Concentration and membrane fluidity dependence of odor discrimination in the turtle olfactory system

In the present study, we examined the concentration dependence of odor discrimination in turtle olfactory bulbar responses using the cross-adaptation technique. In the odorant pairs with diverse molecular structures, the degree of discrimination was unchanged or only slightly decreased with an increase in odorant concentrations, suggesting that odorants are well discriminated even at high concentrations. In the odorant pairs with closely related molecular structures, the degree of discrimination was decreased with an increase in odorant concentrations. An increase in the temperature of turtle olfactory epithelium also decreased the ability to discriminate these odorants. There was a good correlation between changes in the odor discriminating ability induced by an increase in odor concentrations and those induced by a temperature increase. The liposomes were made of lipids extracted from the turtle olfactory epithelia and changes of their membrane fluidity induced by adsorption of odorants were monitored with DPH. There was a good correlation between a decrease in odor discriminating ability and the membrane fluidity changes induced by odorants. We suggest that decreases in odor discriminating ability induced either by an increase in odor concentration or by a temperature increase are ultimately caused by changes in the membrane fluidity.