Synaptic organization of GABAergic inputs from the striatum and the globus pallidus onto neurons in the substantia nigra and retrorubral field which project to the medullary reticular formation.

Anatomical tract-tracing and immunohistochemical techniques involving correlated light and electron microscopy were used to determine whether the descending striatal and pallidal afferents to the substantia nigra pars reticulata converge onto individual neurons projecting to the pontomedullary and medullary reticular formation in the rat. Injections of biocytin into the ventrolateral region of the striatum and Phaseolus vulgaris-leucoagglutinin into the ventrolateral and caudal regions of the globus pallidus led to overlapping anterogradely labelled terminal fields within the dorsolateral substantia nigra pars reticulata. These terminal fields were punctuated by neurons which had been retrogradely labelled following injections of wheatgerm agglutinin conjugated to horseradish peroxidase into the lateral pontomedullary reticular formation. The anterogradely labelled striatal and pallidal terminals displayed different morphological characteristics; the striatal terminals were small and diffusely distributed throughout the neuropil without any particular neuronal association whereas the pallidal terminals were large and formed pericellular baskets around the perikarya of retrogradely and non-retrogradely labelled nigral neurons. In areas of the substantia nigra where there was an overlap between the two terminal fields, individual retrogradely labelled nigroreticular neurons were found to be apposed by both sets of anterogradely labelled terminals. Electron microscopic analysis revealed that the striatonigral and pallidonigral terminals displayed different ultrastructural features, the striatal terminals were small, contained few mitochondria and formed symmetric synaptic contacts predominantly with the distal dendrites of nigroreticular neurons whereas the pallidal terminals were large, contained numerous mitochondria and formed symmetric synaptic contacts preferentially with perikarya and proximal dendrites of nigroreticular neurons. Post-embedding immunohistochemical staining revealed that both striatonigral and pallidonigral terminals, some which formed synaptic contact with nigroreticular neurons, displayed GABA immunoreactivity. Examination of twelve retrogradely labelled neurons in the electron microscope revealed that all received synaptic inputs from both sets of anterogradely labelled terminals. In addition to the substantia nigra pars reticulata, neurons of the retrorubral field were also retrogradely labelled following injections of wheatgerm agglutinin conjugated to horseradish peroxidase into pontomedullary reticular formation. These retrorubroreticular neurons were part of a continuum of labelled cells which extended from the dorsolateral substantia nigra pars reticulata caudally into the retrorubral field. When combined with anterograde tracing methods it was found that the retrorubroreticular neurons received synaptic inputs from pallidal terminals which were morphologically similar to the pallidonigral terminals and formed symmetric synapses with the neuronal somata and proximal dendrites. In contrast to nigroreticular neurons, the stratonigral terminals were not seen in contact with retrorubroreticular cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Non-motoneurons in the facial and motor trigeminal nuclei projecting to the cerebellar flocculus in the cat

Summary The cerebellar projection from the facial and motor trigeminal nuclei was studied in the cat by means of retrograde axonal transport of wheat germ agglutinin-horseradish peroxidase and fluorescent tracers. The feline facial nucleus was cytoarchitectonically subdivided into ventromedial, ventrolateral, lateral, dorsal, intermediate and medial divisions (see Papez 1927), and the motor trigeminal nucleus into medial, ventral, intermediate, lateral and dorsal divisions. The neurons in the facial and motor trigeminal nuclei were classified as small (ovoid to round cells with a maximum diameter of the cell body of about 20 m) or large (polygonal to round cells with maximum diameter of about 40 m). After floccular injections of the wheat germ agglutininhorseradish peroxidase complex, retrogradely labelled cells were found throughout the facial nucleus, but especially in its medial and dorsal divisions. In the motor trigeminal nucleus, labelled neurons were found only in the ventral, intermediate and lateral divisions. Cases with tracer deposition (implants or injections) in other parts of the cerebellar cortex or nuclei were all negative. All facial and motor trigeminal neurons labelled after floccular injections were smaller than the neurons labelled after injections in the facial mimic and masticatory muscles, and only single-labelled neurons were found following floccular injections of Fluoro-Gold and muscular injections of rhodamine-B-isothiocyanate in the same animals. These observations strongly suggest that the neurons in the facial and motor trigeminal nuclei which project to flocculus are of the non-motoneuron type.     

