Regional hypothermia inhibits spinal cord somatosensory-evoked potentials without neural damage in uninjured rats

Postcooling But Not Precooling Benefits Motor Recovery by Suppressing Cell Death After Surgical Spinal Cord Injury in Rats

BACKGROUND

Surgical spinal cord injury (SSCI) is often inevitable in patients with intramedullary lesions. Although regional hypothermia (RH) has been demonstrated neuroprotective, the value of priming RH in SSCI has never been studied. Herein, the authors investigated the impact of pre- and post-RH on neurologic recovery in a clinically relevant model.

METHODS

An SSCI model was established at T10. RH was conducted by focal 4oC saline perfusion; room temperature (RT) saline was used as controls. Animals were randomized into 6 groups: SHAM-RT/RH, Pre-RT/RH, and Post-RT/RH. Motor and sensory functions were evaluated using the Basso, Beattie, and Bresnahan rating scale and Plantar test 2 weeks after surgery. TUNEL assay and Fluoro-Jade C staining were conducted to examine the cell death, and the alterations of apoptotic markers including total and cleaved casepase 3, Bcl-2, and Bax, as well as the pyroptotic proteins including NLRP3, ASC, and caspase 1, were determined.

RESULTS

RH perfusion successfully created an intramedullary hypothermia approximately at 24oC, while RT controls remained above 30oC. Animals receiving postinjury RH had the least cell death and the best motor performance, while pre-RH showed the most dead cells and worst hind limb movements. Immunoblotting depicted that post-RH suppressed both apoptotic and pyroptotic death as the cleaved/total caspase 3, Bcl-2/Bax ratio, and NLRP3/ASC/caspase 1 signaling were inhibited. Priming cooling, on the contrary, elevated pyroptosis and did not affect apoptosis significantly.

CONCLUSIONS

Priming RH before surgical incision could not be supported as it caused excessive cell death. In contrast, instant introduction of RH is beneficial in rescuing neurologic function.

Neuroprotective assessment of prolonged local hypothermia post contusive spinal cord injury in rodent model

BACKGROUND CONTEXT

Although general hypothermia is recognized as a clinically applicable neuroprotective intervention, acute moderate local hypothermia post contusive spinal cord injury (SCI) is being considered a more effective approach. Previously, we have investigated the feasibility and safety of inducing prolonged local hypothermia in the central nervous system of a rodent model.

PURPOSE

Here, we aimed to verify the efficacy and neuroprotective effects of 5 and 8 hours of local moderate hypothermia (30±0.5°C) induced 2 hours after moderate thoracic contusive SCI in rats.

STUDY DESIGN

Rats were induced with moderate SCI (12.5 mm) at its T8 section. Local hypothermia (30±0.5°C) was induced 2 hours after injury induction with an M-shaped copper tube with flow of cold water (12°C), from the T6 to the T10 region. Experiment groups were divided into 5-hour and 8-hour hypothermia treatment groups, respectively, whereas the normothermia control group underwent no hypothermia treatment.

METHODS

The neuroprotective effects were assessed through objective weekly somatosensory evoked potential (SSEP) and motor behavior (basso, beattie and bresnahan Basso, Beattie and Bresnahan (BBB) scoring) monitoring. Histology on spinal cord was performed until at the end of day 56. All authors declared no conflict of interest. This work was supported by the Singapore Institute for Neurotechnology Seed Fund (R-175-000-121-733), National University of Singapore, Ministry of Education, Tier 1 (R-172-000-414-112.).

RESULTS

Our results show significant SSEP amplitudes recovery in local hypothermia groups starting from day 14 post-injury onward for the 8-hour treatment group, which persisted up to days 28 and 42, whereas the 5-hour group showed significant improvement only at day 42. The functional improvement plateaued after day 42 as compared with control group of SCI with normothermia. This was supported by both 5-hour and 8-hour improvement in locomotion as measured by BBB scores. Local hypothermia also observed insignificant changes in its SSEP latency, as compared with the control. In addition, 5- and 8-hour hypothermia rats' spinal cord showed higher percentage of parenchyma preservation.

CONCLUSIONS

Early local moderate hypothermia can be induced for extended periods of time post SCI in the rodent model. Such intervention improves functional electrophysiological outcome and motor behavior recovery for a long time, lasting until 8 weeks.

Oligodendrocyte Precursor Cells in Spinal Cord Injury: A Review and Update

Spinal cord injury (SCI) is a devastating condition to individuals, families, and society. Oligodendrocyte loss and demyelination contribute as major pathological processes of secondary damages after injury. Oligodendrocyte precursor cells (OPCs), a subpopulation that accounts for 5 to 8% of cells within the central nervous system, are potential sources of oligodendrocyte replacement after SCI. OPCs react rapidly to injuries, proliferate at a high rate, and can differentiate into myelinating oligodendrocytes. However, posttraumatic endogenous remyelination is rarely complete, and a better understanding of OPCs' characteristics and their manipulations is critical to the development of novel therapies. In this review, we summarize known characteristics of OPCs and relevant regulative factors in both health and demyelinating disorders including SCI. More importantly, we highlight current evidence on post-SCI OPCs transplantation as a potential treatment option as well as the impediments against regeneration. Our aim is to shed lights on important knowledge gaps and to provoke thoughts for further researches and the development of therapeutic strategies.

Beneficial effects of local profound hypothermia and the possible mechanism after experimental spinal cord injury in rats

OBJECTIVE

The primary focus of this study was to investigate the effects of local profound hypothermia and to explore the possible mechanism in adult rats with spinal cord injury.

