Glutamatergic neurons in the paraventricular nucleus of the hypothalamus participate in the regulation of visceral pain induced by pancreatic cancer in mice.

Background: Visceral pain induced by pancreatic cancer seriously affects patients' quality of life, and there is no effective treatment, because the mechanism of its neural circuit is unknown. Therefore, the aim of this study is to explore the main neural circuit mechanism regulating visceral pain induced by pancreatic cancer in mice. Methods: The mouse model of pancreatic cancer visceral pain was established on C57BL/6N mice by pancreatic injection of mPAKPC-luc cells. Abdominal mechanical hyperalgesia and hunch score were performed to assess visceral pain; the pseudorabies virus (PRV) was used to identify the brain regions innervating the pancreas; the c-fos co-labeling method was used to ascertain the types of activated neurons; in vitro electrophysiological patch-clamp technique was used to record the electrophysiological activity of specific neurons; the calcium imaging technique was used to determine the calcium activity of specific neurons; specific neuron destruction and chemogenetics methods were used to explore whether specific neurons were involved in visceral pain induced by pancreatic cancer. Results: The PRV injected into the pancreas was detected in the paraventricular nucleus of the hypothalamus (PVN). Immunofluorescence staining showed that the majority of c-fos were co-labeled with glutamatergic neurons in the PVN. In vitro electrophysiological results showed that the firing frequency of glutamatergic neurons in the PVN was increased. The calcium imaging results showed that the calcium activity of glutamatergic neurons in the PVN was enhanced. Both specific destruction of glutamatergic neurons and chemogenetics inhibition of glutamatergic neurons in the PVN alleviated visceral pain induced by pancreatic cancer. Conclusions: Glutamatergic neurons in the PVN participate in the regulation of visceral pain induced by pancreatic cancer in mice, providing new insights for the discovery of effective targets for the treatment of pancreatic cancer visceral pain.

Neuroinflammation in the paraventricular nucleus of the hypothalamus precipitates visceral pain induced by pancreatic cancer in mice.

Background: Given the pivotal role of neuroinflammation in chronic pain and that the paraventricular nucleus of the hypothalamus (PVN) is a crucial brain region involved in visceral pain regulation, we sought to investigate whether the targeted modulation of microglia and astrocytes in the PVN could ameliorate pancreatic cancer-induced visceral pain (PCVP) in mice. Methods: Using a mouse model of PCVP, achieved by tumor cell injection at the head of the pancreas, we measure the number of glial cells, and at the same time we employed minocycline to inhibit microglia and chemogenetic methods to suppress astrocytes in order to investigate the respective roles of microglia and astrocytes within the PVN in PCVP. Results: Mice exhibited visceral pain at 12, 15 and 18 days post-tumor cell injection. We observed a significant increase in the population of both microglia and astrocytes. Inhibition of microglial activity through minocycline microinjection into the PVN resulted in alleviation of visceral pain within 30 and 60 min. Similarly, chemogenetic inhibition of astrocyte function at 14 and 21 days post-injection also led to relief from visceral pain. Conclusions: This study found that PVN microglia and astrocytes were involved in regulating PCVP. Our results suggest that targeting glia may be a potential approach for alleviating visceral pain in patients with pancreatic cancer.

Inhibition of GABAergic neurons in the paraventricular nucleus of the hypothalamus precipitates visceral pain induced by pancreatic cancer in mice.

Background: For patients with pancreatic cancer, visceral pain is a debilitating symptom that significantly compromises their quality of life. Unfortunately, the lack of effective treatment options can be attributed to our limited understanding of the neural circuitry underlying this phenomenon. The primary objective of this study is to elucidate the fundamental mechanisms governing visceral pain induced by pancreatic cancer in murine models. Methods: A mouse model of pancreatic cancer visceral pain was established in C57BL/6N mice through the intrapancreatic injection of mPAKPC-luc cells. Abdominal mechanical hyperalgesia and hunch score were employed to evaluate visceral pain, whereas the in vitro electrophysiological patch-clamp technique was utilized to record the electrophysiological activity of GABAergic neurons. Specific neuron ablation and chemogenetics methods were employed to investigate the involvement of GABAergic neurons in pancreatic cancer-induced visceral pain. Results: In vitro electrophysiological results showed that the firing frequency of GABAergic neurons in the paraventricular nucleus of the hypothalamus (PVN) was decreased. Specific destruction of GABAergic neurons in the PVN exacerbated visceral pain induced by pancreatic cancer. Chemogenetics activation of GABAergic neurons in the PVN alleviated visceral pain induced by pancreatic cancer. Conclusions: GABAergic neurons located in PVN play a crucial role in precipitating visceral pain induced by pancreatic cancer in mice, thereby offering novel insights for identifying effective targets to treat pancreatic cancer-related visceral pain.

Enriched environment alleviates adolescent visceral pain, anxiety- and depression-like behaviors induced by neonatal maternal separation.

