Neural Mechanisms of Haptics in the Insect Antenna

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The antennae of an insect function as an active tactile sensor to perceive the physical environment. This study was aimed to clarify neural mechanisms of active tactile sensing (haptics) by the insect antenna. The following results were obtained for these two financial years.1. Spatial behavior of cricketsSpatial preferences of crickets were examined by using both an irregular-shaped arena with different curvatures of walls and a circular arena with different sizes of shelters. The analyses revealed that crickets may perceive the structure of a given closed space as a consequence of preceding search.2. Neural control of antennal muscles in cockroachesIntracellular responses to electrical stimuli to antennal motor nerves were recorded from the antennal muscles. The analyses provided the outline of innervation from the antennal motor center.3. Kinematics of the cockroach antennaIn order to determine kinematic parameters, each of the antennal muscles was electrically stimulated, and the consequent antennal movement was analyzed three-dimensionally.4. Cholinergic control of antennal movement in cockroachesWhen a muscarinic agonist pilocarpine or a nicotinic agonist nicotine was injected into the head capsule, continuous rhythmic movements of both antennae were induced in the restrained cockroach. The trajectories of antennae included some spatially-patterned elements, which resemble those observed during intended orientation. Pilocarpine also induced rhythmic spike activities of the antennal motor nerves in vitro specimens. Significant correlates between the horizontal and vertical motor systems imply the spatial regularity of antennal movement.5. Antennal responses to aversive and attractive odors in cockroachesThe responses of antennae to the aversive odor (female-derived sex pheromone-like odor) and the aversive odor (limonene) were observed and compared with the antennal movement induced by pilocarpine or nicotine.