Ultrastructure of substance P immunoreactive elements in the periaqueductal gray matter of the rat

Substance P (SP) is a non-opioid peptide that generates a potent, analgesia when injected into the periaqueductal gray matter (PAG)The aim of this study was to investigate the fine neuronal structures and synaptic circuits involved in SP action in rats by means of electron microscopy, using immunocytochemical (ICC) pre-embedding methods. A conventional ultrastructural study, carried out to interpret the ICC data correctly, shows small sized nerve cell bodies with a high nucleus–cytoplasmic ratio; absence of an extensive granular endoplasmic reticulum; and few axo-somatic contacts having symmetrical and asymmetrical junctions in equal proportions. The large neuropil is characterized by numerous thin unmyelinated axons and axodendritic synapses mainly showing pleomorphic vesicles and asymmetrical junctions. The ICC analysis showed moderately labeled nerve cell bodies with the same structural, synaptic, and dimensional features as the negative cells. In the neuropil SP immunoreactivity is shown by dendrites, synapses, and thin elements which are unidentifiable structurally. No SP terminals synapsing on SP nerve cell bodies were found and only occasional SP light labeled terminals synapsing on negative perikarya were seen. The SP boutons generally have pleomorphic vesicles and asymmetrical junctions. On the basis of these data a possible excitatory activity of PAG SP synapses could be hypothesized. This activity would take place on postsynaptic neurons generally at a dendritic level. Our ultrastructural findings give support to an excitatory role carried out by SP neurons of the PAG, as suggested by the role of PAG circuitry on spinal nociception.     

Ultrastructure of the pineal gland of the monkey, Macaca fascicularis, with special reference to the presence of synaptic junctions on pinealocytes

Summary The present study described the normal ultrastructure of the monkey pineal gland. The gland was composed of the principal pinealocytes, intramural neurons and glial cells. The nucleus of the pinealocytes was deeply infolded with evenly distributed chromatin materials. The abundant cytoplasm was rich in organelles including the well-developed Golgi apparatuses, multivesicular bodies, dense-cored vesicles and widely scattered free and polyribosomes. A variety of axon terminals was observed and the majority of them contained pleomorphic agranular vesicles with a few large dense-cored vesicles. A few terminals showed flattened vesicles or small dense cored vesicles. Some of the axon terminals formed synaptic contacts with the cell bodies of pinealocytes. These synapses were mainly concentrated in the posterior third of the gland. The occasional intramural neurons observed were postsynaptic to axon terminals containing round agranular vesicles. The sources of the nerve fibres and terminals forming synaptic junctions with pinealocytes and intramural neurons were discussed.     

Synapses upon the axon origin of dorsal horn neurons in the rat spinal cord

Axon terminals synapsing with axon hillocks or origins of Golgi-impregnated and gold-toned neurons in the dorsal horn of the rat were shown in serial electron micrographs. Synapses occurred irrespective of the site (perikaryon or dendrite) and mode (with or without an axon hillock) of the axon origin. The synapsing axon terminals contained 3 populations of vesicles: pleomorphic and flattened synaptic vesicles and a combination of pleomorphic and dense-core vesicles. The membrane thickening in the axon-axon hillock synapses was of the symmetrical type.     

GABAergic and pallidal terminals in the thalamic reticular nucleus of squirrel monkeys

The ultrastructure of synaptic terminals from the external segment of the globus pallidus and of other synaptic terminals positive for gamma-aminobutyric acid (GABA) was examined in the thalamic reticular nucleus (TRN) of squirrel monkeys. Two GABA-positive terminals types were commonly encountered within the TRN neuropil. The most common type of GABAergic terminals (F terminals) are filled with dispersed pleomorphic synaptic vesicles and clusters of mitochondria. These terminals establish multiple symmetric synapses upon the somata and dendrites of TRN neurons. The external pallidal terminals, labeled with WGA-HRP, arise from thinly myelinated axons and correspond to the medium to large F terminals. A less prevalent population of smaller GABAergic synaptic profiles was also identified. The synaptic profiles in this second group contain considerably fewer pleomorphic synaptic vesicles in small irregular clusters and fewer mitochondria, establish symmetric synapses, are postsynaptic to other axonal terminals, are presynaptic to dendrites and soma, and are unlabeled following pallidal injections of WGA-HRP.     

