Effects of glycerol injection into rat sciatic nerve

Gli1 Regulates the Postnatal Acquisition of Peripheral Nerve Architecture

Peripheral nerves are organized into discrete compartments. Axons, Schwann cells (SCs), and endoneurial fibroblasts (EFs) reside within the endoneurium and are surrounded by the perineurium, a cellular sheath comprised of layers of perineurial glia (PNG). SC secretion of Desert Hedgehog (Dhh) regulates this organization. In Dhh nulls, the perineurium is deficient and the endoneurium is subdivided into small compartments termed minifascicles. Human Dhh mutations cause a neuropathy with similar defects. Here we examine the role of Gli1, a canonical transcriptional effector of hedgehog signaling, in regulating peripheral nerve organization in mice of both genders. We identify PNG, EFs, and pericytes as Gli1-expressing cells by genetic fate mapping. Although expression of Dhh by SCs and Gli1 in target cells is coordinately regulated with myelination, Gli1 expression unexpectedly persists in Dhh null EFs. Thus, Gli1 is expressed in EFs noncanonically (i.e., independent of hedgehog signaling). Gli1 and Dhh also have nonredundant activities. Unlike Dhh nulls, Gli1 nulls have a normal perineurium. Like Dhh nulls, Gli1 nulls form minifascicles, which we show likely arise from EFs. Thus, Dhh and Gli1 are independent signals: Gli1 is dispensable for perineurial development but functions cooperatively with Dhh to drive normal endoneurial development. During development, Gli1 also regulates endoneurial extracellular matrix production, nerve vascular organization, and has modest, nonautonomous effects on SC sorting and myelination of axons. Finally, in adult nerves, induced deletion of Gli1 is sufficient to drive minifascicle formation. Thus, Gli1 regulates the development and is required to maintain the endoneurial architecture of peripheral nerves.SIGNIFICANCE STATEMENT Peripheral nerves are organized into distinct cellular/ECM compartments: the epineurium, perineurium, and endoneurium. This organization, with its associated cellular constituents, is critical for the structural and metabolic support of nerves and their response to injury. Here, we show that Gli1, a transcription factor normally expressed downstream of hedgehog signaling, is required for the proper organization of the endoneurium but not the perineurium. Unexpectedly, Gli1 expression by endoneurial cells is independent of, and functions nonredundantly with, Schwann Cell-derived Desert Hedgehog in regulating peripheral nerve architecture. These results further delineate how peripheral nerves acquire their distinctive organization during normal development, and highlight mechanisms that may regulate their reorganization in pathologic settings, including peripheral neuropathies and nerve injury.

Effects on pain of percutaneous treatment of cervical disc herniations using DiscoGel: A retrospective analysis

BACKGROUND AND PURPOSE

Cervical discogenic pain originates from degenerated intervertebral discs and is a common condition in the middle-aged population. Cervical discs may herniate and give compressions to cervical nerves, with pain and functional limitation of the arms. DiscoGel is a device that can be useful in the treatment of cervical disc herniation, with very short operating time and low radiation dose.

MATERIAL AND METHODS

Between March 2018 and April 2019 we performed this procedure on 38 patients with non-fissurated cervical herniation using 0.3-0.4 mL of DiscoGel injected under fluoroscopic guidance. The most common discs affected were C5-C6, C6-C7 and C4-C5. Outcomes were evaluated with Visual Analogue Scale (VAS) and Neuropathic Pain Symptom Inventory (NPSI) scores at 3, 6 and 12 months follow-up. A magnetic resonance imaging (MRI) scan of the cervical spine was performed 3 months after the procedure.

RESULTS

Postoperative examinations showed: VAS 2.15 ± 1.34 and NPSI 2.29 ± 0.71.Postoperative MRI performed 3 months after the procedure showed a good improvement of cervical disc herniation or bulging or protrusion. The mean dose area product (DAP) was 2803 mGy/cm² with a mean fluoroscopy time of 4 minutes 22 seconds.Conclusion DiscoGel is a suitable approach for non-fissurated cervical disc herniations, especially in patients that are not suitable for open surgery, with excellent postoperative results, fast recovery and a low radiation dose.

Peripheral nerve regeneration and intraneural revascularization

Peripheral nerves are particularly vulnerable to injuries and are involved in numerous pathologies for which specific treatments are lacking. This review summarizes the pathophysiological features of the most common traumatic nerve injury in humans and the different animal models used in nerve regeneration studies. The current knowledge concerning Wallerian degeneration and nerve regrowth is then described. Finally, the involvement of intraneural vascularization in these processes is addressed. As intraneural vascularization has been poorly studied, histological experiments were carried out from rat sciatic nerves damaged by a glycerol injection. The results, taken together with the data from literature, suggest that revascularization plays an important role in peripheral nerve regeneration and must therefore be studied more carefully.

An experimental animal model for percutaneous procedures used in trigeminal neuralgia

OBJECT

This study describes an experimental rabbit model that allows the reproduction of percutaneous operations that are used in patients with trigeminal neuralgia (TN). Attention was given to an exact anatomical description of the rabbit's middle cranial fossa as well as the establishment of conditions for a successful procedure.

METHODS

Morphometric measurements were taken from 20 rabbit skulls and CT scans. The anatomy of the trigeminal nerve, as well as its surrounding structures, was assessed by bilateral dissection of 13 New Zealand white rabbits (NWR). An ideal approach of placing a needle through the foramen ovale to reach the TG was sought. Validation of correct placement was realized by fluoroscopy and confirmed by dissection.

RESULTS

Precise instructions for successful reproduction of percutaneous procedures in NWR were described. According to morphological measurements, for balloon compression of the trigeminal ganglion (TG) the maximal diameter of an introducing cannula is 1.85 mm. The diameter of an empty balloon catheter should not exceed 1.19 mm, and the length of the inflatable part of the balloon can range up to 4 mm. For thermocoagulation the needle electrodes must not exceed an external diameter of 1.39, mm and the length of the non-insolated tip can range up to 4 mm. Glycerol rhizolysis can be achieved because the trigeminal cistern in the NWR is a closed space that allows a long dwelling time (>10 min) of the contrast agent.

CONCLUSIONS

An experimental NWR model intended for the reproduction of percutaneous procedures on the TG has been meticulously described. This provides a tool that enables further standardized animal research in the field of surgical treatment of TN.

Endoneurial fibroblast-like cells

Endoneurial fibroblast-like cells (EFLCs) have been described for more than 60 years, but the embryology, functions, and pathology of these cells are not well defined. Several hypotheses of their origin have been proposed. A previous study suggesting that they were of neural crest origin is supported by our data in humans. This lineage might account for EFLCs having multiple biologic functions and involvement in pathological processes. Here, we review what is known about the origin; functions in collagen synthesis, phagocytosis, inflammatory responses, and immune surveillance; and the pathological alterations of EFLCs based on the literature and on our personal observations.

The perineurium modifies the effects of phenol and glycerol in rat sciatic nerve

Endoneurial cell response and type of nerve fibre damage were studied after perineural injections of 7% phenol-aqua and pure glycerol. Our previous studies have shown that phenol and glycerol induce different types of nerve fibre degeneration after intraneural injections: phenol dissolves axons and Schwann cells inside the basal lamina tubes but glycerol breaks them down into cellular flakes. The current study investigated whether the difference in type of endoneurial damage also appears after perineural application and how the perineurium affects the effect of these neurolytic agents. Rat sciatic nerves were treated with perineural injections of 7% phenol-aqua or pure glycerol and were followed up to 6 months. The results support the previous findings that perineural phenol injection induces damage that covers almost the whole endoneurium, but glycerol injection results in minor subperineurial damage. An ultrastructural study showed that the endoneurial effects are much milder after perineural injection than after intraneural injections. Phenol-induced nerve fibre dissolving was only rarely seen and the nerve fibre damage appeared similar to that after regular Wallerian degeneration in both groups. Axonal regeneration began within 2 weeks of the injections. Endoneurial macrophages were numerous in the damaged area in many individual nerves even at 3-6 months in both groups, which may indicate impaired phagocytotic activity. Regenerating axonal sprouts were seen first at 1 week post injection and Schwann cells proliferated within 2 weeks in both groups. However, the number of axonal sprouts was higher (P=0.002) and the size of the sprouts appeared larger after glycerol injection at 4 weeks post injection. The present study shows that the effects of extraneurally applied neurolytic agents phenol and glycerol are modified by the perineurium. Phenol readily penetrates the perineurium, but glycerol causes only subperineurial damage. The type of damage is rather similar to regular Wallerian degeneration in both groups and the endoneurial effects differ from those seen after intraneural injections.

