Analyzing the dynamics of neuronal populations in freely behaving animals is challenging. Therefore, equipment allowing the investigation and the manipulation of neural activity were designed to increase the temporal and spatial resolution of recordings and stimulations.
While the development of new technologies for neuroscience has been abundant over the last decades, three fields have been at the center: optical stimulation (via optogenetics), imaging and electrophysiology. The aim of recording deeper in the brain and in multiple regions is driving the outbreak of various technologies, making once confidential methods available to a growing number of labs.
In vitro techniques such as patch-clamp recordings or single-cell optogenetic stimulation have made their way out of the traditional electrophysiology workstation to embark on freely moving animals. This multiplication of methods has offered scientists the opportunity to diversify their approach to a specific scientific question. By combining brain slices and in vivo techniques for example, researchers can break down neural activity while confirming the behavioral relevance of the finding.
In this post, we introduce the fiber photometry method. It is one of the newest tools available to neuroscientists who want to correlate behavior with neural activity. Easy to set up and relatively inexpensive compared to other technologies – e.g. multiphoton imaging system – fiber photometry is widely used in preclinical neuroscience research labs. We focus on equipment suppliers.
What is fiber photometry?
Fiber photometry is a method allowing the recording of fluorescent signals in the brain of freely moving animals. It is based on the principle of expressing a sensor (sometimes called optogenetic sensor) in targeted neuronal populations. The sensor emits a specific fluorescence when in presence of the chemical of interest, e.g. calcium or a neurotransmitter. Other sensors further report on the vesicular release or the membrane voltage. Then, the system collects the overall activity-induced fluorescence. It is a powerful ultrafast technique used to measure calcium neurotransmitters and other molecules in vivo in real time. Fiber photometry has become a popular tool for measuring the cellular and molecular events in genetically defined groups of cells in behaving animals.
The combination with genetically encoded calcium indicators (GECIs) or genetically encoded voltage indicators (GEVIs) provides real-time information about the neurons of interest. Additionally, it can be associated with optogenetics actuators to simultaneously manipulate and report the activity of neuronal populations. This combination with genetic tools allows for cell-specific and potentially long-term monitoring of neuronal activity.
What are the popular fiber photometry solutions?
According to our idea to bring added value to neuroscience research labs, We have created this selection of available options to start your fiber photometry experiments. This pick is not comprehensive as there are many systems available, some being tailored to specific protocols. However, if you think one system should be mentioned in this post, feel free to let us know and we will be glad to update this list.
RWD Life Science
RWD is a life science equipment company headquartered in China. Known for their solid manufacturing process and their great quality/price ratio, we selected some of their best products to appear on our website (you can find their dedicated page here).
RWD fiber photometry system combines the 410 nm isosbestic reference channel to eliminate motion artifacts, with a dual-wavelength (470 and 560nm) fluorescence excitation. This solution allows the recording of emitted fluorescence in real-time, from varied genetically encoded calcium indicators (GCaMP, RCaMP), dopamine sensors (dLight), and fluorescent proteins (GFp, mCherry, tdTomato, etc…).
Additionally, this system can support up to 7 channels, allowing data acquisition from multiple brain regions or several individual animals.
Doric Lenses is a Canada-based manufacturing company. They are specialized in neuroscience applications such as in vivo fiber photometry, fiber-based optogenetics, fluorescence microscopy and electrophysiology.
Their offer for fiber photometry systems is varied and can fit with several requirements:
USA-based, Plexon is developing equipment for data acquisition and behavioral protocols in the neuroscience field. The company is primarily known for their in vivo electrophysiology equipment.
Plexon’s fiber photometry equipment is their multi-fiber and multi-wavelength photometry system. This solution is similar to other dual-wavelength fluorescence detection equipment. It allows the GCaMP isosbestic point control, as well as the activation of GCaMP and RCaMP, and the measurement of their emitted fluorescence. This fiber photometry system can be combined with up to 4 different fibers, allowing for recording in up to 4 areas / animals simultaneously.
TDT Tucker-Davis Technologies
Tucker-Davis Technologies is an American company specialized in the applications of neurophysiology, optical neuroscience, behavioral experiments, and auditory research. They develop solutions for ephys, optogenetics or fMRI.