GABA-immunoreactive neurons and terminals in the cat periaqueductal gray matter: a light and electron microscopic study

Immunocytochemical and electron microscopic methods were used to study the GABAergic innervation in adult cat periaqueductal gray matter (PAG). A mouse monoclonal antibody against γ -aminobutyric acid (GABA) was used to visualize the inhibitory neuronal system of PAG. At light microscopy, GABA-immunopositive (GABA_IP) neurons formed two longitudinally oriented columns in the dorsolateral and ventrolateral PAG that accounted for 36% of the neuronal population of both PAG columns; their perikaryal cross-sectional area was smaller than that of unlabeled (UNL) neurons found in the same PAG subdivisions. At electron microscopic level, patches of GABA immunoreactivity were readily detected in neuronal cell bodies, proximal and distal dendrites, axons and axon terminals. Approximately 35–36% of all terminals were GABA_IP; they established symmetric synapses with dendrites (84.72% of the sample in the dorsolateral PAG and 86.09% of the sample in the ventrolateral PAG) or with cell bodies (7–10% of the sample). Moreover, 49.15% of GABA_IP axon terminals in the dorsolateral and 52.16% in the ventrolateral PAG established symmetric synapses with GABA_IP dendrites. Immunopositive axon terminals and unlabeled terminals were also involved in the formation of a complex synaptic arrangment, i.e. clusters of synaptic terminals in close contact between them that were often observed in the PAG neuropil. Moreover, a fair number of axo-axonic synapses between GABA_IP and/or UNL axon terminals were present in both PAG subdivisions. Several dendro-dendritic synapses between labeled and unlabeled dendrites were also observed in both PAG subdivisions. These results suggest that in the cat PAG there exist at least two classes of GABArgic neurons. The first class could exert a tonic control on PAG projecting neurons, the second could act on those GABAergic neurons that in turn keep PAG projecting neurons under tonic inhibition. The functional implications of this type of GABAergic synapse organization are discussed in relation to the dishinibitory processes that take place in the PAG.     

Quantitative and ultrastructural study of ascending projections to the medial mammillary nucleus in the rat

Summary We analyzed the termination pattern of axons from the superior central nucleus and the ventral tegmental nucleus of Gudden within the medial mammillary nucleus (MM) in the rat. The neuropil of the MM consists of two classes of terminals, that is, terminals containing round synaptic vesicles and forming asymmetric synaptic contact, and terminals containing pleomorphic synaptic vesicles and forming symmetric synaptic contact. The number of axodendritic terminals with round vesicles is almost equal to that of terminals with pleomorphic vesicles. Almost all axosomatic terminals contain pleomorphic vesicles with symmetric synaptic contact. Injection of WGA-HRP into the central part of the superior central nucleus permitted ultrastructural recognition of many anterogradely labeled terminals within the median region of MM. The labeled terminals contacted mainly intermediate (1–2 m diameter) and proximal dendrites (more than 2 m diameter) as well as the neuronal somata. Serial ultrathin sections of neurons of the median region of the MM revealed that 37% of the axosomatic terminals were labeled anterogradely. The pars compacta of the superior central nucleus had reciprocal connections with the median region of MM. The axon terminals from this nucleus occupied 53% of axosomatic terminals, and contacted mainly intermediate dendrites. Following injection of WGA-HRP into the ventral tegmental nucleus, many labeled terminals were found in the medial and lateral regions of MM. They contacted mainly intermediate dendrites as well as neuronal somata. In the medial region, 78% of axosomatic terminals contacting retrogradely labeled neurons were labeled anterogradely. All labeled terminals from these nuclei contained pleomorphic vesicles, and made symmetric synaptic contact.     