A light and electron microscope study of the connections between the preganglionic fibers and the intralingual ganglion cells in the rat

The topographical distribution of the preganglionic neurons sending projection fibers to the tongue, and the connections between their fibers and the intralingual ganglion cells, were examined in the rat. When horseradish peroxidase injections were made into the anterior two-thirds of the tongue, labeled neuronal cell bodies were distributed mainly in the lateral reticular formation at the level between the rostral part of the facial nucleus and the caudal part of the superior olivary complex. On the other hand, after horseradish peroxidase injections into the posterior one-third of the tongue, labeled neuronal cell bodies were found mainly in the rostromedial part of the nucleus of the solitary tract, and additionally in the lateral reticular formation just ventral to the rostral part of the nucleus of the solitary tract. In both cases, labeled neuronal cell bodies were always found in the hypoglossal nucleus. The anterograde tracing study with Phaseolus vulgaris-leucoagglutinin or Fluoro-ruby confirmed the topographical organization suggested by the retrograde tracing study; when the tracer injections were centered on the lateral reticular formation at the level of the rostral part of the facial nucleus or on the rostral part of the nucleus of the solitary tract, labeled fibers distributed mainly in the anterior or posterior part of the tongue, respectively. It was also shown that the axon terminals of the preganglionic fibers labeled with Fluoro-ruby made close contacts with the intralingual ganglion cells immunopositive for neuron specific enolase. The electron microscopy combined with the anterograde tracing method with biotinylated dextran amine further indicated that the preganglionic fibers made synaptic contacts with the soma and dendritic processes of the intralingual ganglion cells.     

The fine structure of neurones and cellular relationships in the abducens nucleus in the cat

Summary Light and electron microscope studies of the abducens nucleus in the cat have disclosed two populations of neurones: large neurones 25 to 75 m in diameter and small neurones 10 to 25 m in diameter. Characteristic of the large neurones are a highly developed granular endoplasmic reticulum and a large number of axo-somatic synapses. The small neurones have a poorly developed granular endoplasmic reticulum and comparative by few axo-somatic synapses.Injection of horseradish peroxidase (HRP) into the ipsilateral lateral rectus muscle has been used to identify abducens motoneurones which represent 65% of the total number of cells in the abducens nucleus and form part of the large cell population. The remaining unlabelled large neurones (30% of the large cell population) probably represent motoneurones of the retractor bulbi muscles, abducens motoneurones which have failed to transport the HRP, and possibly internuclear neurones. The small neurones (5% of the total cell population) were never labelled by HRP.Axo-somatic and axo-dendritic synapses are numerous. Many of the synaptic terminals form contacts with two or more different postsynaptic elements. Axo-axonic synapses and synapses on the initial segments of large neurones are also present. Nodal synapses and branching of myelinated axons are common findings. Finally, extended areas of close apposition between dendritic membranes are frequently observed.Supported by INSERM (U6), CNRS (GR 25) and grant RCP 391 from the CNRS     

Convergence of synaptic inputs from the striatum and the globus pallidus onto identified nigrocollicular cells in the rat: a double anterograde labelling study.

