Macrophage apolipoprotein synthesis and endoneurial distribution as a response to segmental demyelination.

The synthesis and endoneurial distribution of apolipoproteins in response to myelin degradation was elucidated morphologically and biochemically in rodent models of segmental demyelination. At the onset of acute demyelination induced by tellurium (Te) poisoning, macrophages infiltrated the endoneurium and then began to express cytoplasmic immunoreactivity for apolipoprotein E (apo E). When demyelinating nerve slices were incubated with S35-methionine, radiolabeled apo E was released, showing that apo E was actively synthesized by the macrophages. Macrophages secreted apo E into the endoneurial spaces, leading to dense endoneurial accumulations. Other apolipoproteins (apo A1 and albumin) were not synthesized in the endoneurium, but they entered edematous nerves, presumably through an early breakdown in the blood-nerve barrier. During the phagocytosis of myelin, plasma-derived apolipoproteins accumulated within some of the macrophages. In chronic demyelination caused by lead poisoning, the cellular and extracellular distribution of apolipoproteins was similar to Te neuropathy; the amount of apo E accumulation and the macrophage density were proportional to the prevalence of active demyelination in teased fibers. Similar patterns of endoneurial apo E were present in an inherited form of demyelination in the twitcher mouse, after antibody-mediated demyelination, and in demyelination secondary to axonal degeneration. Human sural nerve biopsies had patterns of apolipoprotein E antigenicity that were comparable to the rodent models. We conclude that secretion of apo E by infiltrating macrophages is a generalized response to demyelination, and that endoneurial edema leads to the accumulation of certain plasma apolipoproteins within macrophages. These data suggest that endoneurial apolipoproteins and macrophages might mediate important functions in patients recovering from primary and secondary demyelination.

Restoration of blood-nerve barrier in neuropathy is associated with axonal regeneration and remyelination.

We investigated the temporal course of blood-nerve barrier (BNB) breakdown during the evolution of tellurium neuropathy, ricin neuropathy, and Wallerian degeneration following nerve transection or nerve crush. Blood-nerve barrier permeability was assessed with a 4,000-molecular weight fluoresceinated dextran from three days to 19 weeks after onset of neuropathy. Blood-nerve barrier breakdown was present during the first two weeks in all four models of neuropathy. Restoration of the BNB to the dextran began within four weeks and was complete by 14 weeks in tellurium neuropathy, a model of demyelinating neuropathy characterized by rapid remyelination, and after nerve crush, a model of Wallerian degeneration characterized by rapid axonal regeneration into distal stump. In contrast, there was persistence of BNB breakdown beyond 14 weeks in ricin neuropathy, a model of neuropathy with no axonal regeneration or remyelination, and after nerve transection, a model of Wallerian degeneration characterized by minimal axonal regeneration into distal stump. We conclude from these data that alterations in the BNB over the course of neuropathy differ among various types of neuropathy, and that these alterations are dependent on the form of nerve fiber injury. The lack of regenerating or remyelinating axons in ricin neuropathy and after nerve transection may be responsible for the persistent BNB breakdown found in these neuropathies.

Schwann cell vulnerability to demyelination is associated with internodal length in tellurium neuropathy.

The frequency of demyelinated fibers in mixed nerve and cutaneous nerve and the relationship of the frequency of demyelination to internodal length were assessed in a model of tellurium neuropathy in the rat. Twenty-day-old Long-Evans rats were fed chow containing 1.25% elemental tellurium for seven days and subsequently killed at 34 or 41 days of age. Teased-fiber preparations revealed a higher frequency of demyelinated fibers in sciatic nerve (mixed nerve) than in sural nerve (cutaneous nerve). The frequency of demyelinated fibers was positively associated with internodal length in both nerves. The type of nerve (mixed or cutaneous) was not a significant predictor of the frequency of demyelinated fibers once internodal length had been taken into account. These data indicate that there is a hierarchy of vulnerability within the population of myelinating Schwann cells to tellurium toxicity, and that this hierarchy is related to internodal length. The hierarchy of vulnerability may reflect intrinsic differences among Schwann cells, such as the volume of myelin each cell is synthesizing and maintaining, or a gradient of unrecognized axonal abnormalities.

Trimethyltin retinopathy. Relationship of subcellular response to neuronal subspecialization.

