[Dynamic changes of locus coeruleus damage in Parkinson's disease-like mice induced by paraquat]

Objective: To observe the dynamic changes of brainstem locus coeruleus (LC) damage in Parkinson' s disease (PD) -like mice by paraquat (PQ) . Methods: In October 2019, 36 male C57BL/6 mice were randomly divided into the exposure group and the control group, with 18 mice in each group. The mice in the exposure group were given intraperitoneal injection of 15 mg/kg PQ, and the mice in the control group were given intraperitoneal injection of 0.9% saline, twice a week for 8 weeks. Neurobehavioral changes (pole climbing test, swimming test, open field test, tail hanging test, high plus maze test and water maze test) were observed at 4 weeks, 6 weeks and 8 weeks, respectively, and the changes of motor ability, emotion and cognitive function were evaluated. The brain tissue of mice were taken and stained with Hematoxylin-Eosin (HE) to observe the pathological changes of LC. Nissl staining was used to detect the changes of neuronal Nissl bodies in LC. Immunohistochemistry (IHC) staining was used to detect the expression of neuron nuclear antigen (NeuN) , dopamine (DA) neurons and norepinephrine (NE) neuron markers tyrosine hydroxylase (TH) , α-synuclein (α-syn) in substantia nigra (SN) and LC. The expression levels of NeuN, TH and α-syn in the midbrain and brainstem were detected by Western blotting. TUNEL staining was used to detect neuronal apoptosis in LC. Results: Compared with the 4th week of PQ exposure group, the time of pole climbing and swimming immobility were gradually increased, the ratio of open arm residence time of high plus maze test and the number of times of the platform and the residence time of platform quadrant in water maze test were gradually decreased (P<0.05) in the exposure group with the progress of exposure time. The results of HE and Nissl staining showed that the neurons in LC gradually arranged loosely, the nucleus were deeply stained, the cytoplasm was pyknosis, and the number of Nissl bodies gradually decreased (P<0.05) in the exposure group with the progress of exposure time. IHC results showed that the number of NeuN and TH positive cells in SN and LC of mice were gradually decreased, and the positive expression of α-syn was gradually increased (P<0.05) in the exposure group with the progress of exposure time. Western blotting results showed that the expression levels of NeuN and TH in the midbrain and brainstem were gradually decreased, and the expression level of α-syn was gradually increased (P<0.05) in the exposure group with the progress of exposure time. TUNEL staining showed that the apoptosis rates of neurons in LC were gradually increased (P<0.05) in the exposure group with the progress of exposure time. Conclusion: PQ induces progressive damage in the LC area of PD-like mice, which may be caused by the abnormal accumulation of pathological α-syn in the LC area.