The origin and termination of the reticulospinal tract were studied with HRP technique in ten cats by injecting HRP into the spinai dorsal horn or gray matter on one side of the cervical or lumbar enlargement, It was discovered that the reticulospinal neurons were located not only in the medial part of the medullopontal tegmentum, but also in its lateral part. There were also a few scattered labeled neurons in the reticular formation of midbrain. The reticulospinal tract ended in the spinal dorsal horn as well as in the ventral horn. The reticulospinal tract mainly originated from the ventromedial part of the medulla and pons. In this region the labeled cells were most numerous in the nucleus gigantocellularis, less in the nucleus medulla oblongatae centralis subnucleus ventralis and the nucleus pontis centralis caudalis, and much less in the nucleus pontis centralis oralis, the nucleus paragigantocellularis laterlris and the paramedium reticularis subnucleus ventralis. Occasionally a few scattered abeled cells could be seen in the nucleus cuneiformis. The reticulospinal fibers from these nuclei projected bilaterally to both cervical and lumbar enlargments of the spinal cord except that the nucleus cuneiformis projected bilaterally to the cervical enlargement only.Two groups of labeled cells were found in the ventrolateral part of the medullary and pontal reticular formation, corresponding to the position of group A 1 and A 7 of noradrenergic neurons respectively.The reticulospinal tract derived from the medial part of the brain stem terminated predominately in the gray matter ventral to the spinal dorsal horn, but a few of them ended in the dorsal horn. These connections provide direct pathways for the control of motor and sensory functions of the spinal cord by medial reticular formation.It has been proved by Brodal with chromatolysis techenique that every cell in the nucleus paramedium reticularis sends its efferent fiber to the spinal area of cerebellum, but in this study labeled cells were found in e nucleus paramedium reticularis subnucleus ventralis. We suppose that the axons of these labeled neurons may be divided into two branches, one projecting to the cerebellum and the other to the spinal cord.It is noteworthy that we also found some labeled neurons in the nucleus medullae oblongatae centralis subnucleus dorsalis and nucleus parvocellularis, the so called "receptive region" of the reticular formation. The fibers originating from this region terminated in the spinal dorsal horn mainly, suggesting that this tract probably influences the sensory function of the spinal cord. It seems that the conception of the lateral reticular formation of the brain stem as a pure "receptive area" of the reticular formation may have be modified.

The projection from Edinger-Westphal (E—W) nucleus to the spinal cord was studied in fifteen rabbits by injecting HRP or WGA—HRP into the cervical, thoracic and lumbar segments of the spinal cord. The normal cytoarchitecture of E—W nucleus was also studied with normal Nissl stained sections.The E—W nucleus of the rabbit is a midline unpaired structure except for the most rostral part which is paired. The shape of the whole nucleus looks like a band with its long axis lying rostrocaudally. It is mainly consisted of medium and small fusiform neurons with their long axis lying dorsoventrally. Neurons of the rostral part of the E—W nucleus, which is called the anterior median nucleus in this paper, are longer and darker than those of the caudal part of the E—W nucleus, or the proper E—W nucleus.Many labelled cells were found in AM and E—W nuclei in all the injected cases. The neurons, projecting to the cervical, thoracic and lumbar segments, were distributed diffusely in E—W nucleus without evident somatotopic organization. In the lumbar injected cases, there were a few labelled cells in the rostral end of AM nucleus where the nucleus was divided into two parts bilaterally.

The dorsal accessory olivary nucleus was studied with electron microscope in seven rabbits.The axo-axonal synapses,an axon being in contact synaptically with a spine of a perikaryon,the glomerulus with an axonal core and a bundle of microfibers within a nucleus of a neuron,as well as the already discovered axo- dendritic synapses,axo-somatic synapses and glomeruli with dendritic cores,were observed in this nucleus. The axo-dendritic synapses were often seen,the postsynaptic components of them were dendrites or spines.The axo-somatic synapses were fewer.An axonal terminal was seen synapsing to both a spine of a perikaryon and a dendrite.Both the presynaptic and postsynaptic components of the axo-axonal synapses contained spherical vesicles.Sometimes the axo-axo-dendritic synapses were observed.There were two kinds of glomeruli in this nucleus,one with dendritic core and the other axonal core.Two axons were discovered simultaneously synapsing with an axon. The complex synaptic pattern in the dorsal accessory olivary nucleus indicated that the afferent impulses would undergo diffusing,converging,presynaptic inhibition or integrating in this nucleus.

A glucose oxidase-3,3′ diaminobenzidine-nickel method was developed.Thistechnique can successfully demonstrate the details of the immunoreactive structuresand PHA-L labeled cell bodies and their processes.It is especially beneficial forvisualizing fibers and terminals.It is more sensitive than the regular 3,3′ diamino-benzidine method and the glucose oxidase-3,3′ diaminobenzidine technique,andvery stabilized.

The projection from the vestibular nuclei to the dorsal horn of the spinal cord in the cat was studied with the horseradish peroxidase method. It has been discovered that the vestibulospinal tracts originate not only from the lateral, medial, and spinal vestibular nuclei but also from the superior vestibular nucleus. The site of termination of the vestibulospinal tracts is in the lateral region of the dorsal horn of the spinal cord as well as in the laminae Ⅶ and Ⅷ of Rexed.

