PHYSIOLOGICAL-CHANGES IN CENTRAL NEURONAL PATHWAYS CONTRIBUTING TO THE GENERATION OF A REFLEX REVERSAL

1. In the stick insect Carausius morosus the properties of the neurona l network governing the femur-tibia joint depend on the behavioral sta te of the animal. In the inactive animal flexion of the femur-tibia jo int results in the generation of a resistance reflex, while in the act ive animal the same stimulus induces the so-called active reaction, th e first part of which is a reflex reversal. 2. Recordings from motoneu rons innervating the extensor tibiae muscle indicated that their time course of activity during the active reaction is due to inputs from in tercalated pathways. We therefore investigated the role of identified nonspiking interneurons that transmit sensory information from the cho rdotonal organ onto the extensor motoneurons in the inactive animal. W e can show that(i) the nonspiking interneurons received altered inputs whereas (ii) they provided qualitatively the same synaptic drive onto leg motoneurons. 3. From our results it is clear that (i) neuronal pa thways contributing to the generation of the resistance reflex are als o involved in the generation of the reflex reversal in the same contro l loop, (ii) thereby adopting the same principle of information proces sing (parliamentary principle), because both, supporting and opposing pathways contribute to the generation of the motor output.