Limited Activity‐Dependent Changes in NMJ Structure and Function During Aging
Bibliographic record
Abstract
Aging has been associated with losses of muscle mass and strength, a phenomenon termed “sarcopenia”. A growing body of evidence suggests that it may originate from alterations (mostly structural fragmentation) of neuromuscular junctions (NMJs). Furthermore some evidence show that physical activity partially prevents age‐related NMJs fragmentation and muscle mass and strength losses, reinforcing the relationship between NMJs and muscle function. However, the efficacy of the NMJ, that is, the ability of the motor neuron to control the muscle fiber, has been largely overlooked. Hence, we investigated NMJ synaptic strength and plasticity, two important indicators of its function. We compared soleus muscles of active adult (12 months) and active old mice (30 months). NMJ structure was assessed by immunolabeling while synaptic properties were studied using electrophysiological recordings. Despite their activity level, soleus muscle mass was lower in older than in young mice (17.9±0.4 mg vs. 22.2±0.3, respectively, p<0.001). Endplates of NMJs of old mice were also more fragmented (6.2±0.3 vs. 1.9±0.2 fragments, p=0.0023). Furthermore, while a high frequency stimulation (60Hz, 30s) resulted in a long‐lasting potentiation in adults (4±2%), it produced a long‐term depression in old mice (−8±2%, p=0.039, 40 min post‐stimulation). However, synaptic strength (Quantal content; the amount of vesicle of neurotransmitters released during a stimulation) was preserved in old mice (3.2±0.3 vs. 3.1±0.2 in young mice, p=0.63). Results suggest that activity reduces some aspects of NMJ aging (structure and synaptic strength). However, other aspects (synaptic plasticity) remained altered, suggesting that they may be implicated in the remaining loss of muscle mass and strength in active elderly.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".