Alleviation of cognitive deficits via upregulation of chondroitin sulfate biosynthesis by lignan sesamin in a mouse model of neuroinflammation.

Lignans are plant-derived compounds that act as partial estrogen agonists. Chondroitin sulfate proteoglycans (CSPGs) represent one of the major components of the extracellular matrix. Here we aimed to understand the role of sesamin (SES), a major lignan compound, in the biosynthesis and degradation of CSPGs in the mouse hippocampus because CSPGs play a key role in the regulation of cognitive functions through the promotion of adult neurogenesis. The expression of the pro-inflammatory cytokine interleukin-1ß was decreased by SES administration in the hippocampus of lipopolysaccharide (LPS)-treated mice, a model of neuroinflammation-induced cognitive deficits. The expression of genes related to biosynthesis and degradation of CSPGs in the hippocampus of LPS-treated mice was both increased and decreased by SES administration. Further, the diffuse extracellular matrix labeling of CSPGs by Wisteria floribunda agglutinin (WFA) in the hippocampus of LPS-treated mice was increased by SES administration. The densities of neural stem cells, late transit-amplifying cells, and newborn-granule cells in the hippocampus of LPS-treated mice were also increased by SES administration. Moreover, SES-induced alterations in gene expression, WFA labeling, and adult neurogenesis in LPS-treated mice were more evident in the dorsal hippocampus (center of cognition) than in the ventral hippocampus (center of emotion). Neither LPS nor SES administration affected locomotor activity, anxiety-like behavior, and depression-related behavior. However, impairments in contextual memory and sensorimotor gating in LPS-treated mice were recovered by SES administration. Our results show that SES can promote adult hippocampal neurogenesis through the upregulation of CSPGs, which may alleviate cognitive deficits induced by neuroinflammation.

Phytoestrogen genistein modulates neuron-microglia signaling in a mouse model of chronic social defeat stress.

Microglia, resident immune cells in the brain, are shown to mediate the crosstalk between psychological stress and depression. Interestingly, increasing evidence indicates that sex hormones, particularly estrogen, are involved in the regulation of immune system. In this study, we aimed to understand the potential effects of chronic social defeat stress (CSDS) and genistein (GEN), an estrogenic compound of the plant origin, on neuron-microglia interactions in the mouse hippocampus. The time spent in the avoidance zone in the social interaction test was increased by CSDS 1 day after the exposure, while the avoidance behavior returned to control levels 14 days after the CSDS exposure. Similar results were obtained from the elevated plus-maze test. However, the immobility time in the forced swim test was increased by CSDS 14 days after the exposure, and the depression-related behavior was in part alleviated by GEN. The numerical densities of microglia in the hippocampus were increased by CSDS, and they were decreased by GEN. The voxel densities of synaptic structures and synaptic puncta colocalized with microglia were decreased by CSDS, and they were increased by GEN. Neither CSDS nor GEN affected the gene expressions of major pro-inflammatory cytokines. Conversely, the expression levels of genes related to neurotrophic factors were decreased by CSDS, and they were partially reversed by GEN. These findings show that GEN may in part alleviate stress-related symptoms, and the effects of GEN may be associated with the modulation of neuron-microglia signaling via chemokines and neurotrophic factors in the hippocampus.

PSA-NCAM Colocalized with Cholecystokinin-Expressing Cells in the Hippocampus Is Involved in Mediating Antidepressant Efficacy.

The extracellular glycan polysialic acid linked to neural cell adhesion molecule (PSA-NCAM) is principally expressed in the developing brain and the adult neurogenic regions. Although colocalization of PSA-NCAM with cholecystokinin (CCK) was found in the adult brain, the role of PSA-NCAM remains unclear. In this study, we aimed to elucidate the functional significance of PSA-NCAM in the CA1 region of the male mouse hippocampus. Combined fluorescence in situ hybridization and immunohistochemistry showed that few vesicular glutamate transporter 3-negative/CCK-positive (VGluT3-/CCK+) cells were colocalized with PSA-NCAM, but most of the VGluT3+/CCK+ cells were colocalized with PSA-NCAM. The somata of PSA-NCAM+/CCK+ cells were highly innervated by serotonergic boutons than those of PSA-NCAM-/CCK+ cells. The expression ratios of 5-HT3A receptors and p11, a serotonin receptor-interacting protein, were higher in PSA-NCAM+/CCK+ cells than in PSA-NCAM-/CCK+ cells. Pharmacological digestion of PSA-NCAM impaired the efficacy of antidepressant fluoxetine (FLX), a selective serotonin reuptake inhibitor, but not the efficacy of benzodiazepine anxiolytic diazepam. A Western blot showed that restraint stress decreased the expressions of p11 and mature brain-derived neurotrophic factor (BDNF), and FLX increased them. Interestingly, the FLX-induced elevation of expression of p11, but not mature BDNF, was impaired by the digestion of PSA-NCAM. Quantitative reverse transcription-polymerase chain reaction showed that restraint stress reduced the expression of polysialyltransferase ST8Sia IV and FLX elevated it. Collectively, PSA-NCAM colocalized with VGluT3+/CCK+ cells in the CA1 region of the hippocampus may play a unique role in the regulation of antidepressant efficacy via the serotonergic pathway.SIGNIFICANCE STATEMENT Polysialic acid (PSA) is composed of eight or more α2,8-linked sialic acids. Here, we examined the functional significance of polysialic acid linked to the neural cell adhesion molecule (PSA-NCAM) in the adult mouse hippocampus. Few vesicular glutamate transporter 3-negative/cholecystokinin-positive (VGluT3-/CCK+) cells were colocalized with PSA-NCAM, but most of the VGluT3+/CCK+ cells were colocalized with PSA-NCAM. The expression ratios of 5-HT3A receptors and p11, a serotonin receptor-interacting protein, were higher in PSA-NCAM+/CCK+ cells than in PSA-NCAM-/CCK+ cells. The efficacy of antidepressants, but not anxiolytics, was impaired by the digestion of PSA-NCAM. The antidepressant-induced increase in p11 expression was inhibited following PSA-NCAM digestion. We hence hypothesize that PSA-NCAM colocalized with VGluT3+/CCK+ cells may play a unique role in regulating antidepressant efficacy.

