DYNAMICS OF IMMOTILE OLFACTORY CILIA IN THE SILKMOTH ANTHERAEA

Living olfactory sensory dendrites of the silkmoth Antheraea which are modified cilia lacking the central microtubule pair have been observe d by means of video microscopy in sensilla from which the apical tips had been pinched off as well as in vitro after isolation. Dendrites pr oject out of the opened hair tips either spontaneously without manipul ation or after application of basal pressure via a syringe connected t o the haemolymph side. Spontaneously appearing dendrites can repeatedl y project up to ca. 60 mum from, and retract back into, the hairs. The y tend to remain straight, but curve if they project too far and bend on meeting an obstacle. The average elongation velocity of the dendrit es is 0-4 mum/sec. After application of basal pressure, large numbers of dendrites immediately slide out of the apically opened hairs. These dendrites usually detach at their bases and float free in the solutio n until settling down at the bottom of the petri dish. They are able t o make active movements, for example bending between points of attachm ent. Dendrites tend to adhere to other dendrites, sometimes making sli ding movements against each other. The ciliary olfactory dendrites are backed by a large number of microtubules which appear to be interconn ected by fine filaments, most probably microtubule-associated proteins (MAPs). The elongation and shortening of the dendrites is explained h ere by a sliding-filament mechanism similar to the one acting in 'true motile' cilia. As the cytoskeleton is not as highly organized as in t he latter, the resulting movements are limited to elongation and contr action, bending being brought about only passively by apical resistanc e. Membrane beads have been observed to appear on, and move along, the dendrites. Their number increases with the age of the preparation.