Ontogenetic studies of flight initiation in Locusta: Wind response of an identified interneurone (TCG)

Abstract

The tritocerebral commissure giant (TCG) wind-sensitive interneurone is involved in initiation and maintenance of flight in adult locusts. In this paper we study this interneurone in the imago and non-flying larval instars. Cobalt fills show that the TCG establishes its adult morphology by the first larval instar. An accompanying axon, apparently representing the peculiar tritocerebral commissure “dwarf” (TCD) is present, too, at least for the last preimaginal instars. Physiological tests show similar responses of the TCG to wind stimuli in the 4th, 5th instar and adult stages. Spike activity, however, is usually higher in adult compared to larval instars. It is possible that all interneurones, involved in adult-specific motor patterns (such as flight), are present in preimaginal stages and can be activated independently of the function of the final motor system.