Watching the Brain of Zebrafish at Work Scientists Combine Microtechnology With Light Sheet Microscopy
The brain of an adult human consists of 86 billion nerve cells. The brain of zebrafish larvae is simpler, but still consists of about 100,000 nerve cells. The larvae, which are five millimetres in size, are almost transparent so that their brain can be observed using high-resolution microscopy. However, the images become blurred as soon as the fish moves. In an interdisciplinary project, scientists in the research focus “Infection and Therapeutics” at Technische Universität Braunschweig developed a sort of parking garage for zebrafish larvae combined with high-resolution microscopy. The paper on the project has now been published in the journal Communications Biology.
In order to better examine and understand the brains of zebrafish, Dr. Kai Mattern and Professor Andreas Dietzel from the Institute of Microtechnology (IMT) developed a tiny parking garage with a counter-current system. Here the animals can be held in water for a short time. What is special about this chamber is that it is made entirely of optically high-quality glass. The scientists removed this glass layer by layer with an ultra-short pulse laser. As “micro-sculptors”, they engraved not only chambers but also tiny flow channels into the inside of the glass. These flow channels, through which water flows, hold the fish in position and can also provide flow stimuli.
In the future it will be possible, for example, to study the activity of nerve cells during the administration of different drugs. Following such tests, the fish can then be set free again by reversing the flow of liquid and swim back into the aquarium. Many work steps were required before the finished chamber was ready: “Many flow profiles had to be simulated and many chambers had to be engraved until everything would fit. We call the finished chamber the ‘NeuroExaminer’,” say the microfluidicists.
Watching the brain at work
NeuroExaminer – the name of the chamber is the agenda for the daily research of the two neurobiologists Dr. Jakob von Trotha and Professor Reinhard Köster from the Department of Cellular and Molecular Neurobiology. They are looking to visualise and understand the activity of the nerve cells of zebrafish. The animals carry a gene that produces a dye in all nerve cells. Whenever the nerve cells are active and communicate with other cells, a short flash of fluorescent light is generated. The challenge is to simultaneously record all the nerve cells of the entire brain of the fish at a high rate of temporal repetition.
To achieve this, Jakob von Trotha has combined the NeuroExaminer with a light sheet microscopy method. A laser beam that has been expanded into a plane illuminates successively superimposed tissue layers of the brain. Within three seconds, a three-dimensional image of the activity state of the entire brain is generated in which every single nerve cell can be reconstructed.
The fish in the NeuroExaminer do not receive any stimuli yet. “We’re currently watching the fish during their spontaneous brain activity,” says neurobiologist Jakob von Trotha. “But even here it is very impressive to see which neuronal storms are already raging through the brain in a resting situation.”
The interdisciplinary interplay of microfluidics, imaging and neurogenetics is exemplary for the close cooperation at the TU Braunschweig across subject boundaries. In order to further develop the project together and then use stimuli, the scientists recently acquired 500,000 euros in funding from the German Research Foundation (DFG).
“Perhaps soon we will even be able to watch the fish think, or at least understand how information is processed in the brain. However, the NeuroExaminer not only enables basic research. In future, we might also be able to characterise known drugs and possibly even identify new active substances,” said Professor Reinhard Köster.