Microscope tracks live brain activity
Image: Open source tracking microscope - NeuBtracker - is an imaging platform for neurobehavioural research.
Germany-based researchers from the Helmholtz Zentrum München and the Technical University of Munich have developed an open source microscope to image the neuronal activities of freely-behaving zebrafish.
'NeuBtracker' is a tracking microscope for simultaneously imaging neuronal activity and behaviour of freely swimming fluorescent reporter fish.
As Professor Gil Westmeyer from the Institutes of Biological and Medical Imaging (IBMI) and Developmental Genetics (IDG) at the Helmholtz Zentrum München highlights, the microscope is equipped with two cameras.
The first camera tracks the unrestrained behavior of the zebrafish larva while the second, automatically remains pointed at the transparent head, and consequently the brain, to record fluorescence images.
Imaging the brains of swimming zebrafish with the neurobehavioral tracking microscope NeuBtracker. [Dr Barth van Rossum]
Crucially, the instrument operates without moving stages, objectives or excitation light beams, provides adjustable magnification and allows for dynamic refocusing.
According to the researchers, tracking of the fish is controlled by a custom-written acquisition software that receives the 1× image from an IR-sensitive camera as input.
The software locates the fish’s head and and moves galvanometric mirrors to the position that keeps the field of view of the fluorescent camera on the fish.
For fluorescence excitation, the instrument uses an LED centered at 460 nm to provide homogeneous illumination across the whole arena.
And magnification is obtained either by using lenses with a fixed focal length or a zoom lens, which can achieve a resolution of up to 150 line pairs per mm for field of views ranging from the whole body of a larva to zoom-ins on only the larval brain.
“This approach makes it possible to observe neuronal activity during unrestrained behavior," says Westmeyer, also from the Department of Nuclear Medicine and Munich School of Bioengineering (MSB) at the Technical University of Munich (TUM). We can test the larvae in different environmental conditions and can immediately analyse the effects.”
For example, by adding substances that influence metabolism, it is possible to observe resulting neuronal events in the brain in vivo.
“Now we can finally simultaneously observe the effects of physiologically active substances on the behaviour and brain activity,” explains Westmeyer's colleague Panagiotis Symvoulidis from the TUM and the Helmholtz Zentrum München. “The selective expression of fluorescent sensor proteins allows us to detect the activity of particular neurons.”
Instructions on how to build the open source microscope are available at neubtracker.org.
"We wanted to give our scientific colleagues the possibility to build their own NeuBtracker because we had been waiting for such a device for years,” says Westmeyer.
“It is finally possible to see the effects of pharmacological substances on the behaviour and the neuronal activity - or other cellular signal processing events - at the same time and across an entire organism," he adds. "This systemic approach enables us to make new discoveries and we will for example seek to use this device in drug discovery and metabolic research."
Research is published in Nature Methods.