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Pre- and postsynaptic changes in the neuromuscular junction in dystrophic mice.

Pratt SJ, Valencia AP, Le GK, Shah SB, Lovering RM - Front Physiol (2015)

Bottom Line: To examine mdx- and age-dependent changes in the relative localization of pre- and postsynaptic structures, we calculated NMJ occupancy, defined as the ratio of the footprint occupied by presynaptic vesicles vs. that of the underlying motor endplate.Finally we found an almost two-fold increase in the number of nuclei and an increase in density (nuclei/area) underlying the NMJ.These outcomes suggest substantial remodeling of the NMJ during dystrophic progression.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedics, University of Maryland School of Medicine Baltimore, MD, USA.

ABSTRACT
Duchenne muscular dystrophy (DMD) is a devastating neuromuscular disease in which weakness, increased susceptibility to muscle injury, and inadequate repair appear to underlie the pathology. While most attention has focused within the muscle fiber, we recently demonstrated in mdx mice (murine model for DMD) significant morphologic alterations at the motor endplate of the neuromuscular junction (NMJ) and corresponding NMJ transmission failure after injury. Here we extend these initial observations at the motor endplate to gain insight into the pre- vs. postsynaptic morphology, as well as the subsynaptic nuclei in healthy (WT) vs. mdx mice. We quantified the discontinuity and branching of the terminal nerve in adult mice. We report mdx- and age-dependent changes for discontinuity and an increase in branching when compared to WT. To examine mdx- and age-dependent changes in the relative localization of pre- and postsynaptic structures, we calculated NMJ occupancy, defined as the ratio of the footprint occupied by presynaptic vesicles vs. that of the underlying motor endplate. The normally congruent coupling between presynaptic and postsynaptic morphology was altered in mdx mice, independent of age. Finally we found an almost two-fold increase in the number of nuclei and an increase in density (nuclei/area) underlying the NMJ. These outcomes suggest substantial remodeling of the NMJ during dystrophic progression. This remodeling reflects plasticity in both pre- and postsynaptic contributors to NMJ structure, and thus perhaps also NM transmission and muscle function.

No MeSH data available.


Related in: MedlinePlus

NMJ occupancy. Overlay images of wild type (WT) and dystrophic (mdx) NMJs showing both the presynaptic terminal bouton (green, synaptophysin) and postsynaptic acetylcholine receptors (red, BTX). NMJ occupancy was calculated as, (presynaptic area/postsynaptic area)*100. Data collected from 58 NMJs (34 WT, 24 mdx). *Indicates significance compared to wild type (p < 0.05). Scale bar = 10 μm.
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Figure 3: NMJ occupancy. Overlay images of wild type (WT) and dystrophic (mdx) NMJs showing both the presynaptic terminal bouton (green, synaptophysin) and postsynaptic acetylcholine receptors (red, BTX). NMJ occupancy was calculated as, (presynaptic area/postsynaptic area)*100. Data collected from 58 NMJs (34 WT, 24 mdx). *Indicates significance compared to wild type (p < 0.05). Scale bar = 10 μm.

Mentions: Structure is clearly a major determinant of function in biology, especially in muscle. In the same way that the development of force relies on the controlled overlap of actin and myosin, the apposition of the nerve terminal and the underlying motor endplate is likely a major determinant of NMJ function. NMJ occupancy describes the overlap between the presynaptic and postsynaptic morphology of the NMJ, which in healthy muscle is high. We used antibodies against synaptic vesicles (synaptophysin) to image the terminal bouton of the neuron and BTX to stain acetylcholine receptors of the motor endplate (Figure 3, green and red, respectively). The orientation of these structures is altered in mdx muscle such that the ratio (percent occupancy) of pre-to postsynaptic area is significantly reduced (WT, 56.2 ± 12.9 %; mdx, 33.5 ± 10.3%). Despite this reduction in pre- to postsynaptic ratio, the overall alignment of the presynaptic terminal bouton and postsynaptic motor endplate remains.


