Yoshihiro Toh

The role of antennal hair plates in object-guided tactile orientation of the cockroach (Periplaneta americana).

Abstract. The searching behavior of blinded cockroaches was examined under unrestrained conditions, in an arena, and on a treadmill. When cockroaches searching in a circular arena touched a stationary object (metal pole) with their antennae, they frequently approached the object more closely, and then climbed up it. Similar orientation behavior was observed in tethered animals in open loop conditions, walking on a Styrofoam ball. In these restrained cockroaches, a single antenna sufficed to distinguish the angular positions of an object, in the horizontal plane (0°, 45°, and 90°). A group of mechanosensitive hairs on the basal segment of the antenna (scapal hair plate) appears to play a major role in antennal object detection in the horizontal plane, as gauged by shaving off these scapal hair plates. In unrestrained cockroaches, shaving the scapal hair plate increased the time needed to approach an object. Under tethered conditions, the ability to turn towards and to establish antennal contact with a test object was significantly impaired.

Morphology of the granular hemocytes of the Japanese horseshoe crabTachypleus tridentatus and immunocytochemical localization of clotting factors and antimicrobial substances

SummaryThe structure of hemocytes in the normal state and during blood coagulation, and the intracellular localization of three clotting factors and two antimicrobial factors were examined in the Japanese horseshoe crabTachypleus tridentatus. Two types of hemocytes were found in the circulating blood: non-granular and granular hemocytes. The latter contained numerous dense granules classed into two major types: L- and D-granules. The L-granules were larger (up to 1.5 μm in diameter) and less electron-dense than the D-granules (less than 0.6 μm in diameter). The L-granules contained three clotting factors and one antimicrobial factor, whereas the D-granules exclusively contained the other antimicrobial factor. After treatment with endotoxin, the L-granules were released more rapidly than the D-granules, although almost all granules were finally exocytosed. The granular hemocyte possessed a single Golgi complex; possible precursor granules of L-granules and D-granules contained tubular and condensed dense material, respectively. These data are discussed in relation to the self-defense mechanisms of the horseshoe crab.

Fine structure of antennal sense organs of the male cockroach, Periplaneta americana.

The ultrastructure of six distinct antennal sensory organs of the cockroach, Periplaneta americana , has been examined. These are as follows: (i) A chaetic sensillum possesses a single long hair bearing a single terminal pore. This type contains one to seven sensory processes, one terminating basally and containing numerous microtubules, and the remainder terminating distally near the pore. This structure is suggestive of a mechanoreceptive and contact chemoreceptive function. (ii) A P-basiconic sensillum has a thin-walled hair perforated by numerous pores. (iii) A trichoid sensillum also has a thin-walled hair with pores limited to the distal part. The perforated wall of these thin-walled hairs is suggestive of an olfactory function. (iv) A G-basiconic sensillum has the shortest hair with a longitudinally grooved surface and a single terminal pore. Many fine channels arise from the grooves and radiate inward towards the sensory processes in the hair lumen. This sensillum appears to function in contact chemoreception and olfaction. (v) A marginal sensillum has no hair and contains a single sensory process with numerous microtubules. This structure is suggestive of a mechanoproprioceptive function. (vi) A campaniform sensillum is similar in structure to the marginal sensillum, though minute differences are present.

Synaptic organization of the fleshfly ocellus

SummaryThe synaptic organization of the fleshfly (Boettcherisca peregrina) ocellus has been studied by transmission electron microscopy. Three types of neuronal element are recognized in the ocellus: (1) 70–100 retinula axons (2) four thick ocellar nerve fibres and (3) several thin ocellar nerve fibres. Synaptic connections accompanied by characteristic presynaptic ribbons have been found between these three elements in five combinations. Four of these are numerous (retinula axons synapsing onto thick ocellar nerve fibres or onto thin ocellar fibres; thin ocellar nerve fibres synapsing onto thick ocellar nerve fibres or onto other thin ocellar fibres). One or two of the thin ocellar nerve fibres are mainly presynaptic elements. The remaining thin fibres are both pre- and postsynaptic. These observations suggest that the thick ocellar nerve fibres are afferent and at least one or two of the thin ocellar nerve fibres are efferent. The function of the remaining thin fibres is not known. The fifth combination is a feedback synapse from thin ocellar nerve fibres onto retinula axons. In addition, neuro-glial synapses have been found between thin ocellar nerve fibres and glial cells. The latter two combinations are less common and may provide alternative neuronal pathways for processing ocellar input.

