Effects of manganese exposure and antioxidant therapy on oxidative stress and stereotypic behaviors in rats

Manganese (Mn) is an essential dietary element required for several important physiological processes. However, accumulation of Mn due to excessive environmental exposure is known to pose neurological health concerns that manifest as movement abnormalities and cognitive impairment. Oxidative stress has been hypothesized to play a role in this dysfunction. In these studies we examined the effect Mn exposure had on oxidative stress in the brain with or without antioxidant therapy, and how brain regional Mn accumulation affected stereotypic behaviors in rats. Sprague-Dawley rats raised on AIN-93G diet were randomized into a Mn free group (deionized water) and Mn exposed group (deionized water with 1 g Mn/L). Each group was then subdivided into three additional groups receiving injections of either saline (vehicle) or antioxidant therapy: 200 mg/kg N-acetyl-cysteine (NAC) or 5 mg/kg (-)-epigallocatechin-3-gallate (EGCG) to yield six groups total, each with an n=6. During the sixth week of treatment, stereotypic rat behaviors (total distance traveled, sleep, sniff, and groom) were monitored using Clever Systems Home Cage Scan. Upon completion of the sixth week the rat brains were removed with the caudate putamen (CP) and hippocampus (HC) sectioned out and analyzed for Mn and iron (Fe) concentrations, total glutathione (GSH) levels, lipid peroxidation in the form of F2-Isoprostanes (F2-IsoPs), along with glutathione peroxidase (GPx) and catalase mRNA levels. Results were considered significant when p≤0.05. Mn exposure significantly increased Mn concentrations in both the CP and HC, accompanied by significantly decreased Fe:Mn ratios in Mn-exposed groups. Mn significantly increased total distance traveled in each Mn-exposed group and decreased sniff behavior in the Mn only group. Only modest alterations in GSH and catalase levels were present in each region, although, a significant positive correlation between Mn concentration and GPx mRNA expression was observed. Additionally, F2-IsoP results showed no evidence of increased oxidative damage compared to CN regardless of EGCG or NAC therapy. These data, compared to the body of Mn toxicity research, suggest that oral Mn exposure may not generate deleterious levels of oxidative stress leading to overt neurological dysfunction. This exposure paradigm, instead, may result in subtle neurochemical alterations associated with behavior change and potential cognitive impairment

The effect of manganese neurotoxicity on the Gamma-Aminobutyric acid (GABA) neurotransmitter system

Manganese (Mn) is an essential metal that functions primarily as a cofactor for metalloenzymes contributing to numerous metabolic pathways. Exposure to excess environmental Mn overwhelms endogenous regulation, and deleterious effects disrupt neurotransmitter systems of the basal ganglia. The following studies examined the effects of Mn on (gamma)-aminobutyric acid (GABA) using in vivo microdialysis, metabolomic analysis, and primary astrocyte cell culture. Microdialysis experiments in Sprague-Dawley rats revealed that 6-week exposure to Mn (1g Mn/L drinking water) significantly elevated extracellular GABA compared to controls. Using nipecotic acid to antagonize GABA transport proteins (GATs), we identified that Mn disrupted GABA homeostasis by inhibiting GAT mediated GABA clearance. Concurrently, metabolomic analysis of Mn exposed rats uncovered drastically altered lipid metabolism highlighted by a 12- and 15-fold increase in oleic and palmitic acids compared to control, respectively. Brain Mn accumulation was accompanied by abnormal stereotypy and was significantly correlated with plasma homogentisic, chenodeoxycholic, and aspartic acids, identifying biomarkers that correspond with Mn neurotoxicity. To elucidate mechanisms driving Mn induced changes in GABA uptake, primary astrocytes were exposed to Mn with or without oleic or palmitic acid. 3H-GABA uptake was significantly reduced by Mn and exacerbated by oleic or palmitic acids. Plasma membrane levels of GAT3 were unaltered by Mn or fatty acids despite increased regulatory protein kinase C (PKC) phosphorylation; however, fatty acid treatments augmented Mn accumulation at the plasma membrane of astrocytes. Moreover, control cells exposed to Mn exclusively during the experimental uptake had significantly reduced 3H-GABA uptake, and the addition of 50 µM GABA blunted cytosolic Mn accumulation. These data indicate that reduced GAT3 function in astrocytes is not driven by PKC signaling, but is likely influenced by Mn and fatty acids interacting with the plasma membrane, thereby inhibiting GABA uptake via GAT3. Together these studies improve our understanding of how Mn alters GABA neurotransmission upon overexposure. Furthermore, these data provide candidate biomarkers to improve early detection of Mn intoxication prior to irreparable damage

Waterborne Manganese Exposure Alters Plasma, Brain, and Liver Metabolites Accompanied by Changes in Stereotypic Behaviors

