Abstract
Substance P (SP), released from thin afferent terminals, is believed to be a neurotransmitter for pain transmission in the spinal dorsal horn. It has been demonstrated that,in addition to analgesia, morphine increases the accumulation of SP possibly due to the inhibition of its release. The present work investigated the level of spinal SP like immunoreactivity (SPLI) following electroacupuncture analgesia in rats using immunohistochemistry and image analysis. Experiment results revealed that formalin injected into the hind paw elicited marked pain response and accumulation of SP in the spinal dorsal horn. Electroacupuncture of Tsu-San-Li could depress the pain response, however increasing further the SP accumulation. It is thus suggested that pain stimulaton itself may activate the endogenous opioid mechanism to inhibit SP release and acupuncture is able to enhance the process. This may be one mechanism of acupuncture analgesia.
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