A preparation for the intracellular analysis of neuronal activity during flight in the locust

Summary1.A simple preparation inLocusta migratoria is described which allowed intracellular recording from interneurons and motoneurons in the thoracic ganglia during flight. Flight activity could be evoked in approximately 95% of the preparations by wind stimulation of the head.2.Intracellular recordings from the neuropile processes of motoneurons showed that spike activity was produced by large amplitude (up to 25 mV) oscillations in membrane potential. Inhibitory input contributed to the repolarizing phase in both elevators and depressors.3.Elevator and depressor motoneurons could be distinguished by their initial response to wind stimulation of the head. Elevators were depolarized beyond their threshold whereas most depressors were hyperpolarized.4.Numerous interneurons phasically modulated during flight were identified in both the meso- and metathoracic ganglia. Some of these interneurons were found to make short-latency excitatory or inhibitory connections to flight motoneurons and contribute significantly to the rhythmic synaptic input to motoneurons.5.A pair of interneurons was identified which, when depolarized by current injection, decreased the frequency of the flight rhythm by up to 50%. These interneurons were phasically modulated only during the expression of the flight rhythm as indicated by the flight activity of motoneurons.6.We conclude that the flight rhythm is generated primarily at the interneuronal level, that spiking premotor interneurons are largely responsible for driving the motoneurons, and that the flight oscillator is not continuously active.