Alteration of 5'-nucleotidase and Na+,K+-ATPase in central and peripheral nervous tissue from dysmyelinating mutants (jimpy, quaking, trembler, shiverer, and mld). Comparison with CNPase in the developing sciatic nerve from trembler

CNPase activity in myelin from adult rat brains after prolonged lead exposure in vivo

The present study investigated the sensitivity of rats cerebral myelin to prolonged toxicity of lead (Pb) that imitates environmental exposure to this metal. The results indicated that 90 days exposure of young adult rats to lead in drinking water affects the morphology of myelin sheaths, expressed in disintegration of its multilamellar structure. Both, the protein content and the activity of the myelin-specific enzyme CNPase (2',3'-cyclic nucleotide 3-phosphodiesterase), were lowered. The Michaelis-Menten kinetic for CNPase in myelin obtained from control and Pb-treated rats was different. Km increased and Vmax decreased when compared to controls. Observed disturbances in enzyme activity may be one of the potential reasons of the ultrastructural changes. It is thus tempting to speculate that Pb may be considered as a one of the factors contributing to demyelinating diseases.

Acute lead intoxication in vivo affects myelin membrane morphology and CNPase activity

The aim of the present study was to assess the sensitivity of central nervous system myelin to acute Pb-toxicity in an animal model, that imitates lead toxicity in occupationally exposed workers, or in occasional incidents of poisoning. Our results indicated that in vivo acute lead intoxication affected both the morphology of myelin and enzymatic activity of the myelin marker, CNPase (2'3'-cyclic nucleotide 3'-phosphodiesterase). The multilayered structure of myelin sheaths was regionally disturbed, with loosely arranged membranes or ovoid-shaped swollen fragments. The activity of CNPase was diminished and Michaelis-Menten kinetics showed a decreased affinity and lower velocity of the enzyme. These data suggest that the disturbances in CNPase activity may contribute, in some extent, to the changes in myelin morphology observed in acute Pb-intoxication.

In vivo effects of deltamethrin on some biochemical parameters of carp (Cyprinus carpio L.)

Thein vivo effects of deltamethrin (DM) on the blood sugar level, the acetylcholinesterase (AChE, EC 3.1.1.7) activities of the blood serum and various organs (heart, liver and intestine), the lactate dehydrogenase (LDH, EC 1.1.2.3), glutamic-oxaloacetic transaminase (GOT, EC 2.6.1.1), and glutamic-pyruvic transaminase (GPT, EC 2.6.1.2) activities of the blood serum, the adenosine triphosphatases (EC 3.6.1.3; Na(+)/K(+)-ATPase and Mg(2+)-ATPase) activities of the erythrocyte plasma membrane and the catalase (EC 1.11.1.6) activity of the liver were examined throughout 96 h in adult carp (Cyprinus carpio L.) Two sublethal concentrations, 1.0 and 1.5 µg/l of deltamethrin, were used. All fish survived the experiment except one, in an aquarium containing 1.5 ppb of DM, which died after 72 h.The AChE specific activity was significantly inhibited in the heart and intestine after 96 h at both concentrations compared to that in the control animals (P<0.05, Student'st-test), while there was no detectable difference between the two treatment. At the same time there was no detectable change in the liver. In the serum, the AChE activity almost remained unchanged; the only significant decrease could be measured after 96 h at 1.5 µg/l deltamethrin concentration. The blood glucose content exhibited interesting changes: after 24 h fish exposed at 1 µg/l DM seemed to be stressed, although this increase was not significant. When these fish became used to the new conditions (in practice this meant the presence of DM), the glucose level decreased, especially after 72 h. At the same time the control animals kept in similar circumstances showed a small insignificant decrease. Meanwhile fish in aquaria containing 1.5 µg/l DM reacted to the treatment with an increased blood glucose level after 48 h, and this did not change until the end of the treatment. The Na(+)/K(+)-ATPase activity decreased in a dose-dependant manner, while Mg(2+)-ATPase was less affected. A small increase in LDH level was observed, indicating damage of different muscle tissues. However, this phenomenon appeared only with the small dosage after 24 h (P<0.05). It has to be mentioned that the individual values varied to a large extent among of the eight fish.The GOT activities of the serum increased during the treatment. However, significant changes were only expressed after 72 and 96 h at 1 µg/l DM concentrations (P<0.01 andP<0.05), and after a similar long treatment at the high dosage (P<0.05, 72 and 96 h). The GPT did not change significantly in aquaria containing 1 µg/l DM. The only larger increase was measured after 96 h at 1.5 µg/l DM concentration (P<0.05). The catalase activity in the liver of treated carp remained practically at the same level compared to that in control fish.All these changes (concerning the primary effects of this compound) demonstrate the effect of DM on different fish enzymes, at low concentrations under laboratory conditions, which might be useful in practice for biomonitoring using fish.

