1. Giant interneurons (GI's) of the cockroach Periplaneta americana were stimulated intracellularly while levator and depressor motor axons of the metathoracic leg were recorded extracellularly. The intracellular stimulus was a train of pulses, each of which evoked one GI action potential. The resultant burst of GI action potentials resembled that elicited by natural stimulation. The GI was identified by Procion Yellow iontophoresis. The motor axons were identified by spike height analysis. 2. Six of the seven identifiable GI's on each side have been studied. Four of these evoked trains of action potentials in the ipsilateral motor axons (Figs. 4, 6, 7, 8 and 9). Two GI's excited contralateral motor axons (Fig. 5). 3. Each GI evoked a characteristic and reproduceable response. 4. Increasing the pulse frequency or train duration of the intracellular stimulus leads to an increase in the number of action potentials evoked. 5. The giant-to-motor response persists, and sometimes increases, following decapitation (Fig. 11). 6. The responses of the motor neurons to each GI, and known responses of each GI to different wind directions, permitted predictions of the response of the motor neurons to different wind directions. These predictions were born out in experiments using controlled wind puffs (Figs. 12 and 13). 7. The results are discussed in relation to the responses of each GI to wind puffs of different directions, and the leg movements which these puffs elicit. © 1978 Springer-Verlag.
