Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease 
characterized by progressive motor dysfunction and loss of large motor neurons 
in the spinal cord and brain stem. While much research has focused on mechanisms 
of motor neuron cell death in the spinal cord, degenerative processes in 
skeletal muscle and neuromuscular junctions (NMJs) are also observed early in 
disease development. Although recent studies support the potential therapeutic 
benefits of targeting the skeletal muscle in ALS, relatively little is known 
about inflammation and glial responses in skeletal muscle and near NMJs, or how 
these responses contribute to motor neuron survival, neuromuscular innervation, 
or motor dysfunction in ALS. We recently showed that human mesenchymal stem 
cells modified to release glial cell line-derived neurotrophic factor 
(hMSC-GDNF) extend survival and protect NMJs and motor neurons in SOD1(G93A) 
rats when delivered to limb muscles. In this study, we evaluate inflammatory and 
glial responses near NMJs in the limb muscle collected from a rat model of 
familial ALS (SOD1(G93A) transgenic rats) during disease progression and 
following hMSC-GDNF transplantation. Muscle samples were collected from 
pre-symptomatic, symptomatic, and end-stage animals. A significant increase in 
the expression of microglial inflammatory markers (CD11b and CD68) occurred in 
the skeletal muscle of symptomatic and end-stage SOD1(G93A) rats. Inflammation 
was confirmed by ELISA for inflammatory cytokines interleukin-1 β (IL-1β) and 
tumor necrosis factor-α (TNF-α) in muscle homogenates of SOD1(G93A) rats. Next, 
we observed active glial responses in the muscle of SOD1(G93A) rats, 
specifically near intramuscular axons and NMJs. Interestingly, strong expression 
of activated glial markers, glial fibrillary acidic protein (GFAP) and nestin, 
was observed in the areas adjacent to NMJs. Finally, we determined whether ex 
vivo trophic factor delivery influences inflammation and terminal Schwann cell 
(TSC) response during ALS. We found that intramuscular transplantation of 
hMSC-GDNF tended to exhibit less inflammation and significantly maintained TSC 
association with NMJs. Understanding cellular responses near NMJs is important 
to identify suitable cellular and molecular targets for novel treatment of ALS 
and other neuromuscular diseases.