Effects of mercury on neurochernical receptors in wild river otters (Lontra canadensis)

Fish-eating wildlife, such as river otters (Lontra canadensis), accumulate mercury (Hg) at concentrations known to impair animal behavior, but few studies have explored the underlying biochemical changes that precede clinical neurotoxicity. The objective of this study was to determine if Hg exposure can be related to concentrations of neurochemical receptors in river otters. River otter carcasses (n = 66) were collected in Ontario and Nova Scotia (Canada) by local trappers in 2002-2004. Concentrations of Hg (total and organic) were measured in the cerebral cortex and cerebellum. Saturation binding curves for the cholinergic muscarinic acetylcholine (mACh) receptor and dopamine-2 (D2) receptor were completed for each animal to calculate receptor density (B-max) and ligand affinity (K-d). Negative correlations were found between concentrations of Hg and mACh receptor B-max (r(total) (Hg) = -0.458, r(inorganic) (Hg) = -0.454, r(organic) (Hg) = -0.443) in the cerebral cortex. A negative correlation was also found between concentrations of total Hg and D2 receptor B-max (r = -0.292) in the cerebral cortex. These results suggest that neurochemical receptors may prove useful as novel biomarkers of Hg exposure and neurotoxic effects in wildlife. Given the importance of cholinergic and dopaminergic systems in animal physiology, the ecological implications of these changes need to be investigated.