Characterization of acute intrastriatal effects of paraoxon on in vivo dopaminergic neurotransmission using microdialysis in freely moving rats

Acute Paraoxon-Induced Neurotoxicity in a Mouse Survival Model: Oxidative Stress, Dopaminergic System Alterations and Memory Deficits

The secondary neurotoxicity induced by severe organophosphorus (OP) poisoning, including paraoxon (POX), is associated with cognitive impairments in survivors, who, despite receiving appropriate emergency treatments, may still experience lasting neurological deficits. Thus, the present study provides a survival mouse model of acute and severe POX poisoning to examine secondary neurotoxicity. Swiss CD-1 male mice were injected with POX (4 mg/kg, s.c.) followed by atropine (4 mg/kg, i.p.), pralidoxime (2-PAM; Pyridine-2-aldoxime methochloride) (25 mg/kg, i.p., twice, 1 h apart) and diazepam (5 mg/kg, i.p.), resulting in a survival rate >90% and Racine score of 5-6. Our results demonstrated that the model showed increased lipid peroxidation, downregulation of antioxidant enzymes and astrogliosis in the mouse hippocampus (HP) and prefrontal cortex (PFC), brain areas involved in cognitive functions. Moreover, dopamine (DA) levels were reduced in the hp, but increased in the PFC. Furthermore, the survival mouse model of acute POX intoxication did not exhibit phenotypic manifestations of depression, anxiety or motor incoordination. However, our results demonstrated long-term recognition memory impairments, which are in accordance with the molecular and neurochemical effects observed. In conclusion, this mouse model can aid in researching POX exposure's effects on memory and developing potential countermeasures against the secondary neurotoxicity induced by severe OP poisoning.

The susceptibility of humans to neurodegenerative and neurodevelopmental toxicities caused by organophosphorus pesticides

The toxicology field is concerned with the impact of organophosphorus (OP) compounds on human health. These compounds have been linked to an increased risk of neurological disorders, including neurodegenerative and neurodevelopmental diseases. This article aims to review studies on the role of OP compounds in developing these neurological disorders and explore how genetic variations can affect susceptibility to the neurotoxicity of these pesticides. Studies have shown that exposure to OP compounds can lead to the development of various neurological disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), attention deficit hyperactivity disorder (ADHD), autism, intellectual disability, and other developmental neurotoxicities. Apart from inhibiting the cholinesterase enzyme, OP compounds are believed to cause other pathological mechanisms at both the extracellular level (cholinergic, serotonergic, dopaminergic, glutamatergic, and GABAergic synapses) and the intracellular level (oxidative stress, mitochondrial dysfunction, inflammation, autophagy, and apoptosis) that contribute to these disorders. Specific genetic polymorphisms, including PON1, ABCB1, NOS, DRD4, GST, CYP, and APOE, have increased the risk of developing OP-related neurological disorders.

Protective effects of antioxidants on striatal dopamine release induced by organophosphorus pesticides

Although the toxic effects of organophosphorus (OP) pesticides have been classically attributed to inhibition of the acetylcholinesterase, other neurotoxic mechanisms, as oxidative stress can also occur. Here we evaluated if antioxidants prevent the excessive dopamine release induced by OP pesticides in conscious and freely moving rats, using cerebral microdialysis technique. Intrastriatal infusion of paraoxon (5 mM), glufosinate (10 mM) or glyphosate (5 mM) significantly increased the dopamine release (1006 ± 106%, 991 ± 142%, and 1164 ± 128%, relative to baseline, respectively). To evaluate if these increased dopamine release could be related to oxidative stress, we pretreated animals with antioxidants glutathione (GSH, 400 or 800 μM), dithiothreitol (DTT, 5 or 10 μM), trolox (1 or 3 mM), and α-lipoic acid (ALA, 400 or 800 μM) before administration of OP pesticides. Intrastriatal administration of the antioxidants GSH, DTT, trolox, and ALA was highly effective in preventing the glyphosate and glufosinate-induced dopamine overflow. However, only GSH (800 μM) significantly decreased the effect of paraoxon on dopamine levels. The high toxicity of this pesticide and the low concentrations used could explain this lack of effect in our experimental conditions. The fact that ROS scavengers prevent the excessive dopamine release induced by OP pesticides, further supports the view that dopamine overflow can cause neuronal damage mediated, at least in part, by oxidative stress.

