Laserfiche WebLink
of these enzyme systems has not been determined, their presence <br />in olfactory tissues suggests ability to eliminate or sequester <br />toxic solutes. <br />If olfactory receptors did become less sensitive to copper <br />and zinc exposure as a result of induction of protective <br />mechanisms, the time-course of toxic effects and response of <br />olfactory sensory cells probably included (1) a degeneration <br />phase as observed in 24-h exposures, followed by (2) induction of <br />protective mechanisms, and (3) regeneration of olfactory receptor <br />cells. Results of the 96-h zinc exposure, in which we observed <br />presence of ciliated receptor cells, are consistent with this <br />time-course. Degeneration induced by zinc ions is rapid. Suzuki <br />and Suzuki (1981) showed that irrigation of the olfactory organ <br />of lamprey (Entosphenus japonicas) with 32 g/L zinc sulfate for a <br />few seconds caused loss of cilia from receptor cells. Similarly, <br />Cancalon (1982) showed that irrigation of the olfactory organ of <br />channel catfish (Ictalurus punctatus) with 19 g/L ZnSO4 for a few <br />seconds caused loss of cilia from receptor cells 1 d after <br />exposure. Cancalon (1982) also studied regeneration of olfactory <br />receptors and reported that the number of regenerated receptors <br />was > 80% of pre-exposure abundance within 7 d after exposure. <br />Similar patterns of degeneration and regeneration have been <br />observed for copper exposure (Gardner and LaRoche 1973; <br />Cancalon 1982; Moran et al. 1987; Klima and Applehans 1990; <br />Klaprat et al. 1992). <br />18 <br />