Effects of exposure to amitraz on noradrenaline, serotonin and dopamine levels in brain regions of 30 and 60 days old male rats

Bisphenol-A Neurotoxic Effects on Basal Forebrain Cholinergic Neurons In Vitro and In Vivo

The widely used plasticizer bisphenol-A (BPA) is well-known for producing neurodegeneration and cognitive disorders, following acute and long-term exposure. Although some of the BPA actions involved in these effects have been unraveled, they are still incompletely known. Basal forebrain cholinergic neurons (BFCN) regulate memory and learning processes and their selective loss, as observed in Alzheimer's disease and other neurodegenerative diseases, leads to cognitive decline. In order to study the BPA neurotoxic effects on BFCN and the mechanisms through which they are induced, 60-day old Wistar rats were used, and a neuroblastoma cholinergic cell line from the basal forebrain (SN56) was used as a basal forebrain cholinergic neuron model. Acute treatment of rats with BPA (40 µg/kg) induced a more pronounced basal forebrain cholinergic neuronal loss. Exposure to BPA, following 1- or 14-days, produced postsynaptic-density-protein-95 (PSD95), synaptophysin, spinophilin, and N-methyl-D-aspartate-receptor-subunit-1 (NMDAR1) synaptic proteins downregulation, an increase in glutamate content through an increase in glutaminase activity, a downregulation in the vesicular-glutamate-transporter-2 (VGLUT2) and in the WNT/β-Catenin pathway, and cell death in SN56 cells. These toxic effects observed in SN56 cells were mediated by overexpression of histone-deacetylase-2 (HDAC2). These results may help to explain the synaptic plasticity, cognitive dysfunction, and neurodegeneration induced by the plasticizer BPA, which could contribute to their prevention.

Integrated gender-related effects of profenofos and paclobutrazol on neurotransmitters in mouse

This study investigated the effects of paclobutrazol and profenofos on six neurotransmitters and their metabolites involving in cholinergic and non-cholinergic neurotransmission systems in mouse. The results revealed that profenofos decreased the levels of 5-hydroxyindole-3-acetic acid (5-HIAA) and normetanephrine (MNE), and increased the level of dopamine (DA) in the mice after four weeks of exposure. The turnovers of serotonergic neurotransmission system (5-HIAA/5-HT) and noradrenergic neurotransmission system (MNE/NE) showed a decline under exposure of profenofos. Exposure to paclobutrazol resulted in decreases of 5-HIAA and MNE in both sexes of mice, and of 5-HT and ACh in the females. Similar to profenofos, the turnovers of serotonergic neurotransmission system and noradrenergic neurotransmission system decreased in the mice exposed to paclobutrazol. The integrated biomarker response (IBR) was introduced to comprehensively evaluate the neurotoxic effects of the two pesticides through integration of the responses of neurotransmitters. The results of IBR indicated that the overall effect of neurotransmitters increased at the beginning of exposure and then decreased in the end. It was also found that the order of neurotoxic effect for the two pesticides is as: paclobutrazol > profenofos referred to their LD50. Furthermore, the effects on neurotransmitters are higher in the males.

Pharmacokinetics and brain distribution of amitraz and its metabolites in rats

Amitraz is an acaricide and insecticide widely used in agriculture and veterinary medicine. Although central nervous system (CNS) toxicity is one of major toxicities following oral ingestion of amitraz, the understanding of the cause of the toxicity is limited. This study evaluated the systemic and brain exposure of amitraz and its major metabolites, BTS27271, 2',4'-formoxylidide, and 2,4-dimethylaniline following administration of amitraz in male Sprague-Dawley rats. Significant metabolism of amitraz was observed following the intravenous and oral administration. Amitraz related metabolites were majority of the total exposure observed, especially following oral administration. BTS27271 had higher brain exposure than amitraz and its other metabolites, which was due to low plasma protein binding but high brain tissue binding of BTS27271. Since BTS27271 has similar or higher toxicity and α₂-adrenoreceptor agonist potency than amitraz, its exposure in brain tissues may be the major cause of CNS toxicity of amitraz in animals and humans.