Retinal neurons from rats acutely intoxicated with trimethyltin (TMT) were examined by light and electron microscopy to determine if there is a relationship between the subcellular response of a neuron to TMT and its morphologic subspecialization. Subcellular pathologic alterations were present in neurons from all three cellular layers of the sensory retina. However, the type and degree of subcellular response varied among the highly subspecialized neurons of the different retinal layers. Clusters of dense-cored vesicles and tubules were mainly limited to neurons of the ganglion-cell layer, large accumulations of dense bodies were mainly limited to neurons of the inner nuclear layer, and neuronal necrosis was mainly limited to the photoreceptor cells. The inner segment of the photoreceptor cell shared with the perikaryon of more conventional neurons a special vulnerability to TMT cytotoxicity. Our results suggest that the morphologic subspecialization of neurons affects the type and the degree of subcellular response to TMT.

Apolipoprotein E is released by rat sciatic nerve during segmental demyelination and remyelination.

Apolipoprotein E (apo E) is synthesized and released in greatly increased amounts by peripheral nerve following Wallerian degeneration; it has been suggested that this protein may function in the transport of degenerated myelin lipid. The purpose of this study was to determine if the amount of apo E released by rat peripheral nerve is increased following selective demyelination, in the absence of significant axonopathy. Using an immunoturbidimetric assay, release of apo E from excised sciatic nerve segments was measured during the phases of acute demyelination and remyelination caused by tellurium (Te) toxicity, during segmental demyelination in chronic lead (Pb) poisoning, and during Wallerian degeneration following nerve crush. Morphologic changes were examined in contralateral sciatic nerves by nerve-fiber teasing or by light and electron microscopy of transverse sections. As in previous studies, the amount of apo E released from the nerves was greatly increased following Wallerian degeneration due to nerve crush. In Te neuropathy, increased release of apo E was first detected on the fourth day of Te exposure, corresponding temporally to the acute onset of paralysis and segmental demyelination. Apolipoprotein E release rose steeply to a maximum of ten times the control values by day 9 and then gradually waned during the next five weeks, corresponding to a period of active remyelination and resolution of the neuropathy. In the demyelinating neuropathy of chronic lead poisoning, apo E release was increased four times over control animals after seven weeks of exposure, with less than 10% of teased fibers showing early paranodal demyelination and no evidence of remyelination.(ABSTRACT TRUNCATED AT 250 WORDS)

Axonal regeneration, but not myelination, is partially dependent on local cholesterol reutilization in regenerating nerve.

A recycling pathway in peripheral nerve permits cholesterol from degenerating myelin to be salvaged by macrophages and resupplied to myelinating Schwann cells by locally produced lipoproteins. A similar reutilization of cholesterol by regenerating axons has been proposed but not demonstrated. Neurites in culture, however, do take up cholesterol and cholesterol-containing lipoproteins, where these molecules are found to promote neurite extension. To test the requirement for cholesterol reutilization in axon regeneration and myelination, we examined 2 models of blocked intracellular cholesterol transport: 1) bone marrow transplants from Niemann-Pick C mice into wild-type recipient mice, and 2) imipramine treatment. Following nerve crush in these models, we found that unusually large, debris-filled macrophages appeared and persisted for many weeks. A morphometric analysis of regenerating nerves revealed that myelination proceeded at a normal rate (normal g-ratios), but that axon growth was retarded (decreased fiber numbers and diameters) in these animals. Cholesterol synthesis was elevated in these nerves, indicating that Schwann cells compensated for the decreased exogenous supply of cholesterol by up-regulating de novo synthesis to support myelination. These data indicate that Schwann cells are not dependent on cholesterol reutilization to support myelination, but that optimal axonal regeneration is dependent on a local supply of cholesterol.

Differential vulnerability of mixed and cutaneous nerves in lead neuropathy.

The prevalence of demyelinated fibers in mixed nerve (sciatic) and cutaneous nerve (sural) and the change in lead levels in various tissues over time were assessed in a model of lead neuropathy in the rat. Long-Evans rats were given drinking water containing 4% lead acetate and killed between one and 213 days of exposure. Lead levels in blood, brain, kidney, and femur increased over the 213-day period. Lead levels in sciatic nerve appeared to increase rapidly during the first few weeks of exposure and then decline to a lower plateau. The neuropathy was characterized by segmental demyelination and remyelination; neither axonal degeneration nor a microangiopathy was found. Sciatic nerve had a significantly greater prevalence of demyelinated fibers than sural nerve; the prevalence of demyelinated fibers was similar in proximal and distal sciatic nerve. The variable, brain-lead concentration times days on lead, which is an indicator of cumulative brain exposure, was the best predictor of the prevalence of demyelination. The differential involvement of sciatic and sural nerves in lead neuropathy may either indicate that Schwann cells myelinating different nerve-fiber populations have different susceptibilities to lead toxicity, or that lead preferentially enters sciatic nerve.

