Trace element changes in the myocardium during coxsackievirus B3 myocarditis in the mouse

During most infections plasma, concentrations of trace elements change, but it is unclear if this reflects changes in infected target tissues. In coxsackievirus B3 (CB3) infection, the myocardium is a target in both humans and mice. The concentrations of 12 trace elements were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) in the myocardium of sham-inoculated controls and infected A/J mice 4 and 7 d postinoculation. The size of the inflammatory lesion was positively correlated to the virus content of the heart, as estimated by histopathology and in situ hybridization, respectively. Iron, cobalt, vanadium, and selenium showed transient changes, whereas for the other elements, tendencies on d 4 were manifest on d 7. A threefold increase in calcium on d 7 suggests prestages of calcification, whereas increases in zinc, selenium, and copper may be the result of the accumulation of immune cells. The magnesium decrease may contribute to the increased sensitivity to cardiac arrhythmias in myocarditis.     

Aggravation of coxsackievirus, group B, type 3-induced myocarditis and increase in cellular immunity to myocyte antigens in pregnant Balb/c mice and animals treated with progesterone

Male Balb/c mice inoculated with a heart-adapted variant of coxsackievirus, group B, type 3 (CVB3M) develop severe myocarditis characterized by extensive focal lesions of inflammatory cells and necrosis of the myocardium. Females generally develop minimal myocarditis except when infected during the first and third trimesters of pregnancy. Enhanced myocarditis is usually accompanied by elevations in virus concentrations in the heart, virus-specific antibody titers, and lymphocyte mediated cytolytic activity to both uninfected and CVB3M-infected myocytes in vitro. As previously shown in males, T-lymphocyte-depleted pregnant female mice inoculated with the virus do not develop significant myocarditis indicating that immune rather than virus-mediated myocyte damage is important in myocarditis. Progesterone increases during gestation reaching maximum concentrations during the third week when heart disease is most severe. Administration of progesterone to castrated male and female mice prior to virus inoculation resulted in increased virus concentrations, cellular and humoral CVB3M-specific immunity, and myocarditis. Two hypotheses for exacerbation of the disease with elevated progesterone concentrations have been postulated: the hormone either indirectly increases cellular immune responses by enhancing virus replication, or independently enhances both T-cell responses and virus replication.     

LPS promotes CB3-induced myocarditis in resistant B10.A mice.

Coxsackie virus B3 (CB3) infection of A/J or A.SW mice results in autoimmune myocarditis characterized by a diffuse mononuclear cell infiltrate and heart-specific autoantibodies. C57BL/10 congenic mice that are identically treated are resistant to this disease. CB3-infected resistant B10.A mice were treated with LPS to determine if this immunomodulator alters disease susceptibility. In contrast to mice infected only with CB3 or treated only with LPS. CB3-infected/LPS-treated (CB3/LPS) B10.A mice developed autoimmune myocarditis similar to that observed in susceptible A/J or A.SW mice. By Day 14, CB3/LPS-induced disease was characterized by significant mortality, myocardial immunoglobulin deposition, and mononuclear cell infiltration of the heart. Immunohistochemical examination revealed deposits of IgG in the heart tissue and serum IgG autoantibodies reactive with sarcolemmal and fibrillary antigens in normal heart tissue. This serum IgG reacted with normal mouse cardiac antigens of a wide range of molecular weights by Western immunoblotting. Because LPS treatment is capable of increasing cytokine levels as well as MHC Class I and Class II expression in heart tissue, it suggests that these factors may contribute to susceptibility to autoimmune myocarditis in CB3-infected mice.     