Two major sources of afferent synaptic inputs to projection neurons in the rat substantia nigra reticulata are the striatum and the globus pallidus. In order to understand better the functional relationships between these two afferents in the control of the activity of nigrofugal neurons, experiments have been performed to test the possibility that single nigrofugal cells receive convergent synaptic inputs from the striatum and the globus pallidus. To address this question we have used two different approaches. First, we have developed a double anterograde labelling technique suitable for both light and electron microscopy and combined this procedure with the retrograde transport of lectin-conjugated horseradish peroxidase in order to retrogradely label the nigrocollicular cells. Second, we have combined the anterograde transport of Phaseolus vulgaris-leucoagglutinin from the globus pallidus and immunocytochemistry for DARPP-32 as a marker for the striatal terminals, with the retrograde transport of lectin-conjugated horseradish peroxidase from the superior colliculus. In the double anterograde labelling experiment, biocytin was injected in the striatum, Phaseolus vulgaris-leucoagglutinin in the globus pallidus and lectin-conjugated horseradish peroxidase in the superior colliculus. Following these injections, rich plexuses of biocytin- and Phaseolus vulgaris-leucoagglutinin-labelled terminals were found in the ventral two-thirds of the substantia nigra. The biocytin-positive terminals (striatonigral) were generally small and formed rich plexuses without any apparent neuronal association whereas the Phaseolus vulgaris-leucoagglutinin-labelled terminals (pallidonigral) were much larger and formed baskets around the perikarya of retrogradely and non retrogradely labelled cells in the substantia nigra reticulata. In areas of the substantia nigra reticulata where the fields of biocytin- and Phaseolus vulgaris-leucoagglutinin-labelled terminals overlapped, the perikarya and the proximal dendrites of retrogradely and non retrogradely labelled cells were found to be apposed by numerous Phaseolus vulgaris-leucoagglutinin-immunoreactive pallidonigral terminals and a few biocytin-labelled striatonigral terminals. In the sections prepared for electron microscopy, the biocytin was localized using 3,3'-diaminobenzidine tetrahydrochloride whereas Phaseolus vulgaris-leucoagglutinin was localized using benzidine dihydrochloride. It was thus possible to distinguish the biocytin- from the Phaseolus vulgaris-leucoagglutinin-labelled terminals in the electron microscope by the texture of the reaction product associated with them.4+ Examination of 231 biocytin-labelled (striatonigral) terminals and 105 Phaseolus vulgaris-leucoagglutinin-immunoreactive (pallidronigral) terminals revealed that the striatonigral terminals were generally small, contained few mitochondria and formed symmetric synapses predominantly with the distal dendrites (77%) and far less frequently with the perikarya (3%) of substantia nigra reticulata cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Glutamatergic input from specific sources influences the nucleus accumbens-ventral pallidum information flow

The nucleus accumbens (NAc) is positioned to integrate signals originating from limbic and cortical areas and to modulate reward-related motor output of various goal-directed behaviours. The major target of the NAc GABAergic output neurons is the ventral pallidum (VP). VP is part of the reward circuit and controls the ascending mesolimbic dopamine system, as well as the motor output structures and the brainstem. The excitatory inputs governing this system converge in the NAc from the prefrontal cortex (PFC), ventral hippocampus (vHC), midline and intralaminar thalamus (TH) and basolateral nucleus of the amygdala (BLA). It is unclear which if any of these afferents innervate the medium spiny neurons of the NAc, that project to the VP. To identify the source of glutamatergic afferents that innervate neurons projecting to the VP, a dual-labelling method was used: Phaseolus vulgaris leucoagglutinin for anterograde and EGFP-encoded adenovirus for retrograde tract-tracing. Within the NAc, anterogradely labelled BLA terminals formed asymmetric synapses on dendritic spines that belonged to medium spiny neurons retrogradely labelled from the VP. TH terminals also formed synapses on dendritic spines of NAc neurons projecting to the VP. However, dendrites and dendritic spines retrogradely labelled from VP received no direct synaptic contacts from afferents originating from mPFC and vHC in the present material, despite the large number of fibres labelled by the anterograde tracer injections. These findings represent the first experimental evidence for a selective glutamatergic innervation of NAc neurons projecting to the VP. The glutamatergic inputs of different origin (i.e. mPFC, vHC, BLA, TH) to the NAc might thus convey different types of reward-related information during goal-directed behaviour, and thereby contribute to the complex regulation of nucleus accumbens functions.     

