Early behavioral and histological outcomes following a novel traumatic partial nerve lesion

Histological Assessment of Wallerian Degeneration of the Rat Tibial Nerve Following Crush and Transection Injuries

BACKGROUND

 Wallerian degeneration (WD) following peripheral nerve injury (PNI) is an area of growing focus for pharmacological developments. Clinically, WD presents challenges in achieving full functional recovery following PNI, as prolonged denervation of distal tissues for an extended period of time can irreversibly destabilize sensory and motor targets with secondary tissue atrophy. Our objective is to improve upon histological assessments of WD.

METHODS

 Conventional methods utilize a qualitative system simply describing the presence or absence of WD in nerve fibers. We propose a three-category assessment that allows more quantification: A fibers appear normal, B fibers have moderate WD (altered axoplasm), and C fibers have extensive WD (myelin figures). Analysis was by light microscopy (LM) on semithin sections stained with toluidine blue in three rat tibial nerve lesion models (crush, partial transection, and complete transection) at 5 days postop and 5 mm distal to the injury site. The LM criteria were verified at the ultrastructural level. This early outcome measure was compared with the loss of extensor postural thrust and the absence of muscle atrophy.

RESULTS

 The results showed good to excellent internal consistency among counters, demonstrating a significant difference between the crush and transection lesion models. A significant decrease in fiber density in the injured nerves due to inflammation/edema was observed. The growth cones of regenerating axons were evident in the crush lesion group.

CONCLUSION

 The ABC method of histological assessment is a consistent and reliable method that will be useful to quantify the effects of different interventions on the WD process.

Dexamethasone as adjuvant to bupivacaine prolongs the duration of thermal antinociception and prevents bupivacaine-induced rebound hyperalgesia via regional mechanism in a mouse sciatic nerve block model

Background

Dexamethasone has been studied as an effective adjuvant to prolong the analgesia duration of local anesthetics in peripheral nerve block. However, the route of action for dexamethasone and its potential neurotoxicity are still unclear.

Methods

A mouse sciatic nerve block model was used. The sciatic nerve was injected with 60ul of combinations of various medications, including dexamethasone and/or bupivacaine. Neurobehavioral changes were observed for 2 days prior to injection, and then continuously for up to 7 days after injection. In addition, the sciatic nerves were harvested at either 2 days or 7 days after injection. Toluidine blue dyeing and immunohistochemistry test were performed to study the short-term and long-term histopathological changes of the sciatic nerves. There were six study groups: normal saline control, bupivacaine (10mg/kg) only, dexamethasone (0.5mg/kg) only, bupivacaine (10mg/kg) combined with low-dose (0.14mg/kg) dexamethasone, bupivacaine (10mg/kg) combined with high-dose (0.5mg/kg) dexamethasone, and bupivacaine (10mg/kg) combined with intramuscular dexamethasone (0.5mg/kg).

Results

High-dose perineural dexamethasone, but not systemic dexamethasone, combined with bupivacaine prolonged the duration of both sensory and motor block of mouse sciatic nerve. There was no significant difference on the onset time of the sciatic nerve block. There was “rebound hyperalgesia” to thermal stimulus after the resolution of plain bupivacaine sciatic nerve block. Interestingly, both low and high dose perineural dexamethasone prevented bupivacaine-induced hyperalgesia. There was an early phase of axon degeneration and Schwann cell response as represented by S-100 expression as well as the percentage of demyelinated axon and nucleus in the plain bupivacaine group compared with the bupivacaine plus dexamethasone groups on post-injection day 2, which resolved on post-injection day 7. Furthermore, we demonstrated that perineural dexamethasone, but not systemic dexamethasone, could prevent axon degeneration and demyelination. There was no significant caspase-dependent apoptosis process in the mouse sciatic nerve among all study groups during our study period.

Conclusions

Perineural, not systemic, dexamethasone added to a clinical concentration of bupivacaine may not only prolong the duration of sensory and motor blockade of sciatic nerve, but also prevent the bupivacaine-induced reversible neurotoxicity and short-term “rebound hyperalgesia” after the resolution of nerve block.