Variation in virulence of Coxsackie virus B3 in the heart of mice, II. Pathological comparison

Histopathological analysis of the heart in adult mice inoculated with Coxsackie virus B3 (CB3) strains revealed that strain SK-74 isolated from a patient suffering from severe diarrhea and fever produced severe myocarditis but strain T-70 isolated from a healthy child induced no lesion in the hearts of mice tested, and that intensities of myocardial lesions in mice inoculated with strain PMH were higher than those in mice inoculated with prototype strain Nancy. The results support the conclusion in the preceding paper that strain SK-74 is virulent but strain T-70 is avirulent in mice. The results also partially indicated that the virulence of prototype strain Nancy in the heart of mice is enhanced by passages of the strain in the heart of mice. All four strains of CB3 produced lesions in the pancreas although lesions induced by strain T-70 were less marked than those induced by the remaining three strains.     

Coxsackievirus B3-Induced Chronic Myocarditis in Mouse: Use of Whole Blood Culture to Study the Activation of TNFα-Producing Cells

The pathogenesis of CVB3-induced chronic myocarditis remains unknown. Activated monocytes and macrophages may maintain ongoing inflammation during a persistent CVB3 infection and possibly represent the major mechanism leading to chronic myocarditis. We decided to study the activation status of cells by studying TNFα secretion in vitro using whole blood culture in CVB3-induced murine chronic myocarditis. Seven DBA/2 +/+ mice and 18 NMRI nu/nu mice were inoculated intraperitoneally with 5 × 10⁵ pfu of CVB3, and mice were mock-infected. Thirty-one days post-infection, all mice were sacrificed, blood samples were obtained from the heart, and the heart was removed. Enteroviral genomic detection by RT-PCR, virus isolation and histological analysis of heart samples were performed. Heparinized whole blood (25 μl) was cultured for 4 hr and 24 hr in sterile 96 well-plate containing 225 μl RPMI in the presence or the absence of activators (LPS + PHA). The TNFα levels in the whole blood from mock-infected DBA/2 (n = 4) and NMRI nu/nu mice (n = 5) were not different. A moderate increase of TNFα was observed in three out of five DBA/2 mice with negative CVB3 that had no histological abnormalities in myocardium. An increased level of TNFα was found in the sole DBA/2 mouse with positive CVB3 detection and chronic myocarditis. An increased level of TNFα was found in one out of nine NMRI nu/nu mice with positive CVB3 detection and chronic myocarditis and in one out of seven mice with positive CVB3 detection exempt of lesions in myocardium. In other infected mice, the level of TNFα was normal. Enteroviral genome was not detected in the blood from infected mice at 31 days post-infection. The increased TNFα level in some mice may be designed for a beneficial inflammatory and immune response, however, an exaggerated release may be associated with an adverse effect. The normal TNFα level in whole blood cultures from mice with chronic myocarditis does not exclude enhanced cytokine production at infected loci such as myocardial tissue. This is the first report to use whole blood cultures to study the production of cytokines in virus-induced disease in a small animal model.     

A study of human myocardial tissue in Chagas' disease: distribution and frequency of inflammatory cell types

Although many reports have described the presence of inflammatory cells in chagasic lesions, the precise role(s) of these cells and whether their numbers in the lesions correlate with lesion severity are not known. In this work, we determined the numbers of mononuclear cells, neutrophils and eosinophils present in lesion sites of heart tissue sections from one acute and nine chronic chagasic patients. These numbers were independently recorded for five types of histologic patterns (HP) defined by the following characteristics: interstitial myocarditis with degeneration and necrosis of muscle fibers (HP I), interstitial myocarditis with preservation of muscle fibers (HP II), minimal or absent myocarditis with essentially preserved myocardium (HP III), interstitial fibrosis (HP IV), and myocytolysis (HP V). The largest numbers of inflammatory cells were found in HP I where substantial numbers of eosinophils were found. Eosinophils were frequently seen in areas showing HP I in the tissue sections from the patients with the most severe myocarditis (in terms of the high frequency of necrotic areas in HP I). Eosinophils were also seen in areas of HP III, i.e. in relatively preserved areas of tissue sections from patients displaying the most severe myocarditis, although in lesser numbers than found in HP I. The smallest numbers of inflammatory cells were seen in HP III, where the myocardium was essentially intact. Although significant numbers of inflammatory cells were seen in HP II and IV, eosinophils were either present in small numbers or absent, and there was no obvious correlation between the content of any of the monitored cell types and the overall intensity of myocarditis. The presence of relatively large proportions of eosinophils in tissue areas with HP I type of lesions would appear to implicate these cells in the production of chagasic heart lesions.     

