Dexamethasone (DEXA) is a commonly used steroid drug with immunosuppressive and analgesic properties. Unfortunately, long-term exposure to DEXA severely impairs brain function. This study aimed to investigate the effects of vitamin D₃ supplementation during chronic DEXA treatment on neurogenesis, mitochondrial energy metabolism, protein levels involved in the BDNF-mediated Akt activity, and specific receptors in the hippocampus. We found reduced serum concentrations of 25-hydroxyvitamin D₃ (25(OH)D₃), downregulated proBDNF and pAkt, dysregulated glucocorticosteroid and mineralocorticoid receptors, impaired mitochondrial biogenesis, and dysfunctional mitochondria energy metabolism in the DEXA-treated group. In contrast, supplementation with vitamin D₃ restored the 25(OH)D₃ concentration to a value close to that of the control group. There was an elevation in neurotrophic factor protein level, along with augmented activity of pAkt and increased citrate synthase activity in the hippocampus after vitamin D₃ administration in long-term DEXA-treated rats. Our findings demonstrate that vitamin D₃ supplementation plays a protective role in the hippocampus and partially mitigates the deleterious effects of long-term DEXA administration. The association between serum 25(OH)D₃ concentration and BDNF level in the hippocampus indicates the importance of applying vitamin D₃ supplementation to prevent and treat pathological conditions.

The disorder of adult neurogenesis is considered an important mechanism underlying the learning and memory impairment observed in Alzheimer’s disease (AD). The sporadic nonhereditary form of AD (sAD) affects over 95% of AD patients and is related to interactions between genetic and environmental factors. An intracerebroventricular injection of streptozotocin (STZ-ICV) is a representative and well-established method to induce sAD-like pathology. Dimethyl fumarate (DMF) has antioxidant and anti-inflammatory properties and is used for multiple sclerosis treatment. The present study determines whether a 26-day DMF therapy ameliorates the disruption of adult neurogenesis and BDNF-related neuroprotection in the hippocampus and olfactory bulb (OB) in an STZ-ICV rat model of sAD. Considering age as an important risk factor for developing AD, this study was performed using 3-month-old (the young group) and 22-month-old (the aged group) male Wistar rats. Spatial cognitive functions were evaluated with the Morris water maze task. Immunofluorescent labelling was used to assess the parameters of adult neurogenesis and BDNF-related neuroprotection in the hippocampus and OB. Our results showed that the STZ-ICV evoked spatial learning and memory impairment and disturbances in adult neurogenesis and BDNF expression in both examined brain structures. In the aged animals, the deficits were more severe. We found that the DMF treatment significantly alleviated STZ-ICV-induced behavioural and neuronal disorders in both age groups of the rats. Our findings suggest that DMF, due to its beneficial effect on the formation of new neurons and BDNF-related neuroprotection, may be considered as a promising new therapeutic agent in human sAD.

Chronic cold exposure is a stressor that may adversely affect the hippocampal structure and cognitive function. Critical for memory formation and learning processes, the hippocampus is particularly susceptible to hypothalamic–pituitary–adrenal (HPA) axis activity and elevated glucocorticoid levels. Vitamin D plays a complex role in regulating mitochondrial function and may provide neuroprotection. This study aimed to investigate the effects of chronic cold exposure on proteins associated with signaling pathways, mitochondrial function, and oxidative stress in the hippocampus of rats and to evaluate the neuroprotective potential of vitamin D3 supplementation. Male Wistar rats (n = 26) were assigned to four groups: control (CON; n = 4), sham stress (WW; n = 6), chronic cold water immersion (CCWI) (CW group; n = 8), and CCWI with 600 IU/kg/day vitamin D3 (VD3) supplementation (CW + D group; n = 8). Exposure to CCWI significantly reduced the hippocampal mass of rats, an effect not reversed by vitamin D3 supplementation. However, vitamin D3 improved mitochondrial function and exhibited antioxidant effects, partially reducing markers of protein and lipid free radicals damage in neural tissue. Our findings demonstrate the antioxidant properties of VD3 and its potential role in mitigating hippocampal damage during prolonged cold exposure, although its neuroprotective effects remain limited.

The amygdala, especially its central nucleus (CeA), is one of the key brain structures regulating fear, anxiety and stress responses and is also involved in gut microbiota signal processing. Amygdala hyperactivity, as well as microbiota alterations, plays an important role in the pathophysiology of anxiety disorders, depression or post-traumatic stress disorder (PTSD). The present study determines whether 3 weeks of galactooligosaccharide (GOS) supplementation alleviates behavioural, haematological, immunological and gut microbiota disturbances induced by long-term electrical stimulation of the CeA in rats (Stim). The unsupplemented Stim group showed locomotor hyperactivity and higher anxiety (measured with an actometer and the elevated plus maze, respectively), as well as a decrease in white blood cells (WBCs), lymphocytes (LYMs), red blood cells (RBCs) and platelets (PLTs); an elevation of TNFα; a reduction in IL-10 concentration in plasma; and microbiota alterations as compared to the control (Sham) group. GOS supplementation alleviated all these Stim-induced adverse effects or even normalised them to the sham group level. The effect of GOS was comparable to citalopram and even more effective in WBC and PLT normalisation and IL-10 induction. The obtained results indicate the high therapeutic potential of GOS in anxiety and stress-related disorders. GOS supplementation may support conventional therapy or the prevention of PTSD, depression and anxiety disorders.

Alzheimer’s disease (AD) is characterized by impaired neurotrophic support, oxidative stress, and metabolic dysfunction. Using the intracerebroventricular streptozotocin (ICV-STZ) rat model of sporadic AD, we investigated whether vitamin D₃ (VitD₃) and dimethyl fumarate (DMF), administered alone or in combination, modulate hippocampal neurotrophin-related signaling and redox balance. Animals were assigned to SHAM, STZ, VITD, DMF, and COMBO groups, representing control, ICV-STZ, VitD₃-treated ICV-STZ, DMF-treated ICV-STZ, and combined VitD₃ + DMF-treated ICV-STZ animals, respectively. Hippocampal neurotrophin processing (proBDNF and mature BDNF), downstream signaling (Akt and pAkt), IGF-1 content, mitochondrial oxoglutarate dehydrogenase (OGDH) content, citrate synthase (CS) activity, and glutathione peroxidase (GPx) activity were assessed. STZ administration showed a trend toward reduced mature BDNF content compared with the SHAM group (p = 0.07), whereas combined VitD₃ and DMF treatment significantly increased mature BDNF content compared with the STZ group. The mature BDNF/proBDNF ratio was reduced in the STZ group compared with the SHAM group and tended to be higher in the COMBO group compared with the STZ group (p = 0.09). proBDNF content remained unchanged. IGF-1, pTrkB, total Akt, and pAkt content did not differ significantly between groups. The pAkt/Akt ratio showed a trend toward reduction in the STZ group compared with SHAM group (p = 0.09). GPx activity increased in the STZ group, while CS activity and OGDH content were not significantly altered. These findings indicate that STZ-induced neurodegeneration is characterized by redox-associated uncoupling of neurotrophic signaling rather than mitochondrial disruption. Combined VitD₃ and DMF treatment partially modulated neurotrophic signaling, supporting a limited but measurable neuroprotective effect.