ScienceDaily News Release - Mercury Can Jump Barrier That Keeps Toxins Out Of Brain

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ScienceDaily News Release Mercury Can Jump Barrier That Keeps

Toxins Out Of Brain

 

http://www.sciencedaily.com/releases/1999/09/990909080318.htm

 

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Source:  

American Chemical Society

 

 

Date:  

1999-09-09

Mercury Can Jump Barrier That Keeps Toxins Out Of Brain

Researchers say they have found the first evidence that mercury can

circumvent the blood-brain barrier that usually prevents such toxins from

entering the brain. Their studies were with brown and rainbow trout - two of

the most popular species for anglers and fish consumers - but may have

implications for humans and other species as well, they say. The study was

carried out by researchers at Canada's Maurice Lamontagne Institute and the

Swedish University of Agricultural Sciences and is published in the October

1 issue of Environmental Science and Technology, a peer-reviewed publication

of the American Chemical Society, the world's largest scientific society.

 

The researchers found that mercury dissolved in lake and river water can

enter the nerves that connect water-exposed sensory receptors (for odor,

taste, vibration and touch) to the fishes' brains. It can go directly to the

brain, they say, circumventing the blood-brain barrier, a nearly impermeable

membrane that prevents most toxins from reaching the brain. They also say

this is the first study concerning mercury levels in fish brains (as opposed

to levels accumulated in other body areas) and the first time it has been

established that mercury can enter fish brains through sensory receptors and

their connected nerves.

 

Mercury's toxic effects on fish and human brains are well established. Fish

depend on their nervous systems to find food, communicate, migrate, orient

themselves and recognize predators. Dissolved mercury usually is taken in by

fish through their gills and dispersed by blood as it circulates through the

body. In most cases, little mercury accumulates in the brain, which is

protected by the blood-brain barrier. However, mercury that does accumulate,

having passed through the bloodstream or through nerves, is concentrated in

specific sites connected to primary sensory nerves critical to the function

of the nervous system.

 

" Considering the importance of complex behavior in the life of fish, and the

well-known deleterious effects of mercury upon the nervous system, the

toxicological significance of this uptake route needs to be assessed, " said

Claude Rouleau, Ph.D., a research scientist at Environment Canada's National

Water Research Institute and the study's primary investigator (Rouleau did

the work at the Swedish University of Agricultural Sciences, Uppsala, and

completed it for publication while at the Maurice Lamontagne

Institute-Department of Fisheries and Oceans Canada, in Mont-Joli, Quebec).

" The accumulation of mercury or other toxic chemicals in the brain via

water-exposed nerve terminals may result in an alteration of these functions

and jeopardize fish survival. We believe that uptake of metals such as

mercury and the subsequent transport along sensory nerves is a process

common to all fish species, and in this respect, it is possible that other

toxins (such as pesticides) also could reach fish brains in this way and

this is a subject worthy of further study. "

 

Rouleau also said that while chemicals in the brains of such fish may not

have direct human implications (people generally don't eat fish brains), the

survival of these species does affect humans. " However, the fact that

mercury is transported along fish nerves can be extrapolated to humans, as

nerve transport also occurs in mammals, including humans, " said Rouleau.

" Thus, mercury and other toxins could possibly accumulate in human brains

via nerve transport. " Earlier research has shown that manganese, cadmium and

mercury can be taken through the nasal mucosa of rodents and transported to

the brain through the olfactory nerves.

 

The study's other main investigator was Professor Hans Tjalve of the Swedish

University of Agricultural Sciences.

 

The accumulated mercury was located by whole-body autoradiography (used by

the pharmaceutical industry to see how drugs are distributed throughout the

body). Fish were exposed to radioactive mercury, frozen, then cut into very

thin slices. The slices were exposed to X-ray film for varying amounts of

time - a few weeks to a few months.

 

The film blackened only in areas where the radioactive metal was present.

The method is particularly useful for obtaining information on fragile

organs or tissues, such as fish brains.

 

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This story has been adapted from a news release issued by American Chemical

Society.