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The Journal of Experimental Biology 204, 4301-4309 (2001)
© 2001 The Company of Biologists Limited

Peripheral representation of antennal orientation by the scapal hair plate of the cockroach Periplaneta americana

J. Okada* and Y. Toh

Department of Biology, Graduate School of Sciences, Kyushu University, Fukuoka 812-8581, Japan

*e-mail: jokadscb{at}mbox.nc.kyushu-u.ac.jp

Accepted 1 October 2001

Arthropods have hair plates that are clusters of mechanosensitive hairs, usually positioned close to joints, which function as proprioceptors for joint movement. We investigated how angular movements of the antenna of the cockroach (Periplaneta americana) are coded by antennal hair plates. A particular hair plate on the basal segment of the antenna, the scapal hair plate, can be divided into three subgroups: dorsal, lateral and medial. The dorsal group is adapted to encode the vertical component of antennal direction, while the lateral and medial groups are specialized for encoding the horizontal component. Of the three subgroups of hair sensilla, those of the lateral scapal hair plate may provide the most reliable information about the horizontal position of the antenna, irrespective of its vertical position. Extracellular recordings from representative sensilla of each scapal hair plate subgroup revealed the form of the single-unit impulses in response to hair deflection. The mechanoreceptors were characterized as typically phasic-tonic. The tonic discharge was sustained indefinitely (>20 min) as long as the hair was kept deflected. The spike frequency in the transient (dynamic) phase was both velocity- and displacement-dependent, while that in the sustained (steady) phase was displacement-dependent.

Key words: cockroach, Periplaneta americana, antenna, hair plate, mechanoreceptor, proprioception.






© The Company of Biologists Ltd 2001