| Background:Locus coeruleus(LC),an important nucleus in the brain stem,is wedge-shaped,located in the bottom of the fourth ventricle and laterally at the upper end of the boundary sulci.The neurons in it are mainly noradrenergic neurons.The fibers emitted by the locus coeruleus are extremely abundant and almost spread throughout the central nervous system,including the spinal cord,brainstem,cerebellum,hypothalamus,amygdala and cerebral cortex.locus coeruleus has complex functions and is involved in breathing,sleep,awakening,cognition,attention,emotion and other physiological functions,and is closely related to neurodegenerative diseases and mental diseases.Alzheimer’s disease(AD)is a neurodegenerative disease characterized by progressive cognitive dysfunction and mental and behavioral impairment,mainly manifested as memory,thinking,spatial orientation and language disorders,as well as emotional disorders.Braak et al.found that locus coeruleus and its nerve fiber bundles were related to the pathogenesis of AD.Before cognitive impairment and other clinical symptoms appeared in AD patients,Tau protein deposition and neurofibrillary tangles appeared in locus coeruleus,and locus coeruleus gradually atrophied and degenerated with the severity of the disease.These pathological changes could damage the neural circuits projected by locus coeruleus to the cerebral cortex,leading to non-cognitive defects such as sleep changes,psychological and behavioral symptoms and depression in patients in the pre-AD period.It has been confirmed that the Entorhinal cortex(EC),Hippocampus(Hip)and Amygdala(Amy)are the early pathological changes in the brain of AD patients,and the changes of them play an important role in the process of AD.Some scholars used retrograde tracing technique to explore the distribution characteristics of projection neurons from locus coeruleus to different brain regions,and found that the distribution of neurons in locus coeruleus had certain rules.However,the distribution characteristics of projection neurons from locus coeruleus to entorhinal cortex,hippocampus and other AD-related brain regions are still unclear.In addition,studies have shown that enhancing or protecting the integrity of neural circuits can effectively improve the cognitive impairment of AD patients.However,at present,the research on locus coeruleus neural circuit in AD is still not perfect,which will not be conducive to the development of AD treatment.Based on the above background,this study selected three brain regions of interest,namely the entorhinal cortex,amygdala and hippocampus,which are related to the early lesions of AD.The distribution characteristics of projection neurons from locus coeruleus to entorhinal cortex,amygdala and hippocampus were studied by retrograde tracing technique.The neural circuits of normal mice and AD mice were observed by retrograde tracing and transmission electron microscope imaging,and the changes of neural circuits of locus coeruleus-entorhinal cortex,locus coeruleus-amygdala and locus coeruleus-hippocampus in AD mice were analyzed,so as to explore the pathogenesis of AD from the perspective of neural circuits and provide anatomic reference for the treatment of AD.This study consists of two parts:1.Distribution characteristics of the projection neurons in the locus coeruleus;2.Changes of locus coeruleus neural circuit in Alzheimer’s disease mice.Part 1:Distribution characteristics of the projection neurons in the locus coeruleusObjective:To reveal the distribution characteristics of projection neurons from locus coeruleus to entorhinal cortex,amygdala and hippocampus,and to provide anatomical basis for studying the structure and function of locus coeruleus at neural circuit level.Methods:Retrograde tracer virus was accurately injected into the left entorhinal cortex,amygdala and hippocampus of different mice by brain stereotactic technique.After 2 weeks of virus transfection,tyrosine hydroxylase immunofluorescence staining was performed,and the coronal image of locus coeruleus was obtained by panoramic digital slice scanning microscope.The spatial distribution of retrograde labeled neurons in locus coeruleus was quantitatively analyzed to determine the distribution characteristics of projection neurons from locus coeruleus to entorhinal cortex,amygdala and hippocampus.Results:(1)The projection neurons from locus coeruleus to entorhinal cortex are distributed between rostral locus coeruleus and caudal locus coeruleus;Among them,93.68%are distributed in ipsilateral locus coeruleus of the injection site,and 6.32%are distributed in contralateral locus coeruleus of the injection site,which tends to be distributed in ipsilateral locus coeruleus;87.35%of them are distributed in the dorsal locus coeruleus,and 12.65%are distributed in ventral locus coeruleus,which tends to be distributed in the dorsal locus coeruleus.50.99%of them are located on medial locus coeruleus and 49.01%are located on lateral locus coeruleus,and they are evenly distributed in the medial/lateral locus coeruleus.