J, Phase-contrast photomicrographs of adult DRG axons photographed immediately after axotomy (A–E) and 1 h after axotomy (F–J), under normal conditions (control; A, F) and after exposure to inhibitors of ERK (U0126; B, G), removal of Ca²⁺ (without calcium; C, H), inhibitors of P38MAPK (SB203580; D, I), and mTOR (rapamycin; E, J). Inhibition of all these pathways attenuated the ability of axons to regenerate. Percentage regeneration of axons (± SEM) is plotted in K (n ≥ 5). ***p < 0.001 (one-way ANOVA). Scale bars, 50 μm.