Figure 5. Phrenic nerve hyperstimulation stimulation accelerated pathological changes at diaphragm neuromuscular junctions in SOD1^G93A rats.

There were no differences in total numbers of NMJs among any groups, as assessed by total numbers of alpha-bungarotoxin⁺ junctions (A). Nearly all wild-type NMJs were completely intact, characterized by: complete overlap of the pre-synaptic axon and pre-synaptic vesicles with post-synaptic acetylcholine receptors, no signs of multiple innervation, absence of pre-synaptic axon thinning (D: NMJ #1, F). While both groups of SOD1^G93A rats showed signs of synaptic disruption, stimulated SOD1^G93A rats had significantly fewer intact junctions, with greater than 60% of junctions being affected (B, E). To specifically examine the types of changes occurring in stimulated diaphragm muscle, NMJ changes were broken down into a number of phenotypic categories. Compared to unstimulated SOD1^G93A rats, a significantly greater percentage of junctions from stimulated SOD1^G93A rats showed signs of partial denervation (C, E: NMJ #4 and #5, H - arrowhead), complete denervation (C), thinning of the pre-synaptic axon (C, E: NMJ #6, I -arrowhead), terminal sprouting (C, E: NMJ #3, G - arrowhead) and reinnervation of denervated junctions by terminal sprouts from adjacent junctions (C, E: NMJ #2, G). In many instances, individual junctions showed signs of more than 1 change. Only rare instances of any of these junctional pathologies were found in wild-type stimulated muscles. Scale bars: 25μm.