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.

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.

It was discovered that there were a group of gigantic neurons scattering in the tegmentum dorsolateral to the oral half of the red nucleus in the midbrain of the rabbit. The form and size of these neurons were similar to the gigantic cells in the gigantocellular reticular nucleus of the medulla oblongata. After injecting HRP or WGA-HRP in the cervical, thoracic or lumbar spinal segment of the rabbit, more than a half of these gigantic cells were labeled. The labeled cells were most crowded at the oral end level of the red nucleus. There were also labeled terminals near the labeld cells in the reticular formation of the midbrain. It is evidently that there are reciprocal connections between the spinal cord and the reticular formation of the midbrain in the rabbit.

Using immunohistochemical method, the distribution of eight kinds of peptidergic neurons, i. e. cholecystokinin(CCK),vasoactive intestinal polypeptide (VIP), substance P(SP), neurotensin (NT), galanin (GAL), calcitonin gene-related peptide (CGRP), corticotropin-releasing factor(CRF) and thyrotropin-releasing hormone(TRH), of the thalamus in the rat was investigated. Immunoreactive cell bodies and fiber terminals were mainly located in the midline nuclei, intralaminar nuclei, habenular nucleus and posterior nuclei of the thalamus, but a few of positive structures in the anterior nuclei, ventral nuclei and reticular nucleus were also found. The distribution of different peptidergic neurons in the thalamus was different from each other. A large quantity of SP-, NT- and GAL- like cell bodies and all of above-mentioned eight peptidergic fiber terminals were observed in the midline nuclei and intralaminar nuclei. More CCK and CGRP positive cell bodies were seen in the posterior nuclei. Some VIP, SP, NT, GAL and CRF positive cell bodies and all kinds of the positive terminals, except CGRP, were found in the habenular nucleus. The immunoreactive structures which were found in present study, particularly the distribution of positive terminals, were more widely than those were reported. The distribution of some CCK, VIP, NT, GAL, CGRP and TRH positive cell bodies and terminals in the thalamus have not been reported previously.

Aging changes of neurotensin-like (NT-L) and galanin-like (GAL-L) cell bodies and fiber terminals in the central amygdaloid nucleus between the young and old rats were studied by means of immunohistochemical and microspectrophotometric techniques. NT-L cell bodies were mainly located in the central part (CeLn) of, centrolateral amygdaloid nucleus, a few of NT-L neurons were also found in the centrolateral amygdaloid nucleus, capsular part (CeLc) and centromedial amygdaloid nucleus (CeM). NT-L fiber terminals were seen mainly in the CeLn and CeLc. GAL-L cell bodies were observed only in the CeM. A marked decrease of density of NT-L cell bodies and fiber terminals in the central amygdaloid nucleus was found in the old rats as compared with young animals. No significant age difference in number of GAL-L cell bodies was observed in the central amygdaloid nucleus, but the staining intensity of GAL-L cell bodies was reduced remarkably. The results show that there are apparent changes with aging of the NT-L and GAL-L neurons in the central amygdaloid nucleus of the rat. The significance of the changes remains to be studied further.

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."