The morphological characteristies and distribution of the choline acetyltransferase (ChAT)-like immunoreactive neuronal elements in the sacral and coccygeal spinal cord of the cat were studied by avidin-biotin combined immunohistochemical technique. The results were as follows:1. The ChAT-positive neuronsIn the ventral horn, ChAT-positive motoneurons were located in the motor columns. These neurons can be divided into three types: the large multipolar neurons, the medium-sized multipolar neurons and the small motoneurons. The color of anti-ChAT reaction product in the large and medium-sized motoneurons varied from light to moderate brown, but the small motoneurons were heavily stained.In the intermediate zone, three groups of ChAT-positive parasympathetic preganglionic neurons were observed in 3 areas: the intermediolateral nucleus (IL) in the lateral part of lamina Ⅶ, the intermediomedial nucleus (IM) dorsal-lateral to the central canal, the intercalated nucleus (IC) looated between IL and IM. The somata of these neurons were round, oval, and fusiform in shape. In the lamina Ⅶ, there were some prominent ChAT medium-sized multipolar neurons named partition cells, scattered among the extended fibers of the parasympathetic preganglionic cells. In the vicinity of the central canal could be observed small CHATpositive cells.In the ventral part of the dorsal commissural nucleus region, a number of ChAT-positive cells were present. They were round, oval and fusiform in shape and small in size (averaging 11.91?m?17.38?m). Occasionally, they were observed in the dorsal part.In addition, some of the ChAT-positive neurons were scattered in laminae Ⅲ-Ⅴ.2. The ChAT-positive fibers and terminals.The ChAT-positive punctate structures were observed throughout the sacral and coccygeal spinal cord resembling terminal branch and terminals. The density of the distribution of the punctate structures was arranged, from high to low, in the following order: the ventral horn, intermediate zone, central gray matter and dorsal commissural nucleus region, and the dorsal horn. In the dorsal horn, many of these punctate structures Were concentrated in two laminae, the major one being lamina Ⅲ and a minor one lamina Ⅰ. But in lamina Ⅱ, they were rare. In the ventral horn such punctate structures were often closely contacted with large and medium-sized ChAT-positive motoneuronal somata and dendrites. Some axonal terminal branch with varicosities closely surrounded a somata and bases of dendrites, and formed contacts with the same somata and its dendrites. In the intermediate zone, there were many transverse fibers associated among the parasympathetic preganglionic nuclei.

HRP solution was injected into the dorsal commissural nucleus (DCN) of segment L_6 or S_1 of the spinal cord and laterodorsal tegmental area(TLD)——take the Barrington's nucleus as its center and lateral parabrachial nucleus (PBL) of the rostral pons in different individuals of the rats. After HRP was injected into the DCN, labelled neurons and dense terminals were found in Barrington's nucleus, and labelled terminals appeared in the PBL. When the unilateral TLD was injected the labelled cells and terminals were found in the DCN and bilateral intermediate zone (IM), and formed a band of labelled neurons and terminals. When the PBL was injected the labelled neurons were observed in the DCN and bilateral IM. A few labelled neurons were found in lamina Ⅰ in the latter two experimental groups.Based on the present and previous studies, the authors got the following understandings:1. Morphylogically, the present study for the first time demonstrated that, the micturition reflex arch through the pontine consists of following parts: the primary afferent neurons of the bladder→secondary relay neurons of DCN→Barrington's nucleus→IM (mainly IML) parasympathetic preganglionic neurons→parasympathetic postganglionic neurons.2. According to the present and previous researches, the authors conjecture that, the secondary fibers of visceral sensation of the pelvic organs originate from the neurons of DCN, IM and lamina I and project into the PBL.3. According to the facts mentioned above, we presume that the DCN and bilateral IM constitute a complex and named it the 'visceral field', and which is closely associated with the pelvic organs. This field has widespread connections with the peripheral efferent and afferent nerves. On the other hand, i t contains a lot of relay neurons projecting into Barrington's nucleus and PBL and receives the terminals of descending fibers of the neurons of the Barrington's nucleus. The descending fibers also project into the Onuf's nucleus.In addition, the present study disscussed the complicated functions of the DCN systematically.

2?l 10% ricin were injected into the pelvic nerve of cats. After 3～5 survival days 20% HRP solution was injected into the ipsilateral lateral parabrachial nucleus, 2～3 days later the animals were perfused with paraformaldehyde and glutaraldehyde, the brain and spinal cord were removed and processed for light and electron microscopy. It was confirmed that the primary afferent terminals (degenerated) of pelvic nerve formed axo-dendritic and axo-somatic synapses with the retrograde labelled neurons projected to the lateral parabrachial nucleus which were located in the dorsal commissure nucleus (DCN), intermediolateral nucleus (IML) and lamina Ⅰ of sacral spinal cord. Hence, the secondary afferent pathway of pelvic visceral sensation, as. indicated at the ultrastructural level, might originate from DCN, IML and lamina Ⅰ of sacral spinal cord and project to the lateral parabrachial nucleus.

The Nissl and Golgi staining methods and electron microscopy were u(?)o investigate the architecture of dorsal commissure nucleus (DCN) of the sacral spinal cord in cat. A morphologically specific nucleus could be identified in the medial part of the lamina Ⅵ of dorsal horn. The nucleus located beside the dorsal funiculus at the lumbar level and gradually moved toward the midline of the dorsal gray commissure in the ventromedial direction as the dorsal gray commissure enlarged at the segments S_(1-2) and two ellipsoid nuclei was formed at the two sides of the midline. A large triangular nucleus was gradually formed by fusion of the two nuclei at S_3-Co_1. Golgi stain positive neurons could be classified into three types: (1) small-triangular neurons (60%); (2) fusiform neurons (30%); (3) oval and irregular neurons (10%). The cell organells of most neurons were plentiful. The cell nucleus was irregular and often with deep invaginations. A large number of free ribosomes and saccules could be found in the canals formed by the nuclear invagination. There were axo-dentritic, axo-axonic, axo-somatic synaptic contacts in the DCN with percentages of 89%, 6%, and 5% respectively. The serial synapse, axo-spinous synapse and crest synapses could also be found.