Quantitative ultrastructural analysis of the periaqueductal gray in the rabbit

The fine structure of the periaqueductal gray (PAG) of the rabbit was examined using the transmission electron microscope. On the basis of synaptic polarity, vesicle size, and the nature of the pre- and postsynaptic elements, 10 essentially different synaptic types could be discerned (6 axo-dendritic, 2 axo-somatic, 1 axo-axonic, and 1 dendro-dendritic). Synaptic contact on the soma of PAG neurons were small and covered, on average, only 1.6% of the soma surface. The most striking feature of the synaptic structure of the PAG was that more than 94.1% of all synapses were axo-dendritic. Of these, 83.5% were of the symmetrical type. Most of these contacts occurred on buttons of small to medium size, and contained either round vesicles of medium size or pleomorphic vesicles of medium size. Boutons containing only flattened vesicles were quite rare. Boutons contacting larger dendrites were generally small-to-medium in size, made asymmetric-type synaptic contacts, and contained pleomorphic vesicles of medium-to-large size. Medium-sized dendrites were contacted principally by small boutons exhibiting either symmetrical or asymmetrical junctions containing medium-sized pleomorphic vesicles, and in addition a few of these boutons contained both large, and small, round vesicles. Dendritic spines were generally provided with only one synaptic contact, stretching the entire width of the spinous process. Boutons and the spines on dendrites were approximately the same size. Synapses between two vesicle-containing structures (axo-axonic or dendro-dendritic synapses) were rare (1.4%). They were generally asymmetric and contained round vesicles of medium size. Complex synapses, where a glial sheet enclosed the synapse, were occasionally observed. Also seen were multiple synapses, with up to 11 contacts on a single dendritic profile. Large dense-core vesicle were seen in approximately 40% of all synapses, whereas small dense-core vesicles were only found in about 3%. Data is provided on how different synaptic features relate to ventral, lateral, dorsal, and medial PAG. Principally this is in relation to neuron size, glia cell content, axonal characterization, and vesicular type. © 1993 Wiley-Liss, Inc.     

Synaptology of the hypoglossal nucleus in the rat

Summary The purpose of this study was to define the types and distribution of synaptic terminals in the hypoglossal nucleus (XII) of the rat. Based on differences in bouton and vesicle size and shape, synaptic specializations and association with postsynaptic organelles, five types of terminals were identified in XII. In order of decreasing frequency they were: 1) S-boutons (spherical vesicles with an asymmetrical synapse); 2) F-boutons (flattened vesicles with a symmetrical synapse); 3) P-boutons (pleomorphic admixture of flattened and spherical vesicles with a symmetrical synapse); 4) C-boutons (pleomorphic vesicles with a subsynaptic cistern); and 5) Tboutons (spherical vesicles with an asymmetrical synapse and subsynaptic dense bodies). S-boutons were the predominant type found on dendrites, while boutons containing flattened vesicles were more prevalent on motoneuron somata. C-boutons were restricted exclusively to cell bodies and large dendrites, and T-boutons were seen primarily on smaller dendritic profiles. These results are, in general, comparable to those previously described in the ventral horn and cranial nerve motor nuclei in several species. However, differences were noted. Specifically, large M-boutons and axo-axonic synapses were not observed in the present study. The functional significance of these findings are discussed in relation to oro-lingual behaviour.     

A light and electron microscopic analysis of the convergent insular cortical and amygdaloid projections to the posterior lateral hypothalamus in the rat, with special reference to cardiovascular function

