TRANSPORT AND SUBCELLULAR-DISTRIBUTION OF NICKEL IN THE OLFACTORY SYSTEM OF PIKES AND RATS

Occupational exposure to nickel by inhalation may result in impaired o lfactory sense. Recent studies have shown that nickel is transported f rom the olfactory epithelium along the axons of the primary olfactory neurons to the brain. In the present study Ni-63(2+) was applied in th e 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 ol factory nerves, which slowly moved toward the olfactory bulbs. The max imal Ni-63(2+) transport rate corresponding to the movement of the bas e of the wave front was found to be about 0.13 mm/h at the experimenta l temperature (10 degrees C). This rate of Ni-63(2+) transport falls i nto the class of slow axonal transport. Radioluminography of tape sect ions of a pike given Ni-63(2+) in the right olfactory chamber showed a selective labeling of the right olfactory nerve. The subcellular dist ribution of Ni-63(2+) in the olfactory nerves and the olfactory epithe lium of the pikes was studied in tissues subjected to homogenizations and centrifugations, and these methods were also used to examine the s ubcellular distribution of Ni-63(2+) in tissues of the olfactory syste m 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 i n association with various particulate cell constituents. Gel filtrati ons 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 hi stidine in vitro. It is likely that the cytosolic nickel may be bound to histidine or possibly to other amino acids which are similar in siz e to histidine. Additionally, in the olfactory tissues of the rat the Ni-63(2+) was partly present in the cytosol in association with a comp onent 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 su bcellular distribution also in other parts of the olfactory system. (C ) 1998 Society of Toxicology.