The Morphological Characteristics Of Cholinergic Neurons In Mouse Cerebral Cortex

As the most complex issue,brain consists of various neuron,including cholinergic neurons,which are a group of modulated neurons that widely distributed in the whole brain.The dysfunction of cholinergic neurons leads to a variety of brain diseases,including Alzheimer's disease and so on.By intricate dendrites and axons,cholinergic neurons constitute neural circuits with other type of neurons to play their roles.Understanding the morphological features of cholinergic neurons in the brain is the basis for understanding its function,and great significance to explore the pathogenesis of corresponding diseases.With traditional sectioning,immunohistochemistry and electrophysiology techniques,preliminary results have been obtained for the morphological and electrophysiological characterization of cholinergic neurons in the cortex.However,there is still a lack of relevant 3D data on the anatomical distribution and morphology of cortical cholinergic neurons.By crossing two mice strains: Chat-Cre mice and enhanced reporter mice,we acquired a transgenic model that the cholinergic neurons were special labelled by Enhanced Green Fluorescent Protein.Using this mouse and combining with fluorescence micro-optical sectioning tomography,we obtained the complete and detailed data sets for the entire brain.With the anatomical information obtained simultaneously,we analyzed the three-dimensional distribution of cholinergic neurons in different layers and different areas including motor cortex,somatosensory cortex and visual cortex.The results showed that most cholinergic neurons distributed in somatosensory cortex more than that in visual and motor cortex,meanwhile they concentrated in the layers 2/3 other than in the deeper layers 5/6.Based on 0.32 × 0.32 × 1 ?m data sets,we reconstructed 139 cortical cholinergic neurons.These neurons can be divided into three major subtypes including BPC,BFC and MPC according to the number of primary branches and traits of dendritic branches.We compared the regularities of distribution of cholinergic neurons in different layers and different brain regions.The results showed that most cholinergic neurons are BFCs in L2/3 and L5/6 and different cortical area.We further found the differences among the cholinergic neurons in the layers 2/3 and primary motor cortex and primary visual cortex on the number of branches,the terminal points and the length of dendrites.With the immunohistochemistry,we studied the biochemical characteristics of different subtypes of cholinergic neurons.The results showed that different morphological cholinergic neurons could express vasoactive intestinal peptide,besides,the ratio of co-express of these two substances is remarkable different in primary motor cortex and primary visual cortex.Summary,this article studied the three-dimensional anatomical information of neuron location and the morphological characteristics of individual cortical cholinergic neurons.The results are very helpful to understand the physiological functions of cholinergic neurons and the logic of cortical circuits.It can provide basic data and new perspectives for brain-like intelligence research.