Effects of the immunomodulator LS 2616 on lymphocyte subpopulations in murine Coxsackievirus B3 myocarditis

Quinoline-3-carboxamide (LS 2616) is a broadly acting immunostimulator with anti-inflammatory effects in Coxsackie virus B3-induced myocarditis in female BALB/c mice. This infection caused extensive inflammatory and necrotic lesions in the myocardium 7 days after inoculation (6.8% of tissue section area). The damaged area was reduced (to 3.7% (p less than 0.05] and the lethality decreased when LS 2616 was administered over 14 days, starting 7 days before the inoculation. The response pattern of lymphocyte subsets in situ in myocardial inflammatory lesions was elucidated by a newly developed immune histochemical staining technique. LS 2616 increased the number of class II-expressing cells 3-fold (p less than 0.01) and the CTL, Ts:Th cell ratio by 55% (p less than 0.05), whereas Lyt-1+ and TIB+ cells were unaffected. After 7 days of LS 2616 treatment, spleen lymphocyte activity tended to increase (T cells by 21% (NS) and B cells by 60% (p less than 0.05), respectively). The activity of NK cells increased by 51% (p less than 0.01). LS 2616 may thus have potential in therapy of human inflammatory disorders, such as myocarditis.     

Cardiac myosin induces myocarditis in genetically predisposed mice

After infection with coxsackie virus B3 (CB3), H-2 congenic mice on an A- background develop immunologically mediated myocarditis associated with an increased titer of myosin autoantibody, part of which is specific for the cardiac myosin isoform. The present study demonstrates that cardiac myosin itself induces severe myocarditis and high titers of myosin autoantibodies in A/J, A.SW/SnJ, and A.CA/SnJ mice. As in CB3-induced myocarditis, one population of these autoantibodies was specific for cardiac myosin. A.BY/SnJ and B10.A/SgSnJ mice also developed the disease after immunization, but the prevalence and the myosin autoantibody titers were lower. In contrast, C57BL/6J and C57BL/10J mice were resistant to myocarditis induced by cardiac myosin and did not develop increased myosin autoantibodies or cardiac myosin-specific autoantibodies. Immunization with skeletal muscle myosin had no effect compared with controls injected with complete Freund's adjuvant, thereby suggesting that the immunogenic epitopes are unique to the cardiac myosin isoform. Furthermore, we found that susceptibility to myocarditis induced by cardiac myosin is influenced by the major histocompatibility complex and by genes not closely linked to the major histocompatibility complex. Because there are parallels between myocarditis induced by cardiac myosin and that induced by CB3, this new animal model can be used to analyze the pathologic mechanisms in autoimmune heart disease.     

病毒性心肌炎所致小鼠心力衰竭心肌组织内质网应激相关的凋亡关系的研究

目的：探讨病毒性心肌炎心力衰竭小鼠心肌组织内质网应激介导的凋亡途径。方法：40只雄性Balb／c小鼠分为病毒性心肌炎组和正常对照组（n=20）,病毒性心肌炎组应用柯萨奇B3病毒制作BALB／c小鼠病毒性心肌炎模型,观察小鼠的一般情况,7d行血流动力学检查后处死取心脏标本,用TUNEL法检测心肌细胞凋亡,RT-PCR检测心肌细胞内质网伴侣蛋白葡萄糖调节蛋白（GAP）78和GRP04的mRNA表达水平。结果：①与正常对照组相比,病毒性心肌炎组小鼠血流动力学指标明显降低（P〈0．01）;②TUNEL染色显示病毒性心肌炎心力衰竭小鼠心肌组织凋亡明显增多（P〈0．01）;③病毒性心肌炎组小鼠内质网伴侣蛋白GRP78和GRP94的mRNA表达水平均明显高于对照组（P〈0．01）。结论：病毒性心肌炎心力衰竭小鼠内质网应激可能介导了心肌细胞凋亡。     

