Fig. 3. Electrophysiological recordings from adult Drosophila external mechanosensory organs. (A) Diagram of a Drosophila mechanoreceptor bristle, adapted from Walker et al. (Walker et al., 2000). The bristle sensory organ is composed of a hollow hair shaft and three cells: the socket cell, the sheath cell and a ciliated mechanosensory neuron. The recording configuration consisted of two electrodes: a reference electrode placed in the abdomen of the fly and a recording/stimulation electrode slipped over the cut end of a bristle. (B-E) Mechanically elicited changes in transepithelial potential (TEP) recorded from single macrochaete bristles in Rfx⁴⁹/TM6B (B,C) and Rfx²⁵³/Rfx⁴⁹ (D,E) flies. (B,D) Representative single traces; the 10 µm stimulating displacement is shown in B. In C,E, the maximum amplitude of the mechanoreceptor potential (MRP) in each bristle is plotted against its resting TEP. Circled points correspond to the traces shown in B,D. (F,G) Transepithelial currents (TEC) recorded from the same bristles, with apical holding potentials of +76 mV and +55 mV, respectively. The stimulus displacement is as in B. No mechanically elicited currents were observed in Rfx mutant flies. (H) Transepithelial resistance in Rfx⁴⁹/TM6B (n=27, mean=243±16 M) and Rfx mutant (n=24; mean=80±12 M) bristles. Points are values for individual bristles; lines indicate the mean resistance. Transepithelial resistance is significantly reduced (P<10^-9) in Rfx mutants. (I) Diagrams of a Drosophila head showing the position of the electrodes used to record sound-elicited potentials, and of an antenna indicating the different segments. The Johnston's organ is situated in the second antennal segment (2). Chordotonal organs attached to the joint between the second and third segments are stimulated by vibration of the arista and third segment (3). (J) Sound-elicited potentials recorded from Rfx⁴⁹/TM6B control or Rfx²⁵³/Rfx⁴⁹ mutant antennae in response to pulse sound stimulation. Each trace is an average of the responses to ten consecutive stimulus trains. No sound-elicited potentials were detected in mutant antennae.

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