Abstract
The honeybee olfactory pathway comprises an intriguing pattern of convergence and divergence: ~60.000 olfactory sensory neurons (OSN) convey olfactory information on ~900 projection neurons (PN) in the antennal lobe (AL). To transmit this information reliably, PNs employ relatively high spiking frequencies with complex patterns. PNs project via a dual olfactory pathway to the mushroom bodies (MB). This pathway comprises the medial (m-ALT) and the lateral antennal lobe tract (l-ALT). PNs from both tracts transmit information from a wide range of similar odors, but with distinct differences in coding properties. In the MBs, PNs form synapses with many Kenyon cells (KC) that encode odors in a spatially and temporally sparse way. The transformation from complex information coding to sparse coding is a well-known phenomenon in insect olfactory coding. Intrinsic neuronal properties as well as GABAergic inhibition are thought to contribute to this change in odor representation. In the present study, we identified intrinsic neuronal properties promoting coding differences between PNs and KCs using in-situ patch-clamp recordings in the intact brain. We found very prominent K+ currents in KCs clearly differing from the PN currents. This suggests that odor coding differences between PNs and KCs may be caused by differences in their specific ion channel properties. Comparison of ionic currents of m- and l-ALT PNs did not reveal any differences at a qualitative level.
Highlights
Olfaction is a crucial sense for almost all animal species, and olfactory systems show striking similarities across a wide range of taxa—like the odorant receptor proteins or the glomerular neuronal architecture of the first relay station in the brain
One important prerequisite for selectively recording from projection neurons (PN) was the identification of the respective neuronal cell bodies in the antennal lobe (AL) tissue, as they are embedded in many cell bodies of AL local interneurons (LNs) [3]
Kenyon cells (KC) proceeding from the mushroom bodies (MB) calyces to the vertical lobe, In-situ recording of PNs and KCs in the honeybee visual commissures connecting the optic lobes, and tracts from SEG PNs and olfactory PNs ascending from the AL to the MBs could be distinguished (Fig 1A)
Summary
Olfaction is a crucial sense for almost all animal species, and olfactory systems show striking similarities across a wide range of taxa—like the odorant receptor proteins or the glomerular neuronal architecture of the first relay station in the brain (for example reviewed by [1]). Honeybees need a powerful olfactory system for the location and evaluation of food sources, social (pheromone) communication, nestmate recognition, and for finding mating partners. Odorants are received by odorant receptors located in olfactory sensory neurons (OSNs) that are housed in different types of olfactory sensilla on the antennae (reviewed in [2]). In-situ recording of PNs and KCs in the honeybee www.uni-konstanz.de/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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