The synaptic organization between and among the insular cortex (IC) axons, central amygdaloid nucleus (ACe) axons and posterolateral hypothalamus (PLH) neurons was investigated in the rat using double anterograde tracing and anterograde tracing combined with postembedding immunogold analysis. After ipsilateral injections of biotinylated dextran amine (BDA) into the IC and Phaseolus vulgaris-leucoagglutinin (PHA-L) into the ACe, the conspicuous overlapping distribution of BDA-labeled axon terminals and PHA-L-labeled axon terminals was found in the PLH region just medial to the subthalamic nucleus ipsilateral to the injection sites. At the electron microscopic level, approximately two-thirds of the IC terminals made synapses with small-sized dendrites and the rest did with dendritic spines of the PLH neurons, whereas about 79%, 16% and 5% of the ACe terminals established synapses with small- to medium-sized dendrites, somata, and dendritic spines, respectively, of the PLH neurons. In addition, the IC axon terminals contained densely packed round clear vesicles and their synapses were of asymmetrical type. On the other hand, most of the ACe terminals contained not only pleomorphic clear vesicles but also dense-cored vesicles and their synapses were of symmetrical type although some ACe terminals contained densely packed round clear vesicles and formed asymmetrical synapses. Most of the postsynaptic elements received synaptic inputs from the IC or ACe terminals, and some of single postsynaptic elements received convergent synaptic inputs from both sets of terminals. Furthermore, almost all the ACe terminals were revealed to be immunoreactive for gamma-aminobutyric acid (GABA), by using the anterograde BDA tracing technique combined with immunohistochemistry for GABA. The present data suggest that single PLH neurons are under the excitatory influence of the IC and/or inhibitory influence of the ACe in the circuitry involved in the regulation of cardiovascular functions.     

The mormyrid brainstem--III. Ultrastructure and synaptic organization of the medullary "pacemaker" nucleus

The ultrastructure and synaptic organization of the presumed medullary pacemaker nucleus, nucleus c of the weakly electric mormyrid fish, Gnathonemus petersii has been investigated. Nucleus c consists of about 12-15 small (20-25 micron) neurones (P-cells), which form a group situated ventrally to the medullary relay nucleus and embedded in a neuropil of myelinated fibres and dendritic processes. The P-cells often exhibit an enhanced electron density of their cytoplasm and dendroplasm. They possess several dendrites of different diameter, a short, thin axon initial segment and a thickly myelinated axon running in dorsal direction. The pacemaker neurons are interconnected by complex electronic coupling, established by somatosomatic, dendrosomatic and dendrodendritic gap junctions. Perikarya and dendrites are frequently interconnected serially by gap junctions; dendrites showed sometimes triadic gap-junction arrangement. It is suggested that this high degree of electrotonic coupling amongst the pacemaker cells represents the first level of the highly ordered synchronization processes which characterize the electric discharge command system of Gnathonemus. Pacemaker cells receive synaptic input from club endings with mixed synapses and from bouton-like terminals with chemical synapses, both of them originating from medium-sized myelinated fibres and contacting mainly neuronal perikarya and dendritic processes. The axon initial segment receives only few synaptic inputs. Bouton-like terminals were found to be of two types according to their vesicle content, namely, boutons with ovoid, clear synaptic vesicles forming Gray type-1 synapses and boutons with pleomorphic clear synaptic vesicles forming Gray type-2 synapses. Different functional roles for the two types of boutons in modulating pacemaker cell activity are suggested.     

大鼠中脑导水管周围灰质腹外侧区5-羟色胺样、P物质样和亮氨酸-脑啡肽样免疫反应阳性亚微结构的电镜观察

本文用免疫电镜技术研究了大鼠中脑导水管周围灰质腹外侧区内5-HT样、SP样和L-ENK样的免疫反应阳性亚微结构。5-HT样免疫反应阳性的胞体较多,常见5-HT样阳性树突与阴性轴突终末形成多为非对称性的轴-树突触;偶见阳性轴突终末与阴性树突以及阴性轴突终末与阳性胞体分别构成轴-树和轴-体突触.SP样阳性胞体数目较少,可见少量含多形性小泡的阴性轴突终末与之形成轴-体突触;由阴性轴突终末与阳性树突所形成的轴-树突触最常见;阳性轴突终末与阴性胞体和阳性树突分别构成轴-体突触和轴-树突触。L-ENK样阳性胞体数目也较少,L-ENK样阳性树突与阴性轴突终末所形成的轴-树突触最多见,可见L-ENK样阳性胞体与阴性轴突终末构成轴-体突触;偶见阳性轴突终末与阴性树突形成轴-树突触。上述各种突触均主要含圆形小泡,有时有少量扁平小泡、椭圆形小泡和颗粒囊泡。     

Unipolar brush cells develop a set of characteristic features in primary cerebellar cultures

