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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

View larger version (36K): [in a new window]   Fig. 1. Scapal hair plates (S-HPs) and their adjacent joint membrane. Views from three different (inner, top and outer) angles. An example of the right antenna. Note the structural partitioning of the joint membrane. HC, head capsule; JM, joint membrane; S, scape; P, pedicel; F, flagellum; Di, distal; Po, posterior; L, lateral; M, medial; Do, dorsal; V, ventral.

View larger version (70K): [in a new window]   Fig. 2. The method used to map the activated area of the scapal hair plate (S-HP). (A) The S-HP and its adjacent joint. (B) The isolated and flattened scapal exoskeleton. (C) A map of the activated area. By comparing the S-HP area lying under the joint membrane (A) with the mapped sensillar pattern (B), the area of the S-HP activated for a given direction of joint movement was identified (shaded region). JM, joint membrane; S, scape; Di, distal; L, lateral; M, medial; P, posterior.

View larger version (52K): [in a new window]   Fig. 3. The area of the scapal hair plate (S-HP) (left antenna) activated at various angles in the horizontal and vertical planes. Shaded areas indicate the activated region located under the joint membrane. The narrow boundaries of pale shading show a region for which it was difficult to determine the margin of the joint membrane exactly. The inset at the top right shows the geometry of the flattened scape and the boundaries of three subgroups of the S-HP. Insets at the bottom and left are dorsal and lateral views, respectively, of the head and an antenna, showing how the horizontal and elevation angles (), respectively, were determined. Di, distal; Do, dorsal; L, lateral; M, medial; P, posterior; d, dorsal S-HP; l, lateral S-HP; m, medial S-HP.

View larger version (27K): [in a new window]   Fig. 4. Relationships between the relative number of hairs deflected (RN) and antennal angle. Each normalized plot derived from seven animals indicates the fraction of the cumulative number of hairs deflected in a given antennal direction with respect to the cumulative maximal number of hairs deflected for all antennal directions. (A) Deflection in the horizontal plane. Note the almost linear relationships for the lateral scapal hair plate (S-HP), with little dispersion. (B) Deflection in the vertical plane (see text for detail).

View larger version (45K): [in a new window]   Fig. 5. Response of a sensillum of the right lateral scapal hair plate to artificial deflection. The hair was deflected distally by 34° from its resting position, held for 11 s, then released (top trace). Single-unit impulses continued for as long as the hair was deflected (second trace). In the dynamic phase of deflection, a transient burst was observed (see expanded region at the onset of deflection), with no additional off-discharge (see expanded region at the offset of deflection).

View larger version (19K): [in a new window]   Fig. 6. Responses of representative hairs from the three different parts of the scapal hair plate (S-HP) to a long-lasting (21 min) deflection. Each point represents the mean number of spikes in a 0.5 min sample. Although the frequencies varied, these sensilla maintained their excitability for at least 21 min.

View larger version (29K): [in a new window]   Fig. 7. The time courses of averaged spike frequencies depend on the deflection angle (A) and the deflection velocity (B). (A) An example from a hair of the lateral scapal hair plate (S-HP); deflection angle was increased from 12 to 60° at a constant deflection velocity (60.1° s–1). (B) An example from a hair of the medial S-HP; deflection velocity (24–245° s–1) was increased at a fixed angle (37°). Sample bin width, 0.1 s (A,B).

View larger version (43K): [in a new window]   Fig. 8. Sustained-phase frequency (SPF) and transient-phase frequency (TPF) in response to different hair deflection angles (A) and velocities (B). The data are from nine dorsal, eight medial and seven lateral hairs. There were no apparent difference in SPFs and TPFs among the three scapal hair plate (S-HP) subgroups. (Ai) Relationship between SPF and hair deflection angle. (Aii) Relationship between TPF and hair deflection angle. These two relationships clearly exhibited angle-dependency. (Bi) Relationship between SPF and hair deflection velocity. (Bii) Relationship between TPF and hair deflection velocity. Positive relationships were observed for most hairs in Bii, but not in Bi.