摘要:

AbstractRetinofugal pathways in the spotted dogfishScyliorhinus caniculaand the thornback rayRaja clavatawere studied with reduced silver techniques following unilateral eye enucleations. Optic nerve axons decussate in the chiasma opticum, except for a small ipsilateral projection to the area preoptica. After crossing, retinal projections distribute to the area preoptica, the thalamus dorsalis pars lateralis, the thalamus ventralis pars lateralis, the corpus geniculatum laterale, the nucleus pretectalis, and the superficial layers of the tectum mesencephali. InScyliorhinusmost primary optic fibers terminate in the stratum medullare externum of the mesencephalic tectum, while inRajathe zona externa of the stratum cellulare externum receives the bulk of the retinal input. A basal optic tract could be identified inRaja, but not inScyliorhinus.The retinofugal pathways of the two species studied are compared with those of other cartilaginous fishes and other anamniotes. It is concluded that the primary visual system in chondrichthyans resembles that of actinopterygians and amphibians. However, there is a striking difference in the way in which the primary optic fibers reach the tectal target areas. In elasmobranch fish the optic nerve fibers enter the tectum through the zona interna of the stratum cellulare externum and send their axons into the more superficial tectal layers, while in actinopterygians and amphibians the majority of the optic fibers enter the tectum through the superficial layer and distribute their axons to deeper tectal layers.

ISSN:0092-7317    

DOI:10.1002/cne.901950103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe efferent connections of the tectum mesencephali in the sharkScyliorhinus caniculaand the rayRaja clavatahave been studied by using the silver impregnation methods of Nauta‐Gygax ('54) and Fink‐Heimer ('67). After a unilateral lesion made through all six tectal layers, three distinct pathways could be observed: (1) an ascending projection both ipsi‐ and contralateral to the pretectal area, the dorsomedial region of the thalamus, and the lateral geniculate body, (2) a commissural projection to the contralateral tectum and intercollicular nucleus, and (3) a descending projection to the rhombencephalic reticular formation. The last mentioned tract can be subdivided into (a) the ipsilateral tractus tectobulbaris ventralis and intermedius, giving off fibers to the intercollicular nucleus, the nucleus reticularis isthmi, and the medial and median reticular formation of the rhombencephalon and (b) the contralateral tractus tectobulbaris dorsalis, which connects the tectum with the contralateral medial reticular formation. Contrary to what has been found in other vertebrates there is no distinct segregation with respect to laterality of tectoreticular connections. Neither an ipsilateral projection to the nucleus isthmi nor a direct tectospinal pathway could be demonstrated with the techniques

ISSN:0092-7317    

DOI:10.1002/cne.901950104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractProjections from the cerebellar and dorsal column nuclei to the midbrain and thalamus of the rhesus monkey were traced with anterograde autoradiographic techniques, or, in a few cases, with the Fink‐Heimer method.The cerebellar nuclei give rise to a massive projection to the contralateral midbrain and thalamus via the ascending limb of the superior cerebellar peduncle. Cerebellar efferent fibers terminate contralaterally in both divisions of the red nucleus, and bilaterally in the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, the oculomotor nucleus, and the central gray.All the deep cerebellar nuclei project upon a broad area of the contralateral ventral thalamus as well as certain intralaminar nuclei. Corresponding ipsilateral thalamic terminations are sparse. The topograpic organization of cerebellothalamic fibers does not correspond to individual cerebellar nuclei or to cytoarchitectonic divisions of the ventral thalamic nuclei. Rather there are longitudinally oriented strips of terminal labeling which extend through all divisions of the ventral lateral nucleus, i.e., the VLps, the VLc, the VLo, as well as nucleus X, the oral division of the ventral posterolateral nucleus (VPLo), the central lateral nucleus (CL), and the most caudal region of the ventral anterior nucleus (VA). The topography of the cerebellothalamic fibers is arranged in a mediolateral pattern with fibers originating from anterior zones of the dentate and interpositus ending most laterally and those from posterior dentate and interpositus terminating most medially. The fastigial contribution is relatively sparse.The longitudinal strips of terminal labeling in the ventral thalamic nuclei are made up of still smaller terminal units consisting of disk‐like aggregates of silver grains separated from one another by grain‐free spaces.The dorsal column nuclei terminate primarily in the contralateral caudal division of the VPL (VPLc) and never extend rostrally into VPLo.These results demonstrate a segregation of cerebellar and dorsal columnar inputs to motor and sensory regions of the thalamus, respectively. Since these regions are separate and discrete in their cortical associations as well (Kalil, 1976), it seems unlikely that fast afferent pathways relaying to motor cortex (Lemon and Porter, 1976) could arise from the dorsal column n

