Mechanism of phospholipase A2-induced conduction block in bullfrog sciatic nerve. I. Electrophysiology and morphology

The effects of exogenously added phospholipase A2 (PLA2) and its hydrolytic products in isolated bullfrog sciatic nerve were investigated. Nerves were pretreated for 3 h with a dose of trypsin which did not affect conduction in order to enhance penetration of the added agents. Treatment of nerves with beta-glucosidase, neuraminidase or chymotrypsin had no effect on conduction. Whereas incubation of the nerves with normal Ringers for 2 h had no significant effect on conduction, incubation with PLA2 in Ringers caused decrements in the height of the compound action potential in a dose-related manner. In addition, incubation of the nerves with 10 mg/ml lysolecithin, arachidonic acid, or docosahexaenoic acid caused marked decrements in the height of the compound action potential. Electron microscopic analysis of nerves after each treatment which caused conduction block revealed varying levels of myelin damage. Although myelin was damaged at the paranodal and/or internodal region, depending on the agents used, the axonal membrane appeared to be intact at the ultrastructural level. It was concluded that the block in conduction resulting from PLA2 was due to the formation of lysolecithin and long chain polyunsaturated fatty acids.

Mechanism of phospholipase A2-induced conduction block in bullfrog sciatic nerve. II. Biochemistry

The biochemical changes associated with conduction block following exogenous application of purified phospholipase A2 to bullfrog sciatic nerves were investigated. Nerves were treated with concentrations of phospholipase A2 needed to produce at least a 50% decrease in the compound action potential after a 2-2 1/2 h incubation. This phospholipase A2-induced conduction block was associated with lipid hydrolysis, depletion of high energy phosphates and decreases in [3H]saxitoxin binding. Forty-two percent of the nerve phosphatidylcholine and 45% of the nerve phosphatidylethanolamine were hydrolyzed. [3H]Saxitoxin binding was decreased by 85% in association with conduction block attained with phospholipase A2 incubation. There were significant decrements in adenosine triphosphate levels (-58%) and in phosphocreatine levels (-78%), but no difference in the specific activities of these phosphate compounds. It is concluded that a number of mechanisms can account for the conduction failure resulting from phospholipase A2, including disruption of sodium channels needed for propagation of regenerative nerve impulses and the depletion of high energy phosphates needed to maintain ionic gradients.

The effect of dexamethasone on L-alpha-lysophosphatidyl choline (lysolecithin)-induced demyelination of the rat spinal cord

Adult male Sprague-Dawley rats were injected intraspinally with 2 microL of 1% lysolecithin to induce demyelination. This was followed by systemic treatment with dexamethasone acetate for two weeks. Control groups were injected with lysolecithin but not treated. The animals were perfused at 8, 12, 28, and 60 days postoperatively, and the spinal cords were processed and examined histopathologically. The intraspinal injection of lysolecithin produced a focal area of primary demyelination followed by remyelination. In the steroid-treated groups, there was a suppression of the mononuclear phagocytic response, accompanied by slow clearance of the disrupted myelin sheaths and an apparent reduction in lesion size. Remyelination was substantially retarded in comparison with the controls. The findings suggest that steroids interfere with the process of remyelination, as they are known to do with myelination during development. Thus, dexamethasone appears to have a dual effect, decreasing demyelination but delaying remyelination.

Treatment of pathologic laughing and weeping with amitriptyline

Patients with bilateral forebrain disease may commonly manifest the syndrome of pathologic laughing and weeping. We investigated the efficacy of low-dose amitriptyline in 12 patients in whom this syndrome was a consequence of multiple sclerosis. In a double-blind crossover study comparing amitriptyline with placebo, eight patients experienced dramatic and significant improvement with amitriptyline (P = 0.02). The mean dose of amitriptyline was 57.8 mg per day and did not exceed 75 mg per day in any patient. Concurrent measurements of depression showed no change during the study. We conclude that amitriptyline is effective in the treatment of this disturbance of affective expression, and that this effect is distinct from the antidepressant effect of the medication.

