Solution pages

  FIBER PHOTOMETRY

Fiber photometry is a powerful neuroimaging technique to monitor the activity of neuronal populations in the behaving animals including rodents and primates.

To observe neuronal activity, prior to the cannula implantation, the targeted brain area is injected with genetically-encoded fluorophore indicators including GCaMP, dLight, GRAB-Ach, RCaMP, jRGECO1, etc. among others. Those indicators possess fluorescence properties, meaning they emit light at a longer wavelength after absorbing light at a shorter wavelength (excitation light). However, for this fluorescence to occur, the indicators must also bind to molecules (ex. dopamine, acetylcholine, calcium ions), which increase during neuronal activity. Therefore, by measuring the fluorescent emission from brain tissue, researchers can indirectly measure the level of molecules as an indicative of neuronal population activity during complex behaviors.
The fiber photometry method offers several advantages, including low invasiveness, low cost, simplicity compared to other methods, and the possibility to monitor deep brain areas. Nonetheless, there are drawbacks to consider, e.g., the spatial resolution of the photometry signal is limited to neuronal population, in contrary to our Miniature Microscopy Systems that resolve single cell imaging.

The fiber photometry method offers several advantages, including low invasiveness, low cost, simplicity compared to other methods, and the possibility to monitor deep brain areas. Nonetheless, there are drawbacks to consider, e.g., the spatial resolution of the photometry signal is limited to neuronal population, in contrary to our Miniature Microscopy Systems that resolve single cell imaging.

Doric Lenses Inc. is a recognized leader in developing cutting-edge products for fiber photometry in behaving animals, driving innovation in this rapidly evolving field. The image below gives an overall summary of all photometry systems so far designed in the company. Each system is meticulously designed to meet specific needs and challenges encountered by users.

Three main categories of photometry systems divided based on their detector: Basic System: photodetector with high sensitivity and high temporal resolution. Bundle Systems: CMOS camera images multiple fibers simultaneously. FluoPulses System: fast photodetector measures changes in fluorescence lifetime.

  BASIC SYSTEMS

Basic Fiber Photometry Systems are designed to record fluorescence signals sampled with one optical fiber per cube. However, it is possible to combine multiple cubes to record from more than one mouse or brain site. Doric Lenses offers three (3) different system configurations to accommodate experiments with freely moving animals. The Fiber Photometry Mini-Cube (FMCs), the Rotary Fiber Photometry Mini-Cube (RFMC), and the Wireless Photometry system.The FMCs  can be subcategorized into 3 types (FMC, iFMC, and ilFMC) depending on their level of integration (see image below). The FMC has an all-optical fluorescence cube with external light sources and detector for recording photometry signals. This modular design makes it highly customizable for different applications. The iFMC though, only requires a separate light source as the photodetector is integrated within the cube purposefully to increase the signal-to-noise ratio. The ilFMC contains all detector and light sources within the cube. Therefore, not only the signal-to-noise ratio improves, but also the system is simpler and user-friendly. Notably all FMC systems can be used with our pigtailed rotary joints (FRJ_1x1_PT, FRJ_2x2_PT & AFRJ_2x2_PT) for either 1-site or 2-site long-term, freely-moving experiments. In Rotary Fiber Photometry Mini-Cube (RFMC) the fluorescence cube, the excitation light and the detectors are embedded on the rotary joints itself. This unique setup minimizes movement artifacts in the signal, resulting in more reliable data collection. Meanwhile, the detector is also embedded inside the cube to increase the signal-to-noise ratio. Therefore, RFMC system boasts the highest quality signal recording among all options, albeit at a slightly higher cost. The rotary joint also contains a hollow channel for passing extra cables or tubes for optogenetic stimulation, fluid delivery, or electrophysiology recording, at a distinct site from the photometry sites. Lastly, considering that wired setups often lead to tangling issues in freely moving animal, especially during social interaction of several mice in the same cage, at Doric Lenses, we have recently developed a new solution, the Wireless Photometry product. Two excitation light, one detector and all electronics and optics are integrated onto lightweight battery operated headstage with wireless communication. This system is ideal to study neural population underpinning social behaviors but is limited to 1-color green emission detection (500-550 nm) with 2 excitations; isosbestic (405, 415 nm) and functional (470 nm). All basic systems use lock-in or interleaved signal demodulation algorithms. The photodetectors of basic systems also capture data at a high sampling rate, which is then down sampled to 60 Hz. Additionally, the FMC systems are compatible with red-shifted optogenetics over the photometry site, while RFMC can only support optogenetic stimulations in a different site.

  BUNDLE SYSTEMS 

While the basic fiber photometry systems are typically designed to record from a single mice brain, still multiple cubes can be combined to record from several mice or several brain regions. However, this approach rapidly increases the complexity of the setup and poses challenges in synchronizing the recordings, especially for 3+ sites/animals To address this issue, Doric Lenses has designed series of Bundle Photometry System, specified for simultaneous recording from multiple animals or various brain regions of a single mice (1-19 target regions), all at a reasonable price. The Bundle Photometry System includes 3 subcategories including the Bundle Fiber Photometry System (BFMC), Bundle Fiber Photometry with Targeted Optogenetic (BFTO) and the Rotary Bundle Fiber Photometry (RBFMC) (see image below). The BFMC has two version depending on the integration level. The newer version of BFMC system has a fully integrated design (CMOS camera, LEDs, LED Driver & console), greatly simplifying the set up compared to the standard BFMC system. However, both BFMC systems are not compatible with optogenetics. The BFTO system is specifically designed to combine multi-fiber photometry and targeted optogenetics. Independent multi-site optogenetic control is ideal for close-loop optogenetics (both multi-animal and/or multi-site) experiments. This system provides the greatest flexibility for common neuroscience experiments. Unlike the BFMC and BFTO systems, the RBFMC has a rotating cube that helps eliminate movement artifacts, allowing for high-quality signals. However, this benefit comes at the cost of being limited to recording different brain regions from a single mouse. Additionally, the RBFMC includes optogenetic capabilities that can illuminate all sites simultaneously. All bundle systems use CMOS camera detector that images entire fiber bundle simultaneously. The power LEDs excite the entire fiber bundle, and the photometry signal is then sampled at 10-20 Hz depending on the configuration.

  LIFETIME

FluoPulse™ is a novel photometry system from Doric Lenses which works by measuring fluorophores lifetime rather than fluorescence intensity level. It is designed to measure fluorescence lifetimes ranging between 1-10 ns and can resolve differences in lifetime of 10-20 ps. The measured photometry lifetimes are then averaged at 10 Hz to obtain photometry signal. Thus, it is compatible with most biosensors designed for Fluorescence Lifetime Microscopy (FLIM) and Förster’s Resonance Energy Transfer (FRET), including FLIM-AKAR, GRAB-Ach3.0, etc.  By sampling fluorophores lifetime rather than intensity, FluoPulse™ offers several advantages, including highly stable fluorescence imaging which is robust to sensor expression level, autofluorescence, photobleaching, excitation power, and movement artifacts and ambient light. This makes it ideal for long-term studies lasting weeks or months, as well as for comparing results across different animals, time points, and brain regions.