Fig. 2. Local nerve growth factor (NGF) activation regulates mitochondrial transport and distribution in neurons. Histograms of mitochondrial rhodamine 123 (R123) fluorescence intensities in the 10 µm region immediately adjacent to an NGF-coated bead vs the 10 µm control regions located 100 µm away in either direction along the axon from the point of bead contact. The mitochondrial fluorescence intensity is significantly higher (shown by the asterisk) in the 10 µm region of the axon adjacent to an NGF-coated bead than in similar proximal and distal non-bead control regions (N=10; paired t-test). No difference in mitochondrial densities was observed when using the control heat-denatured NGF-coated beads (N=8; paired t-test) or with a high background concentration of NGF. Adding 10 ng ml^-1 NGF to the culture medium, which is above the K_d of the high affinity TrkA receptor (approximately 1 ng ml^-1) but below the K_d of the lower affinity p75 receptor (approximately 40 ng ml^-1), significantly reduced the mitochondrial response to NGF-coated beads (N=8; paired t-test). The mitochondrial accumulation was also blocked in the presence of 90 ng ml^-1 NGF (N=9; paired t-test).