A growing body of evidence shows that the electrical stimulation of the vagus nerve can improve mental illness including depression. Here, we investigated whether the vagus nerve stimulation (VNS) is involved in regulating the responsiveness of hippocampal neurons in rats under chronic restraint stress (CRS). c‐Fos protein signals were detected 2 hr after VNS in 5‐HT1A receptor‐positive neurons in the dorsal raphe nucleus (DRN) as well as in the nucleus tractus solitarius (NTS). Chronic VNS was performed on a daily basis for 2 weeks using an implanted microelectrode in rats that had undergone CRS for 2 weeks. We found that the levels of both 5‐HT1B receptors and phospho‐Erk1/2 were decreased in parallel in the hippocampal neurons of CRS animals and then increased to the baseline levels by chronic VNS. Hippocampal induction of 5‐HT1B receptors and phospho‐Erk1/2 by VNS was diminished after the injection of 5,7‐dihydroxytryptamine (5,7‐DHT), a neurotoxin of serotonergic neurons, into the DRN. Hippocampal production of brain‐derived neurotrophic factor (BDNF) was also upregulated by VNS, but the treatment of 5,7‐DHT abrogated the effects of VNS on BDNF induction. VNS in CRS animals improved the behavioral scores in forced swimming test (FST) compared to sham‐stimulated control. Our results suggest that VNS‐mediated serotonergic input via 5‐HT1B receptors into the hippocampal neurons may activate BDNF pathway and improve depressive‐like behaviors in CRS animals.

Background Increasing number of studies provide evidence that the vagus nerve stimulation (VNS) dampens inflammation in peripheral visceral organs. However, the effects of afferent fibers of the vagus nerve (AFVN) on anti-inflammation have not been clearly defined. Here, we investigate whether AFVN are involved in VNS-mediated regulation of hepatic production of proinflammatory cytokines. Methods An animal model of hepatitis was generated by intraperitoneal (i.p.) injection of concanavalin A (ConA) into rats, and electrical stimulation was given to the hepatic branch of the vagus nerve. AFVN activity was regulated by administration of capsaicin (CAP) or AP-5/CNQX and the vagotomy at the hepatic branch of the vagus nerve (hVNX). mRNA and protein expression in target tissues was analyzed by RT-PCR, real-time PCR, western blotting and immunofluorescence staining. Hepatic immune cells were analyzed by flow cytometry. Results TNF-α, IL-1β, and IL-6 mRNAs and proteins that were induced by ConA in the liver macrophages were significantly reduced by the electrical stimulation of the hepatic branch of the vagus nerve (hVNS). Alanine transaminase (ALT) and aspartate transaminase (AST) levels in serum and the number of hepatic CD4+ and CD8+ T cells were increased by ConA injection and downregulated by hVNS. CAP treatment deteriorated transient receptor potential vanilloid 1 (TRPV1)-positive neurons and increased caspase-3 signals in nodose ganglion (NG) neurons. Concomitantly, CAP suppressed choline acetyltransferase (ChAT) expression that was induced by hVNS in DMV neurons of ConA-injected animals. Furthermore, hVNS-mediated downregulation of TNF-α, IL-1β, and IL-6 expression was hampered by CAP treatment and similarly regulated by hVNX and AP-5/CNQX inhibition of vagal feedback loop pathway in the brainstem. hVNS elevated the levels of α7 nicotinic acetylcholine receptors (α7 nAChR) and phospho-STAT3 (Tyr705; pY-STAT3) in the liver, and inhibition of AFVN activity by CAP, AP-5/CNQX and hVNX or the pharmacological blockade of hepatic α7 nAChR decreased STAT3 phosphorylation. Conclusions Our data indicate that the activity of AFVN contributes to hepatic anti-inflammatory responses mediated by hVNS in ConA model of hepatitis in rats.

