Copper kills sense of smell

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The presence of low levels of copper in water causes fish to lose their sense of smell, but it will return when copper is removed, says research.

In a paper due to be published later this year, a team of scientists from the University of Bolgna have shown that low levels of copper Cu(2+) causes loss of the sense of smell through olfactory neuron death in the olfactory epithelium.

However, their study, which used the West African cichlid Tilapia mariae as a model organism, has shown that the fish can recover its sense of smell after a period of time.

The scientists exposed the Tilapia to copper levels of 20, 40 and 100 micrograms per litre for four days and then returned them to unpolluted water to monitor the morphological changes they went through during recovery.

The study says: "Immunostaining with PCNA showed a massive mitotic activity in the basal region of the mucosa immediately after exposure was terminated. The mitotically produced elements were immature neurons since they expressed the neural growth-associated phosphoprotein GAP-43.

"After 3 days of recovery the nuclei had already completed their migration to the upper portion of the epithelium and mitotic activity was much less intensive. After 10 days the olfactory tissue did not present differences when compared to the control tissue. These results suggest that after 10 days the regeneration is completed and the integrity of the tissue restored."

The paper is due to be published in the journal Aquatic Toxicology: Bettini S, Ciani F, Franceschini V (2006) - Recovery of the olfactory receptor neurons in the African Tilapia mariae following exposure to low copper level. Aquatic Toxicology.