Fine structure of sense organs on the antennal pedicel and scape of the male cockroach, Periplaneta americana

The ultrastructure of five types of sensory organs has been examined on the pedicel and scape of the male cockroach Periplaneta americana. Two of the five, chaetic sensillum B and campaniform sensilla, are located on both flagellar and basal segments. Chaetic sensilla B appear to be mechano- and contact chemoreceptive, and are distributed sparsely on the pedicel and scape. Campaniform sensilla are arranged circularly around the distal margin of the pedicel. The remaining three are found only on the basal segments. (i) Chaetic sensillum A: This sensillum possesses a hair bearing no pores either at the tip or the side wall. It contains one receptor cell, the cilium of which has a mechanoreceptive structure and ends near the base of the hair. Chaetic A hairs are distributed all over the surface of the pedicel and scape. (ii) Pedicelar connective chordotonal organ: This organ is an elongated mass lying under the ventral epithelium. The mass is a bundle of about 50 scolopidia. Each scolopidium contains two receptor cells. Sensory cilia of these receptor cells are capped by an attachment cell, which extends distally and joins the hypodermis ventrally beneath the pedicel—meriston joint. (iii) Johnstons organ: This organ also consists of 150 or more scolopidia. Scolopidia lie in the hypodermis of the pedicel. Each scolopidium contains three receptor cells positioned in the distal half of the pedicel. One of the three cilia extends distally and enters the canal within the pedicel—meriston joint articulation. These results suggest that a majority of sense organs on the pedicel and scape are joint mechanoreceptors.

Dorsal ocellar system of the American cockroach. I: Structure of the ocellus and ocellar nerve

The structure of the dorsal ocellus and ocellar nerve has been examined in the American cockroach. The ocellar retina contains more than 10,000 retinular cells whose axons converge synaptically upon three to five thick, second-order neurons in the ocellar neuropil. Efferent processes containing dark vesicles also synapse with second-order neurons in the ocellar neuropil. Additional synapses, i.e., feedback synapses of thick second-order processes, and reciprocal synapses between retinular axons, are also found, infrequently, in the proximal region of the neuropil. A large majority of retinular axons terminate within the ocellar neuropil, but some extend into the ocellar nerve. The ocellar nerve contains three to five thick, second-order processes, 20–30 retinular axons, a few efferent processes, a few cored-vesicle-containing processes, a distal extension of the thick third-order process, and through fibers extending to the ventral nerve cord. Synapses occur among these processes, the second-order processes being pre- and postsynaptic to surrounding thin processes throughout the ocellar nerve. These results suggest that the ocellar nerve is also a synaptic region, but differs functionally from the ocellar neuropil. The ocellar neuropil appears to be an input region for the second-order neurons, whereas the ocellar nerve appears to be an output region, where local interactions occur among many types of neurons.

Spatio-temporal patterns of antennal movements in the searching cockroach

SUMMARY 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 animals behavioral state.

Responses of descending neurons to looming stimuli in the praying mantis Tenodera aridifolia

Responses to visual stimuli of some neurons that descend the nerve cord from the brain were recorded extracellularly in the mantis Tenodera aridifolia. Most of the recorded neurons showed their largest responses to looming stimuli that simulated a black circle approaching towards the mantis. The neurons showed a transient excitatory response to a gradually darkening or receding circle. The neurons showed sustained excitation to the linearly expanding stimuli, but the spike frequency decreased rapidly. The responses of the neurons were affected by both the diameter and the speed of looming stimuli. Faster or smaller looming stimuli elicited a higher peak frequency. These responses were observed in both recordings from the connective between suboesophageal and prothoracic ganglia and the connective between prothoracic and mesothoracic ganglia. There was a one-to-one correspondence of spike firing between these two recordings with a fixed delay. The neurons had the receptive field on ipsilateral side to its axon at the cervical connective. These results suggest that there is a looming-sensitive descending neuron, with an axon projecting over prothoracic ganglion, in the mantis nervous system.

Structure of the visual system of the larva of the tiger beetle (Cicindela chinensis)

The visual system of the larval tiger beetle (Cicindela chinensis) consists of six (two large, two mediumsized, and two small) stemmata on either side of the head, and an underlying neuropil mass. Each stemma exhibits a corneal lens and an underlying rhabdom layer. Retinular cells extend single proximal axons into the neuropil mass. The neuropil mass has a flattened heart-shape, and consists of two juxtaposed identical structures, each being a neuropil complex of each of the two large stemmata. The complex consists of lamina and medulla neuropils. Most retinular axons terminate in the lamina neuropil. Axons of two types of lamina monopolar neurons descend parallel to each other into the lamina neuropil. Moreover, each lamina neuropil contains a single giant monopolar neuron. Possible centrifugal processes and tangential neurons also occur. Lamina monopolar axons descend straight into the medulla neuropil. Medulla neurons spread fan-shaped dendrites distally in the medulla neuropil and send single axons toward the protocerebrum. These data are discussed with respecct to the unique visual behavior of this larva and in comparison with other insect visual systems.

Shade Response in the Escape Behavior of the Cockroach, Periplaneta americana

Abstract The termination of the escape behavior in the cockroach Periplaneta americana was investigated. Escape behavior was effectively terminated when cockroaches were allowed to select a dark shelter and hide beneath it. This shade-induced pause in escape running (a shade response) was observed even in very low-light levels (less than 0.01 lux). Contributions of the ocelli and the compound eyes to the shade response were examined. Removal of both compound eyes resulted in complete disappearance of the shade response. Animals with just the ocelli removed were less likely to shelter in the shadowed area, especially under a low-light condition. Input from compound eyes seems to be essential to the shade response. The ocellus may enhance the function of compound eye, and its modulatory function is effective in low-light conditions.