猫三叉神经尾侧脊束核—丘脑—皮质通路在丘脑水平的突触联系

本文采用HRP逆行追踪与顺行溃变结合法对猫三叉神经尾侧脊束核-丘脑-皮质通路在丘脑腹后内侧核内的突触联系型式进行了研究。在电镜下发现,丘脑腹后内侧核內有五种突触联系形式:(1)溃变轴突终末与HRP标记树突形成轴-树突触;(2)溃变轴突终末与HRP标记的胞体形成轴-体突触,上述两类突触型式为该通路在丘脑水平的直接突触联系方式,此外尚有(3)溃变轴突终末与非HRP标记的树突形成的轴-树突触;(4)HRP标记树突与非溃变轴突终末形成轴一树突触;(5)HRP标记树突与非HRP标记的含有突触小泡的突触前树突形成的树-树突触。本文首次报道了三叉丘系纤维与丘脑皮质投射神经元间的直接突触联系方式为轴-树和轴-体突触。同时也发现了以树突为中心的突触复合体,它是该通路在丘脑水平的一个显著特点。     

猫丘脑腹后外侧核内皮质—丘脑纤维终末与丘脑—皮质投射神经元之间的突触连接

用ＣＢ－ＨＲＰ逆行追踪与顺行溃变相结合的方法，对描丘脑腹后外侧核内的来自大脑皮质体感Ⅰ区的皮质—丘脑纤维终末与丘脑—皮质投射神经元之间的突触连接进行了电镜观察。向猫大脑皮质体感Ⅰ区内注射ＣＢ－ＨＲＰ５ｈ后，电解损毁原注射部位，术后动物存活４ｄ。电镜下发现丘脑瓜后外侧核内存在５种突触连接方式；（１）溃变的轴突终未与ＨＲＰ标记神经元胞体形成轴－体突触；（２）溃变的轴突终末与ＨＲＰ标记的树突形成轴—树突触；（３）溃变的轴突终末和其它突触前成分共同与中央树突形成汇聚型的突触复合体；（４）溃变的轴突终末与未标记树突形成的轴—树突触；（５）正常的轴突终末与ＨＲＰ标记神经元形成对称型的轴—体突触。     

A combined Golgi-electron microscopic study of non-pyramidal neurons in the CA 1 area of the hippocampus

Summary Non-pyramidal neurons of the CA 1 area of the rat hippocampus were identified with a combined Golgi-electron microscopic method. They were observed to have distinctive light and electron microscopic characteristics that are different from those of pyramidal cells. These features included smooth dendrites, locally arborizing axons, infolded cell nuclei with intranuclear rods or sheets, and a well-developed perikaryal cytoplasm with many organelles. In addition, the axon terminals that contact the somata and dendrites of local circuit neurons may form asymmetric as well as symmetric synapses. The axons of these cells form symmetric synapses with dendrites and somata of pyramidal cells. Some of these features were utilized to identify non-pyramidal neurons of the CA 1 area for studies of connectivity. Degenerating commissural terminals were found to form synapses with the dendrites and somata of non-pyramidal neurons. These results indicate that these neurons are a significant population of hippocampal neurons that may provide feed-forward inhibition of pyramidal neurons.     

