The Animal Research On The Role Of Microglia Activationin Pathogenesis Of Negative Symptoms Of Schizophrenia

Objectives:(1) To explor the state of microglia activation after neonatal intrahippocampal injection of LPS in SD rats at the important period of neurol development then to observe their SZ-like behaviors, which illustrates microglia activation in pathogenesis of SZ from the perspective of development;(2) To examine the SZ-like behaviors and to observe the effect of antipsychotic drug (risperidone) and antiinflammatory drug(minocycline) on the SZ-like behaviors and immune activation after neonatal intrahippocampal injection of LPS in SD rats, which are designed to evaluate the reliability of the SZ animal model related with microglia activation.(3) To explor the state of microglia activation after intrahippocampal injection of GM-CSF in adult SD rats then to observe their SZ-like behaviors and to analyze the relationship between the degree of microglia activation and the behavioral deficits.(4) To explor the state of microglia activation in the Poly I:C-induced SZ immune model, which further validates the role of microglia activation in pathogenesis of schizophrenia.(5) To observe the curative effect of minocycline(inhibitor of microglia activation) in SZ animal models especially negative symptoms and cognitive deficit and to explore its treatment mechanism, which provides experimental basis for minocycline in negative symptoms and cognitive deficit of SZ. Methods:(1) Neonatal intrahippocampal injection of LPS or sterilized saline was performed in rats at PD7, and they were separately treated with saline or minocycline by peritoneal injection for3days (PD7-9). Behavioral changes (open field test, social interaction test and PPI) were examined at PD60, and Ibal(for MI) as well as GFAP (for astrocyte) and CD68(for macrophagocyte) in hippocampus, cerebral cortex and thalamus were assessed using IHC at PD9, PD21and PD67.(2) Neonatal intrahippocampal injection of LPS or sterilized saline was performed in rats at PD7. The rats of two groups were randomly assigned to be given risperidone, minocycline, combination of both of them or saline at PD42for two weeks. Then behavioral changes (open field test, social interaction test, PPIand novel object recognition test <NORT>) were examined. MI in hippocampus, cerebral cortex and thalamus was assessed by IHC and IL-1as well as TNF-a in hippocampus, prefrontal cortex and striatum was assessed by western blotting after behavioral tests.(3) We randomly injected saline or GM-CSF into the ventral hippocampus in adult SD rats via micro-pump, and at the same time, the rats were intragastric administrated with saline or minocycline once a day for two weeks. Behavioral tests (open field test, social interaction test and PPI)were examined and MI in hippocampus, cerebral cortex and thalamus were assessed using IHC, then we analyzed the correlation between microglia activation and the behavioral deficits.(4) At embryonic day (ED)9pregnant C57BL/6mice were randomly treated with intraperitoneal injection of Poly I:C or sterilized saline. At PD42, descendants were randomly treated with minocycline or saline for two weeks. Then the behavioral tests(open field test, social interaction test and PPI) and the number of microglia were examined. Results:(1) The adult rats in LPS-injected group showed obvious behavioral alterations especially negative symptoms and cognitive deficit (deficits in social behavior and PPI)and a persistently dramatic increase of number of activated microglia in the hippocampus, cerebral cortex and thalamus. Interestingly, pretreatment with minocycline could significantly prevent the behavioral deficits and microglia activation. There was no difference among the groups of astrocyte and macrophagocyte.(2) Application of either minocycline, risperidone or both of them significantly rescued SZ-like behavioral deficits(deficits in social interaction, novel object recognition and PPI) and attenuated microglia activation (in hippocampus, cerebral cortex and thalamus) induced by neonatal intrahippocampal injection of LPS in SD rats. In addition, minocycline and minocycline combination with risperidone not risperidone inhibited the increased IL-1β and TNF-α in hippocampus; minocycline, risperidone and minocycline combination with risperidone inhibited the increased IL-1β and TNF-α in striatum; but the IL-1β and TNF-a in prefrontal cortex were not different among the groups.(3) GM-CSF-injected group showed significantly SZ-like behavioral deficits (hyperlocomotion, social interaction deficit, PPI deficit) and dramatic increase of number of activated microglia in the hippocampus, cerebral cortex and thalamus. Moreover, locomotor activity was significantly positive correlated with the microglia activation in hippocampus and thalamus; PPI deficit was significantly negative correlated with the microglia activation in hippocampus. In addition, minocycline was able to ameliorate the deficits in social interaction and PPI(which were related with negative symptoms and cognitive deficits) but not hyperlocomotion(which was related with positive symptoms) and inhibited the microglia activation. (4) The adult offspring exposed to Poly Ⅰ:C at ED9showed SZ-like behavioral changes (hyperlocomotion, deficits in social interaction and PPI) and significant microglia activation in these brain areas (hippocampus, thalamus, and cerebral cortex). Moreover, minocycline attenuated the behavioral deficits and inhibited the activated microglia.Conclusions:(1) Microglia activation in rodents during pregnancy, neonatal and adult stage could induce SZ-like behavioral deficits especially negative symptoms and cognitive deficit, which illustrates that microglia activation may be one of the mechanisms of pathogenesis of negative symptoms of SZ;(2) The neonatal intrahippocampal injection of LPS in SD rats model manifests some behavioral deficits especially related with negative symptoms and cognitive deficits, and antipsychotic drug has curative effect on this model, and this model also accords with the neurodevelopmental hypothesis of SZ, which illustrate that this model as a new animal model of SZ deserves to be further studied.(3) Atypical antipsychotic drug-risperidone can inhibit microglia activation and cytokins, which illustrates that inhibition of micrglia activation and cytokins may be one of the mechanisms of improving negative symptoms and cognitive deficit of SZ.(4) Minocycline-inhibitor of microglia activation can improve SZ-like behavioral deficits especially negative symptoms and cognitive deficit, which provides experimental basis for minocycline add-on treatment of SZ and the treatment mechanism may be related with the inhibition of microglia activation and cytokins.