Peripheral and central neural responses examined using quantitative immunohistochemical methods in week 0 (immediately following the training period) or after performing either a LRLF, HRLF, LRHF and HRHF task for 12 weeks. (A & B) Mean number of ED1-immunoreactive (ED1-IH) macrophages in the median nerve at the level of the wrist, in week 0 and 12. (C & D) Representative photos of the median nerve at the level of the wrist, showing an absence of ED1-IH macrophages in a NC rat, but increased macrophages (stained black; arrows indicate a few) in a 12-wk HRHF rat. (E & F) Percent area with substance P immunoreactivity in the dorsal horns of lower cervical spinal cord segments, in week 0 and 12. Data for upper lamina (I and II) of the dorsal horns are presented. (G & H) Representative photos of the dorsal horn of lower cervical spinal cord segments, showing only low grade increases of substance P (SubP) immunoreactivity in a NC rat, but increased SubP in the upper lamina (arrows) in a 12-wk HRHF rat. Symbols: aa: p < 0.01, compared to LRLF rats; bb: p < 0.01, compared to HRLF rats; **: p < 0.01, compared to normal controls (NC) rats (indicated by dashed line). Mean and SEM are shown. Scale bars are as indicated.