Cutaneus Trunci Muscle Reflex as a Model for Neural Plasticity after Spinal Cord Injury Open Access

Malone, Patrick Stephen (2012)

Permanent URL: https://etd.library.emory.edu/concern/etds/4j03cz77z?locale=en
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Abstract

Cutaneus Trunci Muscle Reflex as a Model for Neural Plasticity after Spinal Cord Injury Spinal cord injury (SCI) often results in neuronal plasticity that causes alterations in sensory processing. A physiological model of neural plasticity that could be analyzed quantitatively after injury could greatly advance our understanding of plasticity after SCI. The cutaneus trunci muscle (CTM) reflex produces a skin shrug and is mediated by a 3 neuron circuit: C and Aδ afferents in segmental dorsal cutaneous nerves (DCNs), ascending propiospinal interneurons, and the CTM motoneuron pool.

Female Long Evans rats were divided into 4 experimental groups and analyzed at 3 time points after right T10 hemisection: 1, 3, and 6 weeks, and uninjured controls. Animals were stimulated at C fiber stimulation strength (5 mA, 250 µs pulse width, 1 and 5 Hz) at DCNs L01, T12, T08, and T06 bilaterally and both the Aδ and C-fiber evoked left CTM neurogram signals were recorded and processed. The profile of the hemisection was reconstructed in the cross-sectional plane. Responses were compared between injured (contralateral to CTM recording site) and uninjured (ipsilateral) sides.

The contralateral/ipsilateral early response ratio was significantly higher 6 weeks after injury at L01 (1 Hz) and the late response ratio was significantly higher at T08 (5 Hz) 6 weeks after injury compared to 3 weeks after injury. Analysis of individual sides showed more significant changes on the left side (contralateral to hemisection) and above the level of injury. There was no correlation between extent of hemisection and neurogram, suggesting that anatomy does not easily predict physiology. An increased stimulus response could be characterized as "nociceptive hypereflexia" and raises the possibility of the CTM reflex as an animal model for neuropathic pain after SCI.

Table of Contents

Table of Contents
1. INTRODUCTION 1
2. METHODS 5
2.1. ANIMALS 5
2.2. SPINAL CORD HEMISECTION SURGERIES 5
2.3. CTM RECORDINGS - SURGERY 6
2.4. CTM RECORDINGS - STIMULATION 7
2.5. CTM RECORDINGS - POST PROCESSING 8
2.6. ANALYSIS WINDOWS 8
2.7. HEMISECTION CHARACTERIZATION 8
2.8. STATISTICAL TESTS 9
2.9. CONTRIBUTIONS 10
3. RESULTS
3.1. CTM REFLEX IN UNINJURED ANIMALS 11
3.2. CTM REFLEX IN INJURED ANIMALS - CONTRALATERAL/IPSILATERAL RESPONSE 12
3.3. CTM REFLEX IN INJURED ANIMALS - INDIVIDUAL RESPONSES 13
3.4. CTM REFLEX AND HEMISECTION - ANATOMY VS. PHYSIOLOGY 14
4. DISCUSSION 15
5. REFERENCES 19
6. TABLES AND FIGURES 24
6.1. FIGURE 1 CTM REFLEX CIRCUIT DIAGRAM 24
6.2. FIGURE 2 DORSAL CUTANEOUS NERVES AND CTM MOTOR NERVE BRANCHES 25
6.3. FIGURE 3 DISSECTED BRANCH OF CTM MOTOR NERVE 26
6.4. FIGURE 4 EXPERIMENTAL PREPARATION 27
6.5. FIGURE 5 NEUROGRAM PREPARATION PROCESS 28
6.6. FIGURE 6 REPRESENTATIVE IMAGE OF HEMISECTION STAINING AND MEASUREMENT. 29
6.7. FIGURE 7 FALSE COLOR PLOT OF UNINJURED AND INJURED STIMULUS RESPONSES 30
6.8. FIGURE 8 FALSE COLOR PLOT OF UNINJURED AND INJURED STIMULUS RESPONSES 31
6.9. FIGURE 9 CONTRALATERAL/IPSILATERA RESPONSE RATIO IN UNINJURED ANIMALS 32
6.10. FIGURE 10 CONTRALATERAL/IPSILATERAL RESPONSE RATIOS IN INJURED ANIMALS 33
6.11. FIGURE 11 CONTRALATERAL/IPSILATERAL RESPONSE RATIOS AT L01 AND T08 34
6.12. TABLE 1 STATISTICAL TESTS COMPARING INJURED TO UNINJURED ANIMALS 35
6.13. FIGURE 12 CTM NEUROGRAMS AND RECONSTRUCTIONS 1 WEEK AFTER INJURY 36
6.14. TABLE 2 HEMISECTION DATA 37
6.25. FIGURE 13 CENTRAL PROJECTIONS OF IB4 POSITIVE C FIBERS 38

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