LAUSR

OBJECTIVE Neuroinflammation in the rostral ventrolateral medulla (RVLM) has been reported to be associated with hypertension. The upregulation and activation of the cannabinoid type 2 (CB2) receptor may be part of the active process of limiting or downregulating the inflammatory process. This study was designed to determine the role of the CB2 receptor in blood pressure (BP) through relieving neuroinflammation in the RVLM in spontaneously hypertensive rats (SHRs). METHODS The long-term effects of intracerebroventricular injection of JWH133, a selective CB2 receptor agonist, on BP, heart rate (HR) and renal sympathetic nerve activity (RSNA) in SHR and Wistar-Kyoto (WKY) rats were determined. ELISA was used to measure the levels of proinflammatory cytokines, and western blotting was employed to detect protein expression of the CB2 receptor. Immunofluorescence staining was used to localize the CB2 receptor. Gene silencing of the CB2 receptor was realized by injecting adeno-associated virus (AAV) expressing CB2-specific shRNA (AAV2-r-CB2shRNA) into the RVLM. RESULTS We found that SHRs exhibited higher levels of basal BP, HR, RSNA and proinflammatory cytokines (TNFα, IL-6 and IL-1β) than those in WKY rats. The protein level of the CB2 receptor in the RVLM was robustly increased in SHRs. In addition, the CB2 receptor was mainly expressed on microglia cells of SHRs but not in WKY rats. No expression of the CB2 receptor was found on neurons of either WKY rats or SHRs. Furthermore, intracerebroventricular injection of JWH133 (1 mmol/l, 10 μl) for 28 days decreased the BP, HR, RSNA and proinflammatory cytokines significantly in SHRs, but it had no such effects in WKY rats. These effects were abolished by microinjection of 300 nl AAV2-r-CB2shRNA into the RVLM to knock down the CB2 receptor. CONCLUSION Taken together, our results suggest that exciting the CB2 receptor relieves proinflammatory cytokine levels in the RVLM to decrease the BP, HR and RSNA in SHRs.