STUDY DESIGN AND METHODS

Spinal cord injury models were established by placing aneurysm clips on T10. An epidural perfusion device was applied to maintain a steady temperature (18 °C) for 120 min with gradual rewarming to 37 °C Total hypothermic duration lasted up to about 170 min. The expression of axon regeneration inhibitors was tested by Western blot and real-time PCR. Luxol Fast Blue (LFB) stain and Bielschowsky silver stain were used to observe spinal cord morphology. Motor function of the hind limbs (BBB score) was monitored for 21 days.

RESULTS

The expressions of RhoA, ROCK-II, NG2, Neurocan, Brevican, and Nogo-A were downregulated by regional hypothermia (RH) after spinal cord injury. Subsequent observation showed that rats that had received RH had an alleviated demyelinating condition and a greater number of nerve fibers. Furthermore, the RH group achieved higher BBB scores than the spinal cord injury (SCI) group.

CONCLUSIONS

Recovery of hind limb function in rats can be promoted by local profound hypothermia; this may be caused by the suppression of axon regeneration inhibitors.

Prolonged Local Hypothermia Has No Long-Term Adverse Effect on the Spinal Cord

Hypothermia is known to be neuroprotective and is one of the most effective and promising first-line treatments for central nervous system (CNS) trauma. At present, induction of local hypothermia, as opposed to general hypothermia, is more desired because of its ease of application and safety; fewer side effects and an absence of severe complications have been noted. Local hypothermia involves temperature reduction of a small and specific segment of the spinal cord. Our group has previously shown the neuroprotective effect of short-term, acute moderate general hypothermia through improvements in electrophysiological and motor behavioral assessments, as well as histological examination following contusive spinal cord injury (SCI) in rats. We have also shown the benefit of using short-term local hypothermia versus short-term general hypothermia post-acute SCI. The overall neuroprotective benefit of hypothermia can be categorized into three main components: (1) induction modality, general versus local, (2) invasive, semi-invasive or noninvasive, and (3) duration of hypothermia induction. In this study, a series of experiments were designed to investigate the feasibility, long-term safety, as well as eventual complications and side effects of prolonged, semi-invasive, moderate local hypothermia (30°C±0.5°C for 5 and 8 hours) in rats with uninjured spinal cord while maintaining their core temperature at 37°C±0.5°C. The weekly somatosensory evoked potential and motor behavioral (Basso, Beattie and Bresnahan) assessments of rats that underwent 5 and 8 hours of semi-invasive local hypothermia, which revealed no statistically significant changes in electrical conductivity and behavioral outcomes. In addition, 4 weeks after local hypothermia induction, histological examination showed no anatomical damages or morphological changes in their spinal cord structure and parenchyma. We concluded that this method of prolonged local hypothermia is feasible, safe, and has the potential for clinical translation.

The effect of anaesthesia on somatosensory evoked potential measurement in a rat model

Somatosensory evoked potentials (SEPs) are widely used to study the functional integrity of ascending sensory pathways. For animal studies, SEPs provide a convenient method to quantitatively assess the functionality of the nervous system with low invasiveness. Even though they are frequently used in animal models, little attention is paid to the fact that SEPs are vulnerable to contamination from experimental factors such as anaesthetic delivery. In this study, the effect of isoflurane on SEP measurement was investigated in a rat model. The aim was to find out the adjustments for anaesthetic delivery optimizing the quality of the recordings. Two aspects were studied: the effect of isoflurane dosage on the SEP parameters and on the repeatability of the measurements. The SEP quality was found to be best when 1.5% isoflurane concentration was used. This dosage resulted in the best signal-to-noise ratio and equal repeatability of the measurements compared with the others. Our findings can help in refining the anaesthetic protocols related to SEP recordings in a rat model and, by improving the quality of the measurements, potentially reducing the number of subjects needed to carry out studies.

The effects of local and general hypothermia on temperature profiles of the central nervous system following spinal cord injury in rats

Local and general hypothermia are used to treat spinal cord injury (SCI), as well as other neurological traumas. While hypothermia is known to provide significant therapeutic benefits due to its neuroprotective nature, it is unclear how the treatment may affect healthy tissues or whether it may cause undesired temperature changes in areas of the body that are not the targets of treatment. We performed 2-hour moderate general hypothermia (32°C core) or local hypothermia (30°C spinal cord) on rats that had received either a moderate contusive SCI or laminectomy (control) while monitoring temperatures at three sites: the core, spinal cord, and cortex. First, we identified that injured rats that received general hypothermia exhibited larger temperature drops at the spinal cord (-3.65°C, 95% confidence intervals [CIs] -3.72, -3.58) and cortex (-3.64°C, CIs -3.73, -3.55) than uninjured rats (spinal cord: -3.17°C, CIs -3.24, -3.10; cortex: -3.26°C, CIs -3.34, -3.17). This was found due to elevated baseline temperatures in the injured group, which could be due to inflammation. Second, both general hypothermia and local hypothermia caused a significant reduction in the cortical temperature (-3.64°C and -1.18°C, respectively), although local hypothermia caused a significantly lower drop in cortical temperature than general hypothermia (p<0.001). Lastly, the rates of rewarming of the cord were not significantly different among the methods or injury groups that were tested; the mean rate of rewarming was 0.13±0.1°C/min. In conclusion, local hypothermia may be more suitable for longer durations of hypothermia treatment for SCI to reduce temperature changes in healthy tissues, including the cortex.