Impacts of lesion severity and tyrosine kinase receptor B deficiency on functional outcome of femoral nerve injury assessed by a novel single-frame motion analysis in mice.

Functional recovery after peripheral nerve injury is often poor. Comprehension of cellular and molecular mechanisms limiting or promoting restoration of function and design of efficient therapeutic approaches remain serious challenges for neuroscience and medicine. Progress has been restricted by the lack of reliable methods for evaluation of motor functions in laboratory animals. We describe a novel approach for assessment of muscle function in mice after femoral nerve damage, an injury causing impairment of knee extension. The functional deficit can be precisely estimated by angle and distance measurements on single video frames recorded during movements of the animals with or without body weight support. Using this method we describe here the precise time-course and degree of functional recovery after femoral nerve crush and transection. In addition, we show that restoration of function is considerably impaired in mice with a reduced expression level of the tyrosine kinase receptor B, a cognate receptor for the neurotrophin brain-derived neurotrophic factor. This finding is consistent with known functions of brain-derived neurotrophic factor and tyrosine kinase receptor B and demonstrates the potential of the method. The principles of the approach are highly relevant for the development of novel functional assays in other peripheral and, in particular, central nervous system injury paradigms.