Integrative analysis of multiple pathways in the honeybee olfactory system

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A striking commonality across species is the recurring presence of parallel olfactory systems, such as the main olfactory system, the vomeronasal system, the septal organ and the Grueneberg organ in mammals. Similarly, different subsystems are present in amphibians, fish and insects, suggesting that parallel systems have a highly adaptive value. We use the honeybee Apis mellifera to study a species where two distinct olfactory subsystems of about equal size have been found within the main olfactory system: the l-APT and the m-APT pathway. In addition, the honeybee offers a large body of knowledge and a wealth of paradigms to study olfactory anatomy, physiology and behavior, including learning and memory with close to cognitive capacities. In the first funding period we found important new anatomical and physiological characteristics of this dual olfactory pathway. At the sensory input side, basiconic sensilla are sex-specific and mostly restricted to the m-APT subsystem in females, which is reduced in male drones. Ultrastructural analyses of output synapses in the mushroom body calyx revealed new aspects of synaptic plasticity in the two subsystems. Most importantly, using optophysiological recordings and real-time dual tract multiunit electrophysiology we show that both antennal-lobe output tracts respond to a similar panel of odors indicating true parallel processing. We found evidence for at least two mechanisms of synaptic plasticity in the l-APT subsystem following associative odor learning. Consequently, our current and future physiological experiments focus on these parallel coding properties and their plasticity by using an expanded panel of odor stimuli. Future analyses largely focus on spatial and temporal response properties (latency and coincidence code) using different odor concentrations and mixtures. In addition, we will continue to probe the neurochemical characteristics and intrinsic properties of neurons belonging to the two pathways and test their behavioral relevance. We expect to improve our understanding of parallel olfactory coding mechanisms and of the significance of parallel pathways in sensory systems in general.