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     

Glutamatergic components of the retrosplenial granular cortex in the rat

The ultrastructural characteristics, distribution and synaptic relationships of identified, glutamate-enriched thalamocortical axon terminals and cell bodies in the retrosplenial granular cortex of adult rats is described and compared with GABA-containing terminals and cell bodies, using postembedding immunogold immunohistochemistry and transmission electron microscopy in animals with injections of cholera toxin- horseradish peroxidase (CT-HRP) into the anterior thalamic nuclei. Anterogradely labelled terminals, identified by semi-crystalline deposits of HRP reaction product, were approximately 1 microm in diameter, contained round, clear synaptic vesicles, and established asymmetric (Gray type I) synaptic contacts with dendritic spines and small dendrites, some containing HRP reaction product, identifying them as dendrites of corticothalamic projection neurons. The highest densities of immunogold particles following glutamate immunostaining were found over such axon terminals and over similar axon terminals devoid of HRP reaction product. In serial sections immunoreacted for GABA, these axon terminals were unlabelled, whereas other axon terminals, establishing symmetric (Gray type II) synapses were heavily labelled. Cell bodies of putative pyramidal neurons, containing retrograde HRP label, were numerous in layers V-VI; some were also present in layers I-III. Most were overlain by high densities of gold particles in glutamate but not in GABA immunoreacted sections. These findings provide evidence that the terminals of projection neurons make synaptic contact with dendrites and dendritic spines in the ipsilateral retrosplenial granular cortex and that their targets include the dendrites of presumptive glutamatergic corticothalamic projection neurons.     

Synaptic organization of immunocytochemically identified GABA neurons in the monkey sensory-motor cortex

Neurons in the monkey somatic sensory and motor cortex were labelled immunocytochemically for the GABA synthesizing enzyme, glutamic acid decarboxylase (GAD), and examined with the electron microscope. The somata and dendrites of many large GAD-positive neurons of layers III-VI receive numerous asymmetric synapses from unlabelled terminals and symmetric synapses from GAD-positive terminals. Comparisons with light and electron microscopic studies of Golgi-impregnated neurons suggest that the large labelled neurons are basket cells. Small GAD-positive neurons generally receive few synapses on their somata and dendrites, and probably conform to several morphological types. GAD-positive axons from symmetric synapses on many neuronal elements including the somata, dendrites and initial segments of pyramidal cells, and the somata and dendrites of non-pyramidal cells. Synapses between GAD-positive terminals and GAD-positive cell bodies and dendrites are common in all layers. Many GAD-positive terminals in layers III-VI arise from myelinated axons. Some of the axons form pericellular terminal nests on pyramidal cell somata and are interpreted as originating from basket cells while other GAD-positive myelinated axons synapse with the somata and dendrites of non-pyramidal cells. These findings suggest either that the sites of basket cell terminations are more heterogeneous than previously believed or that there are other classes of GAD-positive neurons with myelinated axons. Unmyelinated GAD-positive axons synapse with the initial segments of pyramidal cell axons or form en passant synapses with dendritic spines and small dendritic shafts and are interpreted as arising from the population of small GAD-positive neurons which appears to include several morphological types.     

Glutamatergic components of the retrosplenial granular cortex in the rat

The ultrastructural characteristics, distribution and synaptic relationships of identified, glutamate-enriched thalamocortical axon terminals and cell bodies in the retrosplenial granular cortex of adult rats is described and compared with GABA-containing terminals and cell bodies, using postembedding immunogold immunohistochemistry and transmission electron microscopy in animals with injections of cholera toxin- horseradish peroxidase (CT-HRP) into the anterior thalamic nuclei. Anterogradely labelled terminals, identified by semi-crystalline deposits of HRP reaction product, were approximately 1 m in diameter, contained round, clear synaptic vesicles, and established asymmetric (Gray type I) synaptic contacts with dendritic spines and small dendrites, some containing HRP reaction product, identifying them as dendrites of corticothalamic projection neurons. The highest densities of immunogold particles following glutamate immunostaining were found over such axon terminals and over similar axon terminals devoid of HRP reaction product. In serial sections immunoreacted for GABA, these axon terminals were unlabelled, whereas other axon terminals, establishing symmetric (Gray type II) synapses were heavily labelled. Cell bodies of putative pyramidal neurons, containing retrograde HRP label, were numerous in layers V–VI; some were also present in layers I–III. Most were overlain by high densities of gold particles in glutamate but not in GABA immunoreacted sections. These findings provide evidence that the terminals of projection neurons make synaptic contact with dendrites and dendritic spines in the ipsilateral retrosplenial granular cortex and that their targets include the dendrites of presumptive glutamatergic corticothalamic projection neurons.     

