Relationships between tongue motility, grip force, and survival in SOD1-G93A rats

• SOD1-G93A rats exhibit heterogeneity with regard to bulbar motor deficits.
• Forelimb deficits were greater in SOD1-G93A rats with tongue motility deficits.
• Hindlimb deficits were similar across SOD1-G93A rats.
• Disease progression was worse for rats with tongue motility deficits.

Most preclinical studies of amyotrophic lateral sclerosis (ALS) have focused on spinal symptoms, despite the importance of bulbar deficits in progression of the disease. We sought to determine how bulbar deficits are related to spinal deficits and survival in the SOD1-G93A rat model of ALS. We examined forelimb and hindlimb grip force and tongue motility in SOD1-G93A rats using statistical cluster analysis. Decrements in forelimb grip force, hindlimb grip force, and tongue motility were used to cluster affected rats into groups. The analysis clustered one group that exhibited primarily forelimb deficits (forelimb group) and a second group that exhibited forelimb and tongue motility deficits (forelimb + bulbar group). The analysis did not identify a distinct hindlimb phenotype group because all SOD1-G93A rats exhibited deficits in hindlimb grip force. Rats in the forelimb + bulbar group exhibited earlier and greater forelimb deficits, and earlier mortality than rats without bulbar deficits. Hindlimb deficits were similar in both groups. There was a significant correlation between forelimb grip force and tongue motility deficits, but not between forelimb and hindlimb deficits. These data extend clinical findings of a more rapid disease progression in individuals with bulbar symptoms to the SOD1-G93A rat model of ALS.