Zinc modulates the electro-olfactogram of the frog

Objective: Zinc is considered an important element in olfaction, however, its exact role is still unclear. A large amount of zinc is contained in the olfactory mucosa, so Zn2+ may behave as a neuromodulator, as in the hippocampus. To reveal the acute effects of Zn2+ on olfactory mucosa, electro-olfactograms (EOG) were recorded with or without Zn2+. Methods: The isolated olfactory mucosa of a bullfrog (Rana catesbiana) was set in an EOG recording chamber and bathed in Ringer’s solution. Effects of ZnSO4 (25 μM) on EOGs were examined. Four types of stimulants, n-amyl acetate (200 μM), menthone (10 μM), forskolin (2 μM), and 3-isobutil-methylxisanthine (IBMX, 100 μM) were tested. Results: Zn2+ (25 μM) charged with the ciliated surface of the olfactory mucosa attenuates EOGs which were produced not only by odorants but also by forskolin and IBMX. The attenuating ratios of EOGs for stimulants were as follows; n-amyl acetate (0.51±0.18, n=4), menthone (0.48±0.28, n=4), forskolin (0.61±0.16, n=4), and IBMX (0.68±0.19, n=4); (mean±S.D.). These attenuations were reversible. The results indicate that Zn2+ may block the c-AMP dependent transduction channels of the olfactory cells. Conclusion: Micro molar Zn2+ attenuates EOG of the frog. Zn2+ may be thought to behave as one of the modulators in olfactory reception.