Occupational mercury exposure in association with prevalence of multiple sclerosis and tremor among US dentists.

BACKGROUND: The effects of chronic occupational exposure to elemental mercury (Hg(0)) are largely unknown. The objective was to evaluate the association of occupational Hg(0) exposure with multiple sclerosis (MS) and tremor. METHODS: The study included 13,906 dentists who attended the American Dental Association's annual meeting over 24 years (1986-2007 and 2011-2012). Participants reported MS and tremor and provided urine specimens for Hg(0) analysis. The authors estimated mean Hg(0) exposures over time and used logistic regression to estimate the associations of 3 Hg(0) exposure measures with MS or tremor. RESULTS: Among participants, 0.18% reported MS and 1.24% reported tremor. Hg(0) exposure was not associated with MS (odds ratio [OR] per 191 micrograms per liter in cumulative Hg(0) exposure, 0.85; 95% confidence interval [CI], 0.39-1.85). Increased prevalent risk of tremor was found with exposure to both urinary Hg(0) exposure (OR, 1.10 [95% CI, 1.00-1.22]) and cumulative Hg(0) exposure among younger dentists (< 51 years; OR, 1.13 [95% CI, 1.05-1.22]). CONCLUSIONS: Occupational Hg(0) exposure in US dentists decreased over time and now is approaching that of the general population. Our results suggest a positive association between Hg(0) exposure and tremor. PRACTICAL IMPLICATIONS: Studies with more sophisticated outcome and exposure measures, and including more retired dentists, would provide critical information toward understanding the relation of Hg(0) exposures to MS and tremor risk.

Methyl mercury exposure in populations at risk: Analysis of NHANES 2011-2012.

BACKGROUND: Ingestion of fish contaminated with methyl mercury can lead to adverse health outcomes, particularly when exposure occurs in utero. NHANES 2011-2012 includes total blood mercury (TBHg) and methyl mercury (MeHg) measurements as well as a unique race/ethnicity category for Asians, allowing for improved analysis of determinants of risk. OBJECTIVE: Our objective was to characterize the current burden of MeHg exposure in the US among subgroups who are at risk of health effects due to their physiologic vulnerability to MeHg's effects and/or due to frequent fish consumption, specifically women of childbearing age (WCBA) and adults ≥50 years of age. METHODS: We calculated 90th and 95th percentile estimates as well as geometric means of MeHg for predictive variables. We used multivariable linear regression analyses to estimate the proportional change in mean MeHg associated with each category of all predictive variables. We calculated the validity of screening procedures using fish consumption questions and TBHg testing to predict elevated MeHg. RESULTS: The geometric mean MeHg levels were highest among Asian WCBA (1.17 µg/L) and Asians ≥50 years old (2.49 µg/L). Over 23% of Asian WCBA had levels ≥3.5 µg/L and 25% of Asians ≥50 years old had levels ≥5.8 µg/L. Frequency of fish consumption explained 21-23% of the variation in MeHg. Twenty-five percent of women eating fish ≥ twice per week had MeHg ≥3.5 µg/L. TBHg showed high validity for MeHg ≥5.8 µg/L, and two-step screening using ≥2 fish meals/month followed by TBHg also showed high validity. CONCLUSION: Asian WCBA continue to have increased MeHg exposure from fish consumption, putting their offspring at risk. Screening for MeHg among high-risk groups should be considered.

Dopaminergic amacrine cells express opioid receptors in the mouse retina.

The presence of opioid receptors has been confirmed by a variety of techniques in vertebrate retinas including those of mammals; however, in most reports, the location of these receptors has been limited to retinal regions rather than specific cell types. Concurrently, our knowledge of the physiological functions of opioid signaling in the retina is based on only a handful of studies. To date, the best-documented opioid effect is the modulation of retinal dopamine release, which has been shown in a variety of vertebrate species. Nonetheless, it is not known if opioids can affect dopaminergic amacrine cells (DACs) directly, via opioid receptors expressed by DACs. This study, using immunohistochemical methods, sought to determine whether (1) µ- and δ-opioid receptors (MORs and DORs, respectively) are present in the mouse retina, and if present, (2) are they expressed by DACs. We found that MOR and DOR immunolabeling were associated with multiple cell types in the inner retina, suggesting that opioids might influence visual information processing at multiple sites within the mammalian retinal circuitry. Specifically, colabeling studies with the DAC molecular marker anti-tyrosine hydroxylase antibody showed that both MOR and DOR immunolabeling localize to DACs. These findings predict that opioids can affect DACs in the mouse retina directly, via MOR and DOR signaling, and might modulate dopamine release as reported in other mammalian and nonmammalian retinas.