Electroacupuncture (EA) on Zusanli (st. 36) and Shangjuxu (st. 38)
(10 Hz, 1.0 ms) was found to produce a long-lasting inhibition of wide
dynamic range neurones in the dorsal horn of the spinal cord and to
prolong the latency of the tail-flick reflex in the lightly
anaesthetized rat. This inhibition was effectively produced at a
stimulation intensity which excited only A13 fibres. The effects of EA
were eliminated by cold-blocking the spinal cord rostral to the
recording site suggesting a supraspinal involvement in the EA-induced
inhibition of spinal cord nociceptive transmission. EA also facilitated
the discharge of non-clock-like dorsal raphe neurones (NCL). Bilateral
lesions of the ventrolateral tract (VLT), but not the dorsolateral
funiculi (DLF), blocked this effect suggesting that the ascending arm of
the loop is via the VLT. The descending arm is located in the DLF since
bilateral lesions of the DLF blocked the effects of EA in the spinal
cord.
Evidence in the literature suggests that the dorsal raphe nucleus
(DRN) may be involved in the above supraspinal loop as well as in an
ascending inhibitory pathway to the nucleus parafascicularis (NPF).
Examination of the DRN revealed three types of neurones: clock-like
(CL), NCL and non-clock-like non-responding neurones (NCLN). The NCL
neurones were excited by noxious and non-noxious natural peripheral
stimuli as well as EA. The other neurones were non-responsive to these
stimuli. NCL neurones of the DRN were also antidromically activated by
11 NPF stimulation indicating that the projection from the DRN to the NPF
is direct. Stimulation of the DRN produced an inhibition of NPF
neurones with sudden onset and offset and a duration correlated with the
length of stimulation. EA also produced long-lasting inhibition of
these cells. The inhibitory pathway from the DRN to the NPF, which is
activated by EA and presumably mediated by NCL neurones, would appear to
be serotonergic. The evidence for this is that the inhibition evoked by
DRN stimulation or EA is enhanced by alaproclate, a 5-FIT uptake blocker,
and blocked by 5,7-DHT, a 5-HT neurotoxic agent, or cyproheptadine, a
serotonin antagonist.Medicine, Faculty ofGraduat
