T5 AM Terrestrial Ecotoxicology
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 321-323

(BAS-1117-834477) Mercury affects neurotransmission in mink: Evidence from the laboratory and field.

Basu, N.^{1, 2}, Scheuhammer, A.², Grochowina, N.³, Rouvinen-Watt, K.⁴, Evans, R³, Chan, H.¹, ¹ McGill University, Montreal, QC, Canada² Canadian Wildlife Service, Ottawa, ON, Canada³ Trent University, Peterborough, ON, Canada⁴ Nova Scotia Agricultural College, Truro, NS, Canada

ABSTRACT- We have previously shown that fish-eating wildlife can bioaccumulate mercury (Hg) to levels known to affect brain chemistry. Field studies on wild trapped mink (Mustela vison) and river otters (Lontra canadensis) have shown that significant correlations exist between the concentrations of brain Hg and levels of muscarinic cholinergic (mACh) receptors. To verify these ecological findings, we characterized the cholinergic system in discrete brain regions of captive mink exposed to methyl Hg (MeHg) as part of a larger feeding experiment with MeHg and selenomethionine. Animals were exposed to MeHg at dietary concentrations of 0, 0.1, 0.5, 1, and 2 ppm for 89 days at the Nova Scotia Agricultural College in late-2004. Our results showed that 0.5-2 ppm MeHg caused significant increases in mACh receptor levels (30-69%), as well as cholinesterase activity (17-34%) in the occipital cortex, basal ganglia, and brain stem regions of the brain. Comparison of normalized regression plots of brain Hg and mACh receptor levels between the field and laboratory studies showed no significant differences. We measured no MeHg-related changes on acetylcholine, and are currently exploring the effects on choline acetyltransferase, nicotinic receptor, and choline transporter, as well as other neurochemical pathways, including the GABAergic and dopaminergic systems. Previous research has established a dietary LOAEL of 1.1 ppm MeHg (based on changes in animal behaviour and tissue pathologies), but our findings show that significant effects on brain chemistry can occur at lower levels of exposure (i.e., 0.5 ppm). These findings are of ecological and physiological concern because wild mink are often exposed to such concentrations in nature. In conclusion, by comparing biological responses in the laboratory and field, we provide strong evidence of a cause-and-effect relationship whereby ecologically realistic levels of Hg can affect brain chemistry in piscivorous wildlife.

Key words: neurotoxicology, mercury, mink, biomarkers