Simultaneous changes in lipid composition, fluidity and enzyme activity in piglet intestinal brush border membrane as affected by dietary polyunsaturated fatty acid deficiency

The effects of dietary polyunsaturated fatty acid (PUFA) deficiency on intestinal brush border membrane (BBM) fluidity, lipid composition and 5'-nucleotidase activity were examined in piglets. Cholesterol/phospholipid and sphingomyelin (SM)/phosphatidylcholine (PC) ratios were unaffected. However, fluidity was decreased in the external regions and also tended to decrease in the core of the PUFA-deficient pig membrane lipid bilayer. Therefore, the change in the membrane physical properties seemed to be due to the large diet-induced alteration in the phospholipid (PL) fatty acid composition and to the concomitant decrease in PC and increase in phosphatidylserine levels. In the membrane total PL, the arachidonic acid level was slightly lowered, while linoleic, eicosapentaenoic and docosahexaenoic acid levels markedly decreased. PC was mainly concerned by the altered distribution of unsaturated fatty acids, but not SM. However, a significant decrease in (n-6)/(n-3) ratio occurred in the latter. These structural changes were associated with a higher 5'-nucleotidase activity in the intestinal BBM of PUFA-deficient as compared to control piglets.

Thioridazine induces lipid peroxidation in myelin of rat brain

In this study, the oxidative effect of the commonly used phenothiazine, thioridazine, on brain tissue has been investigated. Thioridazine (0.1 and 0.5%) supplemented in pellet diet (w/w), produced a significant increase (P < 0.001) in levels of myelin lipid peroxide, after 3 weeks of treatment. Besides myelin, there was a 2-fold increase in the mitochondrial lipid peroxides, as a result of treatment with thioridazine. However, these elevated levels of lipid peroxides returned to normal after withdrawal of thioridazine for 2 weeks. Myelin-associated enzyme activities of Na+,K(+)-ATPase and 5'-nucleotidase became inhibited by 20-25%, but CNPase activity was unaffected. Studies of in vitro lipid peroxidation on purified myelin from untreated rats suggested that extensive lipid peroxidation of myelin in thioridazine-treated rats could underlie inhibition of the myelin enzymes. Morphological studies revealed little or no structural alterations in myelin, produced by thioridazine. These studies suggest that thioridazine induces a reversible lipid peroxidation in myelin, that could result in functional alterations of the myelin-associated enzymes, during use of this drug.

Distribution of P0 protein and the myelin-associated glycoprotein in peripheral nerves from Trembler mice

The Trembler mouse has a dysymelination of peripheral nerves that includes hypomyelination, failure of myelin compaction, and demyelination/remyelination. We have localized the myelin proteins P0 and myelin associated glycoprotein in Trembler peripheral nerve and correlated their distributions with the ultrastructure of myelin internodes. Immunocytochemically, myelin-associated glycoprotein was localized in Schwann cell periaxonal membranes, Schmidt-Lanterman incisures, paranodal loops, and internal and external mesaxons. P0 staining was located over compact myelin and regions of Schwann cell cytoplasm rich in Golgi membranes. An unusual abundance of small, P0-stained, Golgi-related vesicles was found in some Schwann cells. P0 protein was also detected in multiple spiral wraps of myelin-associated glycoprotein-positive mesaxon membranes. At some sites the periodicity of the myelin membranes was intermediate to that found in mesaxon membranes and compact myelin. The distance between apposing extracellular leaflets was similar to that found in mesaxon membranes, while the cytoplasmic leaflets were fused but twice as thick as normal major dense lines. These intermediate membranes were stained by P0 and myelin-associated glycoprotein antiserum. These studies suggest that altered transport and/or translocation of P0 and myelin-associated glycoprotein results in defective myelin compaction in Trembler peripheral nerve.