Origin of projections from the midbrain raphe nuclei to the hypothalamic paraventricular nucleus in the rat: A combined retrograde and anterograde tracing study

A number of neuronal functions governed by the hypothalamic paraventricular nucleus are influenced by serotonin, and it is generally believed that the moderate density of serotonin-immunoreactive fibres and terminals within the paraventricular nucleus originates from the midbrain dorsal and median raphe nuclei. To further evaluate the intricate anatomy of projections from brain stem raphe nuclei of the rat, a combination of retrograde and anterograde tracing experiments were conducted to determine the medullary raphe nuclei projection to the paraventricular nucleus. Rhodamine-labelled latex microspheres, Cholera toxin subunit B and FluoroGold we used as retrograde tracers. Intracerebroventricular injections into the third ventricle of all retrograde tracers labelled a distinct population of neurons in the dorsal raphe situated in the subependymal stratum adjacent to the cerebral aqueduct indicating that these cells take up the tracer from the cerebrospinal fluid. Very few retrogradely labelled neurons were seen in the median raphe after i.c.v. administration of the tracers. Retrograde tracers delivered into the medial part of the paraventricular nucleus labelled no further cells in the midbrain dorsal and median raphe nuclei, whereas a substantial number of retrogradely labelled cells emerged in the pontine raphe magnus. However, when the retrograde tracers were delivered into the lateral part of the paraventricular nucleus, avoiding leakage of the tracer into the ventricle, very few labelled neurons were seen in the dorsal and median raphe, whereas the prominent labelling of raphe magnus neurons persisted. The anatomical organization of nerve fibres terminating in the area of paraventricular nucleus originating from midbrain raphe nuclei was studied in a series of anterograde tracing experiments using the plant lectin Phaseolus vulgaris leucoagglutinin. Injections delivered into the dorsal raphe or median raphe labelled but a few fibres in the paraventricular nucleus proper. A high number of fine calibered nerve fibres overlying the ependyma adjacent to the paraventricular nucleus was, however, seen after the injections into the subependymal rostral part of the dorsal raphe. Injections delivered into the raphe magnus gave rise to a dense plexus of terminating fibres in the parvicellular parts of the paraventricular nucleus and moderately innervated the posterior magnocellular part of the paraventricular nucleus as well as the magnocellular supraoptic nucleus. Concomitant visualization of serotonin-immunoreactive neurons and retrograde FluoroGold-tracing from the paraventricular nucleus revealed that none of the serotonergic neurons of the raphe magnus projects to this nucleus, while a few of the neurons putatively projecting to the paraventricular nucleus from the median raphe are serotonergic.

The current observations suggest that the raphe magnus constitute by far the largest raphe input to the paraventricular nucleus and strongly questions the earlier held view that most raphe fibres innervating the paraventricular nucleus are derived from the midbrain dorsal and median raphe. However, the source of serotonergic innervation of the paraventricular nucleus remains elusive.     

A monosynaptic pathway links the vestibular nuclei and masseter muscle motoneurons in rats

Physiological evidence indicates that vestibular signals modulate the activity of motoneurons innervating the masseter muscle. Recently, experiments using transynaptic retrograde transport of pseudorabies virus provided anatomical evidence that many neurons concentrated in the dorsomedial part of the parvicellular division of the medial vestibular nucleus (MVePC) and the caudal prepositus hypoglossi (PH) provide inputs to motoneurons innervating the lower third of the superficial layer of the masseter muscle. However, it was not clear whether this vestibulo-trigeminal projection was monosynaptic or polysynaptic. The present study sought to determine whether neurons in the MVePC or PH project directly to motoneurons controlling the masseter muscle in rats. For this purpose, an anterograde tracer (biotinylated dextran amine, BDA) was injected into vestibular nuclei (mainly MVePC) or PH and a retrograde tracer (the β-subunit of cholera toxin, b-CT) was injected into the masseter muscle ipsilateral or contralateral to the BDA injection site. Following injections of BDA into the vestibular nuclei or PH, anterogradely labeled axon terminals were observed bilaterally in the motor trigeminal nucleus (Mo5), particularly in the ventral, medial, and lateral portions of the nucleus; projections to dorsal Mo5 were sparse. In addition, retrogradely labeled motoneurons were located in the ventral and lateral portions of the ipsilateral Mo5. Moreover, anterogradely labeled terminals were observed to be in close proximity to motoneurons in the Mo5 that were retrogradely labeled from b-CT injections into the masseter muscle. This study provides direct evidence that a monosynaptic pathway exists between the MVePC and PH and masseter motoneurons.     