Regarding fiber photometry, TDT offers 2 systems based on different processors: the LUX RZ10 and the LUX RZ10x. These processors can drive respectively 3 and 6 LED outputs, and collect fluorescence data from 2 and 4 sensor inputs. LEDs are available in a variety of wavelengths: 405, 415, 465, 560 and 590nm.
TDT’s Lux system also provides optogenetics and electrophysiology incorporations for multi-modal and closed-loop experiments.
NPI is a German company offering data acquisition, processing tools and perfusion systems. Their fiber photometry system is the FiberOptoMeter III.
Using this device, one can combine different wavelengths through the same optical fiber. Thus, the user can perform dual-band excitation, allowing for near simultaneous measurement of neuronal activity and optogenetic stimulation. Short flashes of high-power light in various wavelengths provide the user with the possibility to stimulate a large range of opsins (ChR2, ArchT…). Concurrently, the photomultiplier tube (PMT) detects the light emitted by Ca2+ indicators (GCaMP, RCaMP, OGB1…) and fluorescent proteins (tdTomato, mCherry, eGFP, YFP…). This combination allows the user not only to measure physiological signals from cell populations in freely moving animals, but also to manipulate the activity of neuronal network.
Based in California, Neurophotometrics is the youngest member of this selection. Their only fiber photometry system is the FP3002.
As with other manufacturer solutions, the FP3002 enables recording of bulk signals from calcium and neurotransmitter indicators in two colors, multiple animals, and multiple brain regions simultaneously. The system includes 3 excitation wavelength (isosbestic control 415nm, 470nm and 560nm) and can be coupled with 2 lasers for optogenetic illumination.
Primarily located in Toronto, Mightex is a manufacturer focusing on light delivery and in vivo imaging solutions. Particularly known for their digital mirror device (DMD) patterned illuminator, Mightex has designed a system allowing cellular-resolution optogenetics and photostimulation.
The OASIS Implant is an optical fiberscope. This technology offers a relatively similar approach to neuronal activity recording and manipulation than fiber photometry systems. However, the main difference lies in the complexity of the optical components. The system is designed to not only detect overall fluorescence from a region of interest, but to image deep-tissue with a few micrometers resolution. To achieve this, optical fiberscopes integrate fiber-optic bundles, enabling the user to obtain spatial information.
Mightex’s fiber photometry system is – to put it simply - a downgraded version of their optical fiberscope – the OASIS Implant. Thus, the system comes with an optical fiber similar to alternative systems, instead of the imaging fiber. Therefore, the user loses the possibility for cellular-resolution imaging and stimulation but benefits from the system at a more accessible price. However, due to its original design aim to image individual neurons, this solution is on the higher-end price range of this selection.
Teleopto – Wireless fiber photometry
Teleopto is a Japanese company focusing on equipment for optogenetic and behavioral experiments. Their solution, TeleFipho, is the first commercially available wireless fiber photometry system.
One restriction of the traditional fiber photometry systems is the requirement to have the optical cable attached to the head of the animal. Under certain circumstances, it can limit the movement of the animal when interacting with its environment. It can also cause some artefacts in the recordings, such as ghost movement due to the optical fiber swaying even if the animal stops moving.
Even though the power output is too low for optogenetic stimulation, TeleFipho solves the issues associated to tethered experiments by placing all the system components on the headstage. Thus, this equipment provides the user with a tool to record single-fluorescence from GCaMP and GFP-like indicators while performing the usual behavioral assays. However, the downside of this system is that a 3g headstage as to be mounted on the rodent’s head, which is slightly heavy for a mouse.
Thorlabs – Assemble your own fiber photometry system
Headquartered in Newton, New Jersey, Thorlabs is a manufacturing company with a different business plan. They provide a huge selection of products (approximately 20000) for areas such as imaging, optics, fibers or light sources. Their approach to in vivo neuroscience equipment is different from the other company selected in this post. Thorlabs provides components needed for fiber photometry, such as LEDs, LED drivers, mounting cubes, optical fibers, patch cables, rotary joints, cannulas. This method provides flexibility to the user, with multiple options for each component of the setup. However, this can result in unnecessary downtime while building the setup and finding a software to analyze the collected data.
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