Mineralization of the basal ganglia detected by CT in Hallervorden-Spatz syndrome.

We studied a patient with autopsy-proven Hallervorden-Spatz syndrome (HSS) and the previously unreported finding of high-density lesions in the basal ganglia on CT. The diagnosis of HSS should be considered in a patient with dystonia and basal ganglia mineralization on CT.

Blood-brain barrier dysfunction in acute lead encephalopathy: a reappraisal.

Acute lead encephalopathy was induced in adult guinea pigs by administering daily oral doses of lead carbonate. During the development of the encephalopathy, the structural and functional integrity of the blood-brain barrier was evaluated with electron microscopy and tracer probes. Blood, cerebral gray matter, liver, and kidney were analyzed for lead, calcium, and magnesium content. The animals regularly developed an encephalopathy after four doses of lead. There were no discernible pathomorphologic alterations in the cerebral capillaries or perivascular glial sheaths. Furthermore, no evidence of blood-brain barrier dysfunction was demonstrated with Evans blue-albumin complex or horseradish peroxidase. Blood-brain barrier permeability to radiolead was not increased in the intoxicated animals. During the development of the encephalopathy there was a progressive rise in the lead concentration in all tissues. Concurrently, there was a significant rise in brain calcium. These results suggest that the encephalopathic effects of lead may be mediated directly at the neuronal level.

NGFR-mRNA expression in sciatic nerve: a sensitive indicator of early stages of axonopathy.

Expression of the low-affinity nerve growth factor receptor (NGFR) in the sciatic nerve (particularly Schwann cells) is high during development but is downregulated upon establishment of the mature axon-Schwann cell relationship. NGFR is re-expressed by Schwann cells if this relationship is altered by degeneration of axons (axotomy) or myelin (tellurium intoxication). To determine the sensitivity of NGFR expression to axonal injury, we have assayed NGFR-mRNA levels in proximal and distal regions of nerves exposed to the axonopathic agents acrylamide and isoniazid, as well as in proximal and distal stumps of axotomized nerves. NGFR-mRNA was elevated in all three models and correlated regionally with sites of axonal perturbation. In distal regions of acrylamide- and isoniazid-intoxicated nerves, NGFR-mRNA was elevated at least 2 days prior to visible signs of axonal degeneration as assayed by morphological techniques utilizing light microscopy. NGFR-mRNA was also elevated in proximal regions of axotomized and acrylamide-intoxicated nerves prior to signs of axonal degeneration. In these models, increased mRNA expression correlated with alterations in the size distribution of axonal cross sections. The common response in all of these situations indicates that NGFR expression, in addition to being a marker for axonal degeneration, is also a sensitive indicator of less profound perturbations in normal axon-Schwann cell interactions, including early stages of axonopathy. We suggest that assay for NGFR-mRNA may be utilized as a rapid and simple method (relative to more labor-intensive morphological methods) to screen for peripheral neurotoxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Tellurium causes dose-dependent coordinate down-regulation of myelin gene expression.

Exposure of developing rats to a diet containing elemental tellurium systemically inhibits cholesterol synthesis at the level of squalene epoxidase. At high tellurium exposure levels (> 0.1% in the diet), there is an associated segmental demyelination of the PNS. Low levels of dietary tellurium (0.0001%) led to in vivo inhibition of squalene epoxidase activity in sciatic nerve, and inhibition increased with increasing exposure levels. With increasing dose and increasing exposure times, there was an increasing degree of demyelination and increasing down-regulation of mRNA levels for myelin P0 protein, ceramide galactosyltransferase (rate-limiting enzyme in cerebroside synthesis), and HMG-CoA reductase (rate-limiting enzyme in cholesterol synthesis). Because these were all down-regulated in parallel, we conclude there is coordinate regulation of the entire program for myelin synthesis in Schwann cells. An anomaly was that at early time points and low tellurium levels, mRNA levels for HMG-CoA reductase were slightly elevated, presumably in response to tellurium-induced sterol deficits. We suggest the eventual down-regulation relates to a separate mechanism by which Schwann cells regulate cholesterol synthesis, related to the need for coordinate synthesis of myelin components. Levels of mRNA for the low-affinity nerve growth factor receptor (indicator of alterations in axon-Schwann cell interactions) and for lysozyme (marker for phagocytic macrophages) were both up-regulated in a dose- and time-dependent manner which correlated with the presence of segmental demyelination. Levels of mRNA coding for myelin-related proteins were down-regulated at low tellurium exposure levels, without demyelination or up-regulation of nerve growth factor receptor. This suggests the down-regulation is related to the tellurium-induced cholesterol deficit, and not to the loss of axonal contact associated with early stages of demyelination or to the entry of activated macrophages.

