Repetitive transcranial magnetic stimulation rescues simulated space complex environment-induced emotional and social impairments by enhancing neuronal excitability in the medial prefrontal cortex

Studies have shown that spaceflight affects the emotional and social performance of astronauts. Identifying the neural mechanisms underlying the emotional and social effects of spacefaring-specific environments is essential to specify targeted treatment and prevention interventions. Repetitive transcranial magnetic stimulation (rTMS) has been shown to improve the neuronal excitability and is used to treat psychiatric disorders such as depression. To study the changes of excitatory neuron activity in medial prefrontal cortex (mPFC) in simulated space complex environment (SSCE), and to explore the role of rTMS in behavioral disorders caused by SSCE and the neural mechanism. We found that rTMS effectively ameliorated the emotional and social impairments of mice in SSCE, and acute rTMS could instantaneously enhance the excitability of mPFC neurons. During depression-like and social novelty behaviors, chronic rTMS enhanced the mPFC excitatory neuronal activity that was inhibited by SSCE. Above results suggested that rTMS can completely reverse the SSCE-induced mood and social impairment by enhancing the suppressed mPFC excitatory neuronal activity. It was further found that rTMS suppressed the SSCE-induced excessive dopamine D2 receptor expression, which may be the cellular mechanism by which rTMS potentiates the SSCE-evoked hypoactive mPFC excitatory neurons. Our current results raise the possibility of rTMS being applied as a novel neuromodulation for mental health protection in spaceflight.

Opposing manner of miR-455-3p against NR2B-PSD-95-nNOS complex in the cortex and hippocampus of depressive rats under simulated complex space environment

Depression in astronauts is one of the consequences of space flight effects, negatively impacting their work performances. Unfortunately, the underlying molecular mechanisms in space flight-induced depression are still unknown; however, various neuropsychiatric disorders reported that overexpressed NR2B-PSD-95-nNOS complex in the brain triggers various pathological pathways, and inhibiting NR2B-PSD-95-nNOS complex asserts antidepressant effects. Through our in silico analysis, we found that epigenetic regulator miR-445-3p targets PSD-95 and is hypothesized to down-regulate NR2B-PSD-95-nNOS complex to prevent neuronal damage associated with depression. Therefore, the present study is aimed to determine the novel insight of the miR-455-3p against the NR2B-PSD-95-nNOS complex in the neurobiology of space flight-induced depressive behavior. Using a simulated space environment complex model (SCSE) for 21 days, we induced depressive behavior in rats to analyze miR-455-3p expression and NR2B-PSD-95-nNOS complex in the cortex and hippocampus of the SCSE depressed rats through qRT-PCR and western blot analysis. Further, an in vitro microgravity model using rat hippocampus cell lines (RHNC) was utilized to identify the independent role of miR-455-3p on (1) NR2B-PSD-95-nNOS complex and TrKB-BDNF proteins, (2) oxidative stress, (3) nitric oxide level, (4) inflammatory cytokines, (5) mitochondrial biogenesis/ dynamics, and (6) cell survival. Our results showed that miR-455-3p regulates NR2B-PSD-95-nNOS complex in the SCSE depressed rats in opposite ways, with the cortex revealing a higher level of miR-455-3p and low-level NR2B-PSD-95-nNOS complex and the hippocampus showing down-regulated miR-455-3p and up-regulated NR2B-PSD-95-nNOS complex, indicating a region-specific change in the miR-455-3p and NR2B-PSD-95-nNOS complex in the SCSE depressed rats. Further RHNC results also confirmed down-regulated miR-455-3p and up-regulated NR2B-PSD-95-nNOS complex expression, similar to the findings in the hippocampus of SCSE rats, suggesting that microgravity influences miR-455-3p and associated changes. Additional investigations revealed that miR-455-3p targets PSD-95 and co-regulates NR2B-PSD-95-nNOS complex along with TrkB-BDNF signaling and exert protective effects against NR2B-PSD-95-nNOS complex, oxidative stress, nitric oxide, inflammatory cytokines, and mitochondrial defects, suggesting a valuable biomarker for devising depressive disorders.