Histochemistry of classical neurotransmitters in antennal lobes and mushroom bodies of the honeybee

This paper summarizes histochemical and immunocytochemical investigations of cholinergic, GABAergic, and glutamatergic pathways in the central brain and suboesophageal ganglion of the honeybee. Acetylcholinesterase histochemistry, immunocytochemical staining for nicotinic acetylcholine receptors, and mapping for alpha-bungarotoxin binding sites indicate cholinergic synaptic interactions in the antennal lobe and a cholinergic pathway via a subset of olfactory projection neurons into the mushroom bodies. Calcium imaging experiments in cell cultures prepared from mushroom bodies demonstrate the expression of nicotinic cholinergic receptors on Kenyon cells. Neurons synthesizing GABA and glutamate are stained with well-defined polyclonal antisera against the amino acids. GABA-immunoreactivity is mainly localized in local interneurons of the antennal lobe and in extrinsic neurons innervating the mushroom bodies. High levels of glutamate-immunoreactivity are found in motoneurons of the suboesophageal ganglion, the dorsal lobe, and also in interneurons. A subgroup of the Kenyon cells shows distinct but weaker levels of glutamate-immunoreactivity. The detailed knowledge about the chemical neuroanatomy of the bee provides a framework for behavioral pharmacological approaches, which implicate the involvement of cholinergic mechanisms in olfactory learning and GABAergic mechanisms in odor discrimination.