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
Manual acupuncture to ST 36 Zusanli induces both long-lasting and short-term inhibitory effects on C-evoked discharges of wide dynamic range (WDR) neurons in the lumbar cord. The possible involvement of the central nervous system in producing these two types of inhibitions was investigated in urethane-anesthetized rats. In one expriment, the existence of a descending pain inhibitory system was studied using spinal conduction blocks at the cervical level. In a separate experiment, naloxone was administered systemically to investigate the participation of endogenous opioids.<br>Long-lasting inhibition was found to be due to a descending pain inhibitory system from the upper central nervous system together with the involvement of an opioidergic link. On the other hand, short-term inhibition was attributed to a propriospinal pain inhibitory system and endogenous opioids were not implicated.