Involvement of natural killer cells in coxsackievirus B3-induced murine myocarditis

The role of natural killer cells in the temporal development of coxsackievirus B3-induced myocarditis in adolescent CD-1 male mice was examined. Inoculation of purified CVB3m induced maximum NK cell activity in the splenic populations at 3 days postinoculation (p.i.) as assessed by lysis of YAC-1 cells; maximum virus titers in heart tissues were also found at day 3 p.i. Mice depleted of NK cells after injection of anti-asialo GM1 antiserum i.v. had decreased NK cell activity, increased CVB3m titers in heart tissues, and exacerbated myocarditis. Although lesion number was not increased in heart tissues of the latter mice, lesions in these mice exhibited increased myocyte degeneration and dystrophic calcification above that found in lesions of mice inoculated with CVB3m only. No alteration in interferon titers were observed in CVB3m-infected mice treated with anti-asialo GM1 antiserum as compared with normal CVB3m-infected mice. Measurements of splenic NK cell activity in mice inoculated with doses of 10(2) to 10(8) PFU of CVB3m per mouse or UV-irradiated virus suggest that replication of CVB3m is required for NK cell activation. An amyocarditic variant of CVB3m (ts5R) was shown to replicate in heart tissues and to elicit NK cell activity comparable to that elicited by CVB3m. Therefore, the data suggest that NK cell activation depends on virus replication and that these cells provide some protection against CVB3m-induced myocarditis by limiting virus replication in heart tissues.     

Effects of exposure of DNA to methyl mercury on its activity as a template-primer for DNA polymerases

A previous publication [Frenkel, Cain, and Chao, Biochem. Biophys. Res. Commun. 127, 849-856 (1985)] described the observation that double-stranded DNA which was briefly exposed to methyl mercury (MeHg) and purified to remove free methyl mercury was transcribed at a higher rate by RNA polymerase II from wheat germ. The specificity of this phenomenon has now been investigated by examining the activity of this MeHg-exposed DNA as a template-primer for DNA polymerases. DNA synthesis by the bacteriophage T4-induced DNA polymerase was higher with the MeHg-exposed DNA as a template-primer than with control DNA. In contrast, the rate of DNA synthesis by E. coli DNA polymerase I was lower with the MeHg-exposed DNA as template-primer. With both enzymes (as well as with RNA polymerase II), after denaturation of the MeHg-exposed and control DNAs the differences in template activity were either eliminated or markedly reduced. The enzymes are thus able to detect a MeHg-induced alteration in DNA. In contrast, circular dichroism, a physical method that is sensitive to conformational changes in DNA, did not detect any difference between the MeHg-exposed and control DNAs.     

Impairment of immunoproteasome function by β5i/LMP7 subunit deficiency results in severe enterovirus myocarditis