Effect of macrophage inactivation on the neuropathology of lysolecithin-induced demyelination

The effect of macrophage inactivation on lysolecithin-induced demyelination was studied. Adult rats were pretreated with a single intraperitoneal dose of 200 mg silica quartz dust, which selectively blocks the activity of circulating monocytes. Surgery was performed the following day and 2 microliters of 1% lysolecithin were injected intraspinally. The animals were perfused with aldehydes at 8 to 60 days postoperatively. Tissues were examined by optical and electron microscopy. The injection of lysolecithin produced a localized demyelinating lesion. Myelin debris in controls was phagocytosed by invading macrophages. Axons within the lesion appeared denuded. At later stages remyelination occurred. When animals were pretreated with silica, the macrophage response was remarkably reduced. The clearance of collapsed myelin was delayed. Accumulation of fluid within the sheaths resulted in tissue oedema and persistent spongiform changes. At 28 and 60 days postoperatively, increased fibrillary astrogliosis was observed but did not appear to interfere with remyelination. The findings of this study suggest that (a) active participation of macrophages is essential for the attainment of demyelination in the lysolecithin model and (b) treatment with silica prevents complete demyelination but has no apparent effect on remyelination.

Characterization of muscarinic cholinergic receptors in the brains of copper-deficient rats

In order to assess a possible role for copper as a regulator of muscarinic receptors in vitro, the receptor was characterized in rats made copper deficient by a dietary regimen. In forebrain regions there was a decrease in both the affinity of the receptors for [3H]-1-quinuclidinyl benzilate and the density of receptors in the copper-deficient animals compared with control animals. Copper treatment in vitro of homogenates from deficient animals did not reverse the in vivo effects on antagonist binding but, rather, decreased receptor occupancy and ligand affinity in a manner similar to copper treatment of control homogenates. Minimally deficient rats displayed very similar changes in receptor properties compared with the more severely deficient animals. Minimal copper deficiency produced robust effects on the binding of agonists, increasing ID50 and derived dissociation constants. The addition of copper to the assay medium caused an apparent reversal of the in vivo effect of copper deficiency on agonist binding, decreasing ID50 and derived dissociation constants to values near those observed with homogenates from normal animals in the presence of copper. Since copper deficiency has dramatic effects on both receptor number and the binding of agonists to muscarinic receptors in the central nervous system, it is suggested that copper, because of its ability to form complexes with some proteins, may have an endogenous role in the regulation of the receptor.

Immunocytochemistry of myelin basic proteins in adult rat oligodendroglia

Immunocytochemical demonstration of myelin basic protein (MBP) in oligodendroglia of the developing rat and human central nervous system has been reported. However, reaction with MBP antiserum was detectable only prior to and during the early phase of myelination. The lack of reaction with still actively myelinating and mature oligodendroglia has been puzzling. We report here that by the use of mild fixation and by a modification of the staining technique previously used for detection of MBP on vibratome sections, staining of oligodendroglia in sections of adult rat brain has been achieved.

Ultrastructural evidence for phagocytosis by oligodendroglia

Although the phagocytic ability of brain macrophages and astrocytes is well established, the question of whether oligodendrocytes may become phagocytic remains controversial. Observations reported here indicate that oligodendroglia may become activated and ingest degenerating or foreign material in vivo following experimental injury to the central nervous system.

Isolation of model soluble immune complexes in the fluid phase by monoclonal anti-IgG-ferritin antibodies

Ferritin conjugates of monoclonal IgG anti-human gamma chain (anti-IgG-F) were reacted with soluble heat aggregates of IgG (A-IgG) and with soluble DNA-anti-DNA complexes to increase the S rate of the model soluble immune complexes (ICx) and thus facilitate isolation of ICx in the fluid phase and provide an immunochemical marker for subsequent ultrastructural analysis. A-IgG appeared as globular or curvilinear structures with individual IgG molecules arranged in a random fashion. The technique appears promising for characterization of other soluble ICx.

Mature oligodendrocytes. Division following experimental demyelination in adult animals

Primary demyelination can be caused by injury to oligodendrocytes or to the myelin sheaths that these cells maintain. Although remyelination does take place in multiple sclerosis (MS), its possible role in the recovery from MS attacks has been inadequately considered, partly because of the belief that oligodendrocytes, once destroyed, cannot be replaced in the adult. The injection of lysolecithin into the mouse spinal cord causes primary demyelination, followed by the generation of new oligodendrocytes and remyelination. By using a pulse label of tritiated thymidine, this electron-microscopic autoradiographic study demonstrated a source of these regenerated oligodendrocytes. The replacement of oligodendrocytes can occur through the division of preexisting oligodendrocytes. This is the first demonstration that mature oligodendrocytes are capable of dividing in older animals. These results lend support to recent observations of an apparent proliferation of these cells in an active MS lesion. We believe that the ability of mature oligodendrocytes to divide and to remyelinate axons in the adult may play an important role in the recovery from MS attacks.

