GABA-like immunoreactivity in a population of locust intersegmental interneurones and their inputs.

Intracellular labelling of locust intersegmental interneurones with lucifer yellow or horseradish peroxidase was carried out in combination with light and electron microscope immunocytochemistry by using an antibody raised against gamma amino butyric acid (GABA). Fifteen percent (four out of 27) of intracellularly stained interneurones showed GABA-like immunoreactivity. This is in agreement with previous physiological observations that 20% of the interneurones in this population make inhibitory output connections in the metathoracic ganglion. GABA-like immunoreactivity was also found in processes presynaptic to the interneurones in the mesothoracic ganglion. The presence of such immunoreactive inputs onto the intersegmental interneurones correlates well with physiological evidence that their receptive fields are in part shaped by direct input from GABA-ergic spiking local interneurones.