Quantification of synapses formed with apical dendrites of golgi-impregnated pyramidal cells: Variability in thalamocortical inputs,but consistency in the ratios of asymmetrical to symmetrical synapses

Five pyramidal cells from the posteromedial barrel subfield of mouse SmI cortex were labeled by Golgi impregnation and then gold-toned and de-impregnated (Fairén, Peters & Saldanha, 1977). Subsequently, 40 to 70 μm-long segments of their apical dendrites occurring in layer IV were graphically reconstructed from serial thin sections to determine the distribution of their synapses. Thalamocortical synapses onto these dendritic segments were identified by lesion-induced degeneration.The synaptic pattern of the pyramidal cell apical dendrites was consistent with previous reports in that most synapses occurred on spines and were asymmetrical and the smaller number of shaft synapses were primarily symmetrical. Some axospinous synapses were formed by degenerating thalamocortical axon terminals. The proportion of thalamocortical synapses onto reconstructed dendritic segments was different for different neurons. For example, thalamocortical axon terminals formed 15% of the synapses involving the spines of the reconstructed segment from a medium superficial layer V pyramidal cell and 10% of the synapses onto portions of the segment from a large layer VI pyramidal cell. In contrast, reconstructed dendritic segments of three other layer VI pyramidal cells formed no more than one thalamocortical synapse.An analysis of the distribution of synapses onto reconstructed dendritic segments revealed that the segments of 3 medium and large pyramidal cells had a ratio of about 12.5 asymmetrical synapses per symmetrical synapse, whereas the segments of 2 small pyramidal cells had ratios of only 6.5 asymmetrical synapses per symmetrical synapse. That these ratios fall into 2 distinct groups suggests that the relative number of asymmetrical and symmetrical synapses is stereotyped within populations of neurons.     

The distribution of intrinsic cortical axons in area 3b of cat primary somatosensory cortex

Summary The morphology of single neurons in area 3b of cat primary somatosensory (SI) cortex was examined after horseradish peroxidase (HRP) injections. Neurons were labeled either by intracellular injection of HRP following intracellular recording or by small extracellular iontophoretic HRP injections. Both pyramidal and nonpyramidal neurons were labeled and reconstructed from serial sections. Their axons had local, interlaminar and interareal patterns of termination. Most neurons formed local axonal fields around their cell bodies and dendrites. Pyramidal neurons in cortical layer IV sent axons up into layers II and III, neurons in layers II and III sent axons down to layer V, and layer V neurons sent axons to layer VI as well as back to the upper layers. Layer VI neurons sent axons back to the upper cortical layers in a unique bowl-shaped pattern. The horizontal distribution of axons of pyramidal cells in layer III was extremely widespread. Axons of layer III neurons in area 3b terminated within 3b and area 1, but not in other areas of SI. Layer III neurons in area 1 distributed axon collaterals to all fields of SI as well as projecting a main axon to motor cortex. In general, the axon collaterals of area 3b pyramidal cells outside layer III remained confined to area 3b. Most of the nonpyramidal neurons labeled were basket cells in layers III and VI. These neurons formed dense axonal fields around their cell bodies, and none of their axons could be followed into the underlying white matter. The results of the present study demonstrate that area 3b somatosensory cortical neurons and their axons are vertically organized in a manner similar to that reported for other sensory cortical areas. They also show that widespread horizontal connections are formed by pyramidal neurons of layer III, and that these horizontal axons can travel for great distances in the cortical grey matter.     