ISSN:0092-7317    

DOI:10.1002/cne.901950105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe postnatal development of the axons of the dentate granule cells—the so‐called mossy fibers—was studied at the light microscopic level in Timm and Golgi preparations and also by transmission electron microscopy. In the Timm‐stained material, there was a distinctive coloration in the hilus and incipient stratum lucidum, indicating the presence of mossy fibers, on the first postnatal day. Over the next two weeks, the stained areas became more extensive, the size and density of the stained particles increased, and the particles became more intensely stained. These signs of progressive development of the mossy fibers appeared to reflect, temporally and topographically, the developmental gradients followed by their parent granule cells.The Golgi material confirmed the presence of mossy fibers in the hilus on the first postnatal day. Fasciculi of mossy fibers were observed in the stratum lucidum of the 3‐day‐old hippocampus, and although these immature axons were devoid of large synaptic expansions, they did have prominent growth cones at their termini. Small expansions along the lengths of the axons first appeared on day 7 and these grew to approximately an adult size and complexity by about day 14. The postsynaptic component of the mossy fiber synapse, the “thorny excrescence,” did not begin to emerge from the proximal portion of the pyramidal cell dendrites until sometime after day 9.At the electron microscopic level we observed, on the first postnatal day, small, immature mossy fiber expansions which made both symmetric and asymmetric contacts directly with dendritic shafts. These profiles, which were only one tenth the size of mature expansions, grew rapidly between postnatal days 1 and 9 and increased their mean area by a factor of five. On or about day 9, as the “thorny excrescences” emerged, the asymmetric synapses came to be associated with these spinous processes.Taken together, the Golgi and electron microscopic analyses support the suggestion that mossy fibers establish synaptic contact with pyramidal cell dendrites early in the postnatal period, several days before there is any indication of spine development. Furthermore, the “thorny excrescences” develop after the more typical, pedicellate spines have appeared on the distal pyramidal cell dendrites. Finally, while it is clear that the mossy fibers in our 21‐day‐old material are, for the most part, fully matured, a more subtle and protracted development of the system, long into adulthood, is indicated by the increased area and density of stained particles in the Timm prep

ISSN:0092-7317    

DOI:10.1002/cne.901950106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe posterior lateral line lobe of two high‐frequency weakly electric fish,Apteronotus albifronsandEingenmannia viriscens, was studied at the electron microscopic level. The various cell types previously described by light microscopy (Maler, ′79) were identified on the basis of their unique position or by combined Golgi‐EM. Afferent input to the posterior lobe was identified either by its location and generally accepted characteristics, e.g., parallel fibers in the molecular layer, or by making appropriate lesions and noting the degenerating terminals, e.g., primary electroreceptive afferents.The major cell types of the posterior lobe are as follows: (1) spherical cells—an electron‐dense cytoplasm crowded with ribosomes and other organelles; (2) granule cells—a small pale soma; fairly electron‐dense dendrites, and pale axon terminals with clustered pleomorphic vesicles; (3) pyramidal cells—a large pale soma with a well‐developed golgi apparatus; pale dendrites with evenly distributed microtubules; the somatic dendrites of pyramidal cells have an exceptional quantity of coated vesicles, multivesicular bodies, and smooth endoplasmic reticulum; (4) polymorphic cells—a medium‐sized electron‐dense soma; the dendrites are easily recognized by their content of neurofilaments, while their axon terminals are distinguished by their increased electron density and tightly packed ovoid vesicles.Two types of primary electroreceptive afferents were identified: (1) Latency coder terminals were slightly electron‐dense, with a small number of vesicles but large numbers of mitochondria; (2) Probability coder terminals were electron‐lucent, with a large number of round synaptic vesicles; the diameters of these vesicles were always bimodally distributed. Afferent fibers to the molecular layer of the posterior lobe are organized as parallel fibers at the light microscopic level; ultrastructurally they are similar to parallel fibers of the cerebellum and make appropriate asymetric synapses on all apical dendritic trees within the molecular layer.The circuitry of the posterior lobe is summarized in Figure 17. Latency coders make gap junction contact only with spherical cells, which in turn receive strictly latency coder input. Probability coders make mostly asymmetric chemical synapses onto granule cell and pyramidal cell basilar dendrites. The granule cell axons make symmetric synaptic contacts with the somata and somatic dendrites of both basilar and non‐basilar pyramids; they also synapse on the ascending apical and basilar dendritic processes of granule cells. These ascending processes of granule cells make gap junction contacts with the somata and somatic dendrites of only the non‐basilar pyramids. The consequence of this basic circuit appears to be that the posterior lobe can detect and enhance the contrast of objects with either high conductivity (basilar pyramids) or low conductivity (non‐basilar pyramids).The somatic dendrites of pyramidal cells were found to have extraordinary numbers of coated vesicles, and these were often associated with the postsynaptic densities of granule cell axons. The possible role of these coated vesicles in receptor recycling is discussed.All afferents of the posterior lobe end in specific laminae, and in a given lamina they usually terminate on all potential postsynaptic sites; this was defined as laminar specificity of synaptic connections. The latency coder to spherical cells contacts, and the granule cell ascending process to non‐basilar pyramid contacts are both specific to particular cells within a lamina; this was defined as cellular specificity of synaptic connections. Other examples of both sorts of synaptic specificity are presented and discussed in relation to curre

