The Effect of Melatonin and Exercise on Social Isolation-Related Behavioral Changes in Aged Rats

Hippocampal parvalbumin and perineuronal nets: Possible involvement in anxiety-like behavior in rats

The excitatory-inhibitory imbalance has been considered an important mechanism underlying stress-related psychiatric disorders. In the present study, rats were exposed to 6 days of inescapable foot shock (IFS) to induce stress. The open field test and elevated plus maze test showed that IFS-exposed rats exhibited increased anxiety-like behavior. Immunofluorescence showed that IFS rats had a decreased density of GAD67-immunoreactive interneurons in the dorsal hippocampal CA1 region, while no significant change in the density of CaMKIIα-immunoreactive glutamatergic neurons was seen. We investigated the expression of different interneuron subtype markers, including parvalbumin (PV), somatostatin (SST), and calretinin (CR), and noted a marked decline in the density of PV-immunoreactive interneurons in the dorsal CA1 region of IFS rats. The perineuronal net (PNN) is a specialized extracellular matrix structure primarily around PV interneurons. We used Wisteria floribunda agglutinin lectin to label the PNNs and observed that IFS rats had an increased proportion of PNN-coated PV-positive interneurons in CA1. The number of PSD95-positive excitatory synaptic puncta on the soma of PNN-free PV-positive interneurons was significantly higher than that of PNN-coated PV-positive interneurons. Our findings suggest that the effect of IFS on the hippocampal GABAergic interneurons could be cell-type-specific. Loss of PV phenotype in the dorsal hippocampal CA1 region may contribute to anxiety in rats. The dysregulated PV-PNN relationship in CA1 after traumatic stress exposure might represent one of the neurobiological correlates of the observed anxiety-like behavior.

Therapeutic effect of combination vitamin D3 and siponimod on remyelination and modulate microglia activation in cuprizone mouse model of multiple sclerosis

Stimulation of remyelination is critical for the treatment of multiple sclerosis (MS) to alleviate symptoms and protect the myelin sheath from further damage. The current study aimed to investigate the possible therapeutic effects of combining vitamin D3 (Vit D3) and siponimod (Sipo) on enhancing remyelination and modulating microglia phenotypes in the cuprizone (CPZ) demyelination mouse model. The study was divided into two stages; demyelination (first 5 weeks) and remyelination (last 4 weeks). In the first 5 weeks, 85 mice were randomly divided into two groups, control (n = 20, standard rodent chow) and CPZ (n = 65, 0.3% CPZ mixed with chow for 6 weeks, followed by 3 weeks of standard rodent chow). At week 5, the CPZ group was re-divided into four groups (n = 14) for remyelination stages; untreated CPZ (0.2 ml of CMC orally), CPZ+Vit D3 (800 IU/kg Vit D3 orally), CPZ+Sipo (1.5 mg/kg Sipo orally), and CPZ+Vit D3 (800 IU/kg Vit D3) + Sipo (1.5 mg/kg Sipo orally). Various behavioral tasks were performed to evaluate motor performance. Luxol Fast Blue (LFB) staining, the expression level of myelin basic protein (MBP), and M1/M2 microglia phenotype genes were assessed in the corpus callosum (CC). The results showed that the combination of Vit D3 and Sipo improved behavioral deficits, significantly promoted remyelination, and modulated expression levels of microglia phenotype genes in the CC at early and late remyelination stages. These results demonstrate for the first time that a combination of Vit D3 and Sipo can improve the remyelination process in the cuprizone (CPZ) mouse model by attenuating the M1 microglia phenotype. This may help to improve the treatment of MS patients.

The Impact of Chronic Unpredictable Mild Stress-Induced Depression on Spatial, Recognition and Reference Memory Tasks in Mice: Behavioral and Histological Study

Depression-induced cognitive impairment has recently been given more attention in research. However, the relationship between depression and different types of memory is still not clear. Chronic unpredictable mild stress (CUMS) is a commonly used animal model of depression in which animals are exposed to chronic unpredictable environmental and psychological stressors, which mimics daily human life stressors. This study investigated the impact of different durations of CUMS on various types of memory (short- and long-term spatial memory and recognition memory) and investigated CUMS’ impact on the ultrastructural level by histological assessment of the hippocampus and prefrontal cortex. Twenty male C57BL/J6 mice (6 weeks old, 21.8 ± 2 g) were randomly divided into two groups (n = 10): control and CUMS (8 weeks). A series of behavioral tasks were conducted twice at weeks 5–6 (early CUMS) and weeks 7–8 (late CUMS). A tail-suspension test (TST), forced swimming test (FST), elevated zero maze (EZM), elevated plus maze (EPM), open field test (OFT), and sucrose-preference test (SPT) were used to assess anxiety and depressive symptoms. The cognitive function was assessed by the novel object recognition test (NORT; for recognition memory), Y-maze (for short-term spatial memory), and Morris water maze (MWM: for long-term spatial memory) with a probe test (for reference memory). Our data showed that 8 weeks of CUMS increased the anxiety level, reported by a significant increase in anxiety index in both EPM and EZM and a significant decrease in central preference in OFT, and depression was reported by a significant increase in immobility in the TST and FST and sucrose preference in the SPT. Investigating the impact of CUMS on various types of memory, we found that reference memory is the first memory to be affected in early CUMS. In late CUMS, all types of memory were impaired, and this was consistent with the abnormal histological features of the memory-related areas in the brain (hippocampus and prefrontal cortex).