Evidence for the biosynthesis of ceramide-phosphoethanolamine in brain synaptic plasma membrane vesicles and in sciatic nerve microsomes from normal and Trembler mice

Synaptic plasma membrane vesicles (SPMV) from brains of normal and Trembler mice synthesized ceramide-phosphoethanolamine, and analogue of sphingomyelin from phosphatidylethanolamine (PE) and ceramide. The rate of this synthesis (6 nmol/mg of protein/h) and the (Na+)-K+)ATPase activity (about 70 mumol Pi per mg of protein/h) were very similar in normal and Trembler. The synthesis increased as a linear function of protein when endogenous PE was taken into account, but the addition of exogenous ceramide was without effect. Likewise, PE was the donor of phosphoethanolamine for the synthesis of the ceramide-phosphoethanolamine in normal and Trembler mouse sciatic nerves and this synthesis was 3.5 times greater in the mutant than in controls.

CSF beta-endorphin, HVA and 5-HIAA of dementia of the Alzheimer type and Binswanger's disease in the elderly

Cerebrospinal fluid (CSF) concentration of beta-endorphin (beta-Ep), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) was measured in 15 patients with dementia of the Alzheimer type (DAT) and in 16 patients suspected of having Binswanger's disease (BD) by MRI, which sometimes resembles DAT clinically. These were classified into three stages according to severity of dementia, Stage 1 (mild dementia)-Stage 3 (severe dementia). CSF levels of HVA decreased significantly in severe dementia, but the level of 5-HIAA did not correlate with dementia severity in both dementia groups. beta-Ep levels did not differ significantly between any stages of DAT, and among controls. beta-Ep levels, however, in BD Stage 1 (27.5 +/- 5.9 pg/ml) were significantly higher (p less than 0.05), but level in Stage 3 (6.7 +/- 2.0) was significantly lower (p less than 0.001) than in the controls (19.2 +/- 4.5). These results suggest that CSF beta-Ep may depend on the cause of dementia rather than severity of dementia, and could possibly distinguish the closely resembling BD from true DAT.

Developmental expression of the P0 glycoprotein and basic protein mRNAs in normal and trembler mutant mice

Mice affected by the autosomal dominant Trembler mutation exhibit a severe hypomyelinization of the PNS. Previous biochemical studies have shown that the accumulation of the major PNS myelin proteins, P0 and myelin basic protein (MBP), is strongly diminished in Trembler sciatic nerves during postnatal development. We performed Northern blots which showed that the size of mRNA species for P0 and MBP in normal and mutant mice are indistinguishable. Densitometric analysis of Northern blots showed that, in normal mice, the proportion of P0 mRNA increases up to the 12th day, then decreases slowly. At day 40, the proportion is 60% of the maximal value. In the mutant, the proportion of P0 mRNA increases up to the 12th day and then decreases much faster than in the control. At days 12 and 40, the P0 mRNA proportion measured in Trembler sciatic nerves represents only 40% and 7%, respectively, of the proportion measured in control littermates. The MBP mRNA proportion in the normal mice increases up to the 16th day, and then decreases to attain 45% of the maximum level at day 40. In the Trembler mouse, there is a maximum level at day 12, representing 25% of the normal level, but the MBP mRNA is barely detectable at days 8 or 40. Thus, these data seem to indicate that in the Trembler sciatic nerves, the proportions of P0 and MBP mRNAs are too small to allow the synthesis of normal levels of the corresponding proteins.

