Occupational exposure to nickel by inhalation may result in impaired olfactory sense. Recent studies have shown that nickel is transported from the olfactory epithelium along the axons of the primary olfactory neurons to the brain. In the present study Ni-63(2+) was applied in the olfactory chambers of pikes (Esox lucius) and the rate at which the metal was transported in the primary olfactory neurons was determined by beta-spectrometry. The results showed a wave of Ni-63(2+) in the olfactory nerves, which slowly moved toward the olfactory bulbs. The maximal Ni-63(2+) transport rate corresponding to the movement of the base of the wave front was found to be about 0.13 mm/h at the experimental temperature (10 degrees C). This rate of Ni-63(2+) transport falls into the class of slow axonal transport. Radioluminography of tape sections of a pike given Ni-63(2+) in the right olfactory chamber showed a selective labeling of the right olfactory nerve. The subcellular distribution of Ni-63(2+) in the olfactory nerves and the olfactory epithelium of the pikes was studied in tissues subjected to homogenizations and centrifugations, and these methods were also used to examine the subcellular distribution of Ni-63(2+) in tissues of the olfactory system of rats given the metal intranasally. It was found that the Ni-63(2+), in both the pike and the rat, was present in the cytosol and also in association with various particulate cell constituents. Gel filtrations of the cytosols showed that the Ni-63(2+) mainly was eluted at a V-e/V-o ratio corresponding to a MW of about 250. The same coefficient was obtained in gel filtrations performed with Ni-63(2+) mixed with histidine in vitro. It is likely that the cytosolic nickel may be bound to histidine or possibly to other amino acids which are similar in size to histidine. Additionally, in the olfactory tissues of the rat the Ni-63(2+) was partly present in the cytosol in association with a component with a MW of about 25,000. It is concluded that (i) Ni-63(2+) i, transported in the primary olfactory neurons by means of slow axonal transport, (ii) in this process the metal is bound to both particulate and soluble cytosolic constituents, and (iii) the metal shows this subcellular distribution also in other parts of the olfactory system. (C) 1998 Society of Toxicology.
