Atomic-force microscopy on the olfactory dendrites of the silkmoths antheraea polyphemus and A. pernyi

Olfactory transduction is thought to occur in the outer dendritic membrane of insect olfactory receptor neurons. Electrophysiological studies have indicated that the outer dendritic membrane has non-specific cation channels and inositol-triphosphate-dependent Ca2+ channels. The presence of such channels is further supported by the observation that pheromone-stimulated dendrites take up cobalt. However, to date, there is no structural evidence for these channels. Therefore, in order to search for putative ion channels, we have imaged the membrane of the olfactory dendrites in the scanning electron microscope (SEM) and the atomic-force microscope (AFM), after extruding the dendrites out of the olfactory hairs and fixing them on plastic coverslips. With the aid of the SEM, we could see the beaded structure of the dendrite but no fine structural details, as the membrane was sputtered with gold. With the use of the contact mode of the AFM, we could see "pores" that were deeper than 3 nm and with a diameter of about 15 nm. The density of the "pores" was approximately 20/ microm2 or 10 000 pores per thick dendrite. We believe these to be putative ion channels based on indirect evidence.