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Research exchange between Ayal Lavi and Oliver Weihberger

Final report about the research exchange between Ayal Lavi (Tel Aviv University) and Oliver Weihberger (Bernstein Center Freiburg, BCF)

 

Preface

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Our research project was carried out between Oct 4th and November 20th 2010 in the lab of Prof. Egert at the Institute for Microsystems Engineering – IMTEK in Freiburg. The first days were dedicated to learn how to work with the experimental setup system and the basic functioning of the viral application. In addition, we took part in the yearly retreat of the BCF at the Fachschaftshaus Schauinsland. The Freiburg PhDs and Post-Docs learned about Ayal’s previous work on DOC2B over-expression (a synaptic protein and neuronal Ca2+-sensor that enhances vesicle exocytosis and replenishment) in biological neuronal networks of cortical cell cultures.

 

Experimental Outcome

The experiments utilize a unique virus that co-expresses DOC2B and GFP independently. The first experiments assessed the efficacy of the viral infection by tracking the fluorescence of the infected neurons. We obtained clear fluorescent signals and could verify the timeline of DOC2B over-expression for several hours.
Next we tested the effect of DOC2B over-expression on the spontaneous and synchronous bursting activity of cultured neuronal networks. Spontaneous activity was recorded before and during DOC2B over-expression as well as in GFP over-expressing cultures. We found overall ~ 30% more spikes per network burst with DOC2B compared to the activity before viral application (9 cultures). This effect was stable 3 hours after viral application and lasted for at least 3 more hours (6 hours after infection). The intervals between network bursts, in turn, concomitantly increased by ~ 50 – 100 % and were more variable across recordings. The control recordings (4 cultures) did neither show a change in the no. of spikes nor the intervals between network bursts. This ruled out the possibility of a mere effect by viral application on the spontaneous activity dynamics.
We applied two types of electrical stimulation protocols. Phase-coupled feedback stimulation at various intervals after spontaneous bursts (post-burst stimulation) assessed the network’s excitability and recovery dynamics under control and DOC2B expression. Preliminary results suggest that smaller response delays with DOC2B resulted in stronger synaptic activation and thus more recurrent input during spontaneous and evoked activity. The second stimulation protocol tried to mimic the well-known classical conditioning learning paradigm into neuronal cell cultures. We assessed changes of the various plasticity parameters following the application of a stimulation protocol that induces site-specific plasticity that we developed together. We found that the designated site increased by a relative amount of 20 % (5 recordings). The change for the control sites showed no significant change. Yet, fluctuations of overall excitability over long timescales interfered with these results and gave inconclusive changes all sites (9 recordings). Further experiments and analyses will be required.

 

Summary

We’d like to express our gratitude to the Bernstein Center for generous support during Ayal’s stay in Freiburg. It was an extraordinarily fruitful and exciting collaboration. We both extremely appreciated each other’s expertise and plan to continue our collaboration to develop further ideas in the near future.
 

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