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Anton Tjust, Thomas Brannstrom, Jing-Xia Liu, Fatima Pedrosa-Domellof; Differences In Motor Axon Retraction Patterns In EOMs Versus Limb Muscles In ALS. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2225.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the degree of denervation at neuromuscular junctions (NMJs) in extraocular muscles (EOMs) and limb muscles in G93A mouse model of ALS and wild type controls, as well as in terminal ALS donors.The EOMs are far less affected than limb muscles of end-stage ALS patients. Retraction of motor axons from NMJs is an early event in the limb muscles of the G93A ALS mouse model. We investigated whether differences in motor axon retraction may be a protective factor for the EOMs in ALS.
Serial muscle cross-sections from the EOMs and limb muscles of G93A mice were triple-immunostained with antibodies against synaptophysin and neurofilament protein, to visualize the nerve side of the NMJs and with alpha-bungarotoxin, a marker of the muscle side of the synapse.
In G93A limb muscles loss of axonal contact was seen in 21-82 % of the NMJs. On the contrary, the degree of endplate occupancy in the EOMs did not differ between transgenic mice and wild-type controls. Similar patterns were observed in EOMs vs limb of terminal ALS donors, but there were indirect signs of partial denervation as well as discrete changes in synaptic composition. Wide variation in the percentage of affected NMJs was noted in the EOMs of ALS donors.
We propose that EOM-specific properties make these muscles more resistant, but not immune, to the underlying pathophysiological process of ALS and that they are a useful model to advance our understanding of this disease.
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