Cuprizone-induced demyelination in the mouse hippocampus is alleviated by phytoestrogen genistein.

One of the major female sex hormones, estrogen, can influence a variety of mental states. Individuals with multiple sclerosis (MS) often suffer from mental health issues, which are correlated with the pathology of gray matter. In this study, we aimed to elucidate the validity of phytoestrogen genistein (GEN) for treating the gray matter lesions in MS using the mouse model of cuprizone (CPZ)-induced demyelination. First, we confirmed that 5-week 0.2% CPZ intoxication induced demyelination in the hippocampus, and that myelination was successfully recovered by GEN. Loss of mature oligodendrocytes following CPZ intoxication was counteracted by GEN. Neither CPZ nor GEN affected the densities of oligodendrocyte precursor cells and astrocytes. CPZ-induced activation and proliferation of microglia were not inhibited by GEN. Upregulation of gene expression of the pro-inflammatory cytokine, interleukin-1ß, in sorted microglia by CPZ was not inhibited by GEN either. However, the expression levels of genes related to phagocytosis, such as cluster of differentiation 68 and lysosomal-associated membrane protein 1, in sorted microglia were elevated by CPZ but lowered by GEN. Notably, physical contact of microglia with myelin was increased by CPZ but decreased by GEN. The expression levels of myelin-related genes, such as myelin basic protein and myelin oligodendrocyte glycoprotein, in the whole hippocampal tissue were decreased by CPZ but recovered by GEN. These results show that GEN may act on mature oligodendrocytes in the hippocampus by promoting their survival and myelin formation, and suggest the therapeutic potential of phytoestrogens for treating MS patients suffering from mental health issues.

Reduced synaptic activity precedes synaptic stripping in vagal motoneurons after axotomy.

Activated microglia, which spread on the motor neurons following nerve injury, engage in the displacement of detached afferent synaptic boutons from the surface of regenerating motor neurons. This phenomenon is known as "synaptic stripping." The present study attempted to examine whether changes in the synaptic inputs after motor nerve injury correlated with the microglial attachment to the dorsal motor neurons of the vagus (DMV). DMV neurons in Wistar rats could survive after nerve injury, whereas most of injured DMV neurons in the C57BL/6 mice died. At 2 days after nerve injury, a significant decrease was observed in the frequencies of both spontaneous and miniature EPSCs and IPSCs recorded from DMV neurons in the slice preparation but not from the mechanically dissociated neurons in the Wistar rats. At this stage, no direct apposition of microglia on the injured neurons was observed. High-K(+) stimulation restored their frequencies to control levels. Furthermore, PPADS and DPCPX, antagonists of P2 and adenosine receptors, respectively, also stimulated the recovery of their frequencies. In contrast, no significant change was detected in the spontaneous EPSCs frequency recorded from the severely injured DMV neurons in the slice preparation of the C57BL/6 mice. These observations strongly suggest that presynaptic inhibition through glia-derived ATP and adenosine, thus precedes synaptic stripping in regenerating DMV neurons following nerve injury.

Patterns of expression of neuropeptides in GABAergic nonprincipal neurons in the mouse hippocampus: Quantitative analysis with optical disector.

Neuropeptides are widely distributed in the central nervous system and are considered to play important roles in the regulation of neuronal activity. This study shows the patterns of expression of four neuropeptides [neuropeptide Y (NPY), somatostatin (SOM), cholecystokinin (CCK), and vasoactive intestinal polypeptide (VIP)] in gamma-aminobutyric acid (GABA)-ergic neurons of the mouse hippocampus, with particular reference to the areal and dorsoventral difference. First, we estimated the numerical densities (NDs) of GABAergic neurons containing these neuropeptides using the optical disector. The NDs of NPY- and SOM-positive GABAergic neurons were generally higher than those of CCK- and VIP-positive GABAergic neurons. In the whole area of the hippocampus, the ND of NPY-positive GABAergic neurons showed no significant dorsoventral difference (1.90 x 10(3)/mm(3) in the dorsal level, 2.09 x 10(3)/mm(3) in the ventral level), whereas the ND of SOM-positive GABAergic neurons was higher in the ventral level (1.44 x 10(3)/mm(3)) than in the dorsal level (0.80 x 10(3)/mm(3)). The ND of CCK-positive GABAergic neurons was also higher in the ventral level (0.57 x 10(3)/mm(3)) than in the dorsal level (0.33 x 10(3)/mm(3)). Similarly, the ND of VIP-positive GABAergic neurons was higher in the ventral level (0.61 x 10(3)/mm(3)) than in the dorsal level (0.43 x 10(3)/mm(3)). Next, we calculated the proportions of GABAergic neurons containing these neuropeptides among the total GABAergic neurons. In the whole area of the hippocampus, NPY-, SOM-, CCK-, and VIP-positive neurons accounted for about 31%, 17%, 7%, and 8% of GABAergic neurons, respectively. The present data establish a baseline for examining potential roles of GABAergic neurons in the hippocampal network activity in mice.