Metabotropic glutamate receptor-8 relieves neonatal maternal separation-induced visceral hypersensitivity in rats by regulating expression of TNF-α

BACKGROUND: Visceral hypersensitivity (VH) is one of the most common causes of irritable bowel syndrome (IBS). The anti-hyperalgesic effects of metabotropic glutamate receptor 8 (mGluR8) has been identified in the central nervous system (CNS). However, whether this receptor has a similar function in the gastrointestinal tract has not been well studied. The present study aimed to explore the role of this receptor in a visceral hypersensitivity-related IBS rat model. METHODS: Neonatal rats were separated from their mothers for 3 hours daily from postnatal day 2 to day 14 to establish neonatal maternal separation (NMS) models. The mGluR8 agonist (S)-3,4-DCPG (10 mg/kg) and the mGluR8 antagonist (RS)-α- methylserine-O-phosphate (MSOP) (10 mg/kg) were used to examine the role of mGLuR8 in the NMS rats. The expression of mGluR8, related inflammatory factors, and inflammatory signal pathways were assessed in colon tissues. RESULTS: Our data showed that mGluR8 expression was increased in the colonic mucosa of NMS rats compared to controls. In addition, selective activation of mGluR8 ameliorated visceral hypersensitivity, whereas antagonization of mGluR8 aggravated visceral hypersensitivity. Treatment with (S)-3,4-DCPG (10 mg/kg) reduced the expression of myeloperoxidase (MPO) in intestinal mucosa of NMS rats. Furthermore, activating mGluR8 reduced the expression of tumor necrosis factor-α (TNF-α), whereas antagonizing mGluR8 promoted that. The expressions of toll-like receptor 4 (TLR4) and nuclear factor-κB (NF-κB) did not significantly change upon activation or antagonization of mGluR8 receptor. CONCLUSIONS: The activation of mGluR8 receptor ameliorates visceral hypersensitivity in NMS rats, and the underlying mechanisms may be associated with the inhibition of TNF-α and the suppression of colonic inflammatory response.