Short Communications Initiation of Flight By an Identified Wind Sensitive Neurone (Tcg) in The Locust

Abstract

When the tarsi are not in contact with the ground, brief wind stimuli applied to the wind sensitive hairs on the head elicit flight in the locust (Weis-Fogh, 1949; Camhi, 1969). The descending interneurones mediating this reaction have not been identified but some likely candidates have been reported (Bacon & Tyrer, 1978; Simmons, 1980, 1981). The most extensively studied is the tritocerebral commissure giant (TCG) (Bacon & Tyrer, 1978; Bacon & Möhl, 1979). This large wind sensitive interneurone descends from the brain, crosses to the contralateral side of the nerve cord via the tritocerebral commissure, and makes excitatory connections with some flight motor neurones in the thoracic ganglia (Bacon & Tyrer, 1979). The location of the TCG’s axon in the tritocerebral commissure makes this neurone easily accessible for recording and stimulation in almost intact, freely moving animals. Recordings during flight, for example, have shown that the TCG discharges one or two spikes during each cycle (Bacon & Möhl, 1979). The spike activity results from rhythmic air turbulences caused by flapping of the wings and head movements during flight. This rhythmic activity may play a role in regulating motor output during flight manoeuvres, such as yaw (B. Möhl & J. Bacon, in preparation). It seems unlikely however that this is the only function for the TCG since it is capable of discharging in very high frequency bursts quite unlike those occurring in flying animals. Here we present evidence that the TCG also functions to facilitate the initiation of flight following a jump.