Active inflammatory responses play an important role in the pathogenesis of depression. We hypothesized that the rapid antidepressant effect of ketamine is associated with the down-regulation of pro-inflammatory mediators. Forty-eight rats were equally randomized into six groups (a control and five chronic unpredictable mild stress (CUMS) groups) and given either saline or 10 mg/kg ketamine, respectively. The forced swimming test was performed, and the hippocampus was subsequently harvested for the determination of levels of interleukin (IL)-1β, IL-6, tumour necrosis factor-α (TNF-α), indoleamine 2,3-dioxygenase (IDO), kynurenine (KYN), and tryptophan (TRP). CUMS induced depression-like behaviours and up-regulated the hippocampal levels of IL-1β, IL-6, TNF-α, IDO, and the KYN/TRP ratio, which were attenuated by a sub-anaesthetic dose of ketamine. CUMS-induced depression-like behaviours are associated with a reduction in hippocampal inflammatory mediators, whereas ketamine's antidepressant effect is associated with a down-regulation of pro-inflammatory cytokines in the rat hippocampus.

Ketamine, a commonly used general anesthetic, can produce rapid and sustained antidepressant effect. However, the efficacy and safety of the perioperative application of ketamine on postoperative depression remains uncertain. We performed a meta-analysis to determine the effect of perioperative intravenous administration of ketamine on postoperative depression. Randomized controlled trials comparing ketamine with placebo in patients were included. Primary outcome was postoperative depression scores. Secondary outcomes included postoperative visual analog scale (VAS) scores for pain and adverse effects associated with ketamine. Fifteen studies with 1697 patients receiving ketamine and 1462 controls were enrolled. Compared with the controls, the ketamine group showed a reduction in postoperative depression scores, by a standardized mean difference (SMD) of −0.97, 95% confidence interval [CI, −1.27, −0.66], P < 0.001, I² = 72% on postoperative day (POD) 1; SMD−0.65, 95% CI [−1.12, −0.17], P < 0.001, I² = 94% on POD 3; SMD−0.30, 95% CI [−0.45, −0.14], P < 0.001, I² = 0% on POD 7; and SMD−0.25, 95% CI [−0.38, −0.11], P < 0.001, I² = 59% over the long term. Ketamine reduced VAS pain scores on POD 1 (SMD−0.93, 95% CI [−1.58, −0.29], P = 0.005, I² = 97%), but no significant difference was found between the two groups on PODs 3 and 7 or over the long term. However, ketamine administration distinctly increased the risk of adverse effects, including nausea and vomiting (risk ratio [RR] 1.40, 95% CI [1.12, 1.75], P = 0.003, I² = 30%), headache (RR 2.47, 95% CI [1.41, 4.32], P = 0.002, I² = 19%), hallucination (RR 15.35, 95% CI [6.²4, 37.34], P < 0.001, I² = 89%), and dizziness (RR 3.48, 95% CI [2.68, 4.50], P < 0.001, I² = 89%) compared with the controls. In conclusion, perioperative application of ketamine reduces postoperative depression and pain scores with increased risk of adverse effects.

The gut microbiota may be involved in neuropathic pain. However, the causal association between gut microbiota and neuropathic pain remains unclear. Whether immune cells and inflammatory factors mediate the pathway from gut microbiota to neuropathic pain has not been elucidated. We obtained the summary data of 412 gut microbiota, 731 immune cells, 91 inflammatory factors, and five types of neuropathic pain (drug-induced neuropathy, postherpetic neuralgia, sciatica, trigeminal neuralgia, and unspecified neuralgia) from large-scale genome-wide association study (GWAS) datasets and the FinnGen database. We used bidirectional Mendelian randomization (MR) analysis to explore the causal association between gut microbiota and neuropathic pain. Additionally, we conducted a mediation analysis to identify whether immune cells and inflammatory factors act as mediators within these causal relationships. Our study revealed 30 causal relationships between 26 gut bacterial taxa and five types of neuropathic pain, including four associated with drug-induced neuropathy, six with postherpetic neuralgia, five with sciatica, eight with trigeminal neuralgia, and seven with unspecified neuralgia. Moreover, we identified 35 gut bacterial pathway abundances causally involved in neuropathic pain. The reverse MR analysis showed no evidence of reverse causality from gut microbiota to neuropathic pain. Mediation analysis demonstrated that the immune cell phenotype “HLA-DR++ monocyte % leukocyte” mediated the causal relationship between p_Proteobacteria and sciatica with a mediation proportion of 36.15% (P = 0.038), whereas “CD11c on CD62L+ myeloid dendritic cell” mediated the causal pathway from assimilatory sulfate reduction to trigeminal neuralgia with a mediation proportion of 27.90% (P = 0.041). This study identified the causal relationships between several specific gut microbiota and various neuropathic pain subtypes. Additionally, two immune cells may act as potential mediators in the pathways from gut microbiota to neuropathic pain.

Sepsis-associated encephalopathy (SAE), a devastating neurological complication of systemic inflammation, affects approximately 70% of patients with sepsis