Correlation between autotomy-behavior and current theories of neuropathic pain

The past 10 years have brought several new experimental models with which to study chronic neuropathic pain in animals. Consequently, our knowledge about the mechanisms subserving neuropathic pain in humans has improved. However, the first animal model that was used for studying this type of chronic pain was the autotomy-model which can still be considered as a useful tool for pain studies. The present review assesses some of the similarities and differences between autotomy-model and more recent models of experimental traumatic mononeuropathy. In addition, it considers some of the similarities between the results obtained in clinical studies and in autotomy studies.

Morphologic effects of glycerol on the mental nerve

OBJECTIVES

In recent years, injection of pure glycerol has been used successfully for the treatment of trigeminal neuralgia. However, the mode of action of this therapy remains unclear. The present experiment was undertaken to examine histologically the morphologic changes produced by extraneural injections of pure glycerol into the dog mental nerve.

STUDY DESIGN

Under direct vision, glycerol was injected extraneurally into the mental foramen on one side of the lower jaw of each of nine dogs. Physiologic saline solution was the control on the contralateral side of each animal. Animals were killed at 1, 3, and 7 days after the application of glycerol, and the mental nerve specimens were examined by light microscopy.

RESULTS

Results showed that extraneural application of pure glycerol in the vicinity of the dog mental nerve is not associated with structural changes. No signs of nerve degeneration or other morphologic changes were observed for any of the experimental and control specimens in any of the time intervals studied.

CONCLUSIONS

It can be concluded that despite the encouraging clinical results related to extraneural application of pure glycerol for treatment of trigeminal neuralgia, glycerol produces its effect without inducing any morphologic or destructive changes in the peripheral nerve. A probable explanation of the temporary clinical effectiveness of glycerol in relieving trigeminal neuralgia is discussed.

Glycerol injection into the trigeminal ganglion provokes a selective increase in human cerebral blood flow

Fourteen patients suffering from idiopathic trigeminal neuralgia (refractory to medication) were treated by injection of glycerol into the trigeminal ganglion. The changes in cerebral blood flow (CBF) after glycerol injection were quantified by intravenous 133Xe emission tomography. There was a significant 11% (P less than 0.01) increase in ipsilateral CBF and an 8% (P less than 0.05) increase in contralateral CBF 1 h after glycerol injection. The interhemispheric difference was significant (P less than 0.05). The increase was significantly greater in the ipsilateral internal carotid territory, in the anterior cerebral artery and middle cerebral artery territories (superficial (P less than 0.05), deep territories (P less than 0.001]. We suggest that these changes are due to the release of substance P and/or calcitonin gene-related peptide, from terminals of the trigeminal-vascular system during glycerol injection.

Effects of glycerol on the rat infraorbital nerve: an experimental study

Glycerol was injected into the infraorbital canal of 12 rats to determine neurolytic effects on the peripheral trigeminal nerve. Saline and 90% ethanol were injected in control animals. One week after the injection, histopathological changes were noted in both glycerol and alcohol groups. In the former group, axonolysis and demyelination were restricted to the outer zone of the nerve bundles. Centrally located axons remained undamaged. A total destruction of all axons was found in the alcohol group. Four weeks after the injection in the glycerol group, small sized axons with thin myelin replaced damaged axons at the periphery of the bundle. No signs of regeneration were noted in the alcohol group. A possible mode of action of glycerol injected at the peripheral trigeminal nerve in relieving trigeminal neuralgia is described.

Endoneurial proliferation of perineurial cells in leprosy

In leprous neuropathy the perineurium has very often an abnormal multilayered appearance and is infiltrated by many different types of inflammatory cells. We report here 13 cases characterized by an abnormal endoneurial proliferation of fibroblasts which seems to differentiate in perineurial cells. In several instances there is formation of many intrafascicular microcompartments. Such aspects have been described in various, but infrequent, cases of experimental and human neuropathies. It seems that severe Wallerian degeneration, diffuse endoneurial macrophage infiltration and lesion of the perineurium might lead to such a process.

Ablative neurosurgical procedures for the treatment of chronic pain

This article is devoted to ablative neurosurgical procedures used for the treatment of chronic pain. The authors detail only those procedures that are currently performed. The procedures are classified as those directed to the peripheral nerves, spinal roots and cranial nerves; the dorsal root entry zone; the ascending extra-lemniscal pathways. The authors have analyzed the results of their own series and those published in the literature. They concentrate on the rationale and neurophysiological effects of the operations.