摘要:

AbstractThe development of the electric lobes ofTorpedo marmoratahas been investigated using light and electron microscopical techniques. The lobeAnlagenbecome visible in the rhombencephalon along the floor of the 4th ventricle at the 10‐mm stage. Many of the neuroepithelial cells in theAnlagendifferentiate, becoming postmitotic and axonic by the 24 mm stage. Proliferative zones of neuroepithelial cells disappear from the electric lobes by the 30‐mm stage. After their initial, early differentiation the electromotor neurons remain monopolar until the 40‐mm stage when dendrite formation begins. The differentiation of the electromotor neuron from a mono‐ to an immature multi polar form occurs between the 40‐ and 55‐mm stages and involves, in addition to dendrite formation, a change from a pear‐shaped to a spherical cell body, a dramatic increase in cytoplasmic volume, a centralization of the nucleus, an enlargement of the nucleolus and its migration away from the nuclear membrane, and differentiation of the axon hillock. The electric lobes are invaded by sinusoids at the 24‐mm stage but formation of the capillary network by sprouting cords of endothelial cells begins later at the 40‐mm stage. Neuronal cell death (26–74‐mm stages) appears to be mainly an autolytic process and the debris is removed by immature glial cells. Afferent fiber growth cones are first recognized in the lobes at the 60‐mm stage but synapses are not observed until the 78‐mm stage. Myelination begins in the electric lobes concomitantly with the onset of synaptogenesis. A twofold increase in dendrite length occurs over the period when synapses begin to form in the lobes but dendritic maturation is not complete until the neonatal (120‐mm) stage. The results are discussed in relation to the develop

ISSN:0092-7317    

DOI:10.1002/cne.902110402

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractTo determine whether selective exposure to lines of one orientation modifies the shape of the dendritic fields of cells in visual cortex, we examined the dendritic morphology of neurons in area 17 of five normally reared cats, five cats reared viewing only vertical lines, and three cats reared viewing only horizontal lines. Kittens were placed with their mothers into a totally dark room before their eyes had opened. Beginning at 4 weeks of age, the kittens were brought out for daily periods of exposure wearing masks that limited the vision of each eye to a field of three vertical lines or three horizontal lines. After a minimum of 170 hours of exposure, the animals were killed and blocks of visual cortex were impregnated by the Golgi‐Kopsch procedure and cut tangential to the pial surface. Complete neurons from layers III and IV were drawn with the aid of a camera lucida, and the orientations of the dendritic fields were analyzed using Sholl diagrams. In normal cats, the distributions of the orientations of dendritic fields were uniform, whereas in stripe‐reared cats, the distributions for the layer III pyramidal cells were shifted. The direction of this shift varied with the experience of the cat: In cats reared viewing only vertical lines, the dendritic fields were oriented orthogonal to the representation of the vertical meridian, and in cats reared viewing only horizontal lines, the fields were oriented parallel to the representation of the vertical meridian. In contrast, the distribution of dendritic orientations for the stellate cells was not affected by stripe‐rearing. These results demonstrate a morphological effect of early visual experience that is specific to the particular stimulus presented during rearing and suggest that (1) cortical cells differ in the degree to which they can be modified by such experience, and (2) the dendritic morphology of cortical neurons is related to their preferred orienta

ISSN:0092-7317    

DOI:10.1002/cne.902110403

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractNeurons of the raccoon main (MCN) and external (ECN) cuneate nuclei having terminal fields in the anterior lobe and paramedian lobule of the cerebellum were studied by means of the retrograde transport of horseradish peroxidase (HRP). In the MCN, neurons of the polymorphic regions, but not of the round cell clusters, were labeled following HRP injections of the anterior lobe. HRP‐labeled fusiform, triangular, and stellate cells were observed from 3–4 mm caudal to the obex to 2–3 mm rostral to it. The main body of labeled MCN neurons was located in the 1.25 mm immediately rostral to the obex, there forming a recognizable subnucleus in the ventral MCN. The ECN displayed uniform labeling from the anterior lobe with no particular cell type or nuclear region being labeled preferentially. A minor projection to the anterior lobe appeared to originate in the contralateral MCN and ECN. Injections of the paramedian lobule produced MCN labeling similar to that observed after anterior lobe injections, but the majority of labeled ECN neurons were found in the dorsomedial part of the nucleus.In lobule V of the anterior lobe, sagittal zone c contained the greatest density of cuneocerebellar terminals as judged by the degree of retrograde labeling seen in neurons of both the MCN and ECN. This observation was consistent with evoked potentials recorded in the anterior lobe of the raccoon cerebellum.The position of cuneocerebellar neurons in the ventrolateral MCN suggests that the bulk of the information being transferred to the cerebellumby the raccoon MCN is related to deep, rather than cutaneous, modal

ISSN:0092-7317    

DOI:10.1002/cne.902110404

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe manner in which each retina can be mapped onto a single cross section of the optic tract of the cat has been defined by neuroanatomical methods. It has been found that the contralateral nasal hemi‐retina and both temporal hemi‐retinae are represented in each tract by multiple, rough maps which partially overlap one another. All maps show the same general orientation, with area centralis represented dorsomedially, lower retina represented dorsolaterally, and upper retina represented ventromedially. The peripheral part of the horizontal meridian is represented ventrolaterally.Labeling all of the fibers from one eye by axonal degeneration or autoradiographic methods shows that the crossed map is displaced dorsally and medially relative to the uncrossed map, leaving a dorsomedial crescent of pure crossed fibers. Localized retinal lesions or injections of 3H‐amino acid