The unipolar brush cells (UBCs) are a class of excitatory interneurons recently discovered in the cerebellar granular layer. UBCs differ morphologically and biochemically from granule cells, although they share the same mossy fiber and Golgi cell inputs. To elucidate development of the UBCs, we sought to ascertain their presence in primary cerebellar cultures and the class-specific properties they develop in vitro outside of the context of the tissue. By light and electron microscopy, we demonstrate that primary cultures from embryonic and postnatal mouse and rat cerebella contain UBC-like neurons that are highly polarized and can be distinguished from granule cells on several grounds. Granule cells are more numerous in dissociated postnatal cultures than in embryonic cultures; express little, if any, calretinin immunoreactivity; and develop dendritic processes devoid of typical claw-like endings, but provided with small synaptic junctions. By contrast, UBC-like neurons occur more frequently in embryonic cultures than in postnatal cultures, are intensely calretinin-positive, and develop characteristic cell organelles, dendrites, and large synapses. In embryonic cultures, the UBC-like neurons have a clear nucleus and contain a special cytoplasmic array of ringlet subunits, resembling the botrysome. At 12–28 days in vitro, the UBC dendrites contain abundant mitochondria, are provided with clusters of non-synaptic appendages, and engage in glomerular arrays together with large and small axon terminals. The large terminals contain round synaptic vesicles, form extensive, asymmetric synapses with the cell bodies and the dendrites of the UBC-like neurons, and resemble mossy terminals, while the small terminals contain pleomorphic vesicles, form symmetric synaptic junctions, and resemble Golgi terminals. In postnatal cultures grown for 12 days, UBC-like neurons are rare and resemble in most aspects the cells observed in embryonic cultures, although they rarely develop elaborate dendritic brushes.     

小鼠中脑导水管周围灰质下行投射的SP能终末与中缝大核内SP受体阳性神经元的突触联系

P物质(SP)在中枢神经系统内具有镇痛作用,中脑导水管周围灰质(PAG)和中缝大核(NRM)是中枢内源性镇痛系统的关键结构。本研究采用顺行追踪与免疫组化双重染色相结合的三标方法,观察了起源于PAG的SP能阳性终末与NRM内SP受体(SPR)阳性神经元之间的突触联系。结果显示:将生物素化葡聚糖胺(BDA)注入小鼠PAG的腹外侧区后,BDA顺行标记终末可见于脑干的许多区域,但主要位于NRM。其中的部分BDA顺行标记终末呈SP阳性。NRM内可见到散在分布的SPR阳性神经元。在电镜下可见来自PAG的SP/BDA双标终末与NRM内的SPR阳性神经元的胞体和树突形成以非对称性为主的突触联系。本研究的结果提示起源于PAG的下行投射终末所释放的SP是激活中枢内源性镇痛系统并使之发挥镇痛作用的重要神经活性物质。     

Fine structural survey of the intermediate subnucleus of the nucleus tractus solitarii and its glossopharyngeal afferent terminals

The intermediate subnucleus of the nucleus tractus solitarii (imNTS) receives somatosensory inputs from the soft palate and pharynx, and projects onto the nucleus ambiguus, thus serving as a relay nucleus for swallowing. The ultrastructure and synaptology of the rat imNTS, and its glossopharyngeal afferent terminals, have been examined with cholera toxin-conjugated horseradish peroxidase (CT-HRP) as an anterograde tracer. The imNTS contained oval or ellipsoid-shaped, small to medium-sized neurons (18.2×11.4 μm) with little cytoplasm, few cell organelles and an irregularly shaped nucleus. The cytoplasm often contained one or two nucleolus-like stigmoid bodies. The average number of axosomatic terminals was 1.8 per profile. About 83% of them contained round vesicles and formed asymmetric synaptic contacts (Gray’s type I), while about 17% contained pleomorphic vesicles and formed symmetric synaptic contacts (Gray’s type II). The neuropil contained small or large axodendritic terminals, and about 92% of them were Gray’s type I. When CT-HRP was injected into the nodose ganglion, many labeled terminals were found in the imNTS. All anterogradely labeled terminals contacted dendrites but not somata. The labeled terminals were usually large (2.69±0.09 μm) and exclusively of Gray’s type I. They often contacted more than two dendrites, were covered with glial processes, and formed synaptic glomeruli. A small unlabeled terminal occasionally made an asymmetric synaptic contact with a large labeled terminal. The large glossopharyngeal afferent terminals and the neurons containing stigmoid bodies characterized the imNTS neurons that received pharyngeal afferents.     

