The Study Of Fiber Based Ca²⁺ Recording And Imaging In Freely Moving Mice

Billions of neurons in the brain constitute different functional regions,which project to each other to complete the reception,processing,storage and output of information.Recording the activities of neurons and their projection is the initial step to understanding animal behaviors.Due to the small structure of axon terminals,it is still difficult to record axon terminals in freely moving mice,and the need for multi-site synchronous recording of axon terminals in the same brain area also requires the development of new optical recording technology.This paper focused on the functional recording of nerons and axonal terminals with optical fiber-based approachs.The paper is divided into the following three parts:axonal terminal-spetific fiber photometry to research the roles and activity patterns of different MEC-hippocampus pathways in spatial navigation and spatial memory,axonal terminal-spetific multichannel fiber photometry for mapping axonal terminal activity in a restricted brain region in freely moving mice and the calcium imaging of cortical neurons in freely moving mouse.(1)An axonal terminal-spetific fiber photometry was developed and the Ca²⁺signals at the axonal terminals of two different medial entorhinal cortex(MEC)-hippocampus neural pathways(MECII-DG and MECIII-CA1)were recorded when mouse was doing spatial navigation task.Their respective activity characteristics were described during spatial learning.A sustained Ca²⁺activity began with the beginning of the task and ended with the end of the task in the MECII-DG pathway after spatial learning.This activity was named as persistent task assocatied(PTA)activity.The amplitude of PTA activity was highly related to the task performance.However,there was no significant change in Ca²⁺activity in the MECIII-CA1 pathway after spatical learning.Further test showed that continuous visual input was required to maintain the PTA activity in MECII-DG pathway.PTA activity was generated in familiar environments,encoding traces of spatial memory.Optogenetic inhibition of MECII-DG affected spatial memory,while inhibition of MECIII-CA1 pathway didn't.(2)An axonal terminal-spetific multi-channel fiber photometry was designed to do functional mapping in the axon terminals.Fibers in a diameter of 50?m were used to reduce the recording range of each channel.An integrated fiber probe was also designed for functional mapping in a restricted brain region.It was proved that there was no signal disturbance between adjacent channels.And the recording depth and volume of single channel were measured.The effects of multi-channel probes to the locomotion range of mice were measured.Finally,the multi-channel fiber system was applied to the functional mapping of MECII-DG pathway in the freely explorating mice.Neural activities at different recording sites were found to be asynchronized.This proved that the activity pattern of MECII-DG pathway was heterogeneous.Therefore,a simple but effective method was provided for the functional recording in the subdomain of axonal terminals.(3)Finally,the calcium imaging method of cortical neurons was explored in freely moving mice.A calcium imaging system based on fiber bundle was built up and applied to the calcium imaging of cortical neural structures,the dendrites of cerebellar purkinsite cells,the apical dendrites of the cerebral pymedical cells and the cell bodies in the superficial layer of cerebral cortex.Through the research in this paper,optical fiber-based axon terminal calcium signal recording technologies were developed.The cortical axon terminal,dendrite and cell body wide-field fluorescent calcium imaging technology was explored,and applied to the axon terminal recording in the spatial navigation behavior of freely moving mice.MECII-DG projection was found to be the key loop for visual-guided navigation,which provides theoretical support for the study of memory storage and extraction,memory intervention and artificial intelligence.