ISSN:0092-7317    

DOI:10.1002/cne.901950107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractCultures of dissociated hippocampal neurons from 18‐day‐old rat fetuses were examined by scanning electron microscopy after periods between one hour and 20 days following plating on a poly‐L‐lysine coated substrate. Cell attachment was virtually complete within one hour after plating, and at that stage many cells could be seen which had started to extend processes with broad growth cones. By four hours in culture, process formation was well advanced and some cells had already assumed a pyramidal configuration. After 16 hours in culture, numerous contacts were seen between neighboring growth cones, and this frequently led to fasciculation of the interacting fibers. During the next three weeks the cell bodies enlarged considerably and rounded‐up, and two distinct types of processes became evident: large, rapidly tapering dendrite‐like processes and finer, essentially uniform‐diametered processes that resemble axons. In most of the older cultures a dense plexus of processes was formed, and many of the finer processes appeared to have “bouton‐like” swellings as they traversed the upper surfaces of the neuronal perikarya. Non‐neuronal elements, which comprised only about 5% of the cells initially plated, rapidly proliferated in our cultures and within three to six days formed a confluent monolaye

ISSN:0092-7317    

DOI:10.1002/cne.901950108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe morphology of the dorsal motor nucleus of the vagus nerve (DMV) in the cat was studied with the aid of light and electron microscopy. In frozen sections stained by the Kluver‐Barrera method or stained to show retrograde labeling in the DMV following injections of horseradish peroxidase (HRP) in the cervical vagus nerve and the stomach wall a range of sizes of DMV neurons was observed but it was not possible to distinguish separate types. In contrast, two distinct types of neurons, one medium‐sized and the other small, were identified with the light microscope in Golgi‐Cox and 1‐μm Epon sections and with the electron microscope in ultrathin sections.The medium‐sized neurons had a range of sizes but generally measured 18 × 25 μm and possessed three to four proximal dendrites which branched two or three times. Spines were observed occasionally on the soma and on dendrites. These neurons contained a well‐developed cytoplasm and a noninvaginated round to oval nucleus. The small neurons generally measured 9 × 14 μm and were round or slightly elongated in shape. Their dendritic processes were fewer and thinner than those of the medium‐sized neurons and extended for shorter lengths. Their soma contained scanty cytoplasm and an invaginated nucleus. The medium‐sized neurons outnumbered the small neurons by more than three to one but both neuronal types were distributed evenly throughout the nucleus. The medium‐sized neurons seemed to correspond in size to the parasympathetic efferent neurons of the viscera as indicated by the HRP studies.Axosomatic synapses on both types of neurons and axodendritic synapses were observed in the DMV. Terminals containing mainly small clear round vesicles and making asymmetrical contact with the postsynaptic membrane were involved in the majority of synapses on both the soma and dendrites. Terminals containing predominantly pleomorphic vesicles and making symmetrical contact with the postsynaptic membrane were also common, comprising up to one‐third of all synapses observed. Serial sections revealed that most synaptic terminals contained varying numbers of large (75–110 nm) dense‐cored vesicles. Smaller dense‐cored vesicles (45–55 nm) were sometimes observed, often close to the area of synaptic contact. Terminals 1–2 μm in diameter which contacted dendrites 1–3 μm in diameter formed the most common synaptic combination throughout the rostral to caudal extent of the DMV. No distinct regional differences were observed with res

ISSN:0092-7317    

DOI:10.1002/cne.901950109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901950102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY