GABA-like immunoreactivity of identified interneurons in the flight system of the locust,Locusta migratoria

Summary The transmitter content of identified inhibitory interneurons in the flight system of the locust, Locusta migratoria, has been characterized using antibodies raised against protein-conjugated gamma aminobutyric acid. Identified flight neurons were filled with the fluorescent dye, Lucifer Yellow. Serial sections of dye-filled neurons were incubated with an antibody to gamma aminobutyric acid which was subsequently tagged with a fluorescent marker. Excitatory motoneurons to wing muscles and 13 flight interneurons (3 excitatory, 7 inhibitory, and 3 with unknown synaptic effect) were examined. Neither the moto-neurons nor any of the 3 excitatory interneurons contained immunoreactive material. Six of the 7 inhibitory interneurons did contain immunoreactive material. All the neurons which contained immunoreactive material and whose synaptic effect is known were inhibitory. We conclude that most of the inhibitory flight interneurons which have been described use gamma aminobutyric acid as their transmitter. Interestingly, at least 1 set of interneurons known to be inhibitory does not use gamma aminobutyric acid. We predict that the 2 interneurons which do contain immunoreactive material and whose synaptic effect is not yet known will be found to have inhibitory roles in the operation of the flight circuitry.