Impaired spatial memory in adult vitamin D deficient BALB/c mice is associated with reductions in spine density, nitric oxide, and neural nitric oxide synthase in the hippocampus

'Unpredictable chronic mild stress does not exacerbate memory impairment or altered neuronal and glial plasticity in the hippocampus of middle-aged vitamin D deficient mice'

Vitamin D deficiency is a worldwide health concern, especially in the elderly population. Much remains unknown about the relationship between vitamin D deficiency (VDD), stress-induced cognitive dysfunctions and depressive-like behaviour. In this study, 4-month-old male C57Bl/6J mice were fed with control or vitamin D free diet for 6 months, followed by unpredictable chronic stress (UCMS) for 8 weeks. VDD induced cognitive impairment and reduced grooming behaviour, but did not induce depressive-like behaviour. While UCMS in vitamin D sufficient mice induced expected depressive-like phenotype and impairments in the contextual fear memory, chronic stress did not manifest as an additional risk factor for memory impairments and depressive-like behaviour in VDD mice. In fact, UCMS restored self-care behaviour in VDD mice. At the histopathological level, VDD mice exhibited cell loss in the granule cell layer, reduced survival of newly generated cells, accompanied with an increased number of apoptotic cells and alterations in glial morphology in the hippocampus; however, these effects were not exacerbated by UCMS. Interestingly, UCMS reversed VDD induced loss of microglial cells. Moreover, tyrosine hydroxylase levels decreased in the striatum of VDD mice, but not in stressed VDD mice. These findings indicate that long-term VDD in adulthood impairs cognition but does not augment behavioural response to UCMS in middle-aged mice. While VDD caused cell loss and altered glial response in the DG of the hippocampus, these effects were not exacerbated by UCMS and could contribute to mechanisms regulating altered stress response.

Attenuation of morphine conditioned place preference and reinstatement by vitamin D

Opioid action in the brain involves the dopamine-reward system as well as non-dopamine pathways. Since vitamin D also modulates the brain's dopamine system, the question of this study was how vitamin D might affect the opioid influences on the reward system. Therefore, the objective of this study was to investigate the possible effect of vitamin D on the conditioned place preference (CPP) induced by morphine, as a valuable model of assessment of the reinforcing properties of opioids by associating the context to the rewarding properties of the addictive drugs. Male Wistar rats were randomly divided into two main groups that either received saline (morphine vehicle) or morphine (5 mg/kg, intraperitoneally) for CPP. Each of the main groups was divided into three vitamin D treatment subgroups: vitamin D vehicle and vitamin D (5 and 10 μg/kg, intraperitoneally). Vitamin D injections were started 1 week ahead of the experiment (two injections) or immediately after post-conditioning and in both cases, it was continued twice weekly throughout the CPP. Administration of vitamin D (10 μg/kg) before conditioning in CPP markedly attenuated morphine expression in the post-conditioning test. Receiving vitamin D (5 or 10 μg/kg) before or after conditioning significantly attenuated morphine reinstatement. Administration of vitamin D after opioid conditioning facilitated morphine memory extinction and attenuated morphine reinstatement. Vitamin D is probably a valuable addition to be considered as a part of the treatment for prevention or minimizing the dependency or relapse to opioids.