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Capping off this day of the symposium was the man himself, Randolf Menzel, presenting his version of "Past, presence, future of honeybee neurobiology". He started out by mentioning the shortcomings of the honeybee model system, beginning with the dearth of possibilities to use molecular manipulation in the brain and ending with the scarcity of well-characterized neurons. He then mentioned that experience is the prerequisite for expectation referring to the past-present-future theme of his presentation.

Sticking to this theme, he recounted the history of the proboscis extension response (PER) conditioning. In the 1950s Karl von Frisch studied proboscis extension in the process of which his postdoc Kuwabara discovered and developed a Pavlovian conditioning procedure out of this reflex-like behavior. Menzel started using PER conditioning in the 1970s and began to localize the memory trace by cooling various brain areas. These experiments showed that the antennal lobes and mushroom-bodies are critically involved in forming this memory. For the presence, he picked two recent PER-based experiments to emphasize how important it is to always pay attention the proper conditions are maintained during the experiment and that always the necessary controls are performed. Projecting into the future, Menzel pointed out some important limitations of the PER preparation which could me improved upon in the future: There is very limited level of spontaneous activity limiting the quantification of individual responses and preventing operant conditioning. Visual learning does not work that well and the bees don't survive for very long. Menzel's attempt for such improvements is an experiment in which honeybees run on a floating ball while the can receive reward and the experimenter can record from their brains during the experiment. Projecting far into the future, Menzel is dreaming of a flight simulator for honeybees into which bees could fly directly from the hive already carrying implanted recording electrodes.

The next section, 'neurons' started with a recount of the discovery and work on the VUMmx1 and PE1 neurons by Martin Hammer and Juliane Mauleshagen, respectively. The problems with the PE1 recordings back then were mostly with the recordings having to take place in the isolated head of the bee, because the brain would otherwise move too much. Luckily, later experiments recorded extracellularly in the intact animal and could confirm the early results. Menzel himself recently discovered associative long-term potentiation in PE1. Martin Hammer's work famously showed that stimulating the vumMX1 neuron can replace sucrose stimulation in PR conditioning experiments. Moreover, vumMX1 starts to respond to the CS predicting the US rather than the US itself with progressing training, very much as predicted by the Rescorla-Wagner learning rule and analogous to the results in dopaminergic midbrain neurons in mammals. Today, the entire fine-structure of this complex neuron has been registered in the 3D standard atlas of the honeybee brain. Unfortunately, current functional research on vumMX1 has basically stalled, because the neuron has proved to be exceedingly difficult to study. Addressing future research on single neuron neurobiology, Menzel pushed for new physiological technology developments to make this research less difficult and thus less likely to fail. One such technological improvement he dreams of is to project the predicted location of neurons of interest onto the actual preparation to facilitate neuron localization.

The third past-present-future section concerned Calcium imaging of neural activity. Recounting the story of how a group of graduate students found out how to image the neural activity in the antennal lobes during the presentation of an odor to the antennae. This technique was later extended to also be able to image the neurons in the mushroom-bodies. Presently, two-photon imaging can record Calcium signals at much higher temporal and spatial resolution than conventional microscopy. Another present imaging study concerned MB-extrinsic PCT neurons which receive their input in the alpha lobes of the mushroom-bodies and relay that back into the calyces. This work showed that some aspects of the effects of PER conditioning can be found in these neurons. Menzel told us that the future of this technique needs to include better localization of the calcium indicator dye, preferably by transfection methods. These methods need to be combined with multi-photon microscopy. First steps to transfect neurons with genetically encoded indicators are being taken in his lab.

The last past-presence-future topic was navigation and communication. Menzel revealed to us that probably the biggest mistake he has ever made in his career was to assume that bees orient according to an egocentric vector, when instead bees use a hierarchy of strategies: vector first, then search, then novel shortcuts: bees know where they are and where they are going next. Present experiments concern the motivational and instructive components of dance communication. The future of this area includes automatic individual detection of all the bees in a hive and automated tracking of all their flights and movements within the hive. The transponders for harmonic radar tracking need to be developed which allows the bees to enter the hive. The robot dancing bee should be improved to allow better manipulation of the information conveyed during the waggle dance.

Randolf Menzel concluded his presentation by emphasizing that bees transmit information to each other and we need to understand how this information changes the brains of those individuals that participate in this transmission.
Posted on Saturday 12 June 2010 - 17:52:46 comment: 0

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