Activity Patterns of Inhibitory Motoneurones and their Impact on Leg Movement in Tethered Walking Locusts

Abstract

ABSTRACT A preparation is described which permits intracellular recording of neural activity in tethered walking locusts. Minimal dissection is required, leaving the animal nearly intact. In this preparation, the activities of the three common inhibitory motoneurones (CIs) supplying the muscles of the middle leg were recorded. CIs were completely or almost completely silent in quiescent locusts but often produced a tonic spike discharge during walking activity. This tonic discharge was modulated in the step cycle, bursts of action potentials being generated in conjunction with the swing phase of the leg movement. The bursts peaked at around the start of leg protraction. They were remarkably similar in all three CIs and in a variety of different walking situations (forward and backward walking, searching, etc.). The only notable difference was that bursts of CI1 normally peaked some 40 ms before those of CI2. These results indicate that CI activity is timed according to the muscle group innervated but that no further functional specializations exist. Activity of CI1 was manipulated by current injection. For example, decreasing CI spike discharge by the application of hyperpolarizing current reduced the velocity of leg protraction in the walking animal. This demonstrates that CI1 plays an important role in determining the speed of the swing movement.