Evidence for active role of cilia in sensory transduction.

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Abstract
Combined high-voltage EM and electrophysiological studies strongly suggest that cilia play an active role in sensory transduction in the grasshopper proximal femoral chordotonal organ (FCO), a ciliated mechanoreceptor. The FCO of pro- and mesothoracic legs of Melanoplus bivittatus contains a group of several hundred chordotonal sensilla arranged in a near-parallel bundle and slung between the proximal femur and the knee joint. Both flexion and extension of the tibia stimulate the FCO, which appears to measure the femoro-tibial angle. The FCO U-shaped response curve indicates that progressive flexion or extension from the resting joint angle of 90.degree. increases the response frequency of individual receptors and recruits additional units as well. Since the FCO is a purely tonic mechanoreceptor, it is possible to fix FCO during maximum and minimum states of stimulation and observe changes in the receptor ultrastructure in the EM. The most conspicuous change is the production of a pronounced bend at the base of the sensory cilia in chordotonal sensilla of maximally stimulated femoral chordotonal organs.