Maternal Immune Activation adversely affects the ontogeny of dopamine neurons. Is Vitamin D neuroprotective?

Abstract

Dopamine dysregulation is one of the major hypotheses underlying the pathophysiology and treatment of schizophrenia, which is also widely accepted to be a neurodevelopmental disorder. Two well-established animal models based on prenatal environmental exposures-maternal immune activation (MIA) using poly(I:C) treatment, and developmental vitamin D deficiency (DVD)-both show an early reduction in factors crucial for dopaminergic development in the fetal brain. This is suggestive of a convergent aetiological mechanism, which is supported by our recent evidence showing that vitamin D can ameliorate schizophrenia-related behavioural phenotypes in the poly(I:C) model. We therefore wanted to investigate whether vitamin D is acting to correct the abnormal dopaminergic development induced by poly(I:C). Pregnant mice were co-administered the active vitamin D hormone simultaneously with poly(I:C) at gestational day 9 and embryos were collected at two developmental time-points, embryonic day 11 (E11) and E14. In order to examine dopamine ontogeny, we used immunohistochemistry to analyse the expression of two proteins, Lmx1a and Sox2, which can be used to distinguish dopamine progenitors and postmitotic neurons. Using spinning-disk confocal microscopy coupled with an optimised CellProfiler analysis pipeline, we were able to identify individual dopaminergic cells and quantify the expression of these markers, along with cell number, shape, size and spatial position. In E11 embryos, we showed that poly(I:C) impaired progenitor proliferation, with a reduction in the number of progenitors. While this was not directly rescued by vitamin D, some neuroprotective effects were observed; vitamin D increased Lmx1a expression in progenitors and normalised the lateral positioning of postmitotic cells. These alterations were transient, as we did not observe any effects of treatment at E14. Analysis of additional markers which are present in differentiated dopamine neurons is required to understand whether MIA and vitamin D are affecting later aspects of dopaminergic development. We hope to use these findings to elucidate how different environmental risk factors for schizophrenia converge on developing dopaminergic systems. iii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, financial support and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my higher degree by research candidature and does not include a substantial part of work that has been submitted to qualify for the award of a...