As fiber optics is finding wider use in microscopy, optogenetics and life sciences in general, it is becoming increasingly popular to use wavelength and intensity division or combination of the light within fiber optic circuits.
Fiber-optic Rotary Joints consist of a lens system and high precision bearings which allow a rotation-insensitive optical power transfer between optical fibers. The fixed part of the rotary joint allows the connection to a light source and the rotating part releases the twisting of the optical fiber connected to the animal.
A fiber-optic patch cord connects two distant fiber-optic ends and uses the same type of fiber and connections as the tips of the respective fibers it connects. In the context of optogenetics experiments with the rotary joint, a fiber-optic patch cord is needed to connect the light source and the rotary joint and yet another patch cord to connect the rotary joint and the fiber-optic cannula.
Biomedical and optogenetics applications need fiber-optic cannulas to deliver the light into the body tissue and/or to collect fluorescence or scattered light coming from the tissue.
Instead of cannulation, in vitro and in vivo head-fixed animal optogenetics experiments require thin and long optical probes that easily connect to micro-manipulator probe holders and have minimal obstruction of the observation site.
The observations of neural circuitry in freely moving animals like mice or rats require a wearable fluorescence microscope attached to imaging cannulas chronically implanted in the animal’s brain. To make this microscope mice-wearable, the smallest fluorescence microscope body ever was built. It easily snaps into a chronically implanted imaging cannula via a self-centering latching mechanism. The snap-in microscope body is electrically pigtailed and optically connectorized. In the middle of the visible spectrum, the scattering through the brain tissue limits imaging to about 150 µm. The imaging limited to those depths from the brain surface can be performed without insertion of all-glass relay lenses. At larger brain depths, it is absolutely necessary to use relay lens systems that may consist of homogeneous or gradient-index glass rods or lenses that bring the image into focus of the microscope objective and effectively reduce the optical path through the brain tissue.
In neuroscience, the fiber photometry denotes a method where the optical fiber(s) chronically implanted near the targeted brain region of interest expressing calcium indicator(s) delivers excitation light and collects overall fluorescence induced by calcium-activity during the light excitation. While the fluorescence microendoscopy records activity of individual neurons within the field of view, the fiber photometry sums up the overall fluorescence of neurons expressing a genetically encoded calcium indicator. The typical setup for freely behaving animals consists of the excitation light source, the beamsplitter/combiner that separates excitation and fluorescence light, the fiber-optic rotary joint, the optical cannula and connecting fiber-optic patch cords.
The filming of the animal is complementary information needed to establish correlation between the neuronal activity of the specific brain region and the animal behavior. The Doric Neuroscience Studio Software seamlessly integrates neuronal imaging, fiber photometry, electrophysiological recording, optogenetics stimulation and behavioral tracking of the freely-moving animals.
The system definition starts from the chronically implanted opto-electric cannula for behaving animals or from the opto-electric probes for in vitro or in vivo head-fixed experiments. For behaving animals, there is the tethered and the wireless/fiberless option.