Natalie J. Groves

Adult vitamin D deficiency leads to behavioural and brain neurochemical alterations in C57BL/6J and BALB/c mice

Epidemiological evidence suggests that low levels of vitamin D may predispose people to develop depression and cognitive impairment. While rodent studies have demonstrated that prenatal vitamin D deficiency is associated with altered brain development, there is a lack of research examining adult vitamin D (AVD) deficiency. The aim of this study was to examine the impact of AVD deficiency on behaviour and brain function in the mouse. Ten-week old male C57BL/6J and BALB/c mice were fed a control or vitamin D deficient diet for 10 weeks prior to, and during behavioural testing. We assessed a broad range of behavioural domains, excitatory and inhibitory neurotransmission in brain tissue, and, in separate groups of mice, locomotor response to d-amphetamine and MK-801. Overall, AVD deficiency resulted in hyperlocomotion in a novel open field and reduced GAD65/67 levels in brain tissue. AVD-deficient BALB/c mice had altered behaviour on the elevated plus maze, altered responses to heat, sound and shock, and decreased levels of glutamate and glutamine, and increased levels of GABA and glycine. By contrast C57BL/6J mice had a more subtle phenotype with no further behavioural changes but significant elevations in serine, homovanillic acid and 5-hydroxyindoleacetic acid. Although the behavioural phenotype of AVD did not seem to model a specific disorder, the overall reduction in GAD65/67 levels associated with AVD deficiency may be relevant to a number of neuropsychiatric conditions. This is the first study to show an association between AVD deficiency and prominent changes in behaviour and brain neurochemistry in the mouse.

Vitamin D as a Neurosteroid Affecting the Developing and Adult Brain

Vitamin D deficiency is prevalent throughout the world, and growing evidence supports a requirement for optimal vitamin D levels for the healthy developing and adult brain. Vitamin D has important roles in proliferation and differentiation, calcium signaling within the brain, and neurotrophic and neuroprotective actions; it may also alter neurotransmission and synaptic plasticity. Recent experimental studies highlight the impact that vitamin D deficiency has on brain function in health and disease. In addition, results from recent animal studies suggest that vitamin D deficiency during adulthood may exacerbate underlying brain disorders and/or worsen recovery from brain stressors. An increasing number of epidemiological studies indicate that vitamin D deficiency is associated with a wide range of neuropsychiatric disorders and neurodegenerative diseases. Vitamin D supplementation is readily available and affordable, and this review highlights the need for further research.

Low vitamin D concentration exacerbates adult brain dysfunction

ThelinksbetweenvitaminDandbrainfunctionhavestrength-ened considerably in the past decade (1). The empirical evidenceincludes the following: 1) convincing data from in vitro andanimal experimental studies, 2) inconsistent findings from ob-servational and analytic epidemiology, and 3) inconsistent find-ings from the handful of randomized controlled studies done inthe field. Occasionally, the evidence from these different researchdomains converges. In this issue of the Journal, Suzuki et al (2)report the outcomes of a double-blind, placebo-controlled trialof vitamin D supplementation (1200 IU/d, for 1 y) on variousParkinson disease (PD)–related outcomes. Although the samplesize was modest (n ¼ 114), there were clear group differencesin several of the outcomes. In addition, there were tantalizingfindings showing that vitamin D supplementation interactedwith common polymorphisms in the gene coding for the vitaminDreceptor(VDR) to prevent decline. The findings are informa-tive: those who received placebo (and thus those who were morelikely to have persisting 25-hydroxyvitamin D insufficiency ordeficiency) had a steady worsening on PD outcomes. In contrast,those who received vitamin D supplements had no change in PDoutcomes over the year. The results strongly suggest that lowvitamin D status exacerbates disease progression.TheactiveformofvitaminD(1,25-dihydroxyvitaminD)oper-ates via the VDR, the smallest member of the family of nuclearreceptors (which includes other brain-critical signaling pathwayssuch as retinoic acid, thyroid hormone, sex hormones, etc). Thebrain distributions of the VDR, and the key enzyme required forthe conversion of the prohormone (25-hydroxyvitamin D) to1,25-dihydroxyvitamin D, have been mapped (3). Of particularrelevance to the target article, VDR was most strongly expressedin dopamine-rich areas such as the substantia nigra. We haverecently confirmed that all large tyrosine hydroxylase–positive(dopaminergic) neurons in the human substantia nigra also expressVDR (4). In addition, there is invitro evidence that 1,25-dihydroxy-vitamin D increases the expression of tyrosine hydroxylase (5).The timing of vitamin D deficiency produces variable effectson the brain. There is a growing body of convergent evidencelinking low prenatal vitamin D to an increased risk of neurode-velopmental disorders such as schizophrenia (6). It is thoughtthat the mechanisms linking developmental vitamin D defi-ciency with neurodevelopmental disorders probably relates tothe well-described pro-differentiation, antiproliferative proper-ties of the active form of vitamin D (and of steroids in general).Thus, the absence of vitamin D deprives the developing brainof an expected signal.The links between vitamin D deficiency and adult brain func-tion suggest that other mechanisms may be involved. Animal ex-periments that have examined the impact of transient vitamin Ddeficiency on adult brain outcomes suggest relatively modestneurochemical and behavioral phenotypes (7). However, thereis convergent evidence that vitamin D may have ‘‘neuroprotec-tive’’ properties (8). For example, vitamin D has a direct neuro-protective action against excitotoxic insults by downregulating