Lesions in the rignt (?) colliculus were made in 8 albino rats and the efferent projections were studied by Nauta's technique with the following results:Ipsilateral projections: The overwhelming majority of the degenerating fibers runs by way of the inferior quadrigeminal brachium, a small part of which terminating in the reticular nucleus of the lateral tegmentum of the midbrain and the major part of which terminating in the magnocellular and the parvicellular divisions of the medial geniculate body. A smaller nunber of the degenerating fibers terminate via the tecto-pontine tract in the lateral pontine nucleus. A few degenerating fibers terminate in the central gray of the midbrain and the deep stratum of the superior colliculus.Contralateral projections; With the exception of some feed-back fibers all contralateral projections pass through the commissure of the inferior colliculus. The majority of the degenerating fibers terminate in the dorsal region of the contralateral inferior colliculus. A minor part of the degenerating fibers run by way of the inferior quadrigeminal brachium to terminate in the reticular nucleus of the lateral tegmentum of the midbrain.Feed-back fibers: The feed back fibers are derived from the inferior colliculus and descend in the lateral lemniscus. As they reach the level of the superior olivary complex they divid into two parts: One part passes through the pyramidal tract of both side and terminates in the contralateral trapezoid ventral nucleus, dorsal cochlear nucleus and ventral cochlear nucleus. The other part terminates in the same nuclei ipsilaterally.Based on the observations mentioned above, the impression were obtained that the efferent fibers of the inferior colliculus mostly terminate in the ipsilateral medial geniculate body and the contralateral inferior collicuhs, through the latter impulses may reach the controlateral medial geniculate body indirectly. The inferior colliculus in the albino rat is considered as Woollard et al ('40) put in cat and guinea-pig, "The midbrain auditory nudei subserve very few reflex activities, being almost wholly sensory centres."

It is well known anatomically and physiologically that the raphe nuclei project to the spinal cord. No definite data on somatotopic raphe-spinal relationship, however, are available. The raphe nuclei, especially the nucleus raphe magnus, were found to inhibit nociceptive transmission and pain reflexes in the spinal cord, and they presumably play an important role in acupuncture analgesia. Thus, the question on whether there is a somatotopic raphe-spinal projection has much to do with the analysis of the function of the raphe nuclei and the evaluation of their possible role in acupuncture analgesia. 11 cats were used in the present study. Horseradish peroxidase (HRP) was injected into the dorsal horn of the 7th cervical or 4,5th lumbar spinal cord and labelled cells were traced in the raphe nuclei. In the cases of cervical cord injection, labelled cells were found in the nucleus raphe magnus, nucleus raphe pallidus and nucleus raphe obscurus. In the lumbar injections only the nucleus raphe. magnus and nucleus raphe pallidus were labelled. The labellcd cells were distributed over relatively wide areas in the raphe nuclei after HRP injection into single spinal segments. Nevertheless, a certain degree of somatotopic relationship existed. In the nucleus raphe magnus cells projecting to G7 were distributed more rostrally and those projecting to L4,5, more caudally. In the nucleus raphe pallidus, on the contrary, cells to C7 were located more caudally while those to L4,5 more rostrally. A definite, though diffuse to a certain degree, somatotopie raphe-spinal projection is consistent with the extent of analgesia during acupuncture or electrical stimulation of the nucleus raphe magnus, thus favours the hypothsis of the role of descending inhibition from the raphe nuclei in acupuncture analgesia, and provides a possible explanation for the relative specificity of acupuncture points in their fields of analgesia.

A case of HRP injection into laminae Ⅰ-Ⅲ of the cervical spinal cord of the cat was reported. The labeled cells were found mainly in the dorsal column nuclei, nucleus raphe magnus, reticular nuclei, vestibular nuclei and nucleus of tractus solitarius.

The localization of the neurons which control the inferior oblique muscle in the oculomotor nucleus and their dendritic architecture were studied by injecting the conjugated cholera toxin-horseradish peroxidase (CT-HRP) into the inferior oblique muscle of 7 rabbits.The oculomotor nucleus could be divided into oral, middle and caudal parts. The middle part was further divided into dorsomedial and ventrolateral parts, and the caudal part divided into dorsal and ventral parts. The labeled neurons innervating the inferior oblique muscle were mainly distributed ipsilaterally and occupying two thirds. of the rostrocaudal extent of the oculomotor nucleus, a few were scattered contralaterally.The labeled cells were found in the dorsomedial part of the nucleus orally, and shifted in successive caudal sections to the medial and then to the ventral part. No labeled cells in the oral and caudal ends of the nucleus could be identified.The dendritic branches of the labeled neurons covered the whole nucleus, but densest in its dorsomedial part. Many of them extended beyond the boundary of the nucleus into the central gray matter dorsally, some even approacheding the aqueduct, or through the medial longitudinal fasciculus into the reticular formation laterally and ventrally. A few dendrites crossed the midline into the contralateral nucleus. Therefore the receptive field of the oculomotor nucleus is presumably much larger than the area of the nucleus itself.

Horseradish peroxidase (HRP) was injected into the lumbar enlargement of the spinal cord of the rabbit. A lot of anterograde labeled terminals were observed in the contralateral dorsal accessory olivary nucleus. The synapses contacting these labeled terminals were studied with electron microscope. Most of the labeled terminals contained spherical clear vesicals, only a few of them contained flat or pleomorphic cIear vesicles. The labeled terminals were mainly in contact with dendrites, a few contacting with the perikarya. One of the labeled terminals containsd both round and flat clear vesicoles, presynapticto a dendrite and a perikaryonrespectively. It was notabte that a few of the labeled terminals were included in axon-axonal synapses and glumeruli. The functional meaning of these special structures was discussed tentatively.