The cellular and molecular consequences of maternal immune activation on the cytoarchitecture of the developing spinal cord

Epidemiological studies have suggested that maternal immune activation (MIA) during gestation is a risk factor for the development of neuropsychiatric and neurological disorders. These epidemiological studies have indicated that specific trimesters during human gestation may be more susceptible to the effects of MIA. Studies in animal models have attempted to delineate further the temporal specificity of this vulnerability. These animal studies have corroborated the claims made in epidemiological studies, but have not yet precisely identified individual windows of vulnerability. The first study in this thesis investigated the effect of MIA on the oligodendrocytes of the spinal cord, using immunofluorescence microscopy to investigate the expression of the markers Olig2 and MBP following MIA with 50µg/kg or 100µg/kg at E12 or E16. Olig2 and MBP expression were examined 5h post MIA (Olig2 only) and at P14 (Olig2 and MBP). The number of Olig2+ cell nuclei in the grey and white matter of the rostral spinal cord of offspring decreased 5h post MIA with 100µg/kg LPS. The number of Olig2+ cell nuclei was unchanged at P14 following MIA at E16. Conversely, Olig2+ cell number was unchanged in the E12 spinal cord 5h post MIA. However, Olig2+ cell number was decreased in the ventral grey matter of the rostral spinal cord at P14 following MIA at E12. MBP expression was unchanged at P14 following MIA with 100µg/kg LPS at the E12 and E16 time points. The second study investigated the effect of MIA on microglia and astrocytes of the spinal cord, using immunofluorescence microscopy to investigate expression of the markers Iba-1 and GFAP following MIA with 50µg/kg or 100µg/kg LPS at E12, E14 or E16. Iba-1 and GFAP expression were examined 5h post MIA (Iba-1 only) and at P14 (Iba-1 and GFAP). MIA at E16 with 100µg/kg LPS decreased Iba-1+ cell number in the grey and white matter of the rostral and middle spinal cord 5h post MIA. Iba-1+ cell number was unchanged 5h post MIA at E12, and at P14 following MIA at E12 or E16. GFAP expression was unchanged at P14 following MIA at E12 and E16. The third study investigated the effect of MIA on reelin expression in the spinal cord. The study used immunofluorescence microscopy to investigate Reelin expression after MIA with 50µg/kg or 100µg/kg at E12 or E16. Expression was examined 5h post MIA and at P14. Reelin expression decreased 5h post MIA with 100µg/kg LPS at E16 in the rostral, middle and caudal cord. Semi-quantitative analysis of reelin expression at E12 5h post MIA suggested decreased expression. No change was observed at P14 following MIA at E12 or E16. The fourth study examined gene expression following MIA at E12 and E16 with 100µg/kg LPS using microarray and RNA Seq. Examination points were again 5h and P14. Microarray analysis showed no change in gene expression 5h post MIA at E12. RNA Seq showed that gene expression was also unchanged at P14 after MIA at E12. In contrast, microarray analysis identified 42 differentially regulated genes 5h post MIA at E16. RNA Seq identified 19 differentially regulated genes at P14. The final study used an in-silico investigation to interrogate pathways and processes predicted to be targeted by microRNAs which function in oligodendrogliogenesis and may be vulnerable to episodes of MIA. The study identified inflammatory pathways, developmental pathways and apoptotic pathways which may be modulated by microRNAs during development, and potential targets which may function in the cell’s response to MIA. In conclusion, MIA effects on some aspects of CNS development significantly. E16 may be a particularly vulnerable period, at least in the spinal cord. The acute effects of MIA at E16 have prolonged and far-reaching consequences on the cytoarchitecture and normal functioning of the spinal cord and, indeed, the entire CNS, in later life.