[Study on a role of substance P in the spinal mechanisms of electroacupuncture analgesia].

It was found in the present study that low frequency (2Hz) electroacupuncture (EA) stimulation caused a decrease of the content of substance P immunoreactivity (SP-ir), whereas medium-(15Hz), high-(100Hz) and dense-disperse (D-D)- (2/15Hz) frequencies EA stimulation induced an increase of the content of SP-ir in the rat spinal fluid. EA analgesia induced by medium-, high- or D-D mode frequency was suppressed by nonpeptide SP (NK1) receptor antagonists CP96345 or RP67580 administered intrathecally (i.t.). Both the attenuation of SP release by low frequency EA and the potentiation of SP release by medium frequency EA in the spinal cord were blocked by the opioid receptor antagonist naloxone (i.t.). These results suggest that a decrease of release of SP-ir by low frequency and an increase of it by medium-, high- and D-D mode frequencies in the spinal cord facilitate analgesia.