The neurotoxicity of intrahippocampal kainic acid injection in rats is not accompanied by a reduction of Timm stain.

Histopathological changes induced by intrahippocampal injections of low doses of kainic acid (17.5 ng/site) were investigated in rats. Kainic acid produced a selective loss of CA3 pyramidal and hilar neurons. The development of kainic acid-induced neuronal injury was not accompanied by any detectable loss of histologically demonstrable zinc as assessed by means of a modified Timm's sulphide-silver method. It is suggested that the selective injury of hippocampal neurons induced by kainic acid is not contingent on the release of zinc from mossy-fiber terminals.

Increased synthesis of membrane macromolecules is an early response of retinal neurons to trimethyltin intoxication.

We studied the synthesis and axonal transport of proteins and glycoproteins in the visual system of adult Long-Evans rats that had received 4 weekly doses of trimethyltin hydroxide (TMT, 4 mg/kg b. wt.) by gastric intubation. One week following the last dose, an in vitro assay was used to study the rate of incorporation of radioactive precursors into various macromolecules of isolated retinas. Retinas from TMT-treated rats showed increased apparent rates of synthesis, relative to retinas from control rats, for proteins [( 35S]methionine precursor) and glycoproteins [( 3H]fucose precursor). Gel electrophoretic analysis of newly synthesized proteins indicated that the increased synthesis was a generalized effect, i.e. it was not restricted to a select subset of proteins. The axonal transport of these macromolecules by retinal ganglion cells to axons (optic tract) and nerve endings (superior colliculus) was examined in vivo following intraocular precursor injection. The amount of material transported, relative to that synthesized in the retina, was not appreciably altered in TMT-treated rats, indicating that TMT did not selectively impair axonal transport. The biochemical changes were accompanied by minimal ultrastructural alterations and little neuronal necrosis in the retina. We suggest that TMT induces increased synthesis of membrane macromolecules in retinal neurons; this may reflect an early reactive (compensatory) response rather than a regressive (degenerative) response of retinal neurons to TMT. Our data do not support the hypothesis that TMT induces a functional impairment of neuronal endoplasmic reticulum or Golgi apparatus.

MR imaging and histologic features of capillary telangiectasia of the basal ganglia.

Capillary telangiectasias are being recognized with increasing frequency on MR imaging studies. Most are located in the brain stem and show slightly increased signal intensity on T2-weighted images, low signal intensity on T2*-weighted images (reflecting the presence of deoxyhemoglobin), and contrast enhancement. These findings are considered fairly typical for capillary telangiectasia, and pathologic correlation is not generally pursued. We present a case of a proven capillary telangiectasia in the basal ganglia. The imaging features of the lesion were identical to those described for capillary telangiectasias in the brain stem.

Pseudallescheria boydii infection of the brain: imaging with pathologic confirmation.

Pseudallescheria boydii is a rare opportunistic microorganism that usually infects immunosuppressed hosts. In this patient with cerebral infection by P boydii, imaging findings included enhancement of the ependyma of a lateral ventricle and of the caudate nucleus.

Diffuse leptomeningeal oligodendrogliomatosis: radiologic/pathologic correlation.

We present the radiologic and pathologic findings in a boy who presented with diffuse leptomeningeal enhancement and whose clinical status deteriorated over the course of 5 years. During this period, MR images showed progression of the enhancement in the subarachnoid spaces, formation of intraaxial cysts, and hydrocephalus. Autopsy findings revealed diffuse oligodendroglioma throughout the leptomeninges of the brain and spine, with no definite intraaxial focus. The radiologic and pathologic features of diffuse leptomeningeal oligodendrogliomatosis are reviewed.