Efeito da eletroestimulação no músculo desnervado de animais: revisão sistemática

INTRODUÇÃO: A recuperação funcional após a lesão nervosa periférica está relacionada a fatores intrínsecos e extrínsecos ao sistema nervoso periférico, tais como a gravidade da lesão e a condição dos órgãos-alvo. A atrofia constitui uma das principais alterações do músculo após a lesão nervosa e, uma vez instalada, atua como barreira ao crescimento axonal durante a reinervação muscular. O uso da eletroestimulação é rotineiro no campo da fisioterapia e tem o objetivo de minimizar ou impedir a atrofia muscular e, assim, favorecer a recuperação da lesão nervosa periférica. OBJETIVO: Avaliar os efeitos da eletroestimulação sobre as características tróficas do músculo desnervado. MÉTODOS: Artigos publicados entre 1990 e 2010 e indexados aos bancos de dados da PUBMED foram selecionados utilizando os seguintes descritores: "muscle denervation AND electric stimulation" e "muscular atrophy AND electric stimulation". Foram considerados como critério de inclusão os estudos experimentais em animais (ratos) que utilizassem a lesão nervosa periférica como modelo de desnervação e que avaliassem o efeito da eletroestimulação muscular sobre a área de secção transversa e/ou a massa muscular de músculos desnervados. RESULTADOS: Nove artigos foram selecionados para a revisão. CONCLUSÕES: O efeito da eletroestimulação está diretamente relacionado à característica do protocolo de intervenção, que, quando aplicado de maneira adequada, apresenta o efeito de retardar e, em alguns casos, impedir a atrofia do músculo desnervado.

Local anesthetic sciatic nerve block and nerve fiber damage in diabetic rats

BACKGROUND AND OBJECTIVES

A concern for anesthesiologists is whether local anesthetics are more toxic to peripheral nerves in diabetic patients. A previous study in streptozotocin-induced diabetic rats showed that larger doses of lidocaine produce moderate nerve injury after nerve block in normal rats and worse injury in diabetic rats. However, it is not clear whether a smaller local anesthetic dose that produces negligible nerve fiber damage in normal rats will produce significant nerve damage in diabetic rats and if adding adjuvant drugs modulates this effect.

METHODS

Rats were intravenously injected with 50 mg/kg streptozotocin to induce diabetes (blood glucose levels 9250 mg/dL) and diabetic neuropathy. After waiting 35 days, an injection (0.1 mL) of 1% lidocaine alone, or with 5 kg/mL epinephrine or 7.5 kg/mL clonidine added, or 0.5% ropivacaine alone was performed at the left sciatic notch in both diabetic and nondiabetic rats. The duration of sensory (pin prick) and motor (toe spreading reflex) nerve block in the hind paws was determined.For histologic controls, all rats also received saline vehicle injection into the right sciatic notch. Another group of uninjected rats was used as naive controls. Left and right nerves were removed 2 days after injection and fixed in situ with a 4% glutaraldehyde solution. Myelinated axon profiles suggestive of neuropathy (myelin figures, pale and swollen,or dark-staining axoplasm) were counted and expressed as a percentage of the total number of fibers in each rat sciatic nerve.

RESULTS

All streptozotocin-injected rats became diabetic and had pronounced tactile allodynia. All rats had sensory and motor nerve blocks lasting for at least 50 mins after injection of local anesthetic. The duration of sensory and motor nerve block was longer in diabetic rats than in nondiabetic rats for all drug groups tested. None of the sciatic nerves examined showed greater than 3% nerve fiber degeneration. Although lidocaine in diabetic rats did not produce nerve fiber damage,diabetic rats receiving lidocaine/clonidine or ropivacaine had more abnormal myelinated axon profiles than did nondiabetic rats receiving the same drug.

CONCLUSIONS

The duration of sciatic nerve block with local anesthetics is longer in diabetic compared with nondiabetic rats. A small, but statistically significant, increase in nerve damage occurred in diabetic rats after nerve block with ropivacaine alone or when duration of lidocaine block was extended with clonidine. These findings may have implications for dosing of local anesthetics in diabetic patients undergoing regional analgesia with nerve blocks.