Abstract
.Fiber photometry has been increasingly popular in neuroscience research in freely behaving animals. In combination with genetically encoded calcium indicators, it allows for real-time monitoring of neural activity in neuronal somata, dendrites, and axonal terminals. We developed a multichannel fiber photometry device to map the activity of axonal terminals in a restricted, -wide brain region in freely moving mice. This device consists of four bundled multimode fibers, each with a core diameter and a scientific complementary metal-oxide semiconductor camera to simultaneously acquire fluorescence. We achieved a sampling rate of and sufficient sensitivity to acquire data from axonal terminals. To avoid interference with neighboring channels, the recording depth of each channel was restricted to . Furthermore, the small-core-diameter fibers did not restrict mouse locomotion. Using the indicator GCaMP5G, we validated the system by recording signals in axonal terminals from the medial entorhinal cortex layer II to the hippocampal dentate gyrus (DG) in freely moving mice. We detected spatially separated signals at four different sites in the DG. Therefore, our multichannel fiber photometry device provides a simple but powerful method to functionally map axonal terminals in spatially confined brain areas of freely moving animals.
Highlights
Axons transmit information from one neuron to another mainly through synapses at their terminals
A fiber probe with four channels was implanted above the medial entorhinal cortex layer II (MECII)-dentate gyrus (DG) projection [Fig. 8(a)]
Multichannel fiber photometry using a camera as the detector, rather than a photodetector, is much simpler and easier to extend compared with other kinds of multichannel fiber photometry.[26,32]
Summary
Axons transmit information from one neuron to another mainly through synapses at their terminals. A certain type of neuron in one area often projects to many different downstream regions with varying brain functions.[1] The function and neural dynamics of the subdomains projected from the same cell population, with a distance of hundreds of micrometers, may be different. The retinal ganglion cells project to distant laminae zones of lateral geniculate nucleus and superior colliculus, which participate in different brain functions.[2,3] dopaminergic axons from the ventral tegmental area (VTA) project to both the nucleus accumbens core and shell, which play different roles in reward.[4,5] the axonal terminals from the medial entorhinal cortex layer II (MECII) project to the entire region of the hippocampal dentate gyrus (DG), whose different subdomains may have different functions. A method to record simultaneously from multiple sites in subdomains of an axonal projection target is greatly needed
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