Background: A growing body of evidence shows that neuronal activity is involved in modulating the efficacy of acupuncture therapy. However, it has been seldom investigated whether neuronal activity following acupuncture stimulation is effective at regulating hepatic inflammation. Objective: Using the concanavalin A (ConA) model of hepatitis, we investigated the regulation of inflammatory cytokine tumor necrosis factor (TNF)-α in the liver tissue and the blood after acupuncture stimulation at ST36. Methods: Mice were subjected to ConA injection, acupuncture stimulation at ST36 by manual acupuncture (MA) or electroacupuncture (EA) procedures, and vagotomy (VNX). Liver tissue and blood were collected for TNF-α analysis. TNF-α mRNA was analyzed by real-time polymerase chain reaction (PCR), and TNF-α, CD11b, CD68, and Erk1/2 proteins were analyzed by Western blotting, immunofluorescence staining, and enzyme-linked immunosorbent assay. Results: TNF-α mRNA and protein were induced in CD11b-positive hepatic cells and the plasma at 6–24 h after ConA injection. The application of MA or EA was very effective at attenuating the production of TNF-α. Anti-inflammatory effects of acupuncture were greatly suppressed by VNX in ConA-injected animals, suggesting the requirement of vagus nerve activity in acupuncture-mediated anti-inflammatory responses. Electrical stimulation of the sciatic nerve (SNS) resulted in an anti-inflammatory effect similar to acupuncture stimulation. In parallel with TNF-α, production of phospho-Erk1/2, which was induced in the liver tissue, was downregulated by MA and EA in liver cells. Conclusion: The regulatory effects of acupuncture stimulation on inflammatory responses in the liver may be modulated through the activation of the vagus nerve pathway.

Background: Increasing number of studies provide evidence that the vagus nerve stimulation (VNS) dampens inflammation in peripheral visceral organs. However, the effects of afferent fibers of the vagus nerve (AFVN) on anti-inflammation have not been clearly defined. Here, we investigate whether AFVN are involved in VNS-mediated regulation of hepatic production of proinflammatory cytokines. Methods: An animal model of hepatitis was generated by intraperitoneal injection of concanavalin A (ConA) into rats, and electrical stimulation was given to the hepatic branch of the vagus nerve. AFVN was selectively eliminated by treating animals with capsaicin (CAP). mRNA and protein expression in target tissues was analyzed by RT-PCR, real-time PCR, western blotting and immunofluorescence staining.Results: TNF-α, IL-1β, and IL-6 mRNAs and proteins that were induced by ConA in the liver macrophages were significantly reduced by the electrical stimulation of the hepatic branch of the vagus nerve (hVNS). hVNS also induced an increase in phospho-STAT3 in the liver macrophages of ConA-injected animals, suggesting the activation of STAT3 transcription factor associated with cholinergic anti-inflammation. Capsaicin (CAP) treatment deteriorated transient receptor potential vanilloid 1 (TRPV1)-positive neurons and also induced an increase in apoptotic caspase-3 signals in nodose ganglion (NG) neurons. Concomitantly, CAP suppressed choline acetyltransferase (ChAT) expression that was induced by hVNS in DMV neurons of ConA-injected animals. Furthermore, hVNS-mediated downregulation of TNF-α, IL-1β, and IL-6 expression was reduced by CAP administration. Conclusions: Our data indicate that the activity of AFVN contributes to hepatic anti-inflammatory responses mediated by hVNS in ConA model of hepatitis in rats.

Increasing evidence suggests that parasympathetic vagus nerve activity plays a role in modulating acupunctureinduced anti-inflammatory reaction, but the function of sympathetic nerve is not known. Here, we investigated whether splanchnic sympathetic nerve activity was involved in the regulation of splenic expression of TNF-α mRNA by electroacupuncture (EA) in LPS-injected animals. Methods : DiI was injected into the stomach or celiac ganglion (CG) for retrograde labeling of the target tissues. EA was given at ST36 and the electrical stimulation on the sciatic nerve in LPS-injected mice. c-Fos signals in the tissues were analyzed by immunofluorescence staining, and TNF-α mRNA was analyzed by real-time PCR. Results : Application of EA at ST36 or electrical stimulation on the sciatic nerve induced c-Fos expression in neurons of the spinal cord and celiac ganglion (CG). Then, the vagotomy reduced c-Fos levels in CG neurons but not in the spinal cord in animals given EA. Expression of TNF-α mRNA which was induced in the spleen after LPS was significantly inhibited by EA, then the vagotomy elevated TNF-α mRNA level similar to that in LPS-injected animals. Splanchnectomy in animals given LPS and EA also increased TNF-α mRNA though it was less effective than vagotomy. Conclusions : Our data suggest that EA delivered to the spleen via the splanchnic sympathetic nerve may be involved in attenuating splenic inflammatory responses in LPS-injected animals.