Hybrid voltage sensor imaging of eGFP-F expressing neurons in chicken midbrain slices

Dendritic computation is essential for understanding information processing in single neurons and brain circuits. Optical methods are suited best to investigate function and biophysical properties of cellular compartments at high spatial and temporal resolution. Promising approaches include the use of voltage sensitive dyes, genetically encoded voltage sensors, or hybrid voltage sensors (hVoS) consisting of fluorescent proteins and voltage-dependent quenchers that, so far, are not available in avian neuroscience.

We have adapted a hVoS system for a chicken midbrain slice preparation by combining genetically expressed farnesylated eGFP with dipicrylamine (DPA). Depending on the cellular potential, DPA is shifted in the membrane, resulting in quenching of eGFP fluorescence linearly to the membrane potential by Förster resonance electron transfer.

In ovo electroporation resulted in labelled neurons throughout the midbrain with a high level of fine structural detail. After application of DPA, we were able to optically record electrically evoked action potentials with high signal-to-noise ratio and high spatio-temporal resolution.

Standard methods available for avian neuroscience such as whole-cell patch clamp yield insufficient data for the analysis of dendritic computation in single neurons. The high spatial and temporal resolution of hVoS data overcomes this limitation. The results obtained by our method are comparable to hVoS data published for mammals.

With the protocol presented here, it is possible to optically record information processing in single avian neurons at such high spatial and temporal resolution, that cellular and subcellular events can be analysed.