Adult healthy cats

rabbits and mice were used as experimental animals in this study. The effect of the trigeminal system in facial acupuncture analgesia and its morphological basis were studied. It has been worked out on the following aspects: 1. Subcutaneous ionotophoretic potassium was used for inducing pain. The motor reaction of the fore leg of the rabbit was considered to be an index for pain reaction. Following the section of the trigeminal infra- orbital branch

or after the destruction of the trigeminal spinal caudal nu- cleus

it was shown that the analgesia response was obviously decreased or disappeared in facial acupuncture (i.g."SiBai" and "Jiache").It was suggested that the facial acupuncture impulse was transmitted into the trigeminal spinal caudal nucleus by the trigeminal nerve. 2. Following a complete or partial section of the trigeminal roots

stereotactic coagulation of its spinal caudal nucleus of the rabbit

or fo- llowing a lesion of the trigeminal ganglion of the cat

the trigeminal primary afferent fibers and the fiber projections of the trigeminal spinal caudal nucleus were traced by means of Nauta and Fink-Heimer techniques. The results were as follows. The trigemlnal primary afferent fibers projected into the trigeminal sensory nuclei

posterior horn of cervical spinal cord

the reticular forma- tion of the brain stem

solitary nucleus

nucleus raphe magnus

cuneatus nucleus

vestibular nucleus

etc. The trigeminal spinal caudal nucleus gave rising fibers to the thala- mic ventral posteromedial nucleus

intralaminar nucleus (parafasciculo-cen- tromedian nuclear complex)

medial geniculate nucleus

the reticular for- mation of the brain stem

some nuclei of the cranial nerves(such as so- litary nucleus

dorsal motor nucleus of the vagus

facial nucleus)

the other nuclei unrelated with the cranial nerve(nucleus raphe magnus

cunea- tus and lateral cuneatus nucleus)and the upper cervical spinal segment In addition

after complete transection or partial transection of the spin- al cord ad cervical

thoracic and lumbar levels in young rabbits the secti- ons of the brain stem were stained with the retrograde degeneration meth- od. It was found that the reticulospinal tract took origin from the ventral medullary reticular nucleus

gigantocellular reticular nucleus and nucleus raphe magnus. The trigeminal primary fibers and the trigeminal spinal caudal nucle- us connected with the central nuclei into which the impulses conveying from the somatic and visceral origin were converged. It is preliminarily assumed that the convergence of impulses coming from the facial acupuncture and other sources mentioned above is the neu- rological basis for their interaction. The significant function of the fiber projection connexions of the tri- geminal nerve and of its caudal nucleus is discussed in facial acupuncture analgesia. 3. In the serial sections of the rabbit brain stem stained with thionin and silver impregnation the trigeminal caudal nucleus consists of the ro- stral and caudal part. The latter is divided into the subnucleus marginalis

subnuleus gelatinosus and snbnucleus magnocellularis corresponding to lamina Ⅰ

Ⅱ-Ⅲ and Ⅳ of Rexed

respectively. 4. A piece of tissue of the trigeminal spinal caudal nucleus in the rabbit or mouse was removed under binocular. The thin sections were pre- pared in routine as usual and stained with uranyl acetate and lead citrate. The ultrastrucuures of the synapses in the nucleus were examined. It was found that several types of synapses were present within the nucleus

including axo-dendritic

axo-somatic axo-axonic and dendro-dendritic syna- pses. The translucent vesicles were mostly found in the presynaptic bou- ton

but granular in a few number. It is probable that axo-axonic syapses are the morphological basis for presynaptic inhibition.