All-trans Retinoic Acid-induced Abnormal Hippocampal Expression of Synaptic Genes SynDIG1 and DLG2 is Correlated with Anxiety or Depression-Like Behavior in Mice

Hippocampal RNA sequencing in mice selectively bred for high and low activity

High and Low Activity strains of mice were bidirectionally selected for differences in open-field activity (DeFries et al., 1978, Behavior Genetics, 8: 3-13) and subsequently inbred to use as a genetic model for studying anxiety-like behaviors (Booher et al., 2021, Genes, Brain and Behavior, 20: e12730). Hippocampal RNA-sequencing of the High and Low Activity mice identified 3901 differentially expressed protein-coding genes, with both sex-dependent and sex-independent effects. Functional enrichment analysis (PANTHER) highlighted 15 gene ontology terms, which allowed us to create a narrow list of 264 top candidate genes. Of the top candidate genes, 46 encoded four Complexes (I, II, IV and V) and two electron carriers (cytochrome c and ubiquinone) of the mitochondrial oxidative phosphorylation process. The most striking results were in the female high anxiety, Low Activity mice, where 39/46 genes relating to oxidative phosphorylation were upregulated. In addition, comparison of our top candidate genes with two previously curated High and Low Activity gene lists highlight 24 overlapping genes, where Ndufa13, which encodes the supernumerary subunit A13 of complex I, was the only gene to be included in all three lists. Mitochondrial dysfunction has recently been implicated as both a cause and effect of anxiety-related disorders and thus should be further explored as a possible novel pharmaceutical treatment for anxiety disorders.

Asiatic acid and andrographolide reduce hippocampal injury through suppressing neuroinflammation caused by Salmonella typhimurium infection

Damage caused by Salmonella is not only limited to the gastrointestinal tract, but also occurs in the central nervous system (CNS). The aim of this study was to explore the protective effects of asiatic acid (AA) and andrographolide (AD) on the CNS through simulating common infection in mice by oral administration of Salmonella typhimurium (S. typhimurium). The results showed that the neurons in the hippocampus of mice were damaged after S. typhimurium invaded CNS in mice, and the inflammation was increased, which was manifested by the increased expression of inflammatory factors interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, interferon (IFN)-γ and IL-12b and the activation of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasomes. The damage and inflammatory response of mouse hippocampal neurons were effectively reduced by AA or AD pretreatment. Furthermore, we observed the significant activation of microglia after S. typhimurium infection. AA and AD attenuated S. typhimurium -induced hippocampal injury by reducing the inflammatory response on microglia. The findings suggest that the AA and AD protect CNS from injury caused by S. typhimurium infection through inhibiting over expression of multiple neuroinflammatory mediators and NLRP3 inflammasome in mice.

PSD-93 up-regulates the synaptic activity of corticotropin-releasing hormone neurons in the paraventricular nucleus in depression

Since the discovery of ketamine anti-depressant effects in last decade, it has effectively revitalized interest in investigating excitatory synapses hypothesis in the pathogenesis of depression. In the present study, we aimed to reveal the excitatory synaptic regulation of corticotropin-releasing hormone (CRH) neuron in the hypothalamus, which is the driving force in hypothalamic-pituitary-adrenal (HPA) axis regulation. This study constitutes the first observation of an increased density of PSD-93-CRH co-localized neurons in the hypothalamic paraventricular nucleus (PVN) of patients with major depression. PSD-93 overexpression in CRH neurons in the PVN induced depression-like behaviors in mice, accompanied by increased serum corticosterone level. PSD-93 knockdown relieved the depression-like phenotypes in a lipopolysaccharide (LPS)-induced depression model. Electrophysiological data showed that PSD-93 overexpression increased CRH neurons synaptic activity, while PSD-93 knockdown decreased CRH neurons synaptic activity. Furthermore, we found that LPS induced increased the release of glutamate from microglia to CRH neurons resulted in depression-like behaviors using fiber photometry recordings. Together, these results show that PSD-93 is involved in the pathogenesis of depression via increasing the synaptic activity of CRH neurons in the PVN, leading to the hyperactivity of the HPA axis that underlies depression-like behaviors.