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Published on: January 12, 2012
Optogenetic estimation of synaptic connections in brain slices
Tetsuhiko Kashima1, Takuya Sasaki2, Yuji Ikegaya3
1Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan; Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan.
Background:
Detection of synaptic connections is essential for understanding neural circuits. By using optogenetics, current injection, and glutamate uncaging to activate presynaptic cells and simultaneously recording the subsequent response of postsynaptic cells, the presence of synaptic connections can be confirmed. However, these methods present throughput challenges, such as the need for simultaneous multicellular patch-clamp recording and two-photon microscopy. These challenges lead to a trade-off between sacrificing resolution and experimental throughput.
New Method:
We adopted the laser, typically used for local field ablation, and combined this with post hoc analysis. We successfully approximated the synaptic connection probabilities using only an epi-fluorescence microscope and single-cell recordings.
Results:
We sequentially stimulated the channelrhodopsin 2-expressing cells surrounding the recorded cell and approximated the synaptic connection probabilities. This probability value was comparable to that obtained from simultaneous multi-cell patch-clamp recordings, which included more than 600 pairs.
Comparison With Existing Methods:
Our setup allows us to estimate connection probabilities within 100 s, outperforming existing methods. We successfully estimated synaptic connection probabilities using only the optical path typically used by an epi-fluorescence microscope and single-cell recordings. It may also be suitable for dendritic ablation experiments.
Conclusions:
The proposed method simplifies the estimation of connection probabilities, which is expected to advance the study of neural circuits in conditions such as autism and schizophrenia where connection probabilities vary. Furthermore, this approach is applicable not only to local circuits but also to long-range connections, thus increasing experimental throughput.
