Disclosures: Joline E. Brandenburg, MD: No financial relationships or conflicts of interest
Objective: Motor neurons (MNs), via the motor unit and neurotransmitter signaling, are the ultimate target of most clinical spasticity treatments in conditions of early onset hypertonia like cerebral palsy (CP), but are poorly understood. MN and motor unit development in CP and similar conditions is a critical knowledge gap as the late embryonic and postnatal periods are not only when the supposed brain injury occurs in CP, but is a critical time for spinal cord neuromotor development. Therefore, using an animal model of early onset hypertonia (spa mouse), we evaluated lumbar MN and motor unit physiology.
Design: Basic Science Setting : Laboratory Participants : Adult mice homozygous for a Gly receptor mutation (spa mice) and mice without the mutation (wild-type (WT)) from our spa mouse colony.
Interventions: Not Applicable
Main Outcome Measures: Tibialis Anterior (TA) MN number, MN somal size, electrophysiological measures of TA neuromuscular transmission failure (NMTF), TA muscle mass, fiber number, and innervation ratio.
Results: Spa mice had ~61% fewer TA MNs (P=0.008) with a ~23% reduction in TA MN somal surface area (P < 0.0001). TA muscle in spa mice had ~83% NMTF compared to ~65% in WT (P=0.0004) after 60 s of maximal sciatic nerve stimulation. While the TA muscle in spa mice had a ~20% reduction in mass compared to WT (P=0.009), there was no difference in the number of TA muscle fibers (P=0.69). The TA innervation ratio (i.e. number of muscle fibers innervated by a MN) in spa mice was 2.5-fold greater than that of WT (P=0.03). Conclusions: In adult mice with early onset hypertonia, significant disturbances of the MN and motor unit are noted. This work provides early evidence of MN and motor unit developmental disruption in conditions of early onset hypertonia, like CP. Future work is aimed at identifying when these changes to the MN and motor unit are occurring.
Level of Evidence: Level II
To cite this abstract in AMA style:
Brandenburg JE, Sieck GC, Fogarty MJ. Differences in Motor Neuron and Motor Unit Properties in an Animal Model of Early Onset Hypertonia [abstract]. PM R. 2020; 12(S1)(suppl 1). https://pmrjabstracts.org/abstract/differences-in-motor-neuron-and-motor-unit-properties-in-an-animal-model-of-early-onset-hypertonia/. Accessed May 16, 2025.« Back to AAPM&R Annual Assembly 2020
PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/differences-in-motor-neuron-and-motor-unit-properties-in-an-animal-model-of-early-onset-hypertonia/