The projection of the visual cortex on the Clare-Bishop area in the cat

Summary Following large lesions of the cat visual cortex, the distribution of degenerating terminal boutons in the Clare-Bishop area was studied electron microscopically. Degenerating boutons were found throughout the cortical layers but mostly in layer III (51% of the total number of degenerating boutons) and layer V (24%). A smaller number of boutons were found in layers II (12%) and IV (9%), and very few in layers VI (3%) and I (1%). No degenerating terminals were observed in the upper two-thirds of layer I. Seventy-six per cent of the total degenerating boutons terminated on dendritic spines, 22% on dendritic shafts, and 2% on somata. Some degenerating boutons made synaptic contacts with somata and dendrites of nonpyramidal neurons. For example, one degenerating bouton was observed in contact with an apical dendrite of a fusiform cell. Three examples of dendritic spines, with which degenerating boutons made synaptic contacts, were found to belong to spinous stellate cells. No degenerating boutons were observed making synaptic contacts with profiles that could conclusively be traced to pyramidal cell somata.     

Morphology of synapses formed by cholecystokinin-immunoreactive axon terminals in regio superior of rat hippocampus

Immunocytochemical and electron microscopic methods were used to examine neurons in regio superior of rat hippocampus displaying cholecystokinin octapeptide-like immunoreactivity. Cholecystokinin-immunoreactive synaptic terminals and somata are found in all layers of regio superior but are most numerous in stratum pyramidale. The vast majority of terminals form symmetric synaptic contacts onto the somata and proximal dendrites of hippocampal pyramidal cells and onto smaller dendrites which may also arise from pyramidal cells. A very small number of Cholecystokinin-immunoreactive terminals form synapses that appear asymmetric and contact dendritic shafts or spines. The somata of some pyramidal cells receive symmetric synapses from Cholecystokinin-immunoreactive terminals that are joined by cytoplasmic bridges to form parts of pericellular baskets. These and adjacent pyramidal cell somata are also contacted by terminals that are not immunoreactive for cholecystokinin. No cholecystokinin-positive terminals contacted the initial segments of pyramidal cell axons. Cholecystokinin-immunoreactive cells are found in all layers of regio superior. Their somata receive a few symmetric synapses, most of which are formed by terminals not immunoreactive for cholecystokinin. Their dendrites receive a greater number of both symmetric and asymmetric contacts, some of which are immunoreactive for cholecystokinin.We conclude the following: (1) The localization of cholecystokinin immunoreactivity in synaptic terminals contacting the somata and dendrites of hippocampal pyramidal cells is consistent with the suggestion that cholecystokinin acts as a neurotransmitter at these sites and at sites in other parts of the cerebral cortex. (2) Results from the present and previous studies suggest that cholecystokinin-like immunoreactivity may co-exist with γ-aminobutyrate in some non-pyramidal neurons of regio superior. (3) Cholecystokinin-immunoreactive terminals arise mainly from non-pyramidal cells intrinsic to the hippocampus, one class of which appears to be a type of basket cell.     

Parvalbumin-immunoreactive neurons in the entorhinal cortex of the rat: localization, morphology, connectivity and ultrastructure

Summary We studied the distribution, morphology, ultrastructure and connectivity of parvalbumin-immunoreactive neurons in the entorhinal cortex of the rat. Immunoreactive cell bodies were found in all layers of the entorhinal cortex except layer I. The highest numbers were observed in layers II and III of the dorsal division of the lateral entorhinal area whereas the lowest numbers occurred in the ventral division of the lateral entorhinal area, Most such neurons displayed multipolar configurations with smooth dendrites. We distinguished a type with long dendrites and a type with short dendrites. We also observed pyramidal immunoreactive neurons. A dense plexus of immunoreactive dendrites and axons was prominent in layers II and III of the dorsal division of the lateral entorhinal area and the medial entorhinal area. None of the parvalbuminimmunoreactive cells became retrogradely labelled after injection of horseradish peroxidase into the hippocampal formation. By electron microscopy, immunoreactivity was observed in cell bodies, dendrites, myelinated and unmyelinated axons and axon terminals. Immunoreactive dendrites and axons occurred in all cortical layers. We noted many myelinated immunoreactive axons. Immunoreactive axon terminals were medium sized, contained pleomorphic synaptic vesicles, and established symmetrical synapses. Both horseradish peroxidase labelled and unlabelled immunonegative cell bodies often received synapses from immunopositive axon terminals arranged in baskets. Synapses between immunoreactive axon terminals and unlabelled dendritic shafts and spines were abundant. Synapses with initial axon segments occurred less frequently. In addition, synaptic contacts were present between immunopositive axon terminals and cell bodies and dendrites. Thus, the several types of parvalbumin-containing neuron in the entorhinal cortex are interneurons, connected to one another and to immunonegative neurons through a network of synaptic contacts. Immunonegative cells projecting to the hippocampal formation receive axo-somatic basket synapses from immunopositive terminals. This connectivity may form the morphological substrate underlying the reported strong inhibition of cells in layers II and III of the entorhinal cortex projecting to the hippocampal formation.     

