Involvement of the IL-6 Signaling Pathway in the Anti-Anhedonic Effect of the Antidepressant Agomelatine in the Chronic Mild Stress Model of Depression

miR-29a-5p rescues depressive-like behaviors in a CUMS-induced mouse model by facilitating microglia M2-polarization in the prefrontal cortex via TMEM33 suppression

BACKGROUND

Depression accounts for a high proportion of neuropsychiatric disorders and is associated with abnormal states of neurons in specific brain regions. Microglia play a pivotal role in the inflammatory state during depression development; however, the exact mechanism underlying chronic mood states remains unknown. Thus, the present study aimed to determine whether microRNAs (miRNAs) alleviate stress-induced depression-like behavior in mice by regulating the expression levels of their target genes, explore the role of neuroinflammation induced by microglial activation in the pathogenesis and progression of depression, and determine whether the role of the miR-29a-5p/transmembrane protein 33 (TMEM33) axis.

METHODS

In this study, chronic unpredictable mild stress (CUMS) mouse depression model, various behavioral tests, western blotting, dual-luciferase reporter assay, enzyme-linked immunosorbent assay, real-time quantitative reverse transcription PCR, immunofluorescence and lentivirus-mediated gene transfer were used.

RESULTS

After exposure to the CUMS paradigm, miR-29a-5p was significantly down-regulated. This downregulation subsequently promoted the polarization of microglia M1 by upregulating the expression of TMEM33, resulting in enhanced inflammatory chemokines affecting neurons. Conversely, the upregulation of miR-29a-5p within the prefrontal cortex (PFC) suppressed TMEM33 expression, facilitated microglia M2-polarization, and ameliorated depressive-like behavior.

LIMITATIONS

Only rodent models of depression were used, and human samples were not included.

CONCLUSIONS

The results of this study suggest that miR-29a-5p deficits within the PFC mediate microglial anomalies and contribute to depressive-like behaviors. miR-29a-5p and TMEM33 may, therefore, serve as potential therapeutic targets for the treatment of depression.

Olanzapine Effects on Parvalbumin/GAD67 Cell Numbers in Layers/Subregions of Dorsal Hippocampus of Chronically Socially Isolated Rats

Depression is linked to changes in GABAergic inhibitory neurons, especially parvalbumin (PV) interneurons, which are susceptible to redox dysregulation. Olanzapine (Olz) is an atypical antipsychotic whose mode of action remains unclear. We determined the effect of Olz on PV-positive (+) and glutamate decarboxylase 67 (GAD67) + cell numbers in the layers of dorsal hippocampus (dHIPP) cornu ammonis (CA1-CA3) and dentate gyrus (DG) subregions in rats exposed to chronic social isolation (CSIS), which is an animal model of depression. Antioxidative enzymes and proinflammatory cytokine levels were also examined. CSIS decreased the PV+ cell numbers in the Stratum Oriens (SO) and Stratum Pyramidale (SP) of dCA1 and dDG. It increased interleukin-6 (IL-6), suppressor of cytokine signaling 3 (SOCS3), and copper-zinc superoxide dismutase (CuZnSOD) levels, and it decreased catalase (CAT) protein levels. Olz in CSIS increased the number of GAD67+ cells in the SO and SP layers of dCA1 with no effect on PV+ cells. It reduced the PV+ and GAD67+ cell numbers in the Stratum Radiatum of dCA3 in CSIS. Olz antagonizes the CSIS-induced increase in CuZnSOD, CAT and SOCS3 protein levels with no effect on IL-6. Data suggest that the protective Olz effects in CSIS may be mediated by altering the number of PV+ and GAD67+ cells in dHIPP subregional layers.

Associations between serum estradiol and IL-6/sIL-6R/sgp130 complex in female patients with major depressive disorder

BACKGROUND

It has been hypothesized that the IL-6/sIL-6R/sgp130 complex, an inflammatory complex, plays a critical role in the pathogenesis of major depressive disorder (MDD). Estradiol (E2) is a sex steroid hormone involved in emotional regulation and MDD. This study aimed to investigate the relationship between E2 and IL-6/sIL-6R/sgp130 complex in patients with MDD.

METHODS

Using enzyme-linked immunosorbent assay, the levels of IL-6, sIL-6Rα, and sgp130 were compared between 117 female patients with MDD and 122 healthy controls.The serum concentrations of E2 and other biomarkers were also measured.

RESULTS

(1) The serum levels of IL-6 and sIL-6Rα in patients with MDD were significantly higher than those in the control group, while the serum levels of sgp130 and E2 were significantly lower (all P < 0.05). (2) Low levels of E2 were associated with high levels of IL-6 and low levels of sgp130 (all P < 0.01). (3) HAMD-24 score was positively correlated with the serum level of IL-6, but negatively correlated with the serum levels of sgp130 and E2(all P < 0.05). (4) IL-6 and sgp130 had certain prognostic values in MDD, and the combination of various indicators showed a significantly superior prognostic value.

CONCLUSIONS

The IL6/sIL-6R/sgp130 complex in female patients with MDD was closely related to E2 level. In addition, IL-6 and sgp130 may be valuable serum biomarkers for the diagnosis and prognosis of MDD in women.

Importance of additional behavioral observation in psychopharmacology: a case study on agomelatine's effects on feedback sensitivity in probabilistic reversal learning in rats

Since the second half of the twentieth century, many important discoveries in the field of behavioral psychopharmacology have been made using operant conditioning cages. These cages provide objective data collection and have revolutionized behavioral research. Unfortunately, in the rush towards automation, many mistakes may have been made that could have been avoided by observing experimental animals. The study described in this paper is an excellent example of how important additional behavioral observation can be for interpreting instrumental data. In this study, we evaluated the effects of single injections of 3 different doses of agomelatine (5, 10, and 40 mg/kg) on feedback sensitivity in rats. To this end, we tested 40 animals in the instrumental probabilistic reversal learning task in a Latin square design. The highest applied dose of agomelatine, prima facie, reduced the sensitivity of rats to negative feedback - an effect that can be considered antidepressant. However, additional behavioral observation dramatically changed the interpretation of the results and revealed that the perceived effect of agomelatine on sensitivity to negative feedback can actually be attributed to drug-induced drowsiness.