Proteasomes recognize and degrade poly-ubiquitinylated proteins. In infectious disease, cells activated by interferons (IFNs) express three unique catalytic subunits β1i/LMP2, β2i/MECL-1 and β5i/LMP7 forming an alternative proteasome isoform, the immunoproteasome (IP). The in vivo function of IPs in pathogen-induced inflammation is still a matter of controversy. IPs were mainly associated with MHC class I antigen processing. However, recent findings pointed to a more general function of IPs in response to cytokine stress. Here, we report on the role of IPs in acute coxsackievirus B3 (CVB3) myocarditis reflecting one of the most common viral disease entities among young people. Despite identical viral load in both control and IP-deficient mice, IP-deficiency was associated with severe acute heart muscle injury reflected by large foci of inflammatory lesions and severe myocardial tissue damage. Exacerbation of acute heart muscle injury in this host was ascribed to disequilibrium in protein homeostasis in viral heart disease as indicated by the detection of increased proteotoxic stress in cytokine-challenged cardiomyocytes and inflammatory cells from IP-deficient mice. In fact, due to IP-dependent removal of poly-ubiquitinylated protein aggregates in the injured myocardium IPs protected CVB3-challenged mice from oxidant-protein damage. Impaired NFκB activation in IP-deficient cardiomyocytes and inflammatory cells and proteotoxic stress in combination with severe inflammation in CVB3-challenged hearts from IP-deficient mice potentiated apoptotic cell death in this host, thus exacerbating acute tissue damage. Adoptive T cell transfer studies in IP-deficient mice are in agreement with data pointing towards an effective CD8 T cell immune. This study therefore demonstrates that IP formation primarily protects the target organ of CVB3 infection from excessive inflammatory tissue damage in a virus-induced proinflammatory cytokine milieu.     

Kinetics of development of inflammatory lesions in myocardial and skeletal muscle in experimental Trypanosoma cruzi infection

We studied the kinetics of development of inflammation in the myocardium and skeletal muscles of mice infected with Trypanosoma cruzi by determining the numbers of mononuclear cells (MNC), neutrophils, and eosinophils at tissue sites with varying degrees of damage. In the myocardium, areas with incipient inflammation and preserved tissue had the smallest numbers of inflammatory cells, 96-100% of which were MNC. In lesions where inflammatory cells accumulated in interstitial spaces displacing myofibers, MNC were also predominant (greater than 98%) but were present in larger numbers than in areas with preserved tissue. The number of MNC was even larger in necrotic areas where there was also marked neutrophil infiltration at the time when amastigote nests were frequently present. In skeletal muscle, MNC were also the first cells to infiltrate lesion sites; their numbers increased with the degree of severity of the lesion. Neutrophil accumulation also accompanied skeletal muscle necrosis. A salient difference was eosinophil accumulation in the necrotic lesions of skeletal muscle but not in the myocardium. The results identify MNC as the cell that initiates the inflammatory process in the heart and skeletal muscles of T. cruzi-infected mice. In these tissues the number of MNC appeared to be a good correlate of lesion severity.     

Augmentation of pathogenesis of coxsackievirus B3 infections in mice by exogenous administration of interleukin-1 and interleukin-2.

Two variants of coxsackievirus B3 (CVB3) which differ dramatically in the ability to induce myocarditis in BALB/c mice were studied. H3 virus infection of murine monocytes in vitro resulted in release of concentrations of interleukin 1 (IL-1) and alpha/beta interferon that were high compared with those of cells infected with the H310A1 virus variant. In vivo, H3 virus infection caused substantial inflammatory cell infiltration of the myocardium, and lymphocytes from these animals gave predominantly Th1-cell responses to either whole H3 virus or overlapping peptides of the CVB3 vp1 capsid protein, as determined by IL-2 production. In contrast, H310A1 virus infection produced minimal myocarditis and Th1-cell responses, but Th2-cell activation was more pronounced than in H3 virus-infected mice (as determined by IL-4 concentrations). Exogenous treatment of H310A1 virus-infected mice with either IL-1 or IL-2 restored both myocarditis susceptibility and Th1-cell responses to whole virus and vp1 peptides. Furthermore, H310A1 virus-infected mice given exogenous IL-1 showed substantial in situ IL-2 deposition in the myocardium. These results indicate that CVB3-induced myocarditis may depend upon release of specific cytokines during infection and that activation of Th1 cells may be an important factor in pathogenesis.     

