Ascending interneurons that convey a respiratory signal in the central nervous system of the dragonfly larva

Summary

• 1. Intracellular recordings were made in axonal processes of interneurons in abdominal ganglia of the dragonfly larva,Anax parthenope Julius Brauer. These interneurons produced rhythmic bursts of spikes in phase with expiration. Intracellular staining with a fluorescent dye, Lucifer Yellow, showed that these neurons have their cell bodies in the terminal abdominal ganglion and an axon ascending to the anterior abdominal ganglia via the ipsilateral connective. The axons have secondary processes in all abdominal ganglia in which their structure was determined (4th to 7th abdominal ganglia). These neurons were designated as the ascending expiratory interneurons (AE neurons).

• 2. The injection of depolarizing current into an AE neuron indicated that some expiratory motoneurons were excited by the evoked discharges of the AE neurons, whereas an unidentified motoneuron was inhibited by it.

• 3. The injection of long-lasting current into an AE neuron could not affect the rate of motor burst rhythm. The injection of short current pulse could not alter the timing of the bursts of spikes of the AE neuron. Thus, these tests failed to demonstrate that the AE neurons are elements involved in the rhythm generating system.

• 4. Stimulation of a sensory nerve reset the rhythmic bursts of the AE neuron as well as the respiratory motor rhythm. Consequently the AE neurons appear to be elements that drive the segmental motor systems under the control of the central pattern generator in the last abdominal ganglion.