Po, MBP, histone, and DNA levels in sciatic nerve. Postnatal accumulation studies in normal and trembler mice

We studied the quantitative changes in proteins (total, Po, MBP, and histones) and DNA from sciatic nerves of normal and Trembler mice during postnatal development. Polyacrylamide gel electrophoresis and immunoblotting procedures allowed an accurate characterization of Po, MBP, and histones, as well as the comparison of their respective amounts from d 2 to d 120 after birth. It was found that 1. The immunoblotting procedure ascertains the presence of Po in the sciatic nerve of Trembler. In the 2-d-old mice, Po is detected in essentially similar amounts in Trembler and normal PNS, whereas its level in adult mutant sciatic nerves is never greater than 20% of the control. The sharp increase in Po levels observed during the third week in the normal nerves is not observed in those of the mutant; 2. MBP species are at most 4% of the control in the 10- to 12-d-old Trembler mice, whereas they were not detectable in adult nerves. The distribution of the different MBP species is the same in both mutant and control mice; 3. In normal mice, Po and MBP accumulate at similar rates, but the 14 kDa MBP accumulates faster than the 18.5 kDa MBP; and 4. Histone and DNA contents decrease 3- to 5-fold in normal nerves, whereas they remain constant, or increase slightly, in the mutant.

Myelin composition and activities of CNPase and Na+,K+-ATPase in hypomyelinated "pt" mutant rabbit

A disorder of CNS myelination was found in paralytic tremor ("pt") rabbits. The condition is inherited in a sex-linked recessive mode. Ultrastructurally, an obvious myelin deficiency with aberration of myelin sheath formation is observed. The yield of myelin isolation was reduced to 20-30% of control. Myelin isolated from 4-week-old "pt" rabbits contained reduced amounts of galactosphingolipids and of several myelin protein markers. Moreover, myelin basic protein, analyzed by two-dimensional gel electrophoresis, showed a deficit in its more basic components. All these facts suggest a delay in myelin maturation. Ganglioside content was increased as well as Na+,K+-ATPase specific activity. 2',3'-Cyclic nucleotide phosphodiesterase (CNPase) specific activity was the same in "pt" as in control myelin but differed by having greater sensitivity to detergent activation.

Monospecific antiserum against 5'-nucleotidase from Torpedo electric organ: immunocytochemical distribution of the enzyme and its association with Schwann cell membranes

The cellular and subcellular distribution of 5'-nucleotidase in tissues of the electric ray Torpedo marmorata has been investigated by means of an antiserum raised against the native enzyme purified from the electric organ. As revealed by immunohistochemistry the enzyme is associated with the surface of the axons of the electric nerves and of spinal nerves. Using the post-embedding colloidal gold technique at the electron-microscopical level 5'-nucleotidase could be located at the plasma membrane of the Schwann cells including the myelin and the fine processes covering the terminal axon ramifications. Also the perineurial sheath of the axons inside the electric organ is 5'-nucleotidase positive. The plasma membrane of the axon and the terminal axon region or the postsynaptic membrane do not contain 5'-nucleotidase. Immunoprecipitation studies using polyacrylamide beads suggest that the ecto-Ca2+- or -Mg2+-adenosine 5'-triphosphatase previously ascribed to synaptosomes of the Torpedo electric organ is not associated with the same membranes as 5'-nucleotidase. Within the electric organ the dorsal plasma membrane of the electroplaque cell, blood capillaries and the connective tissue layer surrounding the columns of electroplaque cells also bind the antibodies. In central nervous tissue solely blood vessels show immunofluorescence. Within the electric lobe both the surface of the electromotor neurons as well as the myelinated axons giving rise to the electric nerve are negative. This also applies to the axons of the optic nerve suggesting that the antiserum is Schwann cell specific, and does not bind to a potential oligodendroglial 5'-nucleotidase. In peripheral tissue the surface of skeletal muscle fibres as well as that of individual myofibrils bind the anti-5'-nucleotidase antibodies. Our results demonstrate that the Schwann cell plasma membrane, including myelin, contains 5'-nucleotidase and that one can distinguish by means of a specific antiserum between Schwann cell and oligodendroglia plasma membranes. The functional significance of the association of 5'-nucleotidase with Schwann cells along the entire surface of axons including the synaptic region as well as with other parts of the electric tissue is discussed regarding its catalytic activity and also the possibility that this surface glycoprotein may be involved in mediating cellular interactions.