The technique of double labelling with fluorescent tracers(FB-NY,PI-Bb)has.been used in the following three groups of experiments:1.in 5 rats,one fluorescenttracer was injected into the tibial nerve and the other was injected into the peronealnerve;2.in 14 rats,one fluorescent tracer was injected into the sural cutaneousnerve and the other was injected into the branches to the soleus and gastrocnemiusmuscles;3.in 13 rats,one tracer was injected into the tibial nerve and the otherinto the bladder wall.The sections of the L_(3-6),S_(1-3) dorsal root ganglion were stu-died with a olympus fluorescence microscope using UG-1 excitation filter system.In the first and second groups,double labelled neurons were observed in L_(4-6) dorsalroot ganglion.But in the third group,the double labelled neurons were found onlyin the L_6 segment.The type of the double labelled neurons was mainly small-sized(33.1%)and small-medium sized(40.9%).The findings indicated that,the primary afferent fibers branched towards theperiphery and supplied,with different branches,either two somatic areas or skinand deep structures,or,especially,visceral and somatic sensory fields.This resultsuggests that the peripheral dichotomization of these dorsal root ganglion cells mightconverge sensory inputs from the somatic(tibial nerve)and the visceral(bladderwall)fields and thus provides one of the structural basis for the referred pain andthe neuronal mechanism of acupunctural therapy by which stimulation of somaticstructures could regulate the activities of visceral organs.

1. The subnucleus caudalis of the spinal trigeminal nucleus of cat was injected with 30% HRP (Sigma, type Ⅵ). Well localized groups of labeled neurons were observed in the dorsolateral horn of the contralateral red nucleus. This dorsolateral horn, being present in the rostral and middle thirds of the nucleus, consisted mainly of middle-sized and small neurons.2. Injections were also made into the second and third segments of the cervical spinal cord and the caudal part of the bulbar reticular formation. The labeled neurons appearing in these experiments were diffusely distributed in the red nucleus, yet limited in the rostral third of it.3. Summarizing our findings and the data from the literature, we got the impression that the rostral two thirds of the red nucleus gave projections to the central structures rostral to the upper cervical spinal cord, and the caudal two thirds of it to those caudal to the lower cervical cord, which indicating a somatotopic organization of the red nucleus neurons giving descending projection fibers.

10% and 20% HRP aqueous solution was injected into the anterior wall of the stomach of rabbit, and both the afferent and efferent nerve connections of this region were examined.1. Large number of labeled cells appeared in the dorsal motor nucleus of the vagus nerve (dmnX) on both sides throughout its whole length, except the very rostral and caudal ends of it. The labeled cells were more numerous in the middle part of the nucleus at levels above and below the obex. The distribution of the labeled cells showed certain localization characteristics. Those in the caudal part of the nucleus occupied the medial portion, those in the levels around the obex distributed widely in the nucleus, while in the rostral part they were smaller in number and showed no definite localization.2. In the area between the dorsomedial border of the dmnX and the area pos- trema, the so-called area subpostrema, some disseminated labeled cells, the form of which was similar to that the labeled cells in the dmnX, were also observed.3. Numerous labeled cells appeared in the nodose ganglia on both sides, the number of which was several times more than that in the spinal ganglia, indicating that the afferent connection of the stomach via the vagus nerve predominated over that via the sympathetic nerve. The small-sized labeled cells in the ganglion, however, appeared up to more than 40% of all the labeled cells in it, the functional significance of them, as well as the relation between them and the labeled small cells in the spinal ganglia, is worth further investigation.4. The labeled neurons appeared in the spinal ganglia from Th_3 to L_3, most of them were in Th_3 to Th_(10), showing that the afferents of the stomach via the sympathetic system were diffusely arranged and at the same time concentrated in certain segments.5. Our observations confirmed that the stomach is innervated by elements of bilateral origin. In the vagus system the afferent and efferent neurons appeared almost equally in both dmnX and both nodose ganglia. And in the sympathetic system, the afferent neurons on the left side were 1 to 2 times more than those on the right, i. e., the left side is predominant.

Vmes,

In the present study, the fluoro-gold(FG) and horseradish peroxidase(HRP) combined tracing method was used to investigate the localization of parasympathetic preganglionic neurons and ascending projection neurons in lumbosacral spinal cord of the rat. FG was injected into the lateral parabrachial nucleus(PBL) or into Barrington's nucleus on one side, and HRP was applied to the contralateral pelvic nerve. The retrogradely FG-labeled neurons were found in bilateral "visceral field" at segments L_5-S_2, and the majority of them were concentrated in the intermediolateral nucleus (IML), and the dorsal commissural nucleus (DCN). In addition to these areas, some labeled neurons were also observed in bilateral lamina I and lateral spinal nucleus (LSN). The parasympathetic preganglionic neurons labeled with HRP were seen in the IML at segments L_6-S_1, occasionally appeared in the intercalated nucleus. In the IML area, HRP-labeled parasympathetic preganglionic neurons were located in its ventral part, however, the localization of FG-labeled neurons projected to the PBL and Barrington's nucleus were mainly found in the dorsal and dorsomedial part of the IML, and a few FG-labeled cells were scattered among HRP-labeled cells. Based on the present and other investigations, the nomenclature, organization and function of the IML and the composition of the LSN were discussed.