Organization of the nigro-tecto-bulbar pathway to the parvicellular reticular formation: a light- and electron-microscopic study in the rat

 We examined a nigro-tecto-bulbar pathway to the parvicellular reticular formation (RFp), where many premotor neurons for orofacial motor nuclei are known to be distributed, by using a combined anterograde and retrograde tracing method. After contralateral injections of biotinylated dextranamine (BDA) into the dorsolateral part of the substantia nigra (SNr) and cholera toxin B subunit (CTb) into the RFp, overlapping distributions of BDA-labeled terminals and CTb-labeled neuronal cell bodies were found in the lateralmost part of the superior colliculus (SC) ipsilateral or contralateral to the site of BDA injection or CTb injection, respectively. After contralateral injections of BDA into the SNr and horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) injection into the RFp, ipsilateral labeled axon terminals with BDA were found to make symmetrical synaptic contacts with the somata and dendrites of contralateral labeled neurons with WGA-HRP in the lateralmost part of the SC. Furthermore, we demonstrated that BDA-labeled axon terminals were immunoreactive for GABA, by using the anterograde tracing method combined with immunohistochemistry for GABA. Thus, GABA-like immunoreactive fibers originating from the dorsolateral part of the SNr make monosynaptic contacts with the tectal neurons sending their axons to the RFp. Received: 16 August 1996 / Accepted: 14 March 1997     

Brain afferents to the lateral caudal ventrolateral medulla: a retrograde and anterograde tracing study in the rat

The ventrolateral medulla (VLM) modulates autonomic functions, motor reactions and pain responses. The lateralmost part of the caudal VLM (VLMlat) was recently shown to be the VLM area responsible for pain modulation. In the present study, the brain sources of VLMlat afferent fibers were determined by tract-tracing techniques. Following injection of cholera toxin subunit B into the VLMlat, retrogradely labeled neurons in the forebrain occurred at the somatosensory, insular, motor, limbic and infralimbic cortices, and at the central amygdaloid nucleus. Retrogradely labeled neurons in diencephalic regions were observed in the lateral hypothalamus, posterior hypothalamus and paraventricular nucleus. In the brainstem, retrograde labeling occurred at the periaqueductal gray, red nucleus, parabrachial area, nucleus raphe magnus, nucleus tractus solitarii, lateral reticular nucleus and dorsal and ventral medullary reticular formation. In the cerebellum, retrogradely labeled neurons occurred at the lateral nucleus. Following injections of the anterograde tracer biotinylated dextran amine (BDA) into the lateral hypothalamus or paraventricular nucleus, anterogradely labeled fibers were mainly observed in the VLMlat. Injections of BDA into the periaqueductal gray, red nucleus or lateral nucleus of the cerebellum resulted in anterograde labeling in the VLMlat and lateral reticular nucleus.The present study gives an account of the brain regions putatively involved in triggering the modulatory actions elicited from the VLMlat. These include areas committed to somatosensory processing, autonomic control, somatic and visceral motor activity and affective reactions. The findings suggest that the VLMlat may play a major homeostatic role in the integration of nociception with other brain functions.     

Ultrastructural studies of the nucleus ambiguus in cat and monkey following injection of HRP into the vagus nerve

Summary The fine structure of retrogradely labelled neurons in the nucleus ambiguus (NA) has been examined in cat and monkey (Macaca fascicularis) following injections of horseradish peroxidase (HRP) into the vagus nerve. Many retrogradely labelled neurons were observed in the NA although unlabelled neurons were also present within the boundaries of the NA as identified by the distribution of retrogradely labelled cells. In both species a wide range of sizes of labelled neurons (20–60 m in long axis) was observed from rostral to caudal levels of the NA. Large labelled neurons were generally oval or spindle-shaped while smaller neurons were oval in cross-section. Unlabelled neurons observed among labelled NA neurons tended to be smaller on average than the labelled neurons and ranged in size from 15 to 30 m in long axis. The unlabelled neurons typically had nuclei which were more invaginated than those of the labelled neurons.Quantitative analyses of the synaptic organization in the NA revealed high proportions of terminals containing round vesicles and making asymmetrical or symmetrical contact with the somata in both monkey and cat. Terminals containing pleomorphic vesicles and making symmetrical contact with somata were slightly less numerous. Retrogradely labelled neurons exhibited a positive correlation between the size of neuron and density of synapses on the surface. There tended to be a greater synaptic density on monkey NA neurons than on cat NA neurons of comparable size.     