(Na+ + K+)-adenosinetriphosphatase in the brain of Shiverer (Shi/Shi) mice

The myelin-deficient Shiverer (Shi/Shi) mutant mouse may be a useful model in assessing the dependence of brain (Na+ + K+)-ATPase concentration and composition on myelin membrane formation. Brain microsomal membranes from age-matched control (+/+) and Shiverer (Shi/Shi) mice were fractionated by differential centrifugation and sucrose gradient sedimentation. No reduction in (Na+ + K+)-ATPase specific activity was measured in whole homogenates, high- and low-speed fractions or gradient fractions from brains of Shi/Shi mice as compared to those of +/+ mice. In addition, sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting with antisera specific for mouse brain (Na+ + K+)-ATPase revealed no significant difference in catalytic subunit composition between fractions of +/+ and Shi/Shi brains. The similar results obtained for both +/+ and myelin-deficient Shi/Shi mice suggest that myelin contributes little to total brain (Na+ + K+)-ATPase.

5'-nucleotidase localization in the brains and spinal cords of adult normal and dysmyelinating mutant (shiverer) mice

Immunocytochemical staining with the antibody against mouse liver 5'-nucleotidase revealed 5'-nucleotidase antigenicity in myelinated fibers in the brains and in myelinated fibers and some interfascicular oligodendroglia in the spinal cords of normal adult mice. Although the 5'-nucleotidase specific activity in adult shiverer mouse CNS tissue homogenates had been shown to be normal, immunocytochemical staining with anti-mouse-5'-nucleotidase could be demonstrated in CNS tissue sections from only 2 out of 10 of the mutant animals. In tissue from these animals the staining, which was relatively faint, was localized specifically to cell-bodies, usually arranged in rows, and to material oriented parallel to nerve fibers. This pattern of immunostaining with anti-5'-nucleotidase resembled the immunostaining with anti-carbonic anhydrase but not with anti-glial-fibrillary-acidic-protein. This suggested that the rows of cells were oligodendrocytes, not astrocytes, and that the material parallel to nerve fibers might consist of oligodendrocyte processes wrapped loosely around axons. The antibody against rat 5'-nucleotidase, as distinguished from mouse, immunostained only the blood vessels in the shiverer mouse CNS, a finding similar to a previous observation in the normal mouse CNS. From these findings it was inferred that the primary loci of 5'-nucleotidase in the shiverer mouse CNS were interfascicular oligodendrocytes, their processes, and blood vessels, and in the normal mouse CNS, the myelin in some tracts, the blood vessels, and some interfascicular oligodendrocytes.

Are anti-brain antibodies in multiple sclerosis directed to myelin basic protein? Studies employing the Shiverer mouse mutant

The dysmyelinating mouse mutant Shiverer has a severe and relatively selective deficiency of myelin basic protein (MBP) in the central and peripheral nervous system. Nevertheless, Shiverer brain and control-mouse brain showed similar antigenic titers when tested by a complement fixation assay against a panel of 14 multiple sclerosis (MS) sera and 6 MS CSF samples known to represent several specificities of antibrain antibodies. By analogy with experimental allergic encephalomyelitis, a sensitization to MBP has been proposed in MS. Our results, however, show that antibodies to other CNS antigens are quantitatively more important in this disease.

