Tail Muscles Become Slow but Fatigable in Chronic Sacral Spinal Rats With Spasticity
Bibliographic record
Abstract
Paralyzed skeletal muscle sometimes becomes faster and more fatigable after spinal cord injury (SCI) because of reduced activity. However, in some cases, pronounced muscle activity in the form of spasticity (hyperreflexia and hypertonus) occurs after long-term SCI. We hypothesized that this spastic activity may be associated with a reversal back to a slower, less fatigable muscle. In adult rats, a sacral (S2) spinal cord transection was performed, affecting only tail musculature and resulting in chronic tail spasticity beginning 2 wk later and lasting indefinitely. At 8 mo after injury, we examined the contractile properties of the segmental tail muscle in anesthetized spastic rats and in age-matched normal rats. The segmental tail muscle has only a few motor units (<12), which were easily detected with graded nerve stimulation, revealing two clear motor unit twitch durations. The dominant faster unit twitches peaked at 15 ms and ended within 50 ms, whereas the slower unit twitches only peaked at 30-50 ms. With chronic injury, this slow twitch component increased, resulting in a large overall increase (>150%) in the fraction of the peak muscle twitch force remaining at 50 ms. With injury, the peak muscle twitch (evoked with supramaximal stimulation) also increased in its time to peak (+48.9%) and half-rise time (+150.0%), and decreased in its maximum rise (-35.0%) and decay rates (-40.1%). Likewise, after a tetanic stimulation, the tetanus half-fall time increased by 53.8%. Therefore the slow portion of the muscle was enhanced in spastic muscles. Consistent with slowing, posttetanic potentiation was 9.2% lower and the stimulation frequency required to produce half-maximal tetanus decreased 39.0% in chronic spinals. Interestingly, in spastic muscles compared with normal, whole muscle twitch force was 81.1% higher, whereas tetanic force production was 38.1% lower. Hence the twitch-to-tetanus ratio increased 104.0%. Inconsistent with overall slowing, whole spastic muscles were 61.5% more fatigable than normal muscles. Thus contrary to the classical slow-to-fast conversion that is seen after SCI without spasticity, SCI with spasticity is associated with a mixed effect, including a preservation/enhancement of slow properties, but a loss of fatigue resistance.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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) | 0.000 | 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 teacher head, 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".