NEUROMODULATION OF FLIGHT INITIATION BY OCTOPAMINE IN THE COCKROACH PERIPLANETA-AMERICANA

We have tested the effect of a known insect neuromodulator, octopamine , on flight initiation in the cockroach. Using minimally dissected ani mals, we found that octopamine lowered the threshold for wind-evoked i nitiation of flight when applied to either of two major synaptic sites in the flight circuitry: 1) the last abdominal ganglion, where wind-s ensitive neurons from the cerci excite dorsal giant interneurons, or 2 ) the metathoracic ganglion, where the dorsal giant interneurons activ ate interneurons and motoneurons which are involved in producing the r hythmic flight motor pattern in the flight muscles (Fig. 2). Correlate d with this change in flight initiation threshold, we found that octop amine applied to the last abdominal ganglion increased the number of a ction potentials produced by individual dorsal giant interneurons when recruiting the cereal wind-sensitive neurons with wind puffs (Figs. 3 , 4, 5) or with extracellular stimulation of their axons (Fig. 6). Oct opamine increases the excitability of the giant interneurons (Figs. 7, 8). Also, when we stimulated individual dorsal giant interneurons int racellularly, the number of action potentials needed to initiate fligh t was reduced when octopamine was applied to the metathoracic ganglion (Fig. 9).