Comparative effects of organic and inorganic mercury on in vivo dopamine release in freely moving rats

Abstract

The present study was carried out in order to compare the effects of administration of organic (methylmercury, MeHg) and inorganic (mercury chloride, HgCl 2 ) forms of mercury on in vivo dopamine (DA) release from rat striatum. Experiments were performed in conscious and freely moving female adult Sprague-Dawley (230-280 g) rats using brain microdialysis coupled to HPLC with electrochemical detection. Perfusion of different concentrations of MeHg or HgCl 2 (2 µL/min for 1 h, N = 5-7/group) into the striatum produced significant increases in the levels of DA. Infusion of 40 µM, 400 µM, or 4 mM MeHg increased DA levels to 907 ± 31, 2324 ± 156, and 9032 ± 70% of basal levels, respectively. The same concentrations of HgCl 2 increased DA levels to 1240 ± 66, 2500 ± 424, and 2658 ± 337% of basal levels, respectively. These increases were associated with significant decreases in levels of dihydroxyphenylacetic acid and homovallinic acid. Intrastriatal administration of MeHg induced a sharp concentration-dependent increase in DA levels with a peak 30 min after injection, whereas HgCl 2 induced a gradual, lower (for 4 mM) and delayed increase in DA levels (75 min after the beginning of perfusion). Comparing the neurochemical profile of the two mercury derivatives to induce increases in DA levels, we observed that the time-course of these increases induced by both mercurials was different and the effect produced by HgCl 2 was not concentration-dependent (the effect was the same for the concentrations of 400 µM and 4 mM HgCl 2 ). These results indicate that HgCl 2 produces increases in extracellular DA levels by a mechanism differing from that of MeHg.

Effects of low dose endosulfan exposure on brain neurotransmitter levels in the African clawed frog Xenopus laevis

“…In mammals, dopamine is also considered to be a physiologically relevant mediator of feeding behaviour as the mesolimbic dopamine reward system in human plays a key role in transforming subjective ''liking'' to motivational ''wanting'' of palatable food (Rui, 2013). The exposure to several pesticides induces a release of dopamine in the extracellular part of brain cells (Faro et al, 2009), which supports that this endosulfan effect on neurotransmitter content in the brain is conserved among vertebrates. Similar responses were observed for GABA which is in accordance with interconnected regulations of these neurotransmitters in time and space (Liu et al, 1997).…”

Does prolactin mediate parental and life-history decisions in response to environmental conditions in birds? A review

“…Contaminants may interfere with enzymes involved in steroidogenesis [e.g., hydroxysteroid dehydrogenase (HSD) and cytochrome P450 (CYP) enzymes], or less directly through modulation of the feedback mechanisms in the hypothalamuspituitary-gonadal axis (Sanderson and van den Berg, 2003). Environmental contaminants may also directly alter prolactin secretion through a chemically-induced dysregulation of dopamine neurotransmitters that are involved in the modulation of PRL secretion, as demonstrated in laboratory rodents (Faro et al, 2007;Lafuente et al, 2000).…”

Paraquat neurotoxicity is mediated by the dopamine transporter and organic cation transporter-3

“…To lend further support for this argument, we performed in vivo microdialysis to compare the functional effects of PQ 2+ treatment in freely moving Oct3 −/− and Oct3 +/+ mice. Using DA overflow as a functional response of DA neurons to PQ 2+ (15,16), we detected an increase in extracellular DA ∼120 min after a single PQ 2+ injection (i.p.) in Oct3 −/− mice, but not in their Oct3 +/+ littermates (Fig.…”