The fine structure of macrophages in lysolecithin-induced demyelination: a freeze-fracture study

Focal injection of lysolecithin into the thoracic spinal cord was used to induce experimental demyelination in rats. The macrophages which invaded the demyelinating area to phagocytose the myelin breakdown products were examined by electron microscopy using conventional thin-section and freeze-fracture techniques. The cells had the typical foamy cytoplasm characteristic of lipid macrophages. In freeze-fracture preparations, the P-face of the plasmalemma had scattered 10-18 nm round to oval or elongate particles. The cytoplasm was filled with phagocytic vacuoles containing myelin debris. Occasionally, membranous connections could be demonstrated between lysosomes and phagocytic vacuoles. The debris in the vacuoles varied in structure from material with a normal myelin periodicity to partially digested lamellated structures and pseudocrystalline structures to homogeneous-like, lipid-filled vacuoles. These patterns appeared to represent successive stages in the digestion of the ingested myelin.

An ultrastructural study of cortical remodeling in cytosine arabinoside induced granuloprival cerebellum in tissue culture

Mouse-derived cerebellar explants were exposed for 5 days to cytosine arabinoside, an inhibitor of deoxyribonucleic acid synthesis. They were then maintained in normal nutrient medium until fixation for electron microscopy at 15-20 days in vitro. The cerebellar cortex lacked granule cells, but Purkinje cells, Golgi neurons and a few basket and stellate cells survived. Astrocytes and oligodendrocytes were diminished in number and myelination was absent. Purkinje cell recurrent axon collaterals increased in number and formed synapses with the surviving cortical neurons and their processes. The ultrastructural alterations that occurred in the cytosine arabinoside-treated cultures were consistent with an interpretation of cortical remodeling in which Purkinje cell axon collaterals were the dominant inhibitory elements.

A diagnostic index of active demyelination: myelin basic protein in cerebrospinal fluid

We have developed a radioimmunoassay to measure a specific neurological component, the basic protein of myelin, and have used this test for assessing this component in spinal fluid. The levels of basic protein in spinal fluid correlate closely with the clinical activity of multiple sclerosis; therefore the test can be used for objective evaluation of disease activity in patients with that disorder. Moreover, it is a useful adjunct in the diagnosis of multiple sclerosis and evaluation of potential therapy. In addition, the test is helpful in diagnosing other diseases in which acute breakdown of myelin occurs, especially leukoencephalopathy resulting from irradiation and chemotherapy for treatment of leukemia in children.

Electron microscopic studies of cerebrospinal fluid sediment in demyelinating disease

Cerebrospinal fluid specimens from 31 patients with multiple sclerosis (MS) and 2 with progressive multifocal leukoencephalopathy (PML) were subjected to ultracentrifugation, and the resulting pellets were examined in an electron microscope. Cell types seen in the pellets included lymphocytes, occasional plasma cells, polymorphonuclear leukocytes, monocytes, eosinophils, lipid-laden macrophages, and fibroblasts. The most interesting noncellular elements were extracellular myelin fragments, recognizable by their characteristic alternation of major dense lines and intraperiod lines. Myelin fragments were seen in the CSF from 7 of 9 patients with MS in exacerbation involving areas other than the optic nerve. These fragments were not observed in 4 specimens from patients with acute attacks manifested by optic neuritis. Myelin fragments were present in 1 of the 2 patients with PML. These observations indicate that a portion of the myelin destruction seen in MS and PML occurs extracellularly, with release of myelin fragments and degradation products into the CSF.

Studies of cultured human and simian fetal brain cells. II. Infections with human (BK) and simian (SV40) papovaviruses

Both simian virus 40 (SV40) and BK viruses infected and lysed not only oligodendroblasts and astrocytes, but also neuroblasts and epithelioid or mesenchymal cells in cultures of fetal brain cells derived from human, rhesus, and cynomolgus hosts. Lytic infections of these four cell types differed ultrastructurally in the amount and arrangement of virions in the nucleus, the extent of nuclear membrane redundancy, the presence of nuclear virion arrays, and the amounts of virions in the cytoplasm. However, major differences were not noted between SV40 and BK viruses, nor between different species of origin or region of brain explanted. Modified astrocytic cells persisted in cultures from all three sources after infection by either virus. These cells stained for glial fibrillary acidic protein (GFAP) and polyomavirus tumour (T) antigen, but did not subculture indefinitely.