Morphology and ultrastructure of the antenna of male Periplaneta americana as related to chemoreception

Sensillum-specific, topographic projection patterns of olfactory receptor neurons in the antennal lobe of the cockroach Periplaneta americana

In vertebrates and many invertebrates, olfactory signals detected by peripheral olfactory receptor neurons (ORNs) are conveyed to a primary olfactory center with glomerular organization in which odor-specific activity patterns are generated. In the cockroach, Periplaneta americana, ORNs in antennal olfactory sensilla project to 205 unambiguously identifiable antennal lobe (AL) glomeruli that are classified into 10 glomerular clusters (T1-T10 glomeruli) innervated by distinct sensory tracts. In this study we employed single sensillum staining techniques and investigated the topographic projection patterns of individual ORNs to elucidate the relationship between sensillum types and glomerular organization in the AL. Axons of almost all ORNs projected to individual glomeruli. Axons of ORNs in perforated basiconic sensilla selectively innervated the anterodorsal T1-T4 glomeruli, whereas those in trichoid and grooved basiconic sensilla innervated the posteroventral T5-T9 glomeruli. About 90% of stained ORNs in trichoid sensilla sent axons to the T5 glomeruli and more than 90% of ORNs in grooved basiconic sensilla innervated the T6, T8, and T9 glomeruli. The T5 and T9 glomeruli exclusively receive sensory inputs from the trichoid and grooved basiconic sensilla, respectively. All investigated glomeruli received convergent input from a single type of sensillum except F11 glomerulus in the T6 glomeruli, which was innervated from both trichoid and grooved basiconic sensilla. These results suggest that ORNs in distinct sensillum types project to glomeruli in distinct glomerular clusters. Since ORNs in distinct sensillum types are each tuned to distinct subsets of odorant molecules, the AL is functionally compartmentalized into groups of glomeruli.

Active tactile sensing for localization of objects by the cockroach antenna

Antennal movement during tactile orientation behavior was examined three-dimensionally in American cockroaches during tethered walking. When a wooden rod was presented to the tip of one antenna in an upright orientation at one of the three different horizontal positions (30 degrees , 60 degrees , or 90 degrees from the center of the head), the animal touched it repeatedly with the antenna, and tried to approach it (positive thigmotaxis). Positional shifts were also observed for the contralateral unstimulated antenna. The ipsilateral antenna tended to touch the object during inward movement (adduction) at all three test angles. The cumulative turn angle made during a continuous test period of 24 s clearly depended on the object's position; however, the contact frequencies were almost the same regardless of the position. The relationships between contact frequency and some locomotion parameters were also investigated on a shorter time scale of 3 s. The contact frequency positively correlated with the turn angle, with the accuracy of orientation at all three test angles, and with the translation velocity at test angles of 30 degrees and 60 degrees . It is concluded that the performance during tactile orientation can be represented effectively by the frequency with which the antennae touch the attractive objects.

Spatio-temporal patterns of antennal movements in the searching cockroach

To characterize the spatio-temporal patterns of antennal behavior in insects, the voluntary movement of both right and left antennae was examined in the cockroach Periplaneta americana. The position of the tip of the antenna (flagellum) is controlled by two mobile joints at its base (the scape and the pedicel) and by the neck. Horizontal and vertical components of movement at the antennal basal joints exhibited rhythmic activities during locomotory (walking) and non-locomotory (pausing) states in the searching animal. In both states, the horizontal component was slower than vertical one. Joint-manipulation experiments suggested that the faster vertical component is due mainly to movements of the scape–pedicel joint, while the slower horizontal component may originate from the head–scape joint. Large horizontal deflections of the antenna corresponded consistently with the yaw component of head movement. The trajectories of the antennae showed little patterned regularity in most animals. In a few cases, however, loop-like patterns appeared. The area scanned by an antenna was narrower in the walking state than in the pausing state, mainly because of a decrease in the horizontal angular range. Cross-correlation analyses revealed that the coupling between right and left horizontal antennal motor systems and that for the vertical systems were both significantly stronger in the walking state than during pausing. These results indicate that the spatio-temporal pattern of antennal movements changes dynamically depending on the animal's behavioral state.

Morphology and ultrastructure of the antennal chemoreceptors and mechanoreceptors of worker Coptotermes formosanus Shiraki

Three types of setae were found on the antenna of workers of C. formosanus. Sensilla basiconica function as chemoreceptors. They are non-socketed, with fixed plate base, thin walled, and perforated. Pore tubules are contained within the cuticular pores of s. basiconica. The pore tubules have direct contact with the dendritic branches within the sensilla. The other sensilla are tactile mechanoreceptors. The longest setae (sensilla trichodea) are thick walled, socketed, mononeuronic, and non-perforated. The shorter mechanoreceptors (sensilla chaetica) have the same characteristics as s. trichodea, except that they are sometimes dineuronic. The numbers and distribution of the sensilla were established.