Background and Purpose: Autism spectrum disorders (ASD) are heterogeneous neurodevelopmental disorders with considerably increased risk in male infants born preterm and with neonatal infection. Here, we investigated the role of postnatal immune activation on hippocampal synaptopathology by targeting Reelin+ cells in mice with ASD-like behaviours.Experimental Approach: C57/Bl6 mouse pups of both sexes received lipopolysaccharide (LPS, 1 mgÁkg À1 ) on postnatal day (P) 5. At P45, animal behaviour was examined by marble burying and sociability test, followed by ex vivo brain MRI diffusion kurtosis imaging (DKI). Hippocampal synaptogenesis, number and morphology of Reelin+ cells, and mRNA expression of trans-synaptic genes, including neurexin-3, neuroligin-1, and cell-adhesion molecule nectin-1, were analysed at P12 and P45.
The neuro-gliovascular unit is a crucial structure for providing a balanced well-functioning environment for neurons and their synapses. Activation of the immune system during the developmental period is believed to affect the gliovascular unit, which may trigger neurodevelopmental and neurological/neuropsychiatric diseases. In this study, we hypothesized that vulnerability of the male brain to a neonatal insult was conditioned by sex-dependent differences in the impairment of the hippocampal gliovascular unit. Male and female C57BL/6J pups received lipopolysaccharide (LPS) (1 mg/kg) or saline on postnatal day (P) 5. Brains were collected at P12 and morphological quantifications of hippocampal fibrillary glial acid protein (GFAP+) astrocytes and ionized calcium binding adaptor molecule 1 (Iba1+) microglia were performed by using 3-D image analysis together with measuring the length of CD31+ and aquaporin-4 (AQP4+) vessels. We found a significant increase in the length of CD31+ capillaries in the male LPS group compared to the saline group, however, coverage of capillaries by astrocytic end-feet (AQP4+) was significantly reduced. In contrast, there was a significant increase in AQP4+ capillary length in female pups one week after LPS injection. GFAP+ astrocytes via morphological changes in the hippocampus showed significant enhancement in the activity one week following LPS injection in male mice. We propose that neonatal inflammation could induce susceptibility to neurodevelopmental disorders through modification of hippocampal gliovascular interface in a sex-dependent manner.
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