(2)The projection neurons from locus coeruleus to amygdala are distributed between rostral locus coeruleus and caudal locus coeruleus;Among them,92.64%are distributed in ipsilateral locus coeruleus of the injection site,and 7.36%are distributed in contralateral locus coeruleus of the injection site,which tends to be distributed in ipsilateral locus coeruleus;87.98%of them are distributed in the dorsal locus coeruleus,and 12.02%are distributed in ventral locus coeruleus,which tends to be distributed in the dorsal locus coeruleus.53.88%of them are located on medial locus coeruleus and 46.12%are located on lateral locus coeruleus,and they are evenly distributed in the medial/lateral locus coeruleus.(3)The projection neurons from locus coeruleus to hippocampus are distributed between rostral locus coeruleus and caudal locus coeruleus;Among them,86.15%are distributed in ipsilateral locus coeruleus of the injection site,and 13.85%are distributed in contralateral locus coeruleus of the injection site,which tends to be distributed in ipsilateral locus coeruleus;91.94%of them are distributed in the dorsal locus coeruleus,and 8.06%are distributed in ventral locus coeruleus,which tends to be distributed in the dorsal locus coeruleus.53.15%of them are located on medial locus coeruleus and 46.85%are located on lateral locus coeruleus,and they are evenly distributed in the medial/lateral locus coeruleus.(4)The projection neurons from locus coeruleus to entorhinal cortex amygdala and hippocampus have similar distribution characteristics.They are all distributed between rostral locus coeruleus and caudal locus coeruleus;Although they are distributed bilaterally,they are mainly distributed in ipsilateral locus coeruleus of the injection site;They all tend to be distributed in dorsal locus coeruleus,and less than 13%neurons are distributed in ventral locus coeruleus.They are all evenly distributed in the medial/lateral locus coeruleus.Conclusion:In this study,the spatial distribution of projection neurons from locus coeruleus to entorhinal cortex,amygdala and hippocampus was quantitatively analyzed,and their distribution characteristics in locus coeruleus were revealed,which is of great significance to the study of the structure and function of locus coeruleus.Part 2:Changes of locus coeruleus neural circuit in Alzheimer’s disease miceObjective:To reveal the changes of locus coeruleus-entorhinal cortex,locus coeruleusamygdala and locus coeruleus-hippocampus neural circuits in AD mice,and to provide morphological basis for the treatment of AD.Methods:5×FAD mice were bred as AD mice model.Retrograde tracer virus was used to trace the neural circuits of locus coeruleus-entorhinal cortex,locus coeruleus-amygdala and locus coeruleus-hippocampus,and the synaptic structure of locus coeruleus was observed by transmission electron microscopy to analyze the changes of these three neural circuits in normal mice and AD mice.Results:Compared with normal mice,the three neural circuits in 5×FAD mice were damaged to varying degrees,and the damage degree of locus coeruleus-entorhinal cortex neural circuit was 40.36%.The damage degree of locus coeruleus-amygdala neural circuit was 40.44%;The damage degree of locus coeruleus-hippocampus neural circuit was 62.75%;Microscopically,the synaptic structure of locus coeruleus was also damagedConclusion:Retrograde tracing and transmission electron microscope imaging were used to analyze the changes of locus coeruleus-entorhinal cortex neural circuit,locus coeruleusamygdala and locus coeruleus-hippocampus neural circuits in AD mice.It plays an important guiding role in the research and treatment of AD pathogenesis.Summary:In this study,three brain regions related to early AD lesions,the entorhinal cortex,the amygdala and the hippocampus,were selected as the brain regions of interest.It was found that the distribution characteristics of projective neurons from locus coeruleus to entorhinal cortex,amygdala and hippocampus were similar,which provided anatomical basis for exploring the structure and function of locus coeruleus.In addition,retrograde tracing and transmission electron microscope imaging were used to observe the locus coeruleus-entorhinal cortex,locus coeruleus-amygdala and locus coeruleus-hippocampus neural circuits in AD mice,and it was found that they were all damaged to varying degrees.This study is helpful to reveal the neural circuit mechanism of AD and provide anatomic basis for its treatment. |
PDF Full Text Request