ABSTRACT
<p><b>OBJECTIVE</b>To observe descending inhibition of cardiac nociception induced by microinjection of endomorphin-1 (EM1) in the ventrolateral periaqueductal gray (VLPAG) in rats effect and explore the role of μ-opioid receptor in mediating this effect.</p><p><b>METHODS</b>Male SD rats were randomized into electromyography (EMG) group and c-Fos group, both of which were further divided into 5 subgroups, namely 0.9% NaCl group, bradykinin (BK) group, BK+EM1 group, BK+CTOP group, and BK+CTOP+EM1 group. Rat models of cardiac nociception were established by intrapericardial injection of BK. The changes of cardiaosomatic motor reflex induced by BK were observed by assessing EMG responses of the dorsal spinotrapezius muscle; c-Fos expression in the spinal dorsal horn at levels T-T was tested.</p><p><b>RESULTS</b>Compared with 0.9% NaCl, intrapericardial BK injection induced obvious EMG activities and significantly increased c-Fos expression in the spinal dorsal horn at T-T ( < 0.05). Compared with BK injection, microinjection of EM1 in the VLPAG dose-dependently inhibited EMG activities and significantly decreased c-Fos expression ( < 0.05); microinjection of CTOP in the VLPAG produced no significant effect on EMG or c-Fos expression ( > 0.05). Microinjection of CTOP obviously reversed EM1-induced inhibition of EMG activities and c-Fos expression ( < 0.05).</p><p><b>CONCLUSIONS</b>Microinjection of EM1 in the VLPAG produces descending inhibition of cardiac nociception in rats by activating μ-opioid receptor.</p>
ABSTRACT
Objective To study the modulation of central amygdale (CeA)on cardiac nociception with electrical stimulation in rats.Methods The heart pain model of adult male Sprague-Dawley rats was established with intrapericardial injection of capsaicin; then the evoked electromyography (EMG ) responses in the spinotrapezius (SPT)were observed as an index.Immunohistochemical method was used to observe the expression of c-fos in CeA;The rats were divided into normal control group,intrapericardial saline injection control group,and intrapericardial capsaicin injection group. The changes of EMG responses after electrical stimulation on CeA (intensity of 30μA and 70μA)were observed separately by electrophysiology in different groups.Results① Compared with normal control group, intrapericardial capsaicin injection group had significantly increased expression of c-fos in CeA.However,c-fos expression did not differ significantly between intrapericardial saline injection group and normal control group;② After 30μA electrical stimulation on CeA,EMG response in SPT significantly decreased in intrapericardial capsaicin injection group compared with that in control group;the total discharge rate was (78.58±4.62)% of that of control group (P<0.05).After 70μA electrical stimulation on CeA, the total discharge rate was (54.89±3.98)% of that of control group (P<0.05).Conclusion CeA may be involved in cardiac nociceptive transmission in rats and has inhibitory effects on the modulation of rat cardiac nociception.
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 inj ecting 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 intrathecal 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 ). 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 inhibitory modulation from NRM,and the descending inhibition from NRM is conveyed via the DLF and partially mediated by endogenous 5-HT system.