Contacts of pore tubules and sensory dendrites in antennal chemosensilla of a silkmoth: demonstration of a possible pathway for olfactory molecules.

Antennal olfactory hairs of Antheraea polyphemus were investigated by means of transmission electron microscopy. Adequate preservation of dendrites and extracellular pore tubules is obtained by mechanical opening of the hair lumen and subsequent chemical fixation. The dendritic membrane has a cell coat. The dendrites contain microfilamentous structures in addition to their cytoplasmatic microtubules. The extracellular pore tubules traverse the hair cuticle and reach into the hair lumen for maximally 350 nm. Their diameter varies between 20 and 40 nm, depending on the preparation method. They consist of an electron-dense wall and an electron-lucent core. The wall has a helical substructure and is covered with a fuzzy coat. Contacts of pore tubules and dendritic membranes occur wherever dendrites are near the inner surface of the hair cuticle. Some of the pore tubules terminate approximately at right angles on the dendritic membrane, others lie against the membrane. The contact seems to be made via the surface coats of the tubules and the membrane. The structure of pore tubules which had been negatively stained with uranyl acetate is similar to the conventionally thin-sectioned material. The observations provide support for earlier assumptions that pore tubules are the pathways by which odor molecules reach the dendritic membrane.