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My lab:
The first speaker after the lunch break was Bernd Grünewald presenting his work on the "Cellular physiology of the honeybee brain". Bernd showed us the properties of many of the voltage-sensitive ionic currents in mushroom-body Kenyon cells that he has studied. Surprisingly, despite the existence of many identified and characterized currents, these neurons only fire very rarely. Some of the questions Bernd would like to have answered are: Why do Kenyon cells express so many ionic currents if they hardly spike at all? Is spike modulation relevant for experience-dependent response modulations in MB neurons? How do the membrane properties of Kenyon cells shape the odor response of the MBs?

Next up was Wolfgang Rössler talking as the last speaker of this session about "Plasticity of synaptic microcircuits in the mushroom-body calyx of the honeybee". About 35-40% of the total number of neurons in a honeybee's brain are mushroom-body Kenyon cells, whereas in Drosophila that number is only about 3-4%. What is the functional significance of that? Given the highly complex social life and division of labor in the honeybee hive, Wolfgang hypothesizes that plasticity in MB-calyx synaptic microcircuits may promote behavior adaptations at different time scales. Therefore, he studies the input synapse from the projection neurons providing olfactory input from the antennal lobe. These synapses also receive input from GABAergic inhibitory neurons projecting from the MB alpha-lobe, creating an interesting micro-circuit of excitation and inhibition which makes up the MB micro-glomeruli (MG). These MGs develop much faster in Queens than in workers leading to a lower number of MGs in queens. Adult maturation leads to expansion of MGs. This expansion of MGs is accompanied by a decrease in number of glomeruli, leading to an overall reduction in the total volume of the MB calyx (i.e. dendritic growth accompanied by presynaptic pruning). GABAergic processes decrease with MG expansion. Finally, he showed us evidence that stable olfactory long-term memory triggers in the number of MGs in the lip region of the calyx.

In the next and final session for the day on orientation and navigation, we learned about some answers to the question of "How do honeybees obtain the specific messages from dances in the darkness of the hive?" by Axel Michelsen. His experiments were done using a robotic honeybee and making it transmit different parameters of the waggle dance to see how the following bees would respond. In order to construct such a robot, accurate measurements had to be made from the signals the dancing be emits. The focus was on auditory stimuli, so they recorded the sound pressure of the dancing bee from various directions with microphones. The measurements revealed sound pressures far beyond any legal levels for work places (1-2 Pa). Such high pressures lead to air velocities around the wings of the dancing bee of about 1m/s. However, sound pressure decreases dramatically with distance, preventing individual dancers from jamming each other. Another set of measurements concerned the airflow generated by the 30Hz waggle of the abdomen during the dance. Using the results from all these meticulous measurements, they constructed a robot which would be able to dance in the hive, waggle and beat the wings to generate all the sounds and air movements. The robot could even dispense sugar water to any following bees. The robot was covered in wax and spent the night in the hive with the bees as well. Using this robot they tested, for instance, what would happen if the waggle run was moved from the center lane to any or several of the other lanes. Maybe not all that surprisingly, even with a 'perfect' match of all stimuli, the number of recruited bees that ended up at the place indicated by the dancing robot was always smaller than that recruited by live bees. Therefore, they used a more accurate laser-based method to measure the air flow around the dancing honeybee. One observation among several was that the bees generate vortices around themselves while they are dancing. Another was a jet of air coming out from under the wings and projecting out behind the abdomen of the bee as she vibrates her wings. This latter observation fitted nicely with the earlier finding that followers behind the dancer obtain the specific information for the location of the food source much faster and more accurately than other followers. This has led them to propose the novel hypothesis that the followers obtain the direction information from measuring the timing of these jets, which varies according to the angular position of the follower to the dancing bee. Finally, he told us about the latest measurements where they simultaneously measure behavior, wing vibration sounds and jet airflows. These measurements suggested that the dancer has control over when to generate these air-jets.

Next up was Gene Robinson telling us about "Molecular dissection of honey bee dance language: progress and prospects". This talk was about a project that was still pretty much work in progress and still requires quite a lot of experiments. Basically, they subjected bees to various behavioral treatments and then used 'Omics techniques to see what has happened. He started by mentioning that they didn't find any dance-specific projections of sensory systems in their anatomical studies. Their comparative Transcriptomics on three Apis species (mellifera, dorsata, florea) showed that a number of different molecular processes were modulated by dancing which implicated strong similarities in the gene expression between the central brain and the thoracic ganglia. Training bees to experience either long or short distance flights (manipulated via a tunnel inducing the visual illusion of various distances) showed that a number of genes is modulated by the experience of flights of varying distances. The proteomic approach studied foraging bees before food collection at a feeder, just after they collected food, while they were foraging and when they arrived at the hive. Also in this experiment they found a few peptides which were differentially regulated between these four groups of bees. In the last part of his talk, Gene presented results from bees on cocaine. Cocaine works as an octopamine reuptake inhibitor in insects and - as octopamine - increases the probability of a bee to dance, which is blocked by octopamine receptor antagonists. Similar to mammals, Honeybees show place preference and withdrawal in cocaine experiments as well.
Posted on Saturday 12 June 2010 - 16:39:21 comment: 0

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