Axonal Transport of Cadmium in the Olfactory Nerve of the Pike

¹⁰⁹Cd²⁺ was applied in the olfactory chambers of pikes (Esox lucius) and the dynamics of the axoplasmic flow of the metal was determined in the olfactory nerves by gamma spectrometry and autoradiography. The results showed that the ¹⁰⁹Cd²⁺ is transported at a constant rate along the olfactory nerves. The profile of the ¹⁰⁹Cd²⁺ in the nerves showed a wave front of transported metal followed by a saddle region. When the nasal chambers were washed 2 hr after application of the ¹⁰⁹Cd²⁺ well-defined transport peaks for the metal were seen in the olfactory axons. The maximal velocity for the transport of ¹⁰⁹Cd²⁺, which corresponds to the movement of the wave front, was 2.38±0.10 mm hr (mean±S.E.) at the experimental temperature (10 C). The average velocity for the transport of the ¹⁰⁹Cd²⁺, which corresponds to the peak apex movement of the wave, was 2.18±0.05 mm/hr (mean±S.E.) at 10 C. The transported ¹⁰⁹Cd²⁺ was strongly accumulated in the anterior parts of the olfactory bulbs, whereas in other brain areas the levels of the metal remained low. Autoradiography of a pike exposed to ¹⁰⁹Cd²⁺ via the water showed a strong labelling in the receptor-cell-containing olfactory rosettes, whereas other structures in the olfactory chambers were only weakly labelled. The accumulation and axonal transport in the olfactory neurons may be noxious and constitute an important component in the toxicology of cadmium in fish, and this may apply also to some other heavy metals.