Clinical and pathological features of an autosomal recessive neuropathy.

Two siblings are described, ages 49 and 45 years, having a distinct hereditary motor and sensory neuropathy (HMSN) with severe peroneal nerve involvement. The neuropathic symptoms began in childhood. Both patients have sensorineural deafness. The proband was found to have a cardiac conduction abnormality in the absence of known ischemic heart disease. Electrodiagnostic studies were consistent with a demyelinating peripheral neuropathy. The presence of parental consanguinity and absence of affected individuals in succeeding or preceding generations suggested that the sensorimotor neuropathy in this family is inherited in an autosomal recessive manner. The sural nerve of the proband had significant loss of myelinated fibers and demyelination but few regenerating myelinated fibers and no onion-bulbs. The pathological findings, while nonspecific, are not characteristic of the hypertrophic, neuronal or intermediate types of HMSN.

Metastasis of a rectal carcinoid to the posterior fossa.

We report the metastasis of a rectal carcinoid to the dura mater of the posterior fossa. The clinical presentation was unusual because of a 10-year latent period between resection of the primary rectal tumor and symptoms and signs of the posterior fossa metastasis; the radiological findings were atypical of a metastasis. Gastrointestinal carcinoids, apudomas, and the concept of the APUD endocrine cell family are reviewed.

Immunobiology of primary intracranial tumors. Part 7: Active immunization of patients with anaplastic human glioma cells: a pilot study.

Twenty patients with malignant gliomas were selected for active immunization within 4 weeks following surgery. Each patient had a Karnofsky Functional Rating equal to or greater than 70, a peripheral blood lymphocyte count equal to or greater than 1000 cells/cu mm, skin test responses to one or more of four recall antigens, peripheral blood T-cells equal to or greater than half that of control, and was not receiving steroid therapy at the time of entry into the study. Each patient received subcutaneous inoculations with one of two human glioma tissue culture cell lines (D-54MG or U-251MG) monthly, with 500 micrograms of bacillus Calmette-Guérin cell wall (BCG-CW) being included with the first inoculation. Each patient also received levamisole, 2.5 mg/kg 3 days per week every other week. Radiotherapy and chemotherapy with BCNU were begun after the first month of immunization. Follow-up evaluations included computerized tomography brain scans, neurological examinations, Karnofsky Functional Ratings, and studies of general immune competence. No evidence of allergic encephalomyelitis was noted clinically, nor was any gross or microscopic evidence of such pathology obtained upon autopsy of three of these patients. Serial studies of general immune competence showed no alterations from those previously described with non-immunized patients. Patients who were inoculated with the U-251MG cell line have had a longer survival time compared to those inoculated with the D-54MG cell line (p less than 0.0590) or compared to 58 historical cases of glioma patients treated with levamisole, radiation therapy, and chemotherapy alone (p less than 0.02).

Sequential changes in the permeability of the blood-nerve barrier over the course of ricin neuronopathy in the rat.

We examined the sequential changes in the permeability of the BNB to a 4000-molecular-weight fluoresceinated dextran over an 18-week course of ricin neuronopathy. Neuronopathy was produced by injecting ricin into the tibial nerve of 18-day-old Long-Evans rats; permeability of the BNB in proximal sciatic nerve was evaluated by fluorescence microscopy 12 hours to 18 weeks post injection. BNB breakdown occurred two days after ricin injection and continued to be present over the 18-week course of the experiment. Ultrastructural studies revealed that Wallerian-type axonal degeneration was present in proximal sciatic nerve one day post injection. The degeneration involved only a portion of the fibers and was unaccompanied by subsequent axonal regeneration or ricin-induced injury of Schwann cells, endothelial cells or perineurial cells. Immunocytochemical studies revealed that an increased number of endoneurial macrophages did not appear until after the BNB breakdown. We conclude that (1) breakdown of the BNB occurs early and is longlasting in ricin-induced neuronopathy; (2) the BNB breakdown is a consequence of ricin-induced axonal degeneration and is independent of regenerating axons, a systemic toxic effect of ricin on the BNB, or an influx of macrophages; and (3) toxicant-induced degeneration of less than half of the fibers in a nerve is sufficient to cause a localized, persistent breakdown of the BNB.