CENTRAL ORGANIZATION OF COMMON INHIBITORY MOTONEURONS IN THE LOCUST -ROLE OF AFFERENT SIGNALS FROM LEG MECHANORECEPTORS

Intracellular recordings of mesothoracic common inhibitory neurons (CI 1, CI2 and CI3) were made while tactile hairs of the middle legs of lo custs (Locusta migratoria) were mechanically stimulated. Generally the three common inhibitory neurons were excited by stimulation of tactil e hairs on the ventral and dorsal surface of femur and tibia. The resp onse pattern of all three CI neurons was similar suggesting that they work as a functional unit. Touching hairs on the dorsal surface of tib ia and tarsus in some cases led to inhibition of CIs. The connection b etween sensory cells of tactile hairs and common inhibitory neurons is polysynaptic. To identify interneurons which mediate afferent signals , simultaneous intracellular recordings from CIs and interneurons were made. Different spiking interneurons were identified which made excit atory or inhibitory monosynaptic connections with CIs. Interneurons wi th inhibitory input to CIs belonged to the ventral midline group of sp iking local interneurons. Behavioral and electrophysiological results indicate that reflex movements of the leg are accompanied by activity of CI neurons. Further it appears that CI activity is inhibited when r eflex movements of the leg are actively suppressed by the animal.