Methyl bromide alters catecholamine and metabolite concentrations in rat brain

The neurological effects of methyl bromide intoxication

Used primarily as a fumigant or as a substrate in chemical processes, methyl bromide is a highly toxic gas. The gas is usually absorbed by inhalation and effects on the lungs, gastrointestinal tract, skin, and brain are seen. Numerous instances of acute and chronic neurologic injury have been reported: acute poisoning results in seizures, myoclonus, ataxia or cerebral oedema beginning as early as 30 min after exposure while subacute or chronic intoxication presents with diverse slowly progressive neurological and neurobehavioral symptoms. Serum bromide levels may be elevated, but often return rapidly to normal. Electroencephalography may show frontally-predominant slow waves or polyspikes with following slow wave, and MRI reveals characteristic involvement in the dentate nucleus of the cerebellum, the brainstem, and the splenium of the corpus callosum. Symmetric and selective lesions in characteristic sites are observed on imaging and on histopathological examination. These are likely produced by methylation of intracellular lipids, protein and glutathione; production of toxic metabolites; defective neurotransmitter function; and abnormal oxidative phosphorylation. This article reviews the toxic effects of this gas, the pathophysiology and symptoms of its effects on the nervous system, and characteristic findings on MRI; and presents an illustrative case of methyl bromide intoxication due to exposure at a factory producing the compound commercially.

The alterations in neurotransmitters and their metabolites in discrete brain regions in the rats after inhalation of disinfectant, glutaraldehyde or ortho-phthalaldehyde for 4 weeks

Glutaraldehyde (GA) and ortho-phtalaldehyde (OPA) have been widely used as major components of disinfectants in hospitals. We evaluated the alterations in GA or OPA in rats after subacute inhalation exposure by determining levels of neurotransmitters (norepinephrine [NE], dopamine [DA], DA metabolites, dihydroxyphenylacetic acid [DOPAC] and homovanillic acid [HVA], indoleamine serotonin [5-HT] and 5-HT metabolite, 5-hydroxyindoleacetic acid [5-HIAA]) in discrete brain regions using high performance liquid chromatography (HPLC) equipped with an electrochemical detector. Female Wistar rats were exposed to 0, 50, 100, or 200 ppb gaseous GA or OPA by inhalation for 1 h per day, 5 d per week for 4 wk. Following the exposure, the brain of each rat was removed and dissected into cerebrum, cerebellum, medulla oblongata, midbrain, corpus striatum and hypothalamus. The neurotransmitters and their metabolites were extracted from each brain region, and determined by HPLC. Regarding GA, the daily water intake of the 50 or the 200 ppb exposed groups was significantly lower than that of the control. DA and 5-HIAA levels in the medulla oblongata among the GA exposed groups were significantly lower than those of the control. For OPA, the mean final body weight and daily food intake of the 100 or 200 ppb exposed groups were significantly lower than those of the control. The mean DA concentrations in the cerebrum in the groups exposed to OPA were significantly lower than those of the control. OPA may modulate DA metabolism in the cerebrum of female rats. The levels GA or OPA that induced alienations in neurotransmitters were comparable to those levels usually found in hospitals, further studies are warranted to evaluate the of safety of disinfectants containing GA or OPA.

Alteration of brain levels of neurotransmitters and amino acids in male F344 rats induced by three-week repeated inhalation exposure to 1-bromopropane

The present study investigated the effects of 1-bromopropane (1BP) on brain neuroactive substances of rats to determine the extent of its toxicity to the central nervous system (CNS). We measured the changes in neurotransmitters (acetylcholine, catecholamine, serotonin and amino acids) and their metabolites or precursors in eight brain regions after inhalation exposure to 1BP at 50 to 1,000 ppm for 8 h per day for 7 d per week for 3 wk. Rats were sacrificed at 2 h (Case 1), or at 19 h (Case 2) after the end of exposure. In Case 1, the level of 5-hydroxyindoleacetic acid (5HIAA) was lowered in some brain regions by 1BP exposure. The decrease of 5HIAA in the frontal cortex was statistically significant at 50 ppm 1BP exposure. In Case 2, gamma-amino butyric acid (GABA) and taurine were decreased in many brain regions of exposed rats, and a significant decrease of taurine in the midbrain occurred at 50 ppm 1BP exposure. In both cases of 2-h and 19-h intervals from the end of exposure to sacrifice, aspartate and glutamine levels were elevated in many brain regions, but the acetylcholine level did not change in any brain region. Three-week repeated exposure to 1BP produced significantly changes in amino acid contents of rat brains, particularly at 1,000 ppm.

Effects of perinatal exposure to bisphenol A on brain neurotransmitters in female rat offspring

Pregnant Sprague-Dawley (CD IGS) rats were orally administered doses of bisphenol A (BPA) at 4, 40, and 400 mg/kg, from gestation days 6 to postnatal day 20. Neurotransmitters such as dopamine (DA) and serotonin (5HT) were extracted from the brains of dams and female offspring, and measured using liquid chromatography. BPA at 400 mg/kg was toxic and dosed rats died. At 3 wk after birth, brain levels of 3,4-dihydroxyphenylacetic acid (DOPAC, a DA metabolite), homovanillic acid (HVA, a DA metabolite), 5HT, 5-hydroxyindoleacetic acid (5HIAA, a 5HT metabolite) in female offspring were increased and the HVA/DA ratio was high in some brain areas of BPA-treated groups as compared with controls. At the age of 6 wk, levels of choline (Ch) in BPA-treated groups at 4 and 40 mg/kg were higher than control in all of eight brain areas. No changes were observed in acetylcholine (ACh) contents. In 9-wk-old offspring, changes in monoamines and metabolites were scattered and not great. At 3 wk after delivery, levels of 5HIAA in some brain areas of dams treated with BPA were higher than in control dams. Dose dependent increases in HVA and the HVA/DA ratio of the occipital cortex, and in the HVA/DA ratio of the frontal cortex were observed. The turnover of DA and 5HT was accelerated in 3-wk-old offspring and dams. BPA possesses very weak estrogenic activity. Changes in cerebral neurotransmitters observed in offspring and dams in this study may have been related to the estrogenic activity of BPA. However, further investigation is needed to examine the contribution of hormonal activity to such neurotransmitter changes.

