Animal experiments have revealed that stimulation of the caudate nucleus is able to enhance acupuncture analgesia(AA)

while lesion of it attenuate AA.Electroacupancture modulates the activity of the caudate neurons sensitive to acetylcholine

serotonin

dopamine or etorphine. Evidences accumulated indicate that intracaudate opioid peptidergic

choli- nergic and serotoninergic systems facilitate AA

and dopaminergic system antagonizes it. The caudale is functionally related to brain areas related to algesia and analgesia.Caudate stimulation has been demonstrated to depress the nociceptive neuronal response recorded from the parafafasicular nucleus and the posterior nuclear group of the thalamus.These two areas

especially the parafascicular nucleus are important in the interration of pain sensation.Caudate stimulaion also depresses the nociceptive response of the cingulate gyrus and the habenular nucleus of the limibic system which playsa strategic part in the integration of pain response.It has been demonstrated that there exists a functional connection between the caudate and the periaqueductal gray-nucleus raphe magnus system

which exerts a descending pain modulating function.Caudate stimulation produced analgesia is brought about at least partly by the opioid peptidergic sysytem of the periaqueductal gray.Caudate stimulation activates neurons in the nuclens raphe magnus

and the activation is believed to be related to the peria- queductal gray. It is postulated that afferent impulses arising from the needling points

reaching the Caudate

elicites an interaction among different trans- mitter systems resulting in the inhibition of brain areas involved in the integration of pain sensation and pain response and in the activation of brain areas involved in pain modulation

thus bringing forth analgesia.