Reduced TrkB expression results in precocious age-like changes in neuromuscular structure, neurotransmission, and muscle function

Kulakowski SA, Parker SD, Personius KE. Reduced TrkB expression results in precocious age-like changes in neuromuscular structure, neurotransmission, and muscle function. J Appl Physiol 111: 844-852, 2011. First published July 7, 2011; doi: 10.1152/japplphysiol.00070.2011.-Acute blockade of signaling through the tyrosine kinase receptor B (TrkB) attenuates neuromuscular transmission and fragments postsynaptic acetylcholine receptors (AChRs) in adult mice, suggesting that TrkB signaling is a key regulator of neuromuscular function. Using immunohistochemical, histological, and in vitro muscle contractile techniques, we tested the hypothesis that constitutively reduced TrkB expression would disrupt neuromuscular pre- and postsynaptic structure, neurotransmission, muscle fiber size, and muscle function in the soleus muscle of 6- to 8-mo-old TrkB(+/-) mice compared with age-matched littermates. Age-like expansion of postsynaptic AChR area, AChR fragmentation, and denervation was observed in TrkB(+/-) mice similar to that found in 24-mo-old wild-type mice. Neurotransmission failure was increased in TrkB(+/-) mice, suggesting that these morphologic changes were sufficient to alter synaptic function. Reduced TrkB expression resulted in decreased muscle strength and fiber cross-sectional area. Immunohistochemical and muscle retrograde labeling experiments show that motor neuron number and size are unaffected in TrkB(+/-) mice. These results suggest that TrkB- signaling at the neuromuscular junction plays a role in synaptic stabilization, neurotransmission, and muscle function and may impact the aging process of sarcopenia.