Low grip strength, impaired tongue force and hyperactivity induced by overexpression of neurotrophin-3 in mouse skeletal muscle.

Transgenic mice overexpressing neurotrophin-3 (NT-3) in skeletal muscle (mlc/NT-3 mice) develop abnormal muscle spindles in skeletal muscle and display abnormal motor function in the form of gait and locomotive disturbances. The purpose of this work was to characterize the functional consequences of NT-3 overexpression in skeletal muscle with further behavioral assessments that permitted inferences about muscle weakness in the tongue or forelimbs as well as potential central nervous system (CNS) abnormalities compared to wild-type controls. Wild-type (n=12) and mlc/NT-3 (n=12) male mice were tested in five procedures (in chronological order): lick dynamics, locomotor activity, grid ataxia, go-no-go discrimination procedure, and grip strength. Relative to wild-type mice, the mlc/NT-3 mice exhibited lower tongue force, hyperactivity, slowed limb retrieval in the grid ataxia test, similar discrimination performance, and lower grip strength. Overall, the data suggest that chronically elevated levels of NT-3 in mouse skeletal muscle cause muscle weakness in the mlc/NT-3 mice. Surprisingly, mlc/NT-3 mice also exhibited significant hyperactivity, suggesting that NT-3 overexpression in the periphery may have caused abnormalities in the CNS that are related to the cortical processing of proprioceptive afferent information.