The number of terminal Schwann cells at the neuromuscular junction does not influence the relative susceptibility of motor neurons in SMA.

<p>A/B – Example confocal micrographs showing immunohistochemically labelled terminal Schwann cells (S100; green) at neuromuscular junctions in the LALr (A) and AAL (B) muscles. Nuclei were labelled with TOPRO-3 (blue) and motor endplates were labelled with bungarotoxin (red). The bottom left panel of A and B shows a merge of all three individual channels. Images were acquired on a confocal microscope using sequential capture to ensure no bleed-through from one channel to the next. The arrows in A show a single motor endplate (in the BTX channel), with clear terminal Schwann cell cytoplasm above it (in the S100 channel), but with two nuclei present within the S100 footprint (TO-PRO3 channel). This NMJ was therefore assessed to have 2 associated terminal Schwann cells. The arrows in B show two distinct motor endplates (in the BTX channel), each with clear terminal Schwann cell cytoplasm above it (in the S100 channel), but with only one nucleus present within the S100 footprint (TO-PRO3 channel) at each NMJ. These NMJs were therefore assessed to have 1 associated terminal Schwann cell each. Scale bars = 5 µm. C – Bar chart (mean±SEM) showing the mean number of terminal Schwann cells (tSCs) per NMJ in a range of muscles from P5 healthy littermate control mice (N = 3 mice). D – Scatter plot showing the number of tSCs per NMJ in each muscle examined, plotted against the relative vulnerability of motor neurons innervating that muscle. Statistical analysis showed that there was no significant correlation between the number of tSCs per NMJ and the susceptibility of the motor neuron in SMA (P>0.05, Spearman correlation analysis).