Role Of TRPV1 In Systemic Lps-induced Fever And Hyperalgesia In Rats

Objective An experimental fever and hyperalgesia models of systemic bacterial infection were prepared by intraperitoneal injection LPS, and TRPV1 antagonist capsazepine(CPZ) were administrated via intracerebroventricular injection(I.C.V.) to block TRPV1 channel. The changes of body temperature and hindpaw withdrawal latency were observed, respectively. The expression of TRPV1 in the preoptic area of the hypothalamus(POA) and doral root gangilin(DRG) of rats were monitored by RT-q PCR. This study researched initially the role of TRPV1 in systemic LPS-induced fever with hyperalgesia in rats and possible mechanism.Methods Male SD rats were used in experiments. The rats were randomized into 4 groups(n=8, in each).(1) Control group:rats were pretreated with the dissolvent via I.C.V.,followed by saline via I.P. after 30 minutes;(2) LPS group:rats were pretreated with the dissolvent via I.C.V., followed by LPS1ml/kg(20ug/ml) via I.P. after 30 minutes;(3)Capsazepine(CPZ)group:rats were pretreated with CPZ 5ul(1g/L) via I.C.V., followed by saline via I.P. after 30 minutes;(4) LPS+ CPZ group:rats were pretreated with CPZ5 ul via I.C.V, followed by LPS(1ml/kg) via I.P. after 30 minutes. The temperature and the time of hindpaw withdrawal latency were monitored by microcomputer thermometer and plantar test, respectively. The basic temperature of rats was monitored before administrating relevant reagent. During the test, the temperature was measured every 30 minute, and following the withdrawal latency was recorded immediately with the heat stimulation. Six hours after injection relevant reagent, four rats of each group were anaesthetized with chloral hydrate and killed by decapitation immediately. Using aseptic technique to deal with the sample, the POA and L3-L5 of DRG were collected, and the relative expressions of TRPV1 in POA and DRG were analysed by RT-q PCR. SPSS Statistics 17.0 software and Graph Pad Prism5 software were used to analyse datas and chart, respectively. All data were expressed as the mean±SEM. The tendency of changes about temperature and withdrawal latency in each group was performed with repetitivemeasurement analysis of variance(ANOVA) and the differences of the changes of temperature and withdrawal latency among four groups at different time points were analysed with Two-way ANOVA. The results of RT-q PCR were analysed with one-way ANOVA. P<0.05 was considered to be significant differences.Results1. Results of body temperature and thermal withdrawal latency1.1 Changes of body temperature(1) Control group: In the whole experiment process, there was no obvious change in temperature of rats, at between 37?C-38?C.(2) LPS group: After intraperitoneal injection of LPS(20ug/kg) 0.5h, the temperature of rats started to increase notably(P<0.05) and showed biphasic fever, the first peak was at 2h(38.45±0.059?C) and the second at 4.5h(38.71±0.051?C), dropped to approximate basal temperature(37.29±0.11?C) until the end of experiments.Compared with Control group, the temperature of rats was increased obviously(P<0.05).(3) CPZ group: There was no notable change in temperature of rats. Compared with Control group, the change of temperature in CPZ group wasn’t significant.(4) CPZ+LPS group: After intraperitoneal injection of LPS(20ug/kg) 1.5h, the temperature of rats was increased notably(P<0.05), from 37.57±0.11℃ to 39.66±0.1℃,and duration of fever was longer. The higher body temperature(39.5±0.18℃) was kept until the tests over. Compared with Control group, the temperature of rats in CPZ+LPS group prominently increased(P<0.05). Compared with LPS group, the duration of fever became longer and the altitude of fever was higher, without double peak phenomenon in CPZ+LPS group.1.2 Changes of thermal hindpaw withdrawal latency(1) Control group: In the whole experiment process, there was no obvious change in the withdrawal latency.(2) LPS group: Compared with Control group, thermal withdrawal latency became shorter(P<0.05).(3) CPZ group: Compared with Control group, thermal withdrawal latency wasn’t notably changed.(4) CPZ+LPS group: Compared with Control group, thermal withdrawal latency significantly became longer(P<0.05). Compared with LPS group, thermal withdrawal latency was longer(P<0.01).2. The results of RT-q PCR2.1 The relative expression of TRPV1 m RNA in POA(1) Control group: The expression of TRPV1 m RNA in POA was discovered.(2) LPS group: Compared with Control group and CPZ group, the relative expression of TRPV1 m RNA in POA was notably increased(P<0.05).(3) CPZ group: Compared with Control group, the relative expression of TRPV1 m RNA wasn’t notably changed.(4) CPZ+LPS group: Compared with Control group, the relative expression of TRPV1 m RNA was increasing tendency but no statistical significance. Compared with LPS group, the relative expression of TRPV1 m RNA was decreased but difference was no significant.2.2 The relative expression of TRPV1 m RNA in DRG(1) Control group: The expression of TRPV 1m RNA in DRG was discovered.(2) LPS group: Compared with Control group, the relative expression of TRPV1 m RNA was significantly increased(P<0.05).(3) CPZ group: Compared with Control group, there was no significant change.(4) CPZ+LPS group: Compared with Control group and CPZ group, the relative expression of TRPV1 m RNA was also notably increased(P<0.05), and compared with LPS group, the difference wasn’t significant.2.3 Compared with the relative expression of TRPV1 m RNA in POA and in DRG The relative expression of TRPV1 m RNA in DRG in each group was higher than that of TRPV1 in POA in the same group(P<0.05).Conclusion(1) TRPV1 isn’t involved in fever and hyperalgesia in rats under physiological condition.(2) TRPV1 is activated and it plays the role of inhibition in body temperature in LPS-induced fever rats.(3) TRPV1 m RNA expresses in POA, but the relative expression is lower than thatof in DRG.(4) TRPV1 may be involved in fever and hyperalgesia through the central and peripheral nervous system.