Objective: To investigate the effects of glutamate (Glu) injected into hypothalamic paraventricular nucleus (PVN) on visceral pain of chronic visceral hypersensitivity (CVH) rats and its possible mechanism. Methods: Newborn SD rats were given CVH rat model by colorectal distension (CRD) on the 8th, 10th and 12th day after birth. Thirty rats with successful CVH model were randomly divided into CVH model group (CVH group), CVH + injection of saline into PVN group (NS group), CVH+ injection of Glu into PVN (3, 6, and 12 μg Glu, namely G3, G6, and G12, respectively), 6 rats in each group, and 6 SD rats with matching body mass were taken as sham operation group (Sham group). The pain behavior of the rats was evaluated by pain threshold, abdominal withdrawal reflex (AWR) score, and abdominal external oblique muscle electromyography (EMG). The expression of arginine vasopressin (AVP) and the proliferation of colon tissue were detected by immunohistochemical staining. The apoptosis of colon tissue was detected by TUNEL. Results: Compared with the NS group, the pain thresholds of the G3, G6 and G12 groups increased, and the AWR scores and EMG amplitudes decreased. The differences were statistically significant(Pain threshold: t=7.65, 16.31, 24.78, both P<0.05; AWR scores: t=-2.98, -4.77, -7.29, both P<0.05; EMG amplitudes: t=-3.06, -5.75, -8.92, both P<0.05). Compared with the Sham group, the expression of AVP in PVN of the CVH group and NS group decreased ((42.63±5.20) %, (18.67±2.94) %, (17.53±2.47) %; t=6.95, t=7.56, both P<0.05). The expression of AVP was increased after different doses of Glu into PVN, and the AVP level in G12 group ((18.15±6.49)%) was higher than that of NS group, the difference was statistically significant (t=-4.21, P<0.05). Compared with the Sham group, the expression of PCNA in colonic mucosal cells of the CVH group and NS group decreased ((65.48±1.68) %, (18.39±1.67) %, (17.69±1.68) %; t=34.35, t=34.80, both P<0.05). The expression of PCNA was increased after different doses of Glu injected into PVN, and the PCNA level in G12 group ((59.91±5.63)%) was higher than that of NS group, the difference was statistically significant (t=-12.44, P<0.05). Compared with the Sham group, the expression of apoptotic cells in colonic mucosal cells of the CVH group and NS group increased ((23.38±11.40)%, (83.79±3.57)%, (80.91±2.47)%; t=-8.77, t=-8.54, both P<0.05). The expression of apoptotic cells was decreased after different doses of Glu into PVN, and the G12 group was ((18.15±6.49) %). Compared with NS group, the difference was statistically significant (t=15.65, P<0.05). Conclusion Injection of Glu into hypothalamic PVN can alleviate the visceral pain behaviors in CVH rats, and its mechanism may be related to arginine vasopressin.

Background:Cerebellar fastigial nucleus (FN)is involved in regulation of visceral activities such as cardiovascular, ingestion,respiratory,and acute gastric mucosal injury,yet it is unclear whether it participates in the regulation of visceral hypersensitivity and what is the possible mechanism. Aims:To investigate the effect and possible mechanism of glutamic acid (Glu ) injection into cerebellar FN on chronic visceral hypersensitivity in rats. Methods: Chronic visceral hypersensitivity rat model was established by neonatal colorectal distension (CRD). After 8 weeks,the rats were divided into CRD group,solvent group (0. 2 μL 0. 9% NaCl solution injection into cerebellar FN),high-,medium-,low-dose Glu groups (12,6,3 μg Glu injection into cerebellar FN,respectively),3-MPA +Glu group (12 μg Glu injection after glutamate decarboxylase inhibitor 3-MPA injection into cerebellar FN),Bic + Glu group (12 μg Glu injection into cerebellar FN after GABAAreceptor blocker Bic injection into lateral hypothalamic area). Pain threshold,abdominal withdrawal reflex (AWR)score and abdominal external oblique muscle electromyography (EMG)were used to detect visceral sensitivity,and malondialdehyde (MDA)content and superoxide dismutase (SOD)activity were measured. Results:Chronic visceral hypersensitivity rat model was successfully established. Compared with CRD group,pain threshold was significantly increased (P＜0. 05),AWR score,EMG amplitude,MDA content were significantly decreased (P＜0. 05 ),and SOD activity was significantly increased in a dose-dependent manner in Glu group (P ＜0. 05 ). Compared with 12 μg Glu group,pain threshold was significantly decreased (P＜0. 05),AWR score,EMG amplitude, MDA content were significantly increased (P ＜0. 05),and SOD activity was significantly decreased in 3-MPA +Glu group,Bic+Glu group (P＜0. 05). Conclusions:Glu injection into cerebellar FN can significantly reduce the visceral sensitivity in rats. The mechanism may be that Glu in cerebellar FN produces GABA via glutamate decarboxylase,and then binding GABAAreceptor in lateral hypothalamic area,resulting in increased intestinal mucosal antioxidant capacity, thereby reducing visceral hypersensitivity.