Biology and Biomedical Sciences: Neurosciences
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
The brain contains an enormous number of neurons with diverse gene expression, morphology, and connectivity. These neurons exhibit distinct activity in the course of behaviors. The study of neural coding of a specific behavior necessitates recording activity from multifarious neurons in the circuit.One appealing approach is to simultaneously image the activity of a very large neuronal population at cellular resolution. However, recording calcium signals from tens of thousands of neurons at one time is not trivial. The gold standard technique, two-photon laser-scanning microscopy, typically permits recording from hundreds of neurons. Recently, we developed objective-coupled planar illumination (OCPI) microscopy, which uses thin sheets of light to image whole volumes of ∼ 10, 000 neurons within 2 seconds. Mydissertation includes an application and a further methodological development of such a fast large-scale imaging technique:
1) Large-scale functional imaging revealsindividuality, dimorphism, and plasticity of mouse pheromone-sensing neurons.Different individuals exhibit distinctive behaviors, which is presumably attributed to the neuronal differences between brains. However, studying neural individuality, especially at the level of the function of single neurons, requires an effective approach to measure cellular activity of a diverse neuronal population in a circuit. Here using OCPI microscopy, I performed calcium imaging of pheromone-sensing neurons in the intact mouse vomeronasal organ. Exhaustive recording enabled robust detection of 17 functionally-defined neuronal types in each animal. Inter-animal differences were much larger than expected from random sampling, and different cell types showed distinct degrees of variability. One prominent difference was a neuronal type present in males and virtually absent in females, and animals exhibited a corresponding dimorphism in investigatory behavior. Surprisingly, this dimorphism was not innate but generated by plasticity, as exposure to female scents led to both the elimination of this cell type and alterations in behavior. The finding that an all-or-none dimorphism in neuronal types is controlled by experience--even in a sensory system devoted to "innate" responses--highlights the extraordinary role of "nurture" in neural individuality.
2) A new generation of OCPI microscopy enables unprecedentedlarge-scalein vivoimaging of mouse brain activity by light-sheet microscopy. I have built a new variant of OCPI microscope, horizontal scanning objective-coupled planar lumination (hsOCPI) microscope, with enhanced imaging volume and speed by ∼ 15 fold compared to OCPI, thereby capable of recording ∼ 100, 000 neurons simultaneously. Using this technique, I imaged the entire nervous system of the larval zebrafish (including the spinal cord) and a square-millimeter patch of mouse cortexex vivo. The miniaturized optics around the specimen allowed in vivo imaging through a cranial window of a head-fixed mouse. This technique is the first application of light-sheet microscopy in calcium imaging of mouse cortexin vivo. The exceptional large-scale sampling of cortical activity with cellular resolution should usher new insights into the functions of brain circuits.
Xu, Pei Sabrina, "Large-scale Cellular Imaging of Neuronal Activity: a Study of Neural Individuality and a Method for Imaging Mouse Cortex" (2014). All Theses and Dissertations (ETDs). 1368.