Prenatal hypoxia alters the early ontogeny of dopamine neurons.

Dopaminergic (DA) dysfunction is a significant feature in the pathophysiology of schizophrenia. Established developmental risk factors for schizophrenia such as maternal immune activation (MIA) or developmental vitamin D (DVD) deficiency, when modelled in animals, reveal the differentiation of early DA neurons in foetal brains is delayed suggesting this may be a convergent aetiological pathway. Here we have assessed the effects of prenatal hypoxia, another well-known developmental risk factor for schizophrenia, on developing DA systems. Pregnant mice were exposed to a hypoxic environment of 10% oxygen for 48 h from embryonic day 10 (E10) to E12. Embryonic brains were collected and the positioning of mesencephalic cells, expression of DA specification and maturation factors were examined along with the expression of factors that may govern the migration of these neurons. We show that prenatal hypoxia results in a decrease in dopaminergic progenitors retards early DA neuron lateral migration and reduces expression of the receptors known to govern this process. A second time-point, postnatal day 10 (P10) was also examined in order to assess whether prenatal hypoxia alters early presynaptic architecture in the developing striatum. We show reduced expression of tyrosine hydroxylase (TH) in the postnatal striatum along with increases in the density of high-probability DA release sites within TH varicosities. These findings add to the emerging literature showing that multiple epidemiologically validated environmental risk factors for schizophrenia may induce early alterations to develop DA systems. This may represent a possible convergent mechanism in the onset of presynaptic DA dysfunction in patients.

Vitamin D: Brain and Behavior.

It has been 20 years since we first proposed vitamin D as a "possible" neurosteroid.( 1 ) Our work over the last two decades, particularly results from our cellular and animal models, has confirmed the numerous ways in which vitamin D differentiates the developing brain. As a result, vitamin D can now confidently take its place among all other steroids known to regulate brain development.( 2 ) Others have concentrated on the possible neuroprotective functions of vitamin D in adult brains. Here these data are integrated, and possible mechanisms outlined for the various roles vitamin D appears to play in both developing and mature brains and how such actions shape behavior. There is now also good evidence linking gestational and/or neonatal vitamin D deficiency with an increased risk of neurodevelopmental disorders, such as schizophrenia and autism, and adult vitamin D deficiency with certain degenerative conditions. In this mini-review, the focus is on what we have learned over these past 20 years regarding the genomic and nongenomic actions of vitamin D in shaping brain development, neurophysiology, and behavior in animal models. © 2020 The Author. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Developmental vitamin D deficiency increases foetal exposure to testosterone.

BACKGROUND: Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders which are more common in males. The 'prenatal sex steroid' hypothesis links excessive sex-steroid exposure during foetal life with the behavioural differences observed in ASD. However, the reason why sex steroid exposure may be excessive remains unclear. Epidemiological studies have identified several environmental risk factors associated with ASD, including developmental vitamin D (DVD) deficiency. We have demonstrated in an animal model that DVD-deficiency is associated with a hyper-inflammatory response in placentas from male but not female foetuses. Vitamin D also regulates the expression of several steroidogenic enzymes in vitro. Therefore using this animal model, we have examined whether DVD-deficiency leads to increased sex-steroid levels in both the maternal and foetal compartments. METHODS: Female rats are fed a vitamin D deficient diet from 6 weeks before mating until tissue collection at embryonic day 18. We examined the levels of testosterone, androstenedione and corticosterone in maternal plasma, foetal brains and amniotic fluid. We further examined gene expressions of steroidogenic enzymes and DNA methylation of aromatase promoters in foetal brains as a potential molecular mechanism regulating testosterone expression. RESULTS: We show that DVD-deficiency increases testosterone levels in maternal blood. We also show elevated levels of testosterone and androstenedione in the amniotic fluid of female but not male DVD-deficient foetuses. Testosterone levels were also elevated in DVD-deficient male brains. Vitamin D, like other steroid-related hormones, regulates gene expression via methylation. Therefore we examined whether the significant elevation in testosterone in male brains was due to such a potential gene-silencing mechanism. We show that the promoter of aromatase was hyper-methylated compared to male controls. LIMITATIONS: A reduction in aromatase, in addition to causing excessive testosterone, could also lead to a reduction in estradiol which was not examined here. CONCLUSIONS: This study is the first to show how an epidemiologically established environmental risk factor for ASD may selectively elevate testosterone in male embryonic brains. These findings provide further mechanistic support for the prenatal sex steroid theory of ASD.