Coxsackievirus B3-resistant mice become susceptible in Se/vitamin E deficiency

The severity of the heart damage caused by a coxsackievirus infection in mice is determined by several factors, including the genotype of the infecting virus as well as the genetic background of the infected host. Earlier work by us showed that the cardiovirulence of a given coxsackievirus genotype could be increased substantially by feeding the host a diet nutritionally deficient in either selenium or vitamin E. Here we report that host genetic background as a determinant of viral infection outcome is superseded by feeding the host a diet nutritionally deficient in both selenium and vitamin E. Mice of the C57Bl/6 strain, normally resistant to coxsackievirus B3-induced myocarditis, become susceptible when fed such a doubly deficient diet. Our results demonstrate the powerful influence of host nutritional status on the course of viral infection compared to other variables traditionally considered to play major roles in determining the extent of virally induced inflammatory heart disease.     

Experimental Myocarditis Induced in Mice by Infection with Influenza A2 Virus

A mouse model was established for the study of acute myocarditis that occurs during influenza infection. Challenge with more than 10 LD₅₀ of mouse-adapted influenza A₂ virus (H₂N₂) induced myocarditis macroscopically discernible as white, irregularly shaped lesions which were shown by histological examination to consist of necrotic myofibers surrounded by infiltrating mononuclear inflammatory cells. After challenge with 10 LD₅₀ of the virus, macroscopic myocarditis was found to advance in a progressive manner up to the 7th day, while the virus titer in the heart reached its peak on the 2nd day and began to decrease on the 5th day of infection. However, development of myocarditis was significantly suppressed in mice which were irradiated with 400 R of X-rays before infection. In addition, myocarditis did not develop in congenitally athymic nude mice. These data indicate that myocarditis was not brought about by viral action directly, but that it was mediated by some function of the host against viral in-vasion, which was abolished by X-irradiation. The data also suggest that T cells played a key role in the development of myocarditis.     

Direct gene transfer with IP-10 mutant ameliorates mouse CVB3-induced myocarditis by blunting Th1 immune responses

Background

Myocarditis is an inflammation of the myocardium that often follows the enterovirus infections, with coxsackievirus B3 (CVB3) being the most dominant etiologic agent. We and other groups previously reported that chemokine IP-10 was significantly induced in the heart tissue of CVB3-infected mice and contributed to the migration of massive inflammatory cells into the myocardium, which represents one of the most important mechanisms of viral myocarditis. To evaluate the direct effect of IP-10 on the inflammatory responses in CVB3 myocarditis, herein an IP-10 mutant deprived of chemo-attractant function was introduced into mice to antagonize the endogenous IP-10 activity, and its therapeutic effect on CVB3-induced myocarditis was evaluated.

Methodology/Principal Findings

The depletion mutant pIP-10-AT, with an additional methionine after removal of the 5 N-terminal amino acids, was genetically constructed and intramuscularly injected into BALB/c mice after CVB3 infection. Compared with vector or no treatment, pIP-10-AT treatment had significantly reduced heart/body weight ratio and serum CK-MB level, increased survival rate and improved heart histopathology, suggesting an ameliorated myocarditis. This therapeutic effect was not attributable to an enhanced viral clearance, but to a blunted Th1 immune response, as evidenced by significantly decreased splenic CD4⁺/CD8⁺IFN-γ⁺ T cell percentages and reduced myocardial Th1 cytokine levels.

Conclusion/Significance

Our findings constitute the first preclinical data indicating that interfering in vivo IP-10 activity could ameliorate CVB3 induced myocarditis. This strategy may represent as a new therapeutic approach in treating viral myocarditis.     

