Transport and subcellular distribution of intranasally administered zinc in the olfactory system of rats and pikes.

Zinc is an essential element, which can act as a neuromodulator and also is bound in zinc proteins in the brain. The olfactory bulb contains high concentrations of zinc. In the present study, 65Zn(2+) was applied on the olfactory epithelium of rats and pikes and the transport of the metal in the olfactory system was then examined. Administration of 65Zn(2+) in the nasal cavity of rats or the olfactory chambers in pikes resulted in an uptake of the metal in the olfactory epithelium and a transport of the metal along the primary olfactory neurons to their terminations in the olfactory bulbs. Low levels of 65Zn(2+) passed these terminals and continued into the interior of the bulbs. In the rats 65Zn(2+) was also detected in the anterior parts of the olfactory cortex. Subcellular fractionations of the olfactory mucosa and olfactory bulb of rats given 65Zn(2+) intranasally showed that the metal is bound both to particulate cellular constituents and to cytosolic components in these tissues. Gel chromatography indicated that some of the zinc in the cytosol is bound to metallothionein in the olfactory mucosa and bulb. Inhalation of zinc-containing dusts or fumes occurs in some work-places and may imply high exposure of the nasal tissues. It is not known whether neurotoxicity may be related to uptake of zinc in the olfactory system. However, this is an issue which deserves attention, since zinc dysregulation has been implied to play a role in Alzheimer's disease. In addition, impairment of the sense of smell and degenerative changes of the olfactory tissues have been seen in early stages of some neurodegenerative disorders.