Modification of transduction mechanisms in the frog's olfactory mucosa using a thiol reagent as olfactory stimulus

Abstract

The effects of the thiol-specific reagent N-ethylmaleimide (NEM) used in the vapour phase have been tested on the olfactory epithelium of the frog when recording the electro-olfactogram (EOG) and spike activity from single receptor cells. The reagent was delivered alone or mixed with the odorant isoamyl acetate. At low concentration the reagent induced slow potentials resembling simple EOGs. At higher concentrations (20% of the saturated vapour) three negative and one positive slow components were observed in the response. A complex relationship was found between the amplitude of the slow potential and the concentration of the reagent. Repeated stimulations at high concentration caused the suppression of the negative voltage transients and the development of the positive component. NEM vapour elicited spike discharges in some of the recorded units, with the responses resembling those evoked by usual odorants. After long-lasting stimulations (30 sec) with NEM, the receptors failed to respond to both reagent and odorant. This suppression of response could be partly prevented by exposing the olfactory epithelium to the odorant vapour before and during the exposure to the reagent (protection). The results indicate that NEM acts on the olfactory epithelium in several ways, including an odorant-like action on olfactory receptor sites. An effect on the supporting cells is also suggested. Hypotheses for explaining the protection mechanism are considered.