Response of the neuromuscular junction to saline or IGF-1 treatment. (A) Young saline, (B) aged saline, (C) young IGF-1, and (D) aged IGF-1. The postsynaptic NMJ was stained with fluorescent-labeled α-bungarotoxin and imaged under a confocal microscope. In saline-treated young animals (A), postsynaptic NMJ was highly contiguous, complex, and had deep gutters. In aged saline-treated animals (B), there was a loss of complexity, with flattening of the gutters and a reduction in total postsynaptic area. This morphologic appearance is consistent with chronic denervation. In young IGF-1–treated animals (C), there were no differences when compared with saline-treated animals. In aged IGF-1–treated animals (D), there was an increase in the complexity and gutter depth, similar to the morphology seen in young animals. However, there was increased fragmentation seen in the aged IGF-1 group compared with the young IGF-1 or young saline groups. Scale bar = 20 µm. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]