Fish and Chips Sheet into the Light

Whole-brain in vivo light sheet imaging of zebrafish neural activity in a microfluidic chip


The zebrafish larval brain is small and contains about 1 million times less neurons than the human counterpart. The neural circuitry and the general bauplan of the vertebrate brain, however, is evolutionary conserved. Moreover, zebrafish larvae are optically translucent offering a unique possibility to investigate neural activity throughout the whole brain in real time with advanced imaging techniques such as light sheet microscopy. Microfluidics, on the other hand, allow to apply water soluble chemical stimuli with high spatiotemporal precision, including 3D focusing and concentration gradients. Taking advantage of the trinity of fast light sheet imaging, optically translucent zebrafish larvae, and the capabilities of microfluidics, we have constructed a microfluidic device (NeuroExaminer) that is compatible with whole-brain in vivo imaging.

Made entirely out of glass, the NeuroExaminer offers significant advantages over other devices conventionally made from polydimethylsiloxane (PDMS) that exhibit autofluorescence and tend to absorb small molecules. Although the NeuroExaminer was developed around the Leica digital light sheet (DLS) microscope, its design is thought to be compatible with a variety of selective plane illumination (SPIM) or oblique plane microscopy techniques. Furthermore, gentle manipulation allows to image individual larvae at multiple time points and thereby to observe changes in brain activity not only on short (seconds to minutes) but also on longer (hours to days) time scales. In the future, automatic loading and targeted stimuli application together with whole-brain in vivo imaging will provide a unique opportunity to gain novel insights into brain function in health and disease, and may ultimately also contribute to the development of novel and better treatments of neuropsychiatric disorders such as anxiety, depression, and drug addiction.

Figure 2: In vivo imaging of a live 6 dpf Tg(elavl3:H2B-GCaMP6s); crystal larva using the Leica DLS in combination with the NeuroExaminer. A maximum intensity projection consisting of 21 optical sections at 5 min and 45 s (time is indicated in min:s:ms) depicting nuclear-localized GCaMP6s throughout the larva’s brain is shown. Dotted color-coded lines outline five major brain regions depicted on the lower right.  Scale bar is 500 µm.

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