Maternal Vitamin D Prevents Abnormal Dopaminergic Development and Function in a Mouse Model of Prenatal Immune Activation.

Dysfunction in dopamine (DA) systems is a prominent feature in schizophrenia patients and may result from the abnormal development of mesencephalic (mes)DA systems. Maternal immune activation (MIA) and developmental vitamin D (DVD)-deficiency both induce schizophrenia-relevant dopaminergic abnormalities in adult offspring. In this study, we investigated whether maternal administration of the vitamin D hormone (1,25OHD, VITD) could prevent MIA-induced abnormalities in DA-related behaviors and mesDA development. We administrated the viral mimetic polyriboinosinic-polyribocytidylic (poly (I:C)) simultaneously with 1,25OHD and/or their vehicles, to pregnant mouse dams at gestational day 9. Maternal treatment with VITD prevented MIA-induced hypersensitivity to acute DA stimulation induced by amphetamine, whereas it failed to block prepulse inhibition deficiency in MIA-exposed offspring. MIA and VITD both reduced fetal mesDA progenitor (Lmx1a + Sox2+) cells, while VITD treatment increased the number of mature (Nurr1 + TH+) mesDA neurons. Single-cell quantification of protein expression showed that VITD treatment increased the expression of Lmx1a, Nurr1 and TH in individual mesDA cells and restored normal mesDA positioning. Our data demonstrate that VITD prevents abnormal dopaminergic phenotypes in MIA offspring possibly via its early neuroprotective actions on fetal mesDA neurons. Maternal supplementation with the dietary form of vitamin D, cholecalciferol may become a valuable strategy for the prevention of MIA-induced neurodevelopmental abnormalities.

Developmental Vitamin D (DVD) Deficiency Reduces Nurr1 and TH Expression in Post-mitotic Dopamine Neurons in Rat Mesencephalon.

Developmental vitamin D (DVD) deficiency has been proposed as an important risk factor for schizophrenia. Our previous study using Sprague Dawley rats found that DVD deficiency disrupted the ontogeny of mesencephalic dopamine neurons by decreasing the mRNA level of a crucial differentiation factor of dopamine cells, the nuclear receptor related 1 protein (Nurr1). However, it remains unknown whether this reflects a reduction in dopamine cell number or in Nurr1 expression. It is also unclear if any particular subset of developing dopamine neurons in the mesencephalon is selectively affected. In this study, we employed state-of-the-art spinning disk confocal microscopy optimized for the imaging of tissue sections and 3D segmentation to assess post-mitotic dopamine cells on a single-cell basis in the rat mesencephalon at embryonic day 15. Our results showed that DVD deficiency did not alter the number, morphology, or positioning of post-mitotic dopamine cells. However, the ratio of Nurr1+TH+ cells in the substantia nigra pars compacta (SNc) compared with the ventral tegmental area (VTA) was increased in DVD-deficient embryos. In addition, the expression of Nurr1 in immature dopamine cells and mature dopamine neurons in the VTA was decreased in DVD-deficient group. Tyrosine hydroxylase was selectively reduced in SNc of DVD-deficient mesencephalon. We conclude that DVD deficiency induced early alterations in mesencephalic dopamine development may in part explain the abnormal dopamine-related behaviors found in this model. Our findings may have broader implications for how certain environmental risk factors for schizophrenia may shape the ontogeny of dopaminergic systems and by inference increase the risk of schizophrenia.