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

This paper summarizes histochemical and immunocytochemical investigations o f cholinergic, GABAergic, and glutamatergic pathways in the central brain a nd suboesophageal ganglion of the honeybee. Acetylcholinesterase histochemi stry, immunocytochemical staining for nicotinic acetylcholine receptors, an d mapping for a-bungarotoxin binding sites indicate cholinergic synaptic in teractions in the antennal lobe and a cholinergic pathway via a subset of o lfactory projection neurons into the mushroom bodies. Calcium imaging exper iments in cell cultures prepared from mushroom bodies demonstrate the expre ssion of nicotinic cholinergic receptors on Kenyon cells. Neurons synthesiz ing GABA and glutamate are stained with well-defined polyclonal antisera ag ainst the amino acids. GABA-immunoreactivity is mainly localized in local i nterneurons of the antennal lobe and in extrinsic neurons innervating the m ushroom bodies. High levels of glutamate-immunoreactivity are found in moto neurons of the suboesophageal ganglion, the dorsal lobe, and also in intern eurons. A subgroup of the Kenyon cells shows distinct but weaker levels of glutamate-immunoreactivity. The detailed knowledge about the chemical neuro anatomy of the bee provides a framework for behavioral pharmacological appr oaches, which implicate the involvement of cholinergic mechanisms in olfact ory learning and GABAergic mechanisms in odor discrimination. (C) 1999 Wile y-Liss, Inc.