Overexposure to waterborne manganese (Mn) is linked with cognitive impairment in children and neurochemical abnormalities in other experimental models. In order to characterize the threshold between Mn-exposure and altered neurochemistry, it is important to identify biomarkers that positively correspond with brain Mn-accumulation. The objective of this study was to identify Mn-induced alterations in plasma, liver, and brain metabolites using liquid/gas chromatography–time of flight–mass spectrometry metabolomic analyses; and to monitor corresponding Mn-induced behavior changes. Weanling Sprague–Dawley rats had access to deionized drinking water either Mn-free or containing 1 g Mn/L for 6 weeks. Behaviors were monitored during the sixth week for a continuous 24 h period while in a home cage environment using video surveillance. Mn-exposure significantly increased liver, plasma, and brain Mn concentrations compared to control, specifically targeting the globus pallidus (GP). Mn significantly altered 98 metabolites in the brain, liver, and plasma; notably shifting cholesterol and fatty acid metabolism in the brain (increased oleic and palmitic acid; 12.57 and 15.48 fold change (FC), respectively), and liver (increased oleic acid, 14.51 FC; decreased hydroxybutyric acid, - 14.29 FC). Additionally, Mn-altered plasma metabolites homogentisic acid, chenodeoxycholic acid, and aspartic acid correlated significantly with GP and striatal Mn. Total distance traveled was significantly increased and positively correlated with Mn-exposure, while nocturnal stereotypic and exploratory behaviors were reduced with Mn-exposure and performed largely during the light cycle compared to unexposed rats. These data provide putative biomarkers for Mn-neurotoxicity and suggest that Mn disrupts the circadian cycle in rats

Organic Cation Transporter 3 and the Dopamine Transporter Differentially Regulate Catecholamine Uptake in the Basolateral Amygdala and Nucleus Accumbens

Regional alterations in kinetics of catecholamine uptake are due in part to variations in clearance mechanisms. The rate of clearance is a critical determinant of the strength of catecholamine signaling. Catecholamine transmission in the nucleus accumbens core (NAcc) and basolateral amygdala (BLA) is of particular interest due to involvement of these regions in cognition and motivation. Previous work has shown that catecholamine clearance in the NAcc is largely mediated by the dopamine transporter (DAT), but clearance in the BLA is less DAT‐dependent. A growing body of literature suggests that organic cation transporter 3 (OCT3) also contributes to catecholamine clearance in both regions. Consistent with different clearance mechanisms between regions, catecholamine clearance is more rapid in the NAcc than in the BLA, though mechanisms underlying this have not been resolved. We compared the expression of DAT and OCT3 and their contributions to catecholamine clearance in the NAcc and BLA. We found DAT protein levels were ~ 4‐fold higher in the NAcc than in the BLA, while OCT3 protein expression was similar between the two regions. Immunofluorescent labeling of the two transporters in brain sections confirmed these findings. Ex vivo voltammetry demonstrated that the magnitude of catecholamine release was greater, and the clearance rate was faster in the NAcc than in the BLA. Additionally, catecholamine clearance in the BLA was more sensitive to the OCT3 inhibitor corticosterone, while clearance in the NAcc was more cocaine sensitive. These distinctions in catecholamine clearance may underlie differential effects of catecholamines on behavioral outputs mediated by these regions

Age-dependent effects of protein restriction on dopamine release

FUNDING AND DISCLOSURE This work was supported by the Biotechnology and Biological Sciences Research Council [grant # BB/M007391/1 to J.E.M.], the European Commission [grant # GA 631404 to J.E.M.], The Leverhulme Trust [grant # RPG-2017-417 to J.E.M.] and the Tromsø Research Foundation [grant # 19-SG-JMcC to J. E. M.). The authors declare no conflict of interest. ACKNOWLEDGEMENTS The authors would like to acknowledge the help and support from the staff of the Division of Biomedical Services, Preclinical Research Facility, University of Leicester, for technical support and the care of experimental animals.Peer reviewedPublisher PD

Political Performance, Profanation, and Mundane Interaction: a Revised Cultural Sociology of the 2016 American Presidential Election

For more than a decade, Jeffrey Alexander has been developing the cultural sociology of politics as an alternative to rationalist theories of political life. Nearly every part of the 2016 US presidential election offers some vindication for Alexander’s cultural sociology of politics. The election of Donald Trump suggested that performance, stage craft, and messaging might be more fundamental to presidential campaigns. Yet on closer examination, political performance in the 2016 election challenges certain aspects of the cultural sociology of politics. Specifically, the performance of Donald Trump frequently occasioned the violation of the background representations of American political life. This article uses the 2016 campaign of Donald Trump to investigate how a single candidate can be a successful political performer even while profaning a society’s sacred or animating ideals. In the course of this analysis, I argue for a greater appreciation of the value of mundane social interaction in political performance. In liberal and democratic societies, the value of individualism means that the principles of social interaction will be as important to political performance as the ability to channel other principles and ideals

Sovereignty and Martyrdom: A Sociological Sketch

This paper has two goals: to develop a sociological conception of martyrdom and to use that concept to interpret the history of sovereignty in the West. While recent research on the topic has focused on martyrdom as a terrorist tactic associated with radical Islam, I redress these trends by analyzing martyrdom as a social process, focusing on cases of martyrdom in European history, and cultivating a new perspective on the relationship between religion and politics in the historical development of sovereignty in the West