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J Neurosci. 2014 Aug 6;34(32):10497-510. doi: 10.1523/JNEUROSCI.0697-14.2014.

Presynaptic NCAM is required for motor neurons to functionally expand their peripheral field of innervation in partially denervated muscles.

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Departments of Medical Neuroscience and.
Keck Center for Collaborative Neuroscience, Rutgers University, Piscataway, New Jersey 08854-8082.
Departments of Medical Neuroscience and Medicine (Neurology), Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada, Brain Repair Centre, Life Science Research Institute, Halifax, Nova Scotia B3H 4H7, Canada, and


The function of neural cell adhesion molecule (NCAM) expression in motor neurons during axonal sprouting and compensatory reinnervation was explored by partially denervating soleus muscles in mice lacking presynaptic NCAM (Hb9(cre)NCAM(flx)). In agreement with previous studies, the contractile force of muscles in wild-type (NCAM(+/+)) mice recovered completely 2 weeks after 75% of the motor innervation was removed because motor unit size increased by 2.5 times. In contrast, similarly denervated muscles in Hb9(cre)NCAM(flx) mice failed to recover the force lost due to the partial denervation because motor unit size did not change. Anatomical analysis indicated that 50% of soleus end plates were completely denervated 1-4 weeks post-partial denervation in Hb9(cre)NCAM(flx) mice, while another 25% were partially reinnervated. Synaptic vesicles (SVs) remained at extrasynaptic regions in Hb9(cre)NCAM(flx) mice rather than being distributed, as occurs normally, to newly reinnervated neuromuscular junctions (NMJs). Electrophysiological analysis revealed two populations of NMJs in partially denervated Hb9(cre)NCAM(flx) soleus muscles, one with high (mature) quantal content, and another with low (immature) quantal content. Extrasynaptic SVs in Hb9(cre)NCAM(flx) sprouts were associated with L-type voltage-dependent calcium channel (L-VDCC) immunoreactivity and maintained an immature, L-VDCC-dependent recycling phenotype. Moreover, acute nifedipine treatment potentiated neurotransmission at newly sprouted NMJs, while chronic intraperitoneal treatment with nifedipine during a period of synaptic consolidation enhanced functional motor unit expansion in the absence of presynaptic NCAM. We propose that presynaptic NCAM bridges a critical link between the SV cycle and the functional expansion of synaptic territory through the regulation of L-VDCCs.


NCAM; neuromuscular junction; partial denervation; regeneration; sprouting

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