A quantitative study of thalamocortical and other synapses involving the apical dendrites of corticothalamic projection cells in mouse SmI cortex

Summary Lesion-induced degeneration was combined with the retrograde transport of horseradish peroxidase (HRP) to examine the thalamocortical and other synaptical relationships of corticothalamic projection cells in mouse SmI cortex. Injections containing 40% HRP were placed in the ventrobasal thalamus and the next day, electrolytic lesions were made of the injection site. About four days later, the animals were perfused with aldehydes and SmI cortex ipsilateral to the injection and lesion sites was tissue chopped and reacted for HRP. The somata of HRP-filled corticothalamic cells in SmI cortex had diameters of about 10 m and occurred in the upper half of layer VI and in the lower half of layer V; their apical dendrites usually terminated within or just below layer IV, but in some instances, extended nearly to the pial surface. Reconstructions of serial thin sections through the layer IV portions of the apical dendrites of seven well-labelled corticothalamic cells showed them to form 7 to 20% of their synapses with degenerating thalamocortical axon terminals. In contrast, the proportion of thalamocortical synapses formed by the layer IV dendrites of corticostriatal (Hersch & White, in preparation) and corticocortical (White & Hersch, 1981) projection cells ranges from 0.3 to 0.9% and from 1.5 to 6.8%, respectively. We interpret these findings to indicate that pyramidal cell dendrites are specified to form characteristic proportions of thalamocortical synapses.     

Synaptic connections, axonal and dendritic patterns of neurons immunoreactive for cholecystokinin in the visual cortex of the cat

A subpopulation of gamma-aminobutyric acid (GABA) containing neurons was reported to contain cholecystokinin-immunoreactive material in the visual cortex of cat [Somogyi et al., J. Neurosci. (1984) 4, 2590-2603]. In the present study pre-embedding immunocytochemistry was used to identify which of the several types of presumed GABAergic nonpyramidal cells in areas 17 and 18 contain cholecystokinin immunoreactivity. Most of the cholecystokinin-immunoreactive somata were found in layers II-III, they were less frequent in layers I and VI, and relatively rare in layers IV and V. The distribution and density of the axon terminals resembled that of the cell bodies. Two well defined types of cholecystokinin-immunoreactive neuron were distinguished: (1) double bouquet cells in layers II-III with vertically projecting axons, and (2) small basket cells with local axons either restricted to layers II-III, or descending to layer V. Additional cholecystokinin-positive cells showed features of bitufted or multipolar neurons in layers II-VI and horizontal cells in layer I, but these cells could be defined less well due to partial staining. Cholecystokinin-immunoreactive dendrites were found to run horizontally in layer I for several hundred micrometers. Some of the cholecystokinin-immunoreactive cells in layer VI had very long dendrites ascending radially up to layer III, as did their axons. A few cholecystokinin-immunoreactive cells appeared to have two axons and this was confirmed by electron microscopy. All cholecystokinin-immunoreactive neurons and terminals were separated from the basal lamina of blood vessels by glial endfeet. Random samples of boutons from each layer as well as identified terminals traced to their origin from local neurons were examined in the electron microscope. All of the boutons established symmetrical (type II) synaptic contacts with dendritic shafts, spines or somata. Quantitative electron microscopy of the postsynaptic targets of double bouquet cells and small basket cells demonstrated clear differences between these two types of neuron; basket cells having a higher proportion of their terminals in synaptic contact with somata. The findings that several distinct types of cortical neurons, as defined by their synaptic connections, contain cholecystokinin-immunoreactive material and that identified axons of all examined neurons form type II synaptic contacts suggests that the majority, if not all cholecystokinin-positive boutons forming type II contacts originate from local cortical cells. The distribution of targets postsynaptic to cholecystokinin-positive neurons is compared to those of cells labelled by other methods.     