Myelin-associated glycoprotein and other proteins in Trembler mice

The myelin-associated glycoprotein (MAG) and other myelin proteins were quantitated in homogenates of whole sciatic nerve from adult and 20-day-old Trember mice. In the nerves of adult mice, the concentration of MAG was increased from 1.1 ng/micrograms of total protein in the controls to 1.4 ng/micrograms protein in the Tremblers. By contrast, the concentrations of P0 glycoprotein and myelin basic proteins were reduced to 27% and 20% of control levels, respectively. Immunoblots demonstrated that P2 was also greatly reduced in the Trembler nerves. The specific activity of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) was 65% of the control level. Immunoblot analysis showed that MAG had a higher than normal apparent Mr in the sciatic nerves of the Trembler mice, but its apparent Mr was normal in the brains of these mutants. In 20-day-old Tremblers, the P0 and myelin basic protein were reduced slightly less to about 40% of the level in the nerves of age-matched controls. CNP and MAG levels were not significantly different from those in controls, and MAG exhibited a shift toward higher apparent Mr similar to that in the adults. The maintenance of high MAG levels despite the severe deficit of myelin, as reflected by the decrease of the major myelin proteins, is consistent with the immunocytochemical localization of MAG in periaxonal Schwann cell membranes, Schmidt-Lantermann incisures, lateral loops, and the outer mesaxon and its absence from compact myelin. The abnormal form of MAG in the peripheral nervous system (PNS) of the Trembler mice may contribute to the pathology in this mutant.

Metabolic alterations of endoneurial lipids in developing trembler nerve

In vitro incorporation of [14C]acetate into desheathed sciatic nerve (endoneurium) was studied in developing normal and mutant trembler mice. The total uptake of [14C]acetate peaked 6 days after birth and decreased thereafter for both normal and trembler mice. Substantially less [14C]acetate (approximately 50% of normal) was incorporated in trembler mouse as early as 3 days after birth. In 3 and 6 day-old trembler mice, proportionately less [14C]acetate was incorporated into phospholipids and cerebrosides and more was incorporated into cholesterol. From 9 days, however, less [14C]acetate was incorporated into cholesterol of trembler compared to normal nerve. At later times (greater than or equal to 20 days), the proportion of [14C]acetate in both phospholipids and cerebrosides of trembler nerve was increased above that of controls. Throughout development, the relative incorporation of [14C]acetate into triacylglycerol and cholesteryl esters was about two times higher in trembler than in normal mice. In normal nerve, the 14C-label in free fatty acids increased (4-25%) progressively with age. In contrast, this incorporation in trembler nerves remained constantly low (less than 7%). Morphologically, the nerves of trembler mouse are markedly hypomyelinated. The abnormal myelin sheath undergoes cycles of breakdown and partial regeneration. Thus, the biochemical profile of extended active but perturbed lipid metabolism may provide a basis for the morphologic findings of continued active but ineffective myelination in trembler peripheral nerve.

Alteration of sulfatide synthesis in control and Trembler mice during Wallerian degeneration and remyelination

Sulfatide synthesis from sulfate is much greater in the peripheral nerves of the Trembler mouse. After nerve transection, during Wallerian degeneration, this synthesis rate drops down very rapidly in both normal and Trembler mice. Twenty-four hours after permanent transection, the rate of synthesis is reduced by 80% in the mutant and 50% in the normal mouse. Four days after transection, the synthesis rate in the Trembler is only 9% of that observed in intact nerves, and 21% of that in the intact nerves of normal animals. After 5 d the synthesis remains constant. Thus, enhanced synthesis of sulfatides in the Trembler mouse is probably not caused by Wallerian degeneration. After crush of the sciatic nerve, the synthesis rate decreases very rapidly in the normal mouse as it does after permanent transection. But during regeneration, from the 7th day, it rises dramatically and 14 d after crush, a 2.5-fold increase in the synthesis rate is observed, compared to that in the contralateral control nerve. This synthesis rate returns to normal 1 mo after crush. In the Trembler, the synthesis decreases for 2 d after crush and increases from then on, eventually reaching the value of the contralateral control Trembler nerve within 2 mo. In the mutant there is no prominent peak of sulfatide synthesis during regeneration.

Alterations in the fatty acid composition of rat brain cells (neurons, astrocytes, and oligodendrocytes) and of subcellular fractions (myelin and synaptosomes) induced by a diet devoid of n-3 fatty acids