Review-Recent Advances in FSCV Detection of Neurochemicals via Waveform and Carbon Microelectrode Modification

Fast scan cyclic voltammetry (FSCV) is an analytical technique that was first developed over 30 years ago. Since then, it has been extensively used to detect dopamine using carbon fiber microelectrodes (CFMEs). More recently, electrode modifications and waveform refinement have enabled the detection of a wider variety of neurochemicals including nucleosides such as adenosine and guanosine, neurotransmitter metabolites of dopamine, and neuropeptides such as enkephalin. These alterations have facilitated the selectivity of certain biomolecules over others to enhance the measurement of the analyte of interest while excluding interferants. In this review, we detail these modifications and how specializing CFME sensors allows neuro-analytical researchers to develop tools to understand the neurochemistry of the brain in disease states and provide groundwork for translational work in clinical settings.

Addressing the instability issue of dopamine during microdialysis: the determination of dopamine, serotonin, methamphetamine and its metabolites in rat brain

Dopamine is a catecholamine neurotransmitter that degrades rapidly in aqueous solutions; hence, its analysis following brain microdialysis is challenging. The aim of the current study was to develop and validate a new microdialysis coupled LC-MS/MS system with improved accuracy, precision, simplicity and turnaround time for dopamine, serotonin, methamphetamine, amphetamine, 4-hydroxymethamphetamine and 4-hydroxyamphetamine analysis in the brain. Dopamine degradation was studied with different stabilizing agents under different storage conditions. The modified microdialysis system was tested in vitro, and was optimized for best probe recovery, assessed by %gain. LC-MS/MS assay was developed and validated for the targeted compounds. Stabilizing agents (ascorbic acid, EDTA and acetic acid) as well as internal and cold standards were added on-line to the dialysate flow. Assay linearity range was 0.01-100 ng/mL, precision and accuracy passed criteria, and LOQ and LLOQ were 0.2 and 1.0 pg, respectively. The new microdialysis coupled LC-MS/MS system was used in Wistar rats striatum after 4 mg/kg subcutaneous methamphetamine. Methamphetamine rapidly distributed to rat striatum reaching an average ~200 ng/mL maximum, ~82.5 min post-dose. Amphetamine, followed by 4-hydroxymethamphetamine, was the most abundant metabolite. Dopamine was released following methamphetamine injection, while serotonin was not altered. In conclusion, we proposed and tested an innovative and simplified solution to improve stability, accuracy and turnover time to monitor unstable molecules, such as dopamine, by microdialysis.

Photolysis-Induced Neurotoxicity Enhancement of Chlorpyrifos in Aquatic System: A Case Investigation on Caenorhabditis elegans

Contamination of the environment by toxic pesticides has become of great concern in agricultural countries. Chlorpyrifos (CP) is among the pesticides most commonly detected in the environment owing to its wide agricultural applications. The aim of this study was to compare potential changes in the toxicity of CP after irradiation. To this end, photolysis of CP was conducted under simulated sunlight, and neurotoxicity assessment was carried out at CP of 20 and 50 μg L^-1 and its corresponding irradiated mixture solutions which contain a mixture of identified intermediates using the nematode, Caenorhabditis elegans as a model organism. Photodegradation of 20 μg L^-1 CP for 1 h produced no obvious reduction of physiological damage, and more serious effects on animal movement were detected after exposure of the animals to a solution of 50 μg L^-1 for 1 h irradiation compared with unirradiated solution. GABAergic and cholinergic neurons were selectively vulnerable to CP exposure, and maximal neuropathological alterations were observed after 1 h irradiation of the CP solutions in coherence with the behavioral impairment. The generation of photoproducts was considered to be responsible for the enhanced disturbance on those biological processes. This work provided useful information on the toxicological assessments of chemicals that were produced during the environmental transformation of pesticides.

EDTA Chelation Therapy for the Treatment of Neurotoxicity

Neurotoxicity can be caused by numerous direct agents, of which toxic metals, organophosphorus pesticides, air pollution, radiation and electromagnetic fields, neurotoxins, chemotherapeutic and anesthetic drugs, and pathogens are the most important. Other indirect causes of neurotoxicity are cytokine and/or reactive oxygen species production and adoptive immunotherapy. The development of neurodegenerative diseases has been associated with neurotoxicity. Which arms are useful to prevent or eliminate neurotoxicity? The chelating agent calcium disodium ethylenediaminetetraacetic acid (EDTA)-previously used to treat cardiovascular diseases-is known to be useful for the treatment of neurodegenerative diseases. This review describes how EDTA functions as a therapeutic agent for these diseases. Some case studies are reported to confirm our findings.