Studies on vascular permeability in peripheral nerves. 3. Permeability changes of vasa nervorum and exudation of serum albumin in INH-induced neuropathy of the rat

Usefulness of cervical root magnetic stimulation in assessing proximal motor nerve conduction

OBJECTIVES

To evaluate the reliability and utility of cervical root magnetic stimulation in exploring proximal motor conduction.

METHODS

In 20 patients with demyelinating polyneuropathy (DPN), 20 patients with amyotrophic lateral sclerosis (ALS) and 25 healthy subjects, evoked compound muscle action potentials (CMAPs) were recorded from abductor digiti minimi muscle in response to electrical stimulation up to Erb's point and magnetic stimulation up to the cervical roots.

RESULTS

In all healthy and ALS subjects, magnetic root stimulation confirmed the absence of conduction abnormalities, including those in whom supramaximal responses at Erb's point were not achieved. In the DPN group, conduction block and/or temporal dispersion was revealed by magnetic root stimulation in 9 out of 20 patients (45%), 3 more than those detected at Erb's point.

CONCLUSIONS

Cervical root stimulation allowed clear distinction between motor neuronopathy and DPN. It is recommended as part of the routine evaluation of patients suspected of having DPN, especially when distal nerve studies are inconclusive.

Wallerian degeneration and peripheral nerve conditions for both axonal regeneration and neuropathic pain induction

Wallerian degeneration is a cascade of stereotypical events in reaction to injury of nerve fibres. These events consist of cellular and molecular alterations, including macrophage invasion, activation of Schwann cells, as well as neurotrophin and cytokine upregulation. This review focuses on cellular and molecular changes distal to various types of peripheral nerve injury which simultaneously contribute to axonal regeneration and neuropathic pain induction. In addition to the stereotypical events of Wallerian degeneration, various types of nerve damage provide different conditions for both axonal regeneration and neuropathic pain induction. Wallerian degeneration of injured peripheral nerve is associated with an inflammatory response including rapid upregulation of the immune signal molecules like cytokines, chemokines and transcription factors with both beneficial and detrimental effects on nerve regeneration or neuropathic pain induction. A better understanding of the molecular interactions between the immune system and peripheral nerve injury would open the possibility for targeting these inflammatory mediators in therapeutic interventions. Understanding the pleiotropic effects of cytokines/chemokines, however, requires investigating their highly specific pathways and precise points of action.

Experimental models of peripheral neuropathic pain based on traumatic nerve injuries - an anatomical perspective

Peripheral neuropathic pain (PNP) frequently occurs as a consequence of nerve injury and may differ depending upon the type of insult and the individual patient. Progress in our knowledge of PNP induction mechanisms depends upon the utilization of appropriate experimental models in rodents based on various types of peripheral nerve lesions. In this review, we draw attention to current knowledge on basic cellular and molecular events in various experimental models used to induce the PNP symptoms. Spontaneous ectopic activity of axotomized and non-axotomized primary sensory neurons, the bodies of which are located in the dorsal root ganglion (DRG), seems to be a key mechanism of PNP induction. The primary sensory neurons are directly affected by nerve injury or indirectly by activated satellite glial cells and adjoining immune cells that release a variety of molecules changing the microenvironment of the neurons. Recently, it has become clear that molecules produced during Wallerian degeneration play an important role not only in axon-promoting conditions distal to nerve injury but also in initiation of neuropathic pain. The molecules, transported by the blood, influence afferent neurons and their axons not only in DRG associated, but also those not directly associated with the injured nerve (i.e., in the contralateral DRG or at different spinal segments). Generally, all experimental PNP models based on a partial injury of peripheral nerve segments contain mechanisms initiated by signal molecules of Wallerian degeneration.

Quantitative method for detection of blood-nerve barrier alterations in experimental animal models of neuropathy

A solid phase radioimmunoassay was developed for measuring albumin concentrations in both endoneurium and serum, which were normalized to total endoneurium and serum protein to obtain a blood-nerve barrier index (BNB-index). The BNB-index in experimental lead neuropathy demonstrated barrier dysfunction beginning at 6 weeks of 4% lead carbonate ingestion and at 14 weeks was 5.2 times that of pair-fed controls. These data, therefore, confirmed investigations that indicated a gradual alteration of the BNB beginning at 6 weeks and were based on (i) direct measurement of endoneurial albumin concentration by densitometry after sodium dodecyl sulfate-pore gradient electrophoresis and (ii) intravenous injection of 125I-albumin (J. F. Poduslo, P. A. Low, A. J. Windebank, P. J. Dyck, C. T. Berg, and J. D. Schmeltzer, 1982. J. Neurosci. 2: 1507-1514). The BNB-index after crush injury was 2.2 times that of control nerves at 24 h and gradually decreased toward normal values but was still 1.6 times that of controls at 70 days, a value consistent with the prolonged time course for complete repair. The BNB-index, therefore, can be used to evaluate BNB alterations quantitatively in animal models of neuropathy. Furthermore, we suggest that the BNB-index can also be used on biopsied, neuropathic, human sural nerve for evaluation of blood-nerve barrier abnormality.