Rats were fed through four generations with a semisynthetic diet containing 1.0% sunflower oil (6.7 mg/g n-6 fatty acids, 0.04 mg/g n-3 fatty acids). Ten days before mating, half of the animals received a diet in which sunflower was replaced by soya oil (6.6 mg/g n-6 fatty acids, 0.8 mg/g n-3 fatty acids) and analyses were performed on their pups. Fatty acid analysis in isolated cellular and subcellular material from sunflower-fed animals showed that the total amount of unsaturated fatty acids was not reduced in any cellular or subcellular fraction (except in 60-day-old rat neurons). All material from animals fed with sunflower oil showed an important reduction in the docosahexaenoic acid content, compensated (except in 60-day-old rat neurons) by an increase in the n-6 fatty acids (mainly C22:5 n-6). When comparing 60-day-old animals fed with soya oil or sunflower oil, the n-3/n-6 fatty acid ratio was reduced 16-fold in oligodendrocytes, 12-fold in myelin, twofold in neurons, sixfold in synaptosomes, and threefold in astrocytes. No trienes were detected. Saturated and monounsaturated fatty acids were hardly affected. This study provides data on the fatty acid composition of isolated brain cells.

2',3'-cyclic nucleotide 3'-phosphodiesterase and 5'-nucleotidase in the central nervous system of a myelin-deficient rat mutant

2',3'-Cyclic nucleotide 3'-phosphodiesterase activity was examined in brains and spinal cords of normal and myelin-deficient Wistar rats. While the activity in normal brains increased from 0.2 mumol/min/mg protein (units) at 6-10 days to 3.5 units at 25 days of postnatal age, the activity in the myelin-deficient rat remained at 0.2-0.3 units over the same period. In spinal cord, the normal activities were 5.7 and 10.9 units at 12 and 20 days, respectively, whereas they declined in the myelin-deficient rat from 1.06 to 0.79 units for the same age points. 5'-Nucleotidase activities in brain and spinal cord were normal in the myelin deficient rat at both ages.

PO protein and 2',3'-cyclic-nucleotide 3'-phosphodiesterase activity in the peripheral nerve and subcellular fractions of the Trembler mouse

To investigate the biochemical abnormalities of the Trembler mouse, the level of the PO protein (as % of total protein) and the activity of CNP was compared in the sciatic nerve and subcellular fractions of normal and mutant littermates. There was a significant decrease in both of these myelin markers in total nerve homgenates of the neurological mutant compared with the control animals. Immunoassay of the PO protein and polyacrylamide gel analysis of proteins indicated an accumulation of a protein with an apparent molecular weight of 67K in mutant nerve extracts. The mutant nerve also had relatively decreased levels of a protein of molecular weight about 41K that cross-reacted with antibody to PO protein. The Trembler mouse exhibited a larger percentage recovery of PO protein and CNP activity in subcellular fractions denser than the myelin sheath. Together these results are consistent with the theories that these denser components represent immature forms of myelin and that the Trembler mutant is characterized by hypomyelination.

Distribution of myelin-associated enzymes and myelin proteins into membrane fractions from the brains of adult shiverer and control (+/+) mice

Shiverer, an autosomal recessive mutation in the mouse, is characterized by a severe deficiency in CNS myelin. The concentrations of the myelin basic and proteolipid proteins in the brains of two-month-old shiverer mice, although high enough to be measured, were much lower than in the control (+/+) brains. In contrast, the specific activities of the myelin-associated enzymes, 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNP), 5'-nucleotidase, and carbonic anhydrase, were close to normal in the brains of the mutants. The activities of these enzymes and the concentrations of the myelin large basic and proteolipid proteins were compared in membrane fractions prepared, by differential and density gradient centrifugation, from the brains of shiverer and +/+ control mice. In myelin purified from the brains of shiverer mice the specific activities of 5'-nucleotidase and CNP were close to normal, and the specific activities of all three enzymes were normal in a crude myelin fraction from brains of the mutants. However, in the shi/shi brains abnormally high proportions of the three myelin-associated enzymes were distributed into the P3 (microsomal) fraction and into membrane fractions denser than myelin. The major myelin proteins, although low in total amounts in the mutants' brains, were distributed into the membrane fractions from control and shiverer brains in relative proportions similar to the relative proportions observed for the three enzymes. Thus, carbonic anhydrase, 5'-nucleotidase and CNP in the brains of shiverer mice are not truly dissociated from the major myelin proteins but are, rather, distributed for the most part into the same populations of membranes as are the residual, small amounts of the myelin basic and proteolipid proteins.