Cauda equina repair in the rat: part 1. Stimulus-evoked EMG for identifying spinal nerves innervating intrinsic tail muscles

Cauda equina repair in the rat: Part 3. Axonal regeneration across Schwann cell-Seeded collagen foam

INTRODUCTION

Treatments for patients with cauda equina injury are limited.

METHODS

In this study, we first used retrograde labeling to determine the relative contributions of cauda equina motor neurons to intrinsic and extrinsic rat tail muscles. Next, we transected cauda equina ventral roots and proceeded to bridge the proximal and distal stumps with either a type I collagen scaffold coated in laminin (CL) or a collagen-laminin scaffold that was also seeded with Schwann cells (CLSC). Regeneration was assessed by way of serial retrograde labeling.

RESULTS

After accounting for the axonal contributions to intrinsic vs. extrinsic tail muscles, we noted a higher degree of double labeling in the CLSC group (58.0 ± 39.6%) as compared with the CL group (27.8 ± 16.0%; P = 0.02), but not the control group (33.5 ± 18.2%; P = 0.10).

DISCUSSION

Our findings demonstrate the feasibility of using CLSCs in cauda equina injury repair. Muscle Nerve 57: E78-E84, 2018.

Innervation and function of rat tail muscles for modeling cauda equina injury and repair

INTRODUCTION

The rat tail exhibits functional impairment after cauda equina injury. Our goal was to better understand the innervation and roles of muscles that control the tail.

METHODS

Adult rats received either: (1) ventral root injury; (2) caudales nerve injury; or (3) mapping of sacrococcygeal myotomes. Activation of small muscles within the tail itself (intrinsics) was compared with that of larger lumbosacral muscles acting on the tail (extrinsics). Behavioral testing of tail movement was done 1 week later.

RESULTS

Rats that received ventral root injury exhibited multiple behavioral deficits, whereas rats with injury to caudales nerves maintained more fully preserved tail movement. Mapping studies revealed much broader overlap of myotomes for extrinsic muscles.

CONCLUSIONS

Extrinsic tail muscles play a greater role in tail movement in the rat than their intrinsic counterparts and are innervated by multiple neurological segments. These findings have major implications for future research on cauda equina injury.

Large animal models of human cauda equina injury and repair: evaluation of a novel goat model

Previous animal studies of cauda equina injury have primarily used rat models, which display significant differences from humans. Furthermore, most studies have focused on electrophysiological examination. To better mimic the outcome after surgical repair of cauda equina injury, a novel animal model was established in the goat. Electrophysiological, histological and magnetic resonance imaging methods were used to evaluate the morphological and functional outcome after cauda equina injury and end-to-end suture. Our results demonstrate successful establishment of the goat experimental model of cauda equina injury. This novel model can provide detailed information on the nerve regenerative process following surgical repair of cauda equina injury.

Cauda equina repair in the rat: part 2. Time course of ventral root conduction failure

Treatment for cauda equina (CE) ventral root injury is currently limited. Furthermore, relatively little is known about the time course of nerve root functional degeneration after such injury has occurred. Using a previously developed method for identifying spinal nerve roots that innervate the rat tail, we transected S2, S3, and S4 ventral roots and measured their ability to activate tail muscles out to 72 h post-injury by way of stimulus-evoked electromyography (EMG) recording. Immediately following transection, all distal ventral root stumps successfully activated muscles in the tail upon stimulation with no change in stimulus threshold (0.07±0.04 to 0.07±0.06 V using 0.1-msec pulse duration; 0.04±0.02 to 0.04±0.02 V using 1.0-msec pulse duration). Thresholds increased incrementally at each later time point (24 h: 0.27±0.33 V using 0.1-msec pulse duration; 0.09±0.07 V using 1-msec pulse duration; 48 h: 0.57±1.00 V using 0.1-msec pulse duration; 0.56±1.09 V using 1-msec pulse duration), with the first complete absence of EMG noted at 48 h post-transection in a subset of nerve roots (4/12). We were not able to elicit EMG at 72 h post-transection without moving distally along the nerve root stump. Based on neurofilament staining, only 51% of axons were identifiably intact nearest the site of injury at 24 h post-injury. This percentage dropped to 39% at 48 h, and just 18% at 72 h. Moving 5 mm from the site of injury, we identified 83% intact axons at 24 h post-transection, 77% at 48 h, and 68% at 72 h. Regenerative implications aside, if electrophysiological mapping of injured nerve roots is to be carried out for repair purposes, the rapid nature of conduction failure needs to be considered.