Fine structure of GABA-labeled axonal endings in the inferior colliculus of the cat: immunocytochemistry on deplasticized ultrathin sections.

Antisera to GABA conjugates and postembedding techniques were used to identify GABA-containing axonal endings at the electron microscopic level in the inferior colliculus. Over 90% of the GABA-labeled axonal endings had a similar morphology. They contained pleomorphic synaptic vesicles and made symmetrical synapses. The exceptional endings contained round vesicles and made symmetrical synaptic contacts or had pleomorphic vesicles with asymmetrical contacts. The majority of GABA-labeled axonal endings synapsed on dendrites; however, a few labeled axosomatic synapses were also found. Potential sources for these GABAergic synapses are neurons intrinsic to the inferior colliculus or from the dorsal nucleus of the lateral lemniscus. These findings suggest a basic similarity for most GABAergic endings in the inferior colliculus despite their possible origin from different cell types.     

The lateral vestibular nucleus of the toadfish Opsanus tau: Ultrastructural and electrophysiological observations with special reference to electrotonic transmission

The lateral vestibular nucleus of the toadfish Opsanus tau was localized by means of axonal iontophoresis of Procion Yellow. The ultrastructure of the lateral vestibular nucleus neurons was then correlated with their electrophysiological properties. The lateral vestibular nucleus consists of neurons of various sizes which are distributed in small clusters over a heavily myelinated neuropil. The perikarya and main dendrites of the large and the small neurons are surrounded by a synaptic bed, which is separated from the neighboring neuropil by a layer of thin astrocytic processes. The synaptic bed contains three main classes of axon terminals, club endings, large and small terminals, the first being quite infrequent. All the large terminals as well as the occasionally observed club endings contain a pure population of rounded synaptic vesicles. In some of the small axon terminals there are also rounded vesicles; however, the majority contain flattened vesicles or a pleomorphic population. These data indicate that the small terminals originate from different afferent sources. The synaptic interfaces of the large boutons and of the club endings bear three types of junctional complexes: attachment plates, gap junctions and active zones. Those showing both gap junctions and active zones were designated as morphologically ‘mixed synapses’. Gap junctions, although in large number, have only been observed at the synaptic interfaces between terminals with rounded vesicles and the perikarya or the dendrite of the lateral vestibular nucleus neurons. Therefore electrotonic coupling would only be possible by way of presynaptic fibers. Some axons observed in the neuropil were found to establish gap junctional complexes with two different dendritec profiles and this observation is in favour of electrotonic coupling by way of presynaptic terminals.Field and intracellular potentials were recorded in the lateral vestibular nucleus. The field potential evoked by stimulation of the vestibular nerve consisted of an early positive-negative wave followed by a slow negativity, and that evoked by spinal cord stimulation was composed of an antidromic potential followed by a slow negative wave. Vestibulo-spinal neurons were identified by their antidromic spikes. In these cells, stimulation of the ipsilateral vestibular nerve evoked an excitatory postsynaptic potential with two components. The short delay of the first component of this excitatory postsynaptic potential and its ability to follow paired stimulation at close intervals without reduction of the second response suggest that it is transmitted electrotonically from primary vestibular afferent