延脑中缝大核(NRM)是中枢内源性下行痛抑制系统的重要核团之一

有工作表明

富含吗啡受体和内源性吗啡样物质(OLS)的中脑导水管周围灰质(PAG)是吗啡镇痛和脑刺激镇痛的高效区。在PAG注入吗啡或是进行电刺激

均能下行性抑制脊髓背角神经元的伤害性反应。若损毁NRM

则可阻断这种抑制作用。说明PAG对于痛觉的下行抑制有赖于NRM机能的完整性

PAG-NRM-脊髓背角神The influence of iontophoretic naloxone upon acupuncture effect was observed to explore the central locus of action of the endogenous morphine- -like substance (MLS) released by acupuncture. Extracellular recordings were obtained from 309 neurons located in the NRM with multiplepipettes on urethane anaesthetized male adult rats. Most units were spontaneously active and the majority of them (53 out of 74ne- urons

72%) could be further activated by acupuncture. In most neurons (43 out of 47 neurons

91.5%) two kinds of nociceptive neuronal responses to peripheral noxious stimulation

excitatory and inhiditory manifesting thems- elves by increasing and decreasing the firing rate were attenuated by acu- punctre. The activation of firing (up to 190% of preacupuncture control value; n=10) persisted for more than 15 minutes and gradually recoveed. When naloxone was administered iontophoretically before (for 2 minutes) and du- ring (for 5 minutes) acupuncture

the activation was blocked

the firing rate being slightly decreased (up to 80% of the control

д=10) rather than increased. In addition

the nociceptive response was significantly reduced (up to 54% of control

n=17

P<0.01) and did not recover within 30 minutes aftes cessation of acupuncture. However

in the other group of neurons(n=27)

the nociceptive response was similarly reduced within ten minutes after ac- upuncture

but it was soon recovered to 95% of control following ejection of naloxone for two minutes(11th--13th minutes after acupuncture) indic- ating that the acupuncture inhibitory effect could be reversed. The above findings suggest that the MLS may be involved in acupunc- ture effect and it plays a role in acupuncure analgesia at least in partby activating the NRM neurons directly.