Posttraumatic autoimmune reaction in peripheral nerve: effect of a single injury

This study was conducted to show that local autoimmune reactions could be observed in rat sciatic nerve after a single injury. Furthermore, we attempted to correlate the intensity of the immunological reaction with the severity of nerve damage, with the type of surgical treatment and with the degree of functional recovery. Through the use of direct immunofluorescence techniques, we found that the severity of the initial damage was associated with the intensity of the local immunological response assessed 2.5 months after surgery. There was an association between type of surgical treatment and intensity of the autoimmune reaction. A correlation between autoimmune reaction and degree of long-term functional impairment was not immediately clear. The probable factors that underlie these results are discussed.

Ultrastructural and histophysiological studies on the blood-nerve barrier and perineurial barrier in leprosy neuropathy

Onset and nature of ultrastructural changes in endoneurial vasa nervorum during the pathogenesis of leprosy neuropathy and possibly associated alterations in the "blood-nerve barrier" were investigated, together with perineurial barrier functioning, in mice infected 20-28 months previously with Mycobacterium leprae and in (ageing) non-infected mice. Barriers were tested by i.v. administration of markers (Trypan blue and ferritin) 1-4 days before killing the mice. Twenty-eight months after infection, histopathology of sciatic nerves was comparable to that seen in sensory nerves in clinically early human (borderline-) lepromatous leprosy. Schwann cells and endoneurial macrophages were bacillated, endothelia of endoneurial vessels not, and the perineurium rarely. Many infected mice and all (ageing) controls possessed ultrastructurally and functionally normal endoneurial vessels. Their continuous endothelium with close junctions had prevented marker passage, even when surrounding endoneurial tissue cells were quite heavily bacillated. The perineurium was also normal. By contrast, in infected mice showing hind limb paralysis serious histopathologic involvement and large globi of bacilli intrafascicularly in sciatic nerves, endoneurial blood vessels were abnormal. Open endothelial junctions, extreme attenuation, fenestrations, and luminal protrusions were all features comparable to neural microangiopathy encountered in leprosy patients (Boddingius 1977a, b). The "blood-nerve barrier" clearly had become defective allowing excessive exudation of Trypan blue and ferritin, via four pathways from the vessel lumen, deep into surrounding endoneurial tissues but halted by a normal perineurial barrier. Markers in such "blue" nerves were not found in bacillated or non-bacillated Schwann cells, thus denying significant phagocytotic and lysosomal activities of Schwann cells at this stage of neuropathy. Possible implications of barrier performances for anti-leprosy drug treatment of patients are discussed.

Morphometric evaluation of degenerative and regenerative changes in isoniazid-induced neuropathy

Morphometric studies of the pathologic changes were carried out on the peripheral nerves, spinal roots, and different levels of the Goll's tract in rats given isoniazid and killed 1, 2, 3, 4, 5, 6, 7, 14, and 30 days after intoxication. In teased fiber preparations, axonal degeneration was the main change present, and this was seen as early as day 2 in the peroneal and distal sural nerves. The frequency of myelinated fibers showing axonal degeneration was higher in the distal than the proximal sural nerve, and in the ventral than the dorsal root. In the group of rats killed on 5, 6, 7, and 14 days, a significant decrease of the myelinated fiber density was observed in the distal and proximal sural nerves, ventral root, and at the third cervical level of the Goll's tract. The degree of fiber degeneration was more severe in the distal than in the proximal sural nerve and in the third cervical than the fifth thoracic level of the Goll's tract. Preferential decrease of large myelinated fibers was noted in all the affected nerves. No definite abnormalities, however, were seen in nerve cells of the 6th lumbar spinal ganglia and anterior horn cells of the lumbar spinal cord on light microscopy. On 30 days, regeneration at varying degrees was discerned in all the affected nerves with significant increase of small myelinated fibers, particularly in the ventral root. The findings indicate that both centrally and peripherally directed myelinated axons are more affected in the distal than in the proximal segments while the neuronal cell bodies are spared. The spatio-temporal evolution of this pattern of change is compatible with the concept of the "dying back" process or central-peripheral distal axonopathy.

Permeability barriers to cytochrome-c in nerves of adult and immature rats

Nerves in the tongues of adult and immature rats were examined with respect to their permeability to exogenous cytochrome-c (mol wt 12,000) injected into the tongue. The distribution of cytochrome-c was determined in cryostat sections on the basis of the peroxidase activity of this protein. Nerves of 14-day-old rats were permeable to injected cytochrome-c. The larger nerves of older animals showed only localized accumulations of cytochrome-c reaction product both between and within axons adjacent to endoneurial blood vessels. Reaction product was not found, however, in association with blood vessels penetrating nerves of the tongue that were not within the limits of tracer spread. In the smallest nerve brances, thin linear strands of reaction product filled the interstices between the nerve fibers.