The effects of linalool on transient receptor potential vanilloid 1 pathway and its role in alleviating visceral hypersensitivity in rats with irritable bowel syndrome / 中华消化杂志

ABSTRACT

Objective:To observe the effects of linalool on central and alleviating peripheral nervous system through transient receptor potential vanilloid 1 (TRPV1) pathway and its role in alleviating visceral hypersensitivity in irritable bowel syndrome (IBS).Methods:Thirty-six female newborn Sprague-Dawley (SD) rat pups in specific pothogen free was selected, among which 30 rats were used for behavioral experiments and 6 rats for electrophysiological experiment. In behavioral experiments, 30 newborn SD rats were randomly divided into normal control group (0.2 mL 0.9% sodium chloride solution was injected into the colorectal), neonatal colonic inflammation (NCI) group (0.2 mL 0.5% acetic acid was injected into the colorectal), linalool 20, 50 and 100 mg/kg groups (after NCI model successfully established, the rat were gavaged with linalool 20, 50 or 100 mg/kg at 5 weeks old). At 6 weeks old, abdominal withdrawal reflex (AWR) and pressure value of pain threshold (inflation pressure value at AWR score of 3) was observed by colorectal distention test. One hour after behavioral experiments, the expression of TRPV1 at protein level in colonic mucosa and spinal cord of each group was detected by Western blotting and immunohistochemistry. In electrophysiological experiment, female SD rats aged 6 to 7 weeks were selected to make in vitro transverse sections of the spinal cord. Five to eight neurons were randomly selected from each rat for whole-cell patch-clamp recording. The effects of linalool, tetrodotoxin and anti capsaicinand on the spontaneous excitatory postsynaptic current (sEPSC) of substantiagelatinosa neurons was recorded. Independent sample t test and paired t test were used for statistical analysis. Results:The AWR score of rats in NCI group was higher than those in normal control group, linalool 20 mg/kg group, linalool 50 mg/kg group and linalool 100 mg/kg group at 40 mmHg (1 mmHg=0.133 kPa) pressure (2.5±0.2 vs. 1.0±0.3, 1.5±0.3, 1.5±0.2, and 1.5±0.2, respectively), at 60 mmHg pressure the AWR score was higher than those in normal control group, linalool 50 mg/kg group and linalool 100 mg/kg group (3.8±0.2 vs. 2.3±0.4, 2.3±0.5, and 2.0±0.3, respectively), and the differences were statistically significant ( t=4.39, 2.45, 3.16, 3.16, 3.31, 2.88 and 5.97; P=0.001, 0.034, 0.010, 0.010, 0.008, 0.028, and<0.001). The pain threshold of rats in NCI group was lower than those of normal control group, linalool 20 mg/kg group, linalool 50 mg/kg group and linalool 100 mg/kg group ((35.8±2.0) mmHg vs. (55.8±1.5), (49.2±2.4), (53.3±2.1), and (55.0±1.8) mmHg, respectively), and the differences were statistically significant ( t=-7.91, -4.28, -6.01, and -7.06; P<0.001, =0.002, <0.001, and <0.001). The results of Western blotting showed that the relative expression of TRPV1 at protein level in colorectal tissues of rats in NCI group was higher than those of normal control group, linalool 20 mg/kg group, linalool 50 mg/kg group and linalool 100 mg/kg group (0.86±0.03 vs. 0.32±0.03, 0.68±0.01, 0.45±0.03, and 0.56±0.02, respectively), and the relative expression of TRPV1 at protein level in spinal dorsal horn was higher than those of normal control group, linalool 20 mg/kg group, linalool 50 mg/kg group and linalool 100 mg/kg group (0.91±0.02 vs. 0.34±0.03, 0.72±0.03, 0.51±0.06, and 0.63±0.05), and the differences were statistically significant ( t=12.44, 5.14, 9.68, 7.69, 19.14, 5.13, 6.72, and 5.60; P<0.001, <0.001, <0.001, <0.001, <0.001, <0.001, =0.001, and <0.001). There were no statistically significant differences in the frequency and the outward current of sEPSC in neurons of same glial region among rats with 2 mmol/L linalool gavaged for 4 minutes, 0.5 μmol/L tetrodotoxin and 2 mmol/L linalool gavaged for 4 minutes ( n=5, (23.84±4.81) Hz vs. (20.54±5.71) Hz, (7.60±0.35) pA vs. (7.62±0.75) pA, both P>0.05). The frequency of sEPSC administered with 2 mmol/L linalool gavaged for 4 minutes was higher than that of neurons in the same glial area administered with 10 μmol/L capsazepine and 2 mmol/L linalool gavaged for 4 minutes ( n=5, (20.17±2.55) Hz vs.(14.09±2.98) Hz), and the difference was statistically significant ( t=3.58, P=0.021); however there was no statistically significant difference in the outward current ((7.42±0.78) pA vs. (7.03±1.32) pA, P>0.05). Conclusion:Linalool can relieve visceral hypersensitivity in IBS partially through TRPV1 pathway, which may be related to the hyperpolarization of the membrane potential of neurons in glial region.