Altered dopamine turnover in murine hypothalamus after low-dose continuous oral administration of aluminum

Aluminum, a known neurotoxic substance, has been suggested as a possible contributing factor in the pathogenesis of Alzheimer's disease. Ground-water pollution by aluminum has been recently reported. In the current study groups of 5 male BALB/c mice were administered aluminum ammonium sulfate in drinking water ad libitum at 0, 5, 25, and 125 mg/L aluminum for 4 weeks. At the termination of aluminum exposure, their brains were removed and dissected into cerebrum, cerebellum, medulla oblongata, midbrain, corpus striatum, and hypothalamus. The concentration of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA), were determined in each brain area. DA, DOPAC, and HVA levels were lower in the hypothalamus of aluminum-treated mice, most notably in the low-dose group, as compared with control. No marked alterations in NE, 5-HT, and 5-HIAA levels were detected in any brain region. Changes in the concentration of DA and its metabolites measured in the hypothalamus suggest an inhibition of DA synthesis by aluminum.

Fumonisin B1-induced increases in neurotransmitter metabolite levels in different brain regions of BALB/c mice

Fumonisin B1, a toxin produced by Fusarium moniliforme, causes a variety of diseases in animals, including those involving the central nervous system, such as equine leukoencephalomalacia (ELEM). The changes of biogenic amines may reflect fumonisin B1 neurotoxicity. It was previously reported that consumption of feed contaminated with Fusarium moniliforme cultures produced an elevation of 5-hydroxyindoleacetic acid (5-HIAA), the major metabolite of 5-hydroxytryptamine (5-HT), in whole rat brains. In a subsequent study from the same laboratory, rats given fumonisin B1 orally for 4 weeks showed no changes in neurotransmitter levels of the whole brain. In the current study, groups of five male BALB/c mice were injected with fumonisin B1 subcutaneously at doses of 0, 0.25, 0.75, 2.25, 6.75 mg kg-1 body weight daily for 5 days. One day after the last treatment, their brains were dissected into cerebrum, cerebellum, medulla oblongata, midbrain, corpus striatum and hypothalamus. Levels of norepinephrine (NE), dopamine (DA), DA metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and 5-HT and 5-HIAA were determined. A significant elevation of HVA was observed in mice treated with high doses of fumonisin B1 in most brain regions. In striatum, a decrease of 5-HT was observed by the fumonisin B1 treatment. Ratios of neurotransmitters to metabolites such as HVA/DA and 5-HIAA/5-HT were elevated in several brain regions of the treated groups. An accumulation of neurotransmitter metabolites is suggestive of increased neuronal activity or interference with their efflux from cells.

Effect of methyl bromide on regional brain glutathione, glutathione-S-transferases, monoamines, and amino acids in F344 rats

Both metabolic and neurotransmitter changes have been implicated in the pathogenesis of monohalomethane neurotoxicity in rodents. This study in male and female F344 rats examined the effects of methyl bromide (MeBr) on regional brain glutathione-S-transferase (GST) activities and concentrations of glutathione (GSH), monoamines, and amino acid. Inhalation exposure to 150 ppm MeBr (6 hr/day x 5 days) yielded no histologic evidence of brain lesions but resulted in a number of biochemical changes. GSH depletion and GST inhibition were detected in the frontal cortex, caudate nucleus, hippocampus (examined for GSH only), brain stem, and cerebellum from animals of both sexes. Differences between sexes were detected for GSH depletion. Simultaneous treatment of rats with the inhibitor of monohalomethane toxicity, BW 755C (3-amino-1-[m-(trifluoromethyl)phenyl]-2-pyrazoline; 10 mg/kg bw ip, 1 hr pre- and 1 hr postexposure) completely protected against GST inhibition in all brain regions of both sexes. Partial protection by BW 755C against GSH depletion was observed in the cerebral cortex and in the cerebellum only. In males, MeBr exposure had no effect on the regional concentrations of the monoamines dopamine and serotonin and the amino acids glutamate, glutamine, taurine, and gamma-aminobutyric acid. Regional increases of brain aspartate and glycine levels were observed after exposure of males to MeBr but BW 755C had no effect on these changes induced by MeBr. Thus, of all the parameters studied, only GST, and in some brain areas GSH, correlated with inhibition of toxicity. It is concluded that, in contrast to the monoamines and the amino acids, GST and GSH are sensitive and potentially relevant indicators of MeBr neurotoxicity which could explain sex and regional differences in response to the monohalomethanes.

Inhibition of tyrosine hydroxylase activity by methyl bromide exposure

Rats were exposed to methyl bromide gas (16-250 ppm) for 8 hr, and tyrosine hydroxylase (TH) activity in the striatum, hypothalamus, frontal cortex, midbrain, and medulla oblongata was measured in brain homogenates from exposed rats, and in vivo following administration of decarboxylase inhibitor. Exposure to methyl bromide dose-dependently inhibited both in vitro and in vivo TH activity. Of the five brain areas, TH activity in the hypothalamus was most sensitive to methyl bromide. The time course of enzyme inhibition after exposure was similar to those of decreases in catecholamine concentrations, locomotor activity change, and body temperature reported previously. These results suggest methyl bromide reduces catecholaminergic neuronal activity in the brain via inhibition of TH activity.