Lipopolysaccharide-Induced Systemic Inflammation in the Neonatal Period Increases Microglial Density and Oxidative Stress in the Cerebellum of Adult Rats.

Jaime Moreira Pires,Clivandir Severino Silva,Débora Bandeira Rêgo,Ana Teresa F Leslie,Luiz Eugênio Mello,Michele Longoni Calió,Maira Licia Foresti,Thabatta Karollynne Estevam Nakamura,Amanda Cristina Mosini

doi:10.3389/fncel.2020.00142

Abstract

Inflammatory processes occurring in the perinatal period may affect different brain regions, resulting in neurologic sequelae. Injection of lipopolysaccharide (LPS) at different neurodevelopmental stages produces long-term consequences in several brain structures, but there is scarce evidence regarding alterations in the cerebellum. The aim of this study was to evaluate the long-term consequences on the cerebellum of a systemic inflammatory process induced by neonatal LPS injection. For this, neonatal rats were randomly assigned to three different groups: naïve, sham, and LPS. Saline (sham group) or LPS solution (1 mg/kg) was intraperitoneally injected on alternate postnatal days (PN) PN1, PN3, PN5, and PN7. Spontaneous activity was evaluated with the open field test in adulthood. The cerebellum was evaluated for different parameters: microglial and Purkinje cell densities, oxidative stress levels, and tumor necrosis factor alpha (TNF-α) mRNA expression. Our results show that administration of LPS did not result in altered spontaneous activity in adult animals. Our data also indicate increased oxidative stress in the cerebellum, as evidenced by an increase in superoxide fluorescence by dihydroethidium (DHE) indicator. Stereological analyses indicated increased microglial density in the cerebellum that was not accompanied by Purkinje cell loss or altered TNF-α expression in adult animals. Interestingly, Purkinje cells ectopically positioned in the granular and molecular layers of the cerebellum were observed in animals of the LPS group. Our data suggest that neonatal LPS exposure causes persistent cellular and molecular changes to the cerebellum, indicating the susceptibility of this region to systemic inflammatory insults in infancy. Further investigation of the consequences of these changes and the development of strategies to avoid those should be subject of future studies.

Highlights

MATERIALS AND METHODSSystemic inflammation in the premature neonate is associated with increased risk of adverse neurologic sequelae (Patra et al, 2017)
Understanding the pathophysiological mechanisms of brain injury caused by systemic inflammatory states in perinatal animals and its long-term consequences is of great relevance to neuroscience and might have clinical relevance
The concentration of tumor necrosis factor alpha (TNF-α) mRNA was investigated through qPCR in the cerebellum of adult rats, 3 months after LPS administration as neonates

Summary

MATERIALS AND METHODS

Systemic inflammation in the premature neonate is associated with increased risk of adverse neurologic sequelae (Patra et al, 2017). Given the cerebellar vulnerability during the perinatal period and the already known influence of this structure to different motor, cognitive, and behavioral functions, the aim of this study was to investigate the long-term consequences of an early life inflammatory insult to the cerebellum of adult rats. The association between immunohistochemical data and superoxide anion detection (DHE/DAPI fluorescence ratio) was analyzed by means of the Pearson correlation test. The expression of TNF-α was normalized by the mean of hypoxanthine-guanine phosphoribosyltransferase (Hprt) and β-actin (Actb) gene expression and calculated using the 2− Ct method For this analysis, we used n = 3 for the naïve group, n = 3 for the sham group, and n = 4 for the LPS group.

RESULTS

DISCUSSION

ETHICS STATEMENT

CONCLUSION