PORE STRUCTURES IN INSECT OLFACTORY SENSILLA - A REVIEW OF DATA AND CONCEPTS

An historical overview is given of the most important discoveries and hypotheses regarding stimulus transport in insect olfaction. The great structural similarity between the pore tubules of olfactory single-wa lled wall-pore sensilla and the epicuticular filaments of non-olfactor y cuticle may reflect not only a similar composition but also a simila r transport mechanism. The new ''wick concept'' of pore tubules compri ses 2 developmental periods. First, during ontogeny of the sensillum, pore tubules may be involved in the secretion of the material of the o utermost epicuticular layers. The pore tubules may function like the w ick in an oil lamp, taking up lipoid molecules from the sensillum lymp h for outward transport. During the second period, after the sensillum has been completed, the pore-tubule wick may work as a dispenser of o dorant molecules in an inward direction. The large surface of pore tub ules as compared with the cross section of the outer pores could facil itate the binding of odorant molecules by the odorant-binding proteins in the sensillum lymph. In double-walled wall-pore sensilla, on the o ther hand, pore tubules are not involved in stimulus transport. In thi s class of olfactory sensilla, the dendrites are protected by a palisa de of cuticular ringers, and openings between these fingers, the spoke channels, are the stimulus transport pathways. The fundamentally diff erent topology of sensillar wall pores hints at a separate phylogeneti c origin of the two categories of insect olfactory sensilla. (C) 1997 Elsevier Science Ltd. All rights reserved.