Sex-specific attentional deficits in adult vitamin D deficient BALB/c mice

Epidemiological studies have shown an association between vitamin D deficiency and cognitive impairment. However, there is a paucity of preclinical data showing that vitamin D deficiency is a causal factor for impaired cognitive processing. The aim of this study was to assess two cognitive tasks, the 5 choice-serial reaction task and the 5 choice-continuous performance task in adult vitamin D (AVD) deficient BALB/c mice. Ten-week old male and female BALB/c mice were fed a control or vitamin D deficient diet for 10 weeks prior to, and during behavioural testing. We found sex-dependent impairments in attentional processing and showed that male AVD-deficient mice were less accurate, took longer to respond when making a correct choice and were more likely to make an omission, without a change in the motivation to collect reward. By contrast, female AVD-deficient mice had a reduced latency to collect reward, but no changes on any other measures compared to controls. Therefore, we have shown that in otherwise healthy adult mice, vitamin D deficiency led to mild cognitive impairment in male but not female mice and therefore this model will be useful for future investigations into unravelling the mechanism by which vitamin D affects the adult brain and cognitive function.

Behavioural Effects of Adult Vitamin D Deficiency in BALB/c Mice Are not Associated with Proliferation or Survival of Neurons in the Adult Hippocampus

Epidemiological studies have shown that up to one third of adults have insufficient levels of vitamin D and there is an association between low vitamin D concentrations and adverse brain outcomes, such as depression. Vitamin D has been shown to be involved in processes associated with neurogenesis during development. Therefore, the aim of this study was to test the hypothesis that adult vitamin D (AVD) deficiency in BALB/c mice was associated with (a) adult hippocampal neurogenesis at baseline, b) following 6 weeks of voluntary wheel running and (c) a depressive-like phenotype on the forced swim test (FST), which may be linked to alterations in hippocampal neurogenesis. We assessed proliferation and survival of adult born hippocampal neurons by counting the number of cells positive for Ki67 and doublecortin (DCX), and incorporation of 5-Bromo-2’-Deoxyuridine (BrdU) within newly born mature neurons using immunohistochemistry. There were no significant effects of diet on number of Ki67+, DCX+ or BrdU+ cells in the dentate gyrus. All mice showed significantly increased number of Ki67+ cells and BrdU incorporation, and decreased immobility time in the FST, after voluntary wheel running. A significant correlation was found in control mice between immobility time in the FST and level of hippocampal neurogenesis, however, no such correlation was found for AVD-deficient mice. We conclude that AVD deficiency was not associated with impaired proliferation or survival of adult born neurons in BALB/c mice and that the impact on rodent behaviour may not be due to altered neurogenesis per se, but to altered function of new hippocampal neurons or processes independent of adult neurogenesis.

Adult vitamin D deficiency exacerbates impairments caused by social stress in BALB/c and C57BL/6 mice

Vitamin D deficiency is prevalent in adults throughout the world. Epidemiological studies have shown significant associations between vitamin D deficiency and an increased risk of various neuropsychiatric and neurodegenerative disorders, such as schizophrenia, depression, Alzheimers disease and cognitive impairment. However, studies based on observational epidemiology cannot address questions of causality; they cannot determine if vitamin D deficiency is a causal factor leading to the adverse health outcome. The main aim of this study was to determine if AVD deficiency would exacerbate the effects of a secondary exposure, in this case social stress, in BALB/c mice and in the more resilient C57BL/6 mice. Ten-week old male BALB/c and C57BL/6 mice were fed a control or vitamin D deficient diet for 10 weeks, and the mice were further separated into one of two groups for social treatment, either Separated (SEP) or Social Defeat (DEF). SEP mice were placed two per cage with a perforated Plexiglas divider, whereas the DEF mice underwent 10days of social defeat prior to behavioural testing. We found that AVD-deficient mice were more vulnerable to the effects of social stress using a social avoidance test, and this was dependent on strain. These results support the hypothesis that vitamin D deficiency may exacerbate behavioural outcomes in mice vulnerable to stress, a finding that can help guide future studies. Importantly, these discoveries support the epidemiological link between vitamin D deficiency and neuropsychiatric and neurodegenerative disorders; and has provided clues that can guide future studies related to unravelling the mechanisms of action linking adult vitamin D deficiency and adverse brain related outcomes.

Chapter 115 – Adult Vitamin D Deficiency and Adverse Brain Outcomes

Vitamin D deficiency is prevalent throughout the world, and growing evidence supports a requirement for optimal vitamin D levels for healthy brain function. Vitamin D deficiency has been associated with a wide range of neuropsychiatric disorders and neurodegenerative diseases. In addition, there is a growing body of animal experiments and in vitro studies that provide important insights into mechanisms of action linking vitamin D and adverse brain outcomes. In this chapter, we will focus on clinical studies that provide links between vitamin D deficiency and brain outcomes in adults. We also present an overview from preclinical studies on rodents, in which vitamin D deficiency during adulthood may exacerbate underlying brain disorders and/or worsen recovery from brain stressors. Vitamin D supplementation is readily available and affordable, and this review highlights the need for further research.

Animal vitamin D deficiency and adverse brain outcomes

Vitamin D deficiency is prevalent throughout the world, and growing evidence supports a requirement for optimal vitamin D levels for healthy brain function. Vitamin D deficiency has been associated with a wide range of neuropsychiatric disorders and neurodegenerative diseases. In addition, there is a growing body of animal experiments and in vitro studies that provide important insights into mechanisms of action linking vitamin D and adverse brain outcomes. In this chapter, we will focus on clinical studies that provide links between vitamin D deficiency and brain outcomes in adults. We also present an overview from preclinical studies on rodents, in which vitamin D deficiency during adulthood may exacerbate underlying brain disorders and/or worsen recovery from brain stressors. Vitamin D supplementation is readily available and affordable, and this review highlights the need for further research.