Morphological diversity of immunocytochemically identified GABA neurons in the monkey sensory-motor cortex

GABAergic neurons have been identified in monkey sensory-motor cerebral cortex by light microscopic, immunocytochemical localization of the GABA synthesizing enzyme, glutamic acid decarboxylase (GAD). All GAD-positive neurons are non-pyramidal cells. Their somata are present in all layers and are evenly distributed across layers II-VI of the motor cortex (area 4), but are found in greater concentrations in layers II, IV and VI of all areas of first somatic sensory cortex (SI; areas 3a, 3b and 1-2). GAD-positive puncta (putative axon terminals) are present throughout the sensory-motor cortex, and they are found immediately adjacent to the somata, dendrites and presumptive axon initial segments of GAD-negative pyramidal cells. In addition, they are observed in close approximation to the somata of both large and small GAD-positive neurons. In area 4, the density of puncta is highest in the superficial cortical layers (layers I-III) and gradually declines throughout the deeper layers. In SI, the highest densities of puncta are present in layer IV, while moderately high densities are found in layers I-III and VI. In areas 3a and 3b, the puncta in layers IV and VI are particularly numerous and form foci that exhibit greater density than adjacent regions. GAD-positive neurons with large somata, 15-33 micron in diameter, are present in layers IIIB-VI of all areas. Such cells have many primary dendrites that radiate in all directions. In addition they have axons that ascend either from the superficial aspect of the somata or from primary dendrites, and that exhibit horizontal collateral branches. These neurons closely resemble the large basket cells (Marin-Padilla, 1969; Jones, 1975), and they may give rise to many of the GAD-positive endings surrounding the somata and proximal dendrites of pyramidal cells in layers III-VI. In addition, small GAD-positive somata are present in all layers, but they are most numerous in layers II and IIIA of all areas and in layer IV of SI. The somata and proximal dendrites of these cells vary from a multipolar shape with small, beaded dendrites, found primarily in layer IV, to bitufted and multipolar shapes with larger, smooth dendrites. The diversity of somal sizes and locations, the variety of dendritic patterns, and the different distributions of GAD-positive puncta, all combine to suggest that several different morphological classes of intrinsic neurons comprise the GABA neurons of monkey cerebral cortex.     

Ultrastructural identification of synaptic terminals from cortical axons and from collateral axons of geniculo-cortical relay cells in the perigeniculate nucleus of the cat

Summary Electron microscopic analysis of sections of the perigeniculate nucleus (PGN) of the cat processed with horseradish peroxidase (HRP) histochemistry after massive injections of this enzyme in the visual cortex showed two types of synaptic terminals labeled with HRP reaction products. One type (RLD terminals) is characterized by round synaptic vesicles, large size, dark mitochondria and asymmetrical synaptic contacts with somata and dendrites. The second type (RSD terminals) is characterized by round synaptic vesicles, small size, dark mitochondria and asymmetrical synaptic contacts with dendrites. The HRP + RSD terminals, which were also found in the dorsal lateral geniculate nucleus (LGN), are interpreted as terminals of cortical origin both in the PGN and LGN, since previous studies have identified cortical terminals as being of RSD type in the LGN and in other thalamic nuclei. The HRP + RLD terminals are interpreted as synaptic terminals of collaterals axons of geniculo-cortical relay cells in the PGN labeled by retrograde transport of HRP from the cortex. In addition, in semithin and ultrathin sections somata in the PGN were never found labeled with HRP products indicating the absence of a PGN projection to the visual cortex.     