fibers. By contrast the latency of the second peak of the vestibular evoked excitatory postsynaptic potential and its sensitivity to high stimulus frequencies are compatible with monosynaptic chemically mediated transmission from primary vestibular afferents. Spinal stimulation evoked graded antidromic depolarizations in vestibulo-spinal neurons. The latency of these potentials was too short to allow for chemical transmission through afferents or recurrent collaterals and suggests electrotonic spread of antidromic activity from neighboring neurons. An important finding is that the graded antidromic depolarizations can initiate spikes; thus coupling between neurons in the lateral vestibular nucleus is sufficiently close that a cell can be excited by activity spread from neighboring cells. Similar graded depolarizations were recorded in identified primary vestibular afferents; their latencies and time course indicate that they were brought about by electrotonic spread of postsynaptic potentials and spikes to the impaled presynaptic fibers; this confirms the morphological evidence that coupling between lateral vestibular nucleus neurons occurs, at least in part, by way of presynaptic vestibular axons. As the spinal stimulus strength was increased, these graded depolarizations became large enough to initiate spikes which presumably propagate to the vestibular receptors. Thus antidromic invasion of the presynaptic terminals may provide negative feedback by preventing their re-excitation at short intervals after a synchronous discharge of an adequate number of postsynaptic cells. Excitatory inputs to the neurons of the lateral vestibular nucleus were identified from the spinal cord and from the contralateral vestibular nerve. Long latency excitatory postsynaptic potentials large enough to excite the cells were recorded following spinal stimulation; the threshold intensity for evoking them was consistently higher than that adequate to generate the graded antidromic depolarizations. Field potentials recorded after stimulation of the contra lateral vestibular nerve consisted of an initial positive negative wave followed by a slow negative wave. the stimulus intensity for evoking these potentials was the same or slightly above the threshold for those evoked in the lateral vestibular nucleus on the stimulated side. Also lateral vestibular nucleus neurons exhibited excitatory postsynaptic potentials large enough to excite the cells following stimulation of the contralateral vestibular nerve. but no inhibitory postsynaptic potentials were detected. This lack of commissural inhibition indicates a qualitative difference between the central organization of these cells in the toadfish and in mammals.The presence of neurons in the lateral vestibular nucleus which send their axons to the labyrinth was confirmed by their heavy staining with Procion Yellow following axonal iontophoresis. In a number of vestibular neurons. abruptly rising spikes were evoked at short latencies after adequate stimulation of the ipsilateral vestibular nerve. Graded stimuli applied to the vestibular nerve evoked graded short latency depolarizations as well as long latency excitatory postsynaptic potentials in these presumed efferent neurons to the labyrinth; the former could indicate electrotonic coupling of the efferent cells or electrotonic transmission from primary afferents, resulting in a short latency feedback loop.From these studies, the synaptic organization of the lateral vestibular nucleus neurons is compared with that of the Mauthner cells of teleosts, and the possibility of a dual mode of transmission, electrical and chemical, by primary vestibular afferents is discussed.     

高血压大鼠某些周缘神经节中氧化一氮合酶的分布

高血压大鼠某些周缘神经节中氧化－氮合酶的分布（北京医科大学解剖学教研室，北京１０００８３，于恩华，沈丽，杨嘉，许鹿希）氧化－氮（ｎｉｔｒｉｃｏｘｉｄｅ，ＮＯ）作为一种特殊的神经活性物质已经为人们接受，氧化－氮合酶（ｎｉｔｒｉｃｏｘｉｄｅｓｙｎｔｈａｓ...     

大鼠三叉神经脊束核尾侧亚核Ⅱ层内CB样、PV样阳性终末与向臂旁核投射神经元的突触联系

为了观察三叉神经脊束核尾侧亚核 层神经元与向臂旁核投射神经元的突触关系 ,选用 Calbindin D-2 8k和 Parvalbu-min作为标志物 ,采用 HRP逆行追踪与免疫组织化学技术相结合的双重反应技术对 层内的 Calbindin D-2 8k样和 Parvalbumin样阳性神经元与三叉神经脊束核尾侧亚核向臂旁核投射神经元之间的突触联系进行了观察。HRP注入臂旁核后 ,逆标神经元主要位于同侧三叉尾侧亚核 层至 层。Calbindin D-2 8k和 Parvalbumin样阳性胞体、纤维和终末主要集中在 层内侧带。电镜下观察 ,此二者的阳性反应产物呈弥散分布 ;两者的阳性终末与 HRP逆标神经元的胞体和树突之间主要形成轴 -树突触 ,偶见轴 -体突触 ;Calbindin D-2 8k样阳性终末与 HRP逆标神经元的树突形成的非对称性突触占 83% ,Parvalbumin样阳性终末与 HRP逆标神经元的树突形成的对称性突触占 85 %。此外 ,还观察到参与突触小球组成的初级传入纤维终末与 HRP逆标神经元的树突形成突触联系。以上结果提示 :(1)三叉神经脊束核尾侧亚核 层的 Calbindin D-2 8k样或 Parvalbumin样阳性神经元可通过突触传递机制对三叉神经脊束核尾侧亚核向臂旁核投射的神经元进行调控 ,影响外周伤害性信息向上位脑结构的传递 ;(2 )三叉神经脊束核尾侧亚核向臂旁核投?     

Ultrastructural identification of substance P immunoreactive neurons in the main olfactory bulb of the hamster

The neurons containing substance P immunoreactivity in the main olfactory bulb of the hamster are located in the glomerular layer. Their cell bodies lie in the periglomerular region and contain spherical or ovoid nuclei which lack invaginations of the nuclear membrane and tend to be positioned eccentrically in the cell body. Dendrites of these neurons extend throughout the periglomerular region and project into the glomerular neuropil. Within the glomerular neuropil, processes with substance P immunoreactivity contain agranular, spherical synaptic vesicles. Primary olfactory axons, and processes of uncertain origin which contain pleomorphic synaptic vesicles, form synaptic contacts with substance P immunoreactive processes.These ultrastructural findings confirm that the substance P immunoreactive neurons are external tufted cells. Their likely physiological properties are considered in relation to the synaptic organization in the glomerular layer of the main olfactory bulb and to the other putative neurotransmitters or neuromodulators located in this layer.     

Ultrastructure and synaptic relations of neural elements containing glutamic acid decarboxylase (GAD) in the perigeniculate nucleus of the cat

Summary The perigeniculate nucleus of the cat (PGN) was examined at light and electron microscopic levels after immunocytochemical labeling for the gamma-aminobutyric acid (GABA) synthesizing enzyme, glutamic acid decarboxylase (GAD). In light microscopic sections, virtually all perikarya were found to be labeled (GAD+), as well as proximal dendrites, fibres and punctiform elements. Cells in the thalamic reticular nucleus (TRN) dorsal to PGN were also labeled. Ultrastructural analysis of PGN showed immunoreactivity in all somata, in dendrites and in the following vesicle containing profiles: 1.) F1 terminals, which are characterized by large size, dark mitochondria, and pleomorphic vesicles. These terminals form symmetrical synaptic contacts with somata, somatic spines and with dendrites of GAD+ PGN cells. 2.) F2 terminals, which are smaller than F1 terminals, contain also pleomorphic vesicles and frequently make serial synapses of the symmetric type with other F2 terminals. Presumably, F1 terminals are formed by collaterals of PGN-cell axons and F2 terminals by vesicle containing dendrites of PGN cells. Terminals devoid of immunoreactivity included: 1.) RLD terminals characterized by large size, round vesicles, dark mitochondria, and by asymmetric synaptic contacts with somata, especially with somatic spines, and with dendrites of GAD+ perigeniculate neurons; 2.) RSD terminals, characterized by small size, round vesicles and dark mitochondria, which make asymmetric synapses with GAD+ dendrites of medium and small size; 3.) Multivesicular (MV) terminals with variably shaped vesicles including dense core vesicles synapsing on GAD+ dendrites. There are reasons to believe that RSD terminals belong to corticofugal axons and RLD terminals to collateral axons of LGN relay cells. The origin of MV terminals remains to be determined. The GABAergic nature of the PGN cells conforms with the presumed function of these cells as mediators of inhibition of LGN relay cells. The complex synaptic relations observed between GAD+ elements in the PGN would allow for reciprocal inhibition between perigeniculate cells.Supported in part by NIH grants EY02877 to V.M. Montero and HD 03352 to the Waisman Center