Plateau Potentials in Sacrocaudal Motoneurons of Chronic Spinal Rats, Recorded In Vitro
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Bibliographic record
Abstract
Intracellular recordings were made from sacrocaudal tail motoneurons of acute and chronic spinal rats to examine whether plateau potentials contribute to spasticity associated with chronic injury. The spinal cord was transected at the S2 level, causing, over time, exaggerated long-lasting reflexes (hyperreflexia) associated with a general spasticity syndrome in the tail muscles of chronic spinal rats (1-5 mo postinjury). The whole sacrocaudal spinal cord of chronic or acute spinal rats was removed and maintained in vitro in normal artificial cerebral spinal fluid (ACSF). Hyperreflexia in chronic spinal rats was verified by recording the long-lasting ventral root responses to dorsal root stimulation in vitro. The intrinsic properties of sacrocaudal motoneurons were studied using intracellular injections of slow triangular current ramps or graded current pulses. In chronic spinal rats, the current injection triggered sustained firing and an associated sustained depolarization (plateau potential; 34/35 cells; mean, 5.5 mV; duration >5 s; normal ACSF). The threshold for plateau initiation was low and usually corresponded to an acceleration in the membrane potential just before recruitment. After recruitment and plateau activation, the firing rate changed linearly with current during the slow ramps [63% of cells had a linear frequency-current (F-I) relation] despite the presence of the plateau. The persistent inward current (I(PIC)) producing the plateau and sustained firing was estimated to be on average 0.8 nA as determined by the reduction in injected current needed to stop the sustained firing [DeltaI = -0.8 +/- 0.6 (SD) nA], compared with the current needed to start firing (I = 1.7 +/- 1.5 nA; 47% reduction). In motoneurons of acute spinal rats, plateaus were rarely seen (3/22), although they could be made to occur with bath application of serotonin. In motoneurons of chronic spinal rats there were no significant changes in the mean passive input resistance, rheobase or amplitude of the spike afterhyperpolarization (AHP) as compared with acute spinal rats. However, there were significant increases in AHP duration and initial firing rate at recruitment and decreases in minimum firing rate and F-I slope. We suggest that the higher initial firing rate resulted from the plateau activation at recruitment and the lower F-I slope resulted from an increase in active conductance during firing, due to I(PIC). Brief dorsal root stimulation also triggered a plateau and sustained discharge (long-lasting reflexes; 2-5 s) in motoneurons of chronic (but not acute) spinal rats. When the plateau was eliminated by a hyperpolarizing current bias, the reflex response was significantly shortened (to 1 s). Thus plateaus contributed substantially to the long-lasting reflexes in vitro and therefore should contribute significantly to the corresponding exaggerated reflexes and spasticity in awake chronic spinal rats.
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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 | 0.001 | 0.001 |
| 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 it