Neurotransmitter Systems in the Honey Bee Brain: Functions in Learning and Memory

Synaptic correlates of olfactory learning within the honey bee brain ­utilize several transmitters and receptors. Experiments unraveled distinct roles of these transmitter systems in cognitive processes. Cholinergic synaptic transmission is involved in acquisition and retrieval processes. At least two subtypes of nicotinic acetylcholine receptors exist in the honey bee brain, one involved in retrieval processes and another one linked to the formation of long-term memory. The electrophysiological and pharmacological properties of the underlying nicotinic acetylcholine receptors (nAChR) are well described whereas muscarinic acetylcholine receptors (mAChR) are physiologically unknown. The reward processing pathway largely depends on octopaminergic neuromodulation. Serotonin (5-HT) impairs the conditioned response during acquisition. Whether dopamine (DA) mediates aversive learning while octopamine (OA) mediates appetitive learning remains to be analyzed. Several studies indicated that GABA receptors play a role during odor learning, but the specific function of inhibition is not yet clear. Both inhibitory and excitatory glutamate receptors are required for certain forms of learning and for memory retrieval.