Pre- and postsynaptic changes in the neuromuscular junction in dystrophic mice.

Pratt SJ, Valencia AP, Le GK, Shah SB, Lovering RM - Front Physiol (2015)

NMJ occupancy. Overlay images of wild type (WT) and dystrophic (mdx) NMJs showing both the presynaptic terminal bouton (green, synaptophysin) and postsynaptic acetylcholine receptors (red, BTX). NMJ occupancy was calculated as, (presynaptic area/postsynaptic area)*100. Data collected from 58 NMJs (34 WT, 24 mdx). *Indicates significance compared to wild type (p < 0.05). Scale bar = 10 μm.
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Figure 3: NMJ occupancy. Overlay images of wild type (WT) and dystrophic (mdx) NMJs showing both the presynaptic terminal bouton (green, synaptophysin) and postsynaptic acetylcholine receptors (red, BTX). NMJ occupancy was calculated as, (presynaptic area/postsynaptic area)*100. Data collected from 58 NMJs (34 WT, 24 mdx). *Indicates significance compared to wild type (p < 0.05). Scale bar = 10 μm.
Mentions: Structure is clearly a major determinant of function in biology, especially in muscle. In the same way that the development of force relies on the controlled overlap of actin and myosin, the apposition of the nerve terminal and the underlying motor endplate is likely a major determinant of NMJ function. NMJ occupancy describes the overlap between the presynaptic and postsynaptic morphology of the NMJ, which in healthy muscle is high. We used antibodies against synaptic vesicles (synaptophysin) to image the terminal bouton of the neuron and BTX to stain acetylcholine receptors of the motor endplate (Figure 3, green and red, respectively). The orientation of these structures is altered in mdx muscle such that the ratio (percent occupancy) of pre-to postsynaptic area is significantly reduced (WT, 56.2 ± 12.9 %; mdx, 33.5 ± 10.3%). Despite this reduction in pre- to postsynaptic ratio, the overall alignment of the presynaptic terminal bouton and postsynaptic motor endplate remains.

Bottom Line: To examine mdx- and age-dependent changes in the relative localization of pre- and postsynaptic structures, we calculated NMJ occupancy, defined as the ratio of the footprint occupied by presynaptic vesicles vs. that of the underlying motor endplate.Finally we found an almost two-fold increase in the number of nuclei and an increase in density (nuclei/area) underlying the NMJ.These outcomes suggest substantial remodeling of the NMJ during dystrophic progression.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedics, University of Maryland School of Medicine Baltimore, MD, USA.

ABSTRACT
Duchenne muscular dystrophy (DMD) is a devastating neuromuscular disease in which weakness, increased susceptibility to muscle injury, and inadequate repair appear to underlie the pathology. While most attention has focused within the muscle fiber, we recently demonstrated in mdx mice (murine model for DMD) significant morphologic alterations at the motor endplate of the neuromuscular junction (NMJ) and corresponding NMJ transmission failure after injury. Here we extend these initial observations at the motor endplate to gain insight into the pre- vs. postsynaptic morphology, as well as the subsynaptic nuclei in healthy (WT) vs. mdx mice. We quantified the discontinuity and branching of the terminal nerve in adult mice. We report mdx- and age-dependent changes for discontinuity and an increase in branching when compared to WT. To examine mdx- and age-dependent changes in the relative localization of pre- and postsynaptic structures, we calculated NMJ occupancy, defined as the ratio of the footprint occupied by presynaptic vesicles vs. that of the underlying motor endplate. The normally congruent coupling between presynaptic and postsynaptic morphology was altered in mdx mice, independent of age. Finally we found an almost two-fold increase in the number of nuclei and an increase in density (nuclei/area) underlying the NMJ. These outcomes suggest substantial remodeling of the NMJ during dystrophic progression. This remodeling reflects plasticity in both pre- and postsynaptic contributors to NMJ structure, and thus perhaps also NM transmission and muscle function.

No MeSH data available.


Related in: MedlinePlus