TEMPERATURE INCREASE ABOLISHES ABILITY OF TURTLE OLFACTORY RECEPTOR TO DISCRIMINATE SIMILAR ODORANT

We examined the effects of temperature changes on odor-discriminating ability of turtle olfactory receptors in vivo by applying the cross-ad aptation method to the olfactory bulbar responses. The olfactory syste m discriminated well all eight pairs of odorants examined at 5 and 18 degrees C. The ability of the olfactory receptors to discriminate pair s of odorants having similar structures (e.g., trans-3-hexenol and cis -3-hexenol; d-carvone and l-carvone) was reversibly abolished by incre asing the temperature up to 40 degrees C, whereas discrimination of od orants having quite different structures was much less affected. The m embrane fluidity of cells isolated from turtle olfactory epithelia and liposomes made of lipids extracted from the epithelia changed in a si milar temperature range as for the decrease of the odor-discriminating ability, suggesting that an increase in membrane fluidity is correlat ed with the abolishment of the odor-discriminating ability. The presen t results also suggest that in vivo desensitization (adaptation) occur s not at the cellular level but at the receptor level. This mechanism was supported by the data recorded from a single olfactory cilium, sho wing that a single cell has both receptors for l-carvone and d-carvone and that the response to d-carvone appeared after the response to l-c arvone was adapted.