Minoru Tsuji

The association between gut microbiota imbalance and depression is well known; however, its underlying mechanisms remain unclear. Angiotensin (Ang)-converting enzyme 2 (ACE2) transforms Ang II into Ang (1–7), which exerts antidepressant effects via the Mas receptor (MasR). However, the role of ACE2 in dysbiosis-related depression in the brain remains unclear. In this study, we assessed changes in brain ACE2 expression and whether diminazene aceturate (DIZE), an ACE2 activator, alleviates depression-like behavior in an antibiotic-induced (ABX) dysbiosis mouse model. The tail suspension test revealed depression-like behavior in ABX mice. Western blotting and immunohistochemistry revealed decreased expression levels of ACE2, Ang (1–7), p-CAMKII, p-CREB, BDNF, synaptophysin, p-PPARγ, CD206, TREM2, and IL-10 and reduced neurogenesis in the dentate gyrus of the hippocampus. Iba1, CD86, iNOS, IL-1β, TNF-α, and cleaved caspase-3 levels were increased, indicating microglial activation in the hippocampus. MasR staining was observed in neurons and microglia in the hippocampus of ABX mice. Furthermore, p-CAMKII and p-CREB staining was observed in neurons, while p-PPARγ staining was observed in microglia in the hippocampus of ABX mice treated with DIZE. DIZE administration prevented ABX-induced changes, whereas the effects of DIZE were abolished by co-administration with A779, a MasR inhibitor. These findings suggest that hippocampal ACE2 expression plays a crucial role in dysbiosis-related depression associated with gut microbiota imbalance, potentially offering a target for therapeutic interventions.

Ulcerative colitis (UC) is a refractory inflammatory bowel disease, which is known to cause psychiatric disorders such as anxiety and depression at a high rate in addition to peripheral inflammatory symptoms. However, the pathogenesis of these psychiatric disorders remains mostly unknown. While prior research revealed that the Enterococcus faecalis 2001 (EF-2001) suppressed UC-like symptoms and accompanying depressive-like behaviors, observed in a UC model using dextran sulfate sodium (DSS), whether it has an anxiolytic effect remains unclear. Therefore, we examined whether EF-2001 attenuates DSS-induced anxiety-like behaviors. Treatment with 2% DSS for seven days induced UC-like symptoms and anxiety-like behavior through the hole-board test, increased serum lipopolysaccharide (LPS) and corticosterone concentration, and p-glucocorticoid receptor (GR) in the prefrontal cortex (PFC), and decreased N-methyl-d-aspartate receptor subunit (NR) 2A and NR2B expression levels in the PFC. Interestingly, these changes were reversed by EF-2001 administration. Further, EF-2001 administration enhanced CAMKII/CREB/BDNF-Drebrin pathways in the PFC of DSS-treated mice, and labeling of p-GR, p-CAMKII, and p-CREB showed colocalization with neurons. EF-2001 attenuated anxiety-like behavior by reducing serum LPS and corticosterone levels linked to the improvement of UC symptoms and by facilitating the CAMKII/CREB/BDNF-Drebrin pathways in the PFC. Our findings suggest a close relationship between UC and anxiety.

Morphine-induced antinociception is partially reduced in interleukin-31 (IL-31) receptor A (IL-31RA)-deficient mice, indicating that IL-31RA is crucial for morphine-induced peripheral antinociception. Herein, we examined the combined effects of IL-31 and morphine on the antinociceptive activity and itch-associated scratching behavior (LLS) in mice and elucidated the regulatory mechanisms. A hot-plate test was used to assess antinociception. LLS was automatically detected and recorded via a computer. IL-31RA mRNA expression was assessed using real-time polymerase chain reaction. Repeated pre-treatment with IL-31 resulted in significant antinociceptive activity. Repeated administration of morphine decreased the morphine-induced antinociceptive activity, LLS counts, and regular dose and inhibited IL-31-induced LLS. These results suggested that the repeated administration of morphine depleted inter-neuronal IL-31RA levels, preventing morphine-induced antinociception. Therefore, IL-31 may be helpful as an adjunct analgesic to morphine. To explore the benefits of IL-31, its influence on morphine-induced antinociceptive tolerance in mice was examined. An IL-31 and morphine combination increased the analgesic action, which increased the expression of DRG neuronal IL-31RA, elucidating the site of peripheral antinociception of morphine. This site may induce exocytosis of IL-31RA in the sensory nervous system. Collectively, the suppressive effect of IL-31 on morphine-induced antinociceptive tolerance may result from IL-31RA supplementation in sensory nerves.

Morphine-induced antinociception is partially reduced in interleukin-31 (IL-31) receptor A (IL-31RA)-deficient mice, indicating that IL-31RA is crucial for morphine-induced peripheral antinociception. Herein, we examined the combined effects of IL-31 and morphine on antinociceptive activity and itch-associated scratching behavior (LLS) in mice, and elucidated the regulatory mechanisms. A hot-plate test was used to assess antinociception. LLS was automatically detected and recorded via computer. IL-31RA mRNA expression was assessed using real-time polymerase chain reaction. Repeated pre-treatment with IL-31 resulted in significant antinociceptive activity. Repeated administration of morphine decreased the morphine-induced antinociceptive activity, LLS counts, and regular dose, and inhibited IL-31-induced LLS. These results suggested that repeated administration of morphine depleted inter-neuronal IL-31RA levels, preventing morphine-induced antinociception. Therefore, IL-31 may be helpful as an adjunct analgesic to morphine. To explore the benefits of IL-31, its influence on morphine-induced antinociceptive tolerance in mice was examined. IL-31 and morphine combination increased analgesic action which increased the expression of DRG neuronal IL-31RA, elucidating the site of peripheral antinociception of morphine. This site may induce exocytosis of IL-31RA in the sensory nervous system. Collectively, the suppressive effect of IL-31 on morphine-induced antinociceptive tolerance may result from IL-31RA supplementation in sensory nerves.