Biochemical evidence on the potential role of methyl mercury in hepatic glucose metabolism through inflammatory signaling and free radical pathways

Methylmercury (MeHg) is an extremely important environmental toxicant posing serious health risks to human health and a big source of environmental pollutant. Numerous evidence available showing a link between nervous system toxicity and MeHg exposure. Other forms of mercury are reason of metabolic toxic effects and alteration of DNA in the human body. The sources of exposure could be occupational or other environmental settings. In the present study MeHg was orally gavaged to mice, at doses of 2.5, 5, and 10 mg/kg for 4 weeks. Fasting hyperglycemia, activity of hepatic phoshphoenolpyruvate carboxykinase and glucose 6-phoshphate were reported high as compared to control group. Inflammatory markers like, tumor necrosis factor α, the actual end product of inflammatory mediators’ cascade pathway was also raised in comparison to control group. Hyperinsulinemia observed in serum showed clear understanding of mercury induced insulin resistance. Moreover, tissue damage due to increased oxidative stress markers like, hepatic lipid peroxidation, 8-deoxygunosine, reactive oxygen species, and carbonyl groups was significantly higher as compared to control group. MeHg caused a significant reduction in antioxidant markers like ferric reducing antioxidant power and total thiol molecules. The present study highlighted that activity of key enzymes involved in glucose metabolism is changed, owing to MeHg induced toxicity in the liver. Induction of similar toxic effects assumed to be stimulated by the production of high quantity free radicals.     

Host selenium status selectively influences susceptibility to experimental viral myocarditis

The purpose of the present work was to determine whether dietary selenium (Se) deficiency could influence the injurious effect of human viruses other than Coxsackie virus B3 (CVB3) on mouse heart. Weanling C3H/HeN mice were fed a Se-deficient or Se-adequate diet for 4 wk and then were inoculated intraperitoneally with one of the following viruses: Coxsackie virus B1 (CVB1), echovirus 9 (EV9), Coxsackie virus A9 (CVA9), or herpes simplex 1 (HSV1). Polio virus 1 (PV1) was employed as a negative control. Prior to inoculation, mean serum Se levels were 430 versus 61 ng/mL in adequate versus deficient mice, respectively. Ten days later, hearts were removed and processed by routine histological procedures. Cardiac lesions were scored according to the number and size of myocarditic foci. Significantly greater heart damage resulting from CVB1 and EV9 was observed in Se-deficient than in Se-adequate mice, and the Se status had no influence on CVA9-induced myocarditis. In contrast, heart damage caused by HSV1 was significantly milder in Se-deficient than in Se-adequate mice. Therefore, it may be concluded that the Se status of the murine host selectively influences the degree of viral-induced myocarditic lesions.     

Protective effect of Bacopa monniera on methyl mercury-induced oxidative stress in cerebellum of rats

Methyl mercury (MeHg) is a ubiquitous environmental pollutant leading to neurological and developmental deficits in animals and human beings. Bacopa monniera (BM) is a perennial herb and is used as a nerve tonic in Ayurveda, a traditional medicine system in India. The objective of the present study was to investigate whether Bacopa monniera extract (BME) could potentially inhibit MeHg-induced toxicity in the cerebellum of rat brain. Male Wistar rats were administered with MeHg orally at a dose of 5 mg/kg b.w. for 21 days. Experimental rats were given MeHg and also administered with BME (40 mg/kg, orally) for 21 days. After the treatment period, we observed that MeHg exposure significantly inhibited the activities of superoxide dismutase, catalase, glutathione peroxidase, and increased the glutathione reductase activity in cerebellum. It was also found that the level of thiobarbituric acid-reactive substances was increased with the concomitant decrease in the glutathione level in MeHg-induced rats. These alterations were prevented by the administration of BME. Behavioral interference in the MeHg-exposed animals was evident through a marked deficit in the motor performance in the rotarod task, which was completely recovered to control the levels by BME administration. The total mercury content in the cerebellum of MeHg-induced rats was also increased which was measured by atomic absorption spectrometry. The levels of NO(2) (-) and NO(3) (-) in the serum were found to be significantly increased in the MeHg-induced rats, whereas treatment with BME significantly decreased their levels in serum to near normal when compared to MeHg-induced rats. These findings strongly implicate that BM has potential to protect brain from oxidative damage resulting from MeHg-induced neurotoxicity in rat.