Acetylcholine, GABA, glutamate and NO as putative transmitters indicated by immunocytochemistry in the olfactory mushroom body system of the insect brain.

The distribution of glutamate, GABA and ChAT and of NADPH-diaphorase was immunocytochemically and histochemically investigated in the mushroom bodies of the cricket (Gryllus bimaculatus) and of the fruitfly (Drosophila melanogaster). Glutamate and NO are considered as putative transmitters of mushroom body Kenyon cell types. In the input area (calyces) of the mushroom bodies of Drosophila, the majority of olfactory projection neurons is stained with antibodies against ChAT. In addition, small GABA-immunoreactive presynaptic fibres of extrinsic neurons occur intermingled with the ChAT-immunoreactive elements in the calyces, and occupy distinct compartments in the stalk and lobes. Complex synaptic connectivity of putatively cholinergic and GABAergic extrinsic neurons and of Keyon cell dendrites within the calycal glomeruli of mushroom bodies is discussed.