Amitraz changes NE, DA and 5-HT biosynthesis and metabolism mediated by alterations in estradiol content in CNS of male rats

Amitraz is a formamidine insecticide/acaricide that alters different neurotransmitters levels, among other neurotoxic effects. Oral amitraz exposure (20, 50 and 80 mg/kg bw, 5 days) has been reported to increase serotonin (5-HT), norepinephrine (NE) and dopamine (DA) content and to decrease their metabolites and turnover rates in the male rat brain, particularly in the striatum, prefrontal cortex, and hippocampus. However, the mechanisms by which these alterations are produced are not completely understood. One possibility is that amitraz monoamine oxidase (MAO) inhibition could mediate these effects. Alternatively, it alters serum concentrations of sex steroids that regulate the enzymes responsible for these neurotransmitters synthesis and metabolism. Thus, alterations in sex steroids in the brain could also mediate the observed effects. To test these hypothesis regarding possible mechanisms, we treated male rats with 20, 50 and 80 mg/kg bw for 5 days and then isolated tissue from striatum, prefrontal cortex, and hippocampus. We then measured tissue levels of expression and/or activity of MAO, catechol-O-metyltransferase (COMT), dopamine-β-hydroxylase (DBH), tyrosine hydroxylase (TH) and tryptophan hydroxylase (TRH) as well as estradiol levels in these regions. Our results show that amitraz did not inhibit MAO activity at these doses, but altered MAO, COMT, DBH, TH and TRH gene expression, as well as TH and TRH activity and estradiol levels. The alteration of these enzymes was partially mediated by dysregulation of estradiol levels. Our present results provide new understanding of the mechanisms contributing to the harmful effects of amitraz.

Thyroid Hormone-Otx2 Signaling Is Required for Embryonic Ventral Midbrain Neural Stem Cells Differentiated into Dopamine Neurons

Midbrain dopamine (DA) neurons are essential for maintaining multiple brain functions. These neurons have also been implicated in relation with diverse neurological disorders. However, how these neurons are developed from neuronal stem cells (NSCs) remains largely unknown. In this study, we provide both in vivo and in vitro evidence that the thyroid hormone, an important physiological factor for brain development, promotes DA neuron differentiation from embryonic ventral midbrain (VM) NSCs. We find that thyroid hormone deficiency during development reduces the midbrain DA neuron number, downregulates the expression of tyrosine hydroxylase (TH) and the dopamine transporter (DAT), and impairs the DA neuron-dependent motor behavior. In addition, thyroid hormone treatment during VM NSC differentiation in vitro increases the production of DA neurons and upregulates the expression of TH and DAT. We also found that the thyroid hormone enhances the expression of Otx2, an important determinant of DA neurogenesis, during DA neuron differentiation. Our in vitro gene silencing experiments indicate that Otx2 is required for thyroid hormone-dependent DA neuron differentiation from embryonic VM NSCs. Finally, we revealed both in vivo and in vitro that the thyroid hormone receptor alpha 1 is expressed in embryonic VM NSCs. Furthermore, it participates in the effects of thyroid hormone-induced Otx2 upregulation and DA neuron differentiation. These data demonstrate the role and molecular mechanisms of how the thyroid hormone regulates DA neuron differentiation from embryonic VM NSCs, particularly providing new mechanisms and a potential strategy for generating dopamine neurons from NSCs.

Amitraz

In the asymmetric unit of the title compound {systematic name: N'-(2,4-di-methyl-phen-yl)-N-[N-(2,4-di-methyl-phen-yl)carbox-imido-yl]-N-methyl-methanimidamide}, C19H23N3, which is a formamidine pesticide, there are two independent and conformationally similar mol-ecules, with the dihedral angle between the mean planes of the 2,4-di-methylbenzene rings in each mol-ecule being 41.63 (6) and 42.09 (5)°. The crystal structure is stabilized by a C-H⋯N hydrogen bond, as well as weak inter-molecular C-H⋯π and π-π inter-actions [ring centroid separation = 3.7409 (15) Å], giving one-dimensional chains extending down the b direction.