Histological bulbar manifestations in the ALS rat

Background: Almost all patients with amyotrophic lateral sclerosis (ALS) develop bulbar symptoms; therefore, it is important to have valid animal models that accurately reflect these features. While the SOD1-G93A rat is extensively used as an ALS model, bulbar symptoms in this model are not well characterized. Objective: In the present study, we aimed to better characterize bulbar dysfunction in terms of histology to determine whether the SOD1-G93A rat is a useful model for bulbar-onset ALS. Methods: Sixty-day-old SOD1-G93A rats on a Sprague-Dawley background and age-matched wild-type controls were assessed weekly for global motor function, facial nerve function, and vagal nerve function. The study endpoint was determined when an SOD1-G93A rat could not right itself within 30 s of being placed on its side. At that point, neuronal counts were assessed in different brainstem cranial nerve nuclei. In addition, the masseter muscle, posterior belly of the digastric muscle, and tongue muscle were evaluated for intact neuromuscular junctions. Results: Our data demonstrate decreases in the number of motor neurons in the trigeminal, facial, and hypoglossal nuclei, as well as compromised neuromuscular junction integrity in the muscles they innervate. Conclusion: These findings suggest that, from a histological standpoint, the SOD1-G93A rat is a valid model of ALS bulbar symptoms.