Myelin basic protein in brains of rats with low dose lead encephalopathy

Abnormal behaviors and microstructural changes in white matter of juvenile mice repeatedly exposed to amphetamine

Amphetamine (AMP) is an addictive CNS stimulant and has been commonly abused by adolescents and young adults, during which period brain white matter is still developing. This study was to examine the effect of a nonneurotoxic AMP on the white matter of juvenile mice. d-AMP (1.0 mg/kg) was given to young male C57BL/6 mice once a day for 21 days. The spatial working memory and locomotion of mice were measured at the end. Then, mice were sacrificed and their brains were processed for morphological analyses to examine the white matter structure and for Western blot analysis to measure three main proteins expressed in mature oligodendrocytes. AMP-treated mice displayed higher locomotion and spatial working memory impairment and showed lower levels of Nogo-A and GST-pi proteins in frontal cortex and lower MBP protein in the frontal cortex and hippocampus. They also had fewer mature oligodendrocytes and weak MBP immunofluorescent staining in the same two brain regions. But the striatum was spared. These results suggest that the late-developing white matter is vulnerable to AMP treatment which is able to increase striatal and cortical dopamine. Both the compromised white matter and increased dopamine may contribute to the observed behavioral changes in AMP-treated mice.

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.

Chronic lead intoxication affects the myelin membrane status in the central nervous system of adult rats

The aim of the experiments presented here was to discern whether prolonged consumption of leaden water, which imitates an environmental exposure, affects the structure of myelin in the central nervous system of adult rats and whether the observed morphological destruction is reflected in biophysical and/or biochemical changes. The results indicated that during chronic lead (Pb) intoxication, the Pb level of the myelin fraction increases significantly. Electron microscopy studies show that myelin in control experiments is built up of ordered layers, whereas in a Pb-intoxicated sample, this order is destroyed in large areas of all preparations. Morphological disturbances in Pb-intoxicated in vivo myelin were reflected by changes in myelin membrane fluidity measured by spectrofluorometry and electron paramagnetic resonance (EPR). Prolonged Pb toxicity also caused significant changes in the morphological structure of oligodendrocytes, an increase of phosphatidylethanolamine, and decrease of protein SH group levels. Simultaneously, we found that the protein and total phospholipid content and levels of phosphatidylinositol, sphingomyelin, phosphatidyloserine, cholesterol, and the pattern of total myelin protein obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in Pb-intoxicated myelin did not change compared to control values. Also, Pb intoxication did not induce peroxidation by itself and did not accelerate peroxidation produced by iron (Fe) in brain myelin.

Decreased nerve conduction velocity in optic nerve following early post-natal low-dose lead exposure

A study was made on nerve conduction velocity of the optic nerve in rats subjected to lead exposure during the first 2 weeks of post-natal life. The rats were given intraperitoneal injections with a calculated daily exposure of 7.6 micrograms (low-dose) or 15.8 micrograms (high-dose) lead g-1 body weight. Growth retardation at 30 days was seen only with the higher dose. Littermates of low-dose exposed rat were injected with vehicle only and served as controls. Lead concentrations in blood and brain were measured in rats of 20 days of age in order to ascertain that exposure was adequate in the present litters. Nerve conduction velocity of the optic nerve was examined in 14 rats of 30 days of age taken from 10 different litters. The optic nerve(s) was prepared in anaesthetized rats and placed in a flow-through incubation chamber. One stimulating and two recording tungsten electrodes were used. In all rats, three positive-negative waves, regarded as representing three functional groups of optic nerve axons, could be recorded. The last one often had a long duration and a small amplitude without distinct peaks and hence was omitted from further analysis. The mean conduction velocities for the two faster axonal groups were 16.8 and 5.4 m s-1 in control rats, 10.3 and 5.8 m s-1 in low-dose rats and 9.4 and 5.2 m s-1 in high-dose rats. The difference in conduction velocity for the fastest axons was significant for controls versus low-dose and high-dose but not for low-dose versus high-dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of lead in the cerebellum of suckling rats following low and high dose lead exposure. A micro-PIXE analysis

The distribution of lead in the cerebellum of suckling Sprague-Dawley rats was examined using a nuclear microprobe for elemental mapping of tissue sections (particle-induced X-ray emission, 3-microns beam of 2.5 MeV protons; micro-PIXE). The rats were injected intraperitoneally with a lead-containing vehicle or vehicle only from ages 1 to 14 days. The calculated doses were 7.8 (low-dose) and 15.6 (high-dose) micrograms lead/g body weight. The rats were killed at 20 days of age. The vascular system was rinsed quickly with 0.15 M ammonium acetate to obtain determinations of intra-parenchymal lead with minimal influence of lead bound to erythrocytes and plasma proteins. Brains were frozen in propane/propylene in liquid nitrogen. Cryostat sections, 15 microns thick, were air dried on formvar coats that covered a hole, 15 mm in diameter, in a plastic disc, and were used for lead analysis by micro-PIXE. Very low concentrations of lead were found in the brain of controls. Lead levels in homogenates from cerebrum and cerebellum measured by atomic absorption spectrometry (AAS) were: low-dose 1.2-2.2 micrograms/g wet weight and high-dose 1.4-2.4 micrograms/g wet weight. The lead levels measured with the micro-PIXE method were in good agreement with the levels found with AAS. Lead was present in the cerebellar white matter in two to three times higher amounts than in the cortical grey (low-dose white matter 11-18 micrograms/g dry weight, grey matter 2.0-5.5 micrograms/g dry weight). This was true for both low and high dose exposed rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular edema and glial response to it in the cerebellum of suckling rats with low-dose lead encephalopathy. An electron microscopic and immunohistochemical study

Newborn rats were exposed to daily intraperitoneal injections of 10 mg lead nitrate per kg body weight for the first 15 postnatal days. The growth and mortality of the lead-exposed animals did not differ from their control litter-mates, injected with vehicle only. In our previous studies, focal hemorrhages and spongy areas as well as breakdown of blood-brain barrier to plasma proteins were shown by light microscopy in the cerebellar parenchyma of 15-day-old rats exposed to this dose. In spite of these signs of edema, measurements of brain tissue specific gravity did not show increased water content. In the present investigation we examined the ultrastructure of the brain lesions in these rats with low-dose lead encephalopathy, focusing on signs of edema, and evaluated astroglial reaction by immunocytochemical staining for glial fibrillary acidic protein (GFAP). The electron microscopic findings were compatible with extracellular edema in the cerebellum of 15-day-old lead exposed rats. The number of GFAP-positive cell bodies in the gray substance of the cerebellar cortex was increased in the 15-day-old lead-exposed rats as compared with the controls of the same age, a finding which is presumably related to the leakage of plasma proteins. Both these findings were lacking at 20 days of age, suggesting reversibility of the lead-induced changes.