Background: Neonatal maternal separation (NMS), a major kind of early life stress, increases the risk of visceral pain, anxiety- and depression-like behaviors in adulthood. An enriched environment (EE) has been shown to successfully rescue the brain from various early life psychological stressors. Therefore, this study aimed to investigate whether NMS induces visceral pain, anxiety- and depression-like behaviors in adolescents and to evaluate the impact of EE in infancy on these symptoms. Methods: Male C57BL/6 J mice that had been subjected to NMS were used in this study. The visceral pain threshold test (PTT), open field test (OFT), and sucrose preference test (SPT) were conducted to evaluate visceral pain, anxiety- and depression-like behaviors in mice, respectively. An enzyme linked immunosorbent assay (ELISA) for tumor necrosis factor-α (TNF-α), interleukin-1ß, (IL-1ß), and interleukin-10 (IL-10) was performed to assess neuroinflammatory responses. Then, the effects of EE (free-turning running wheels, pipes, stairs, and various colored ocean balls, etc.) on NMS-induced behaviors and neuroinflammatory factors were examined. Results: The impacts of NMS included adolescent visceral pain, anxiety- and depression-like behaviors. The medial prefrontal cortex (mPFC), basolateral amygdala (BLA), and paraventricular nucleus (PVN) were biased towards pro-inflammatory features. Further, EE alleviated adolescent visceral pain, anxiety- and depression-like behaviors. The application of EE up-regulated the expression of IL-10, and down-regulated the expression of IL-1ß and TNF-α in mPFC, BLA, and PVN. Conclusions: The effects of NMS include adolescent visceral pain, anxiety- and depression-like behaviors, accompanied by an imbalance of neuroinflammation. Intervention with EE in pediatric mice relieved these symptoms by reducing neuroinflammation in the central nervous system.

The role of SOCS3 in the hypothalamic paraventricular nucleus in rat model of inflammatory pain.

BACKGROUND: Inflammatory molecular signals are modulated by a variety of intracellular transduction pathways, the activation of which may induce and amplify the spread of inflammatory response. Suppresser of cytokine signaling 3 (SOCS3) is an established negative feedback regulation transcription factor associated with tumor, diabetes mellitus, inflammation and anaphylaxis. Herein, we investigated whether SOCS3 in the paraventricular nucleus (PVN) can attenuate pro-inflammatory responses, and thereby relieve the inflammatory pain. METHODS: Adeno-associated virus (AAV) overexpressing SOCS3 was pre-injected into the PVN. Three weeks later, rat model of chronic inflammatory pain was established via subcutaneous injection of complete Freund's adjuvant (CFA) into the plantar center of hind paws. The therapeutic effect of SOCS3 was tested by the measurement of thermal and mechanical allodynia. In mechanistic study, the protein level of SOCS3 was evaluated by Western blotting, and the expression of c-fos and Iba-1 were assessed by immunofluorescent staining. RESULTS: Inflammatory pain was associated with upregulated interleukin 6 (IL-6) and SOCS3 in PVN in the acute phase. Thermal hyperalgesia can be relieved by intra-PVN injection of IL-6 neutralizing antibody (NA). Meanwhile, the upregulated c-fos and microglial activation was reversed. Furthermore, SOCS3 expression in PVN was downregulated in the chronic phase. Intra-PVN injection of AAV overexpressing SOCS3 suppressed the activation of neurons and attenuated thermal hyperalgesia and mechanical allodynia. CONCLUSION: Inhibition of IL-6 signaling attenuated inflammatory hyperalgesia in the acute phase. SOCS3 overexpression in the PVN attenuated inflammatory pain in the chronic phase via suppression of neuronal activation.

Toll-Like Receptor 4 in Paraventricular Nucleus Mediates Visceral Hypersensitivity Induced by Maternal Separation.

Neonatal maternal separation (MS) is a major early life stress that increases the risk of emotional disorders, visceral pain perception and other brain dysfunction. Elevation of toll-like receptor 4 (TLR4) signaling in the paraventricular nucleus (PVN) precipitates early life colorectal distension (CRD)-induced visceral hypersensitivity and pain in adulthood. The present study aimed to investigate the role of TLR4 signaling in the pathogenesis of postnatal MS-induced visceral hypersensitivity and pain during adulthood. The TLR4 gene was selectively knocked out in C57BL/10ScSn mice (Tlr4-/-). MS was developed by housing the offspring alone for 6 h daily from postnatal day 2 to day 15. Visceral hypersensitivity and pain were assessed in adulthood. Tlr4+/+, but not Tlr4-/-, mice that had experienced neonatal MS showed chronic visceral hypersensitivity and pain. TLR4 immunoreactivity was observed predominately in microglia in the PVN, and MS was associated with an increase in the expression of protein and/or mRNA levels of TLR4, corticotropin-releasing factor (CRF), CRF receptor 1 (CRFR1), tumor necrosis factor-α, and interleukin-1ß in Tlr4+/+ mice. These alterations were not observed in Tlr4-/- mice. Local administration of lipopolysaccharide, a TLR4 agonist, into the lateral cerebral ventricle elicited visceral hypersensitivity and TLR4 mRNA expression in the PVN, which could be prevented by NBI-35965, an antagonist to CRFR1. The present results indicate that neonatal MS induces a sensitization and upregulation of microglial TLR4 signaling activity, which facilitates the neighboring CRF neuronal activity and, eventually, precipitates visceral hypersensitivity in adulthood. Highlights (1)Neonatal MS does not induce chronic visceral hypersensitivity and pain in Tlr4-/- mice.(2)Neonatal MS increases the expression of TLR4 mRNA, CRF protein and mRNA, CRFR1 protein, TNF-α protein, and IL-1ß protein in Tlr4+/+ mice.(3)TLR4 agonist LPS (i.c.v.) elicits visceral hypersensitivity and TLR4 mRNA expression in the PVN.