Abstract:

Abstract:Objective To observe the cardiosomatic motor reflex (CMR) of rats,and to clarify the descending modulation of  nucleus  raphes magnus (NRM) in  cardiac nociception and its pathway.Methods 34 male healthy SD rats were randomly divided into NRM electrical stimulation group (n=8),NRM stimulation combined with  dorsolateral funiculus (DLF) transection group (n=8),NRM stimulation combined with antagonist of 5-hydroxytryptamine (5-HT) methysergide intrathecal administration group (n=18).The rat model of CMR was established through injecting capsaicin into the pericardial sac of the rats in various groups.The electromyogram (EMG) response of dorsal spinotrapezius muscle was used as detection index,and by placing the stimulation electrode in NRM and (or) intrathecal catheterization,the   descending inhibitory modulation of NRM in CMR and the influence of  DLF tansection or methysergide in
trathecal administration in descending inhibitory modulation of NRM were observed.Results Compared with  before stimulation,the EMG response was decreased after NRM electrical stimulation (75 μA) (P<0.05); after bilateral DLF transection,the EMG response after NRM stimulation was significantly increased compared with before DLF transection(P<0.05),and there was no significant difference compared with its control (P>0.05).In addition,after intrathecal administration of methysergide,the EMG response after NRM stimulation was significantly increased compared with before intrathecal treatment of methysergide (P<0.05),but it was still significantly smaller than that of its  control (P<0.05).Conclusion Cardiac nociception evoked by capsaicin stimulation is subject to descending inhibitorymodulation from NRM,and the descending inhibition from NRM is conveyed via the DLF and partially mediated by endogenous 5-HT system.

Key words: nucleus raphes magnus, cardiac nociception, dorsolateral funiculus, electrical stimulation, electromyogram, 5-hydroxytryptamine