猫丘脑中央外侧核内脊丘系终末与丘脑-皮质投射神经元之间的突触联系

本实验应用顺行溃变和HRP逆行追踪相结合的方法，首次在电镜水平对猫丘脑中央外侧核内脊丘系终末与丘脑-皮质投射神经元之间的突触联系进行了研究．在脊髓第4颈段刀切损毁一侧侧索和前索后，将HRP注射于同侧大脑前上薛氏回和中上薛氏回前端。在电镜下于损毁同侧中央外侧核内可见下列突触连结：（1）溃变的脊丘系轴突终末与标记树突形成的轴-树突触；（2）溃变的脊丘系轴突终末与非标记树突形成的轴-树突触，个别非标记树突含有突触小泡；（3）正常的轴突终末与HRP标记树突和胞体形成的轴-树突触和轮一体突触；（4）正常的两个轴突终末与HRP标记树突形成的轴-轴-树连续性突触；（5）非标记的含突触小泡的突触前树突与HRP标记树突形成的树-树突触。同时可见大量汇聚型突触复合体。本文首次报道在丘脑中央外侧核内，脊丘系终末与丘脑-皮质投射神经元之间存在着直接的突触联系。     

猫丘脑腹后外侧核内皮质投射神经元超微结构及其突触联系——HRP法电镜研究

本文应用HRP逆行追踪法在电镜水平上对猫丘脑腹后外侧核内皮质投射神经元的超微结构及其突触联系进行了研究。该核内投射神经元超微结构特点为胞核较大,核仁清晰,核膜常有凹陷,常染色质较多,异染色质较少,胞浆丰富,含有大量的游离核糖体、粗面内质网及线粒体。标记的皮质投射神经元胞体和树突与非标记轴突形成轴-体突触和轴-树突触;标记树突还可以和突触前树突形成树-树突触,并做为中央树突参与形成汇聚型突触复合体。此外在标记的胞体与非标记的树突之间,标记的树突与非标记的树突之间,两标记的树突之间还存在着非突触丝状连接。     

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. I. General description.

Lesions were made in the lateral geniculate nucleus of the rat and the consequent degeneration in area 17 of the cerebral cortex was studied by light and electron microscopy. These lesions produced prominent degeneration of axon terminals in layer IV extending into layer III and a much lesser amount in layers I and VI. The darkened degenerating axon terminals forming asymmetric synaptic junctions and were frequently surrounded by hypertrophied astrocytic processes. These terminals appeared to be disposed randomly, forming no discernible patterns. In layer IV 83% of the synapsing, degenerating terminals formed junctions with dendritic spines, 15% with dendritic shafts, and 2% with neuronal perikarya. The dendritic shafts and neuronal perikarya appeared to belong to spine-free stellate cells. The dendrites giving rise to the spines receiving degenerating axon terminals could not be identified, for most of the spines appeared as isolated profiles that could not be traced back to their dendritic shafts. One example of a degenerating axon terminal synapsing with an axon initial segment was encountered. Small, degenerating myelinated axons were prevalent in layers VI, V and IV, but were only infrequent in the supragranular layers. These results are compared with those obtained in other studies of thalamocortical projections.     

皮质丘脑投射神经元的超微结构及突触联系

采用ＨＲＰ逆行追踪技术与电镜相结合的方法，对猫大脑皮质体感Ⅰ区内皮质丘脑投射神经元超微结构及突触联系进行了研究。结果证明，皮质丘脑投射神经元超微结构的特点为锥体形的胞体，胞浆丰富，含有多量的粗面内质网，游离核糖体及线粒体。ＨＲＰ标记的皮质丘脑投射神经元作为突触后成份与轴突和树突分别形成轴－树突触，轴－体突触和树－体实触。这些结果提示：皮质丘脑投射神经元接受广泛的传入联系和皮质间的联系。