The airway-related parasympathetic motoneurones in the ventrolateral medulla of newborn rats were dissociated anatomically and in functional control

The respiratory-related synaptic control of the airway-related preganglionic parasympathetic motoneurones (APPMs) has not been investigated, and whether differently targeted APPMs receive differential respiratory-related synaptic modulation is unknown. In this study, putative APPMs in the ventrolateral medulla of newborn rats were retrogradely traced with fluorescent tracer and were examined using the patch-clamp method in brainstem slices with respiratory rhythm. The results indicate that tracer application directly to the recurrent laryngeal nerve only labelled the putative APPMs within the compact portion of nucleus ambiguus (cNA), while tracer injection into the trachea wall labelled the putative APPMs both in cNA and in the area ventral/ventrolateral to cNA (vNA). The putative APPMs within cNA received mainly inhibitory inputs, which in some (9 of 20) neurones showed an inspiratory-related attenuation and in others (7 of 20) showed an inspiratory-related augmentation. At least some putative APPMs within cNA, of which the inhibitory synaptic inputs showed inspiratory-related changes, might be related to the control of laryngeal muscles. The putative APPMs in vNA receive both excitatory and inhibitory inputs, and central inspiratory activity excited some (11 of 19) neurones via augmentation of their excitatory inputs and inhibited others (8 of 19) via augmentation of their inhibitory inputs. At least some putative APPMs in vNA might be trachea-related motoneurones. These results provide evidence that APPMs controlling different segments of the airway might be dissociated in the ventrolateral medulla both anatomically and in functional control.     

Hippocampal input to a “visceral motor” corticobulbar pathway: an anatomical and electrophysiological study in the rat

Summary The hippocampus has previously been shown to influence cardiovascular function, and this effect appears to be mediated by the connection the hippocampus has with the infralimbic area of the medial frontal cortex (MFC), a region which projects directly to the nucleus of the solitary tract (NTS) in the dorsal medulla. In the present study, anatomical and electrophysiological techniques were utilized to determine the degree of convergence of hippocampal input to the MFC on neurons in the MFC which project to the NTS. Injections of the anterograde and retrograde neuroanatomical tracer wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) into the NTS retrogradely labelled cells in the infralimbic and prelimbic regions of the MFC. Injections of WGA-HRP into the ventral hippocampus anterogradely labelled terminals in the MFC which, at the light microscopic level, closely overlapped the origin of the descending projection from the MFC to the brainstem. Electron microscopic analysis revealed that anterogradely labelled terminals make synaptic contact primarily on dendritic processes in the neuropil adjacent to retrogradely labelled cells. In addition, anterogradely labelled terminals did, in some cases, make synaptic contact on the somas of retrogradely labelled cells. Electrical stimulation of the NTS antidromically activated cells in the infralimbic and prelimbic areas of the MFC. The average latency of antidromic activation was 30 msec, corresponding to a conduction velocity of approximately 0.7 m/s. Electrical stimulation of the ventral hippocampus orthodromically activated cells in the MFC. With an appropriate delay between the hippocampal and NTS stimuli, the orthodromic and antidromic potentials could be made to collide. The results of this study establish a structural as well as functional link between the hippocampus and NTS-projection neurons in the MFC.     

鲤鱼脊髓的上行通路与脑至脊髓的下降通路

应用赖氨酸钴复合物顺行、逆行标记方法,分别研究了鲤鱼脊髓上升的和下降至脊髓的纤维联系。把赖氮酸钴复合物注入脊髓第1——3节段,然后分别观察标记纤维与标记细胞。标记纤维主要在三叉神经脊剩束、网状结构、迷走神经运动核和半圆隆起。发现标记细胞主要于脊髓的前角和后角、脑的迷走神经运动核、网状结构和内耳侧线区等部位。本文与其他鱼类、其他脊椎动物及哺乳类动物进行了比较。     

家兔脊髓长下行固有束与坐骨神经运动神经元之间的突触联系

本实验采用成年家兔12只,在上颈髓单侧往入海人酸后,将HRP注入同侧的坐骨神经内,应用HRP逆行追踪结合顺行溃变技术的电镜方法,首次在电镜水平对脊髓长下行固有束终末与坐骨神经运动神经元之间的突触联系进行了研究,结果表明,在坐骨神经运动神经元的胞体及近侧树突表面发现有少量的溃变终扣.根据溃变终扣的外形可分为圆形和长形,根据溃变终扣内突触小泡的形状可分为圆形和椭圆形.突触联系包括:(1)溃变终扣与标记胞体及树突形成轴一体、轴一树突触;(2)溃变终扣与非标记胞体及树突形成轴一体、轴一树突触;(3)正常轴突终末与标记胞体及树突形成轴一体、轴一树突触.本文首次报道,起源于上颈髓的脊髓长下行固有束终末与坐骨神经运动神经元之间存在着直接的突触关系.     

Central distributions of the efferent and afferent components of the pharyngeal branches of the vagus and glossopharyngeal nerves: an HRP study in the cat

Summary The central distributions of efferent and afferent components of the pharyngeal branches of the vagus (PH-X) and glossopharyngeal (PH-IX) nerves in the cat were studied by soaking their central cut ends in a horseradish peroxidase (HRP) solution. HRP-labelled PH-X neurones were distributed ipsilaterally in the rostral part of the nucleus ambiguus (NA) and the retrofacial nucleus (RFN); HRP-labelled PH-IX neurones were found in the ipsilateral RFN and the bulbopontine lateral reticular formation (RF). Vagal pharyngeal neurones constituted a large population of brainstem motoneurones. The population of HRP-labelled glossopharyngeal neurones was divided into two components. Indeed, on the basis of their location and somal morphology, the most ventral cells were identified as cranial motoneurones and those scattered in the lateral RF as parasympathetic preganglionic neurones. Application of HRP to the PH-IX nerve resulted also in the labelling of fibres and terminals in the alaminar spinal trigeminal nucleus and the nucleus of the solitary tract (NTS). The afferent fibres entered the lateral medulla with the glossopharyngeal roots, ran dorsomedially, then turned caudally toward the NTS and the caudal part of the alaminar spinal trigeminal motor (V) nucleus. In the NTS, labelled fibres ran mainly along the solitary tract, projecting to terminals in the dorsal and dorsolateral nuclei of the NTS.     

猫后索核—丘脑—皮质通路在丘脑水平的突触联系

应用顺行溃变和ＨＲＰ逆行追踪相结合的方法对猫内侧丘系与丘脑皮质投射神经元在丘脑腹后外侧核内的突触联系组合型式进行了研究。电损毁一侧后索核后将ＨＲＰ注射于对侧皮质躯体感觉颈、躯干、四肢代表区，电镜下在注射区同侧的丘脑腹后外侧核内可见到下列七种突触形式；（１）溃变的内侧丘系轴突终末与ＨＲＰ标记树突形成的轴－树突触，较多；（２）溃变的内侧丘系轴突终末与ＨＲＰ标记的神经元体形成的轴－体突触较少；（３）溃变     

A re-examination of the rubro-olivary tract in the cat,using horseradish peroxidase as a retrograde and an anterograde neuronal tracer

Most authors using free horseradish peroxidase as a retrograde tracer have had difficulties in demonstrating a rubro-olivary tract. Injections of this tracer into the inferior olive in animals of different species resulted in only a few retrogradely labelled rubral cells within the rostral part of the ipsilateral nucleus. The present study, which is based on the highly sensitive technique of Mesulam (1978), confirms this observation. Injections of free horseradish peroxidase (Serva or Sigma VI type) into the dorsal lamella of the principal olive in eleven cats gave a positive retrograde labelling of rostral rubral cells in only three animals, with a very few cells in each case. In contrast to this, olivary injections of horseradish peroxidase labelled lectin (wheat germ agglutinin) result in an abundance of retrogradely labelled cells within the rostral part of the ipsilateral red nucleus, the great majority of these cells being of the small and medium-sized type. Many of the retrogradely labelled rubral cells are only faintly stained. However, free horseradish peroxidase appears to be well suited as an anterograde tracer for a demonstration of the rubro-olivary tract.The findings are discussed in relation to the observation that in the cat only peroxidase conjugated to lectin can be used successfully as a retrograde tracer for a visualization of the rubro-olivary connection.     

Connections of the caudal ventrolateral medullary reticular formation in the cat brainstem

 A region of the caudal ventrolateral medullary reticular formation (CVLM) participates in baroreceptor, vestibulosympathetic, and somatosympathetic reflexes; the adjacent retroambigual area is involved in generating respiratory-related activity and is essential for control of the upper airway during vocalization. However, little is known about the connections of the CVLM in the cat. In order to determine the locations of terminations of CVLM neurons, the anterograde tracers Phaseolus vulgaris leucoagglutinin and tetramethylrhodamine dextran amine were injected into this region. These injections produced a dense concentration of labeled axons throughout the lateral medullary reticular formation (lateral tegmental field), including the retrofacial nucleus and nucleus ambiguus, regions of the rostral ventrolateral medulla, the lateral and ventrolateral aspects of the hypoglossal nucleus, nucleus intercalatus, and the facial nucleus. A smaller number of labeled axons were located in the medial, lateral, and commissural subnuclei of nucleus tractus solitarius, the A5 region of the pontine reticular formation, the ventral and medial portions of the spinal and motor trigeminal nuclei, locus coeruleus, and the parabrachial nucleus. We confirmed the projection from the CVLM to both the rostral ventrolateral medulla and lateral tegmental field using retrograde tracing. Injections of biotinylated dextran amine or Fluorogold into these regions resulted in retrogradely labeled cell bodies in the CVLM. However, the neurons projecting to the lateral tegmental field were located mainly dorsal to those projecting to the rostral ventrolateral medulla, suggesting that these neurons form two groups, possibly with different inputs. Injections of retrograde tracers into the lateral tegmental field and rostral ventrolateral medulla also produced labeled cell bodies in other regions, including the medial and inferior vestibular nuclei and nucleus solitarius. These data are consistent with the view that the CVLM of the cat is a multifunctional area that regulates blood pressure, produces vocalization, affects the shape of the oral cavity, and elicits contraction of particular facial muscles. Received: 18 February 1997 / Accepted: 27 March 1997     

Fine structure of the dorsal part of the nucleus submedius of the rat thalamus: an anatomical study with reference to possible pain pathways

The dorsal portion of the nucleus submedius of the rat thalamus receives spinal and trigeminal projections which may convey noxious inputs. The present study was undertaken to analyse the fine structure of the nucleus with particular reference to a possible trigemino-thalamo-prefrontal cortical pathway relaying in nucleus submedius. Presynaptic terminals in the dorsal portion of the nucleus submedius were classified into three broad categories usually observed in thalamic nuclei: "small round", "flat" and "large round" types. Axonal tracing using either anterograde transport of horseradish peroxidase or degeneration methods indicated that some "small round" terminals originate from the pre-frontal cortex. Some "large round" terminals were labelled from the trigeminal subnucleus caudalis. These "large round" terminals exhibited distinct morphological features when compared with trigeminal terminals in other thalamic nuclei. In particular they made synaptic contacts predominantly with dendritic protrusions and were surrounded by multilamellate astrocytic processes. Double-labelling experiments were performed by means of the combined retrograde transport of horseradish peroxidase and Wallerian degradation techniques. Terminals degrading after lesion of the trigeminal subnucleus caudalis contacted submedius neurons labelled retrogradely from the prefrontal cortex. These observations demonstrate the existence of a direct monosynaptically relayed pathway from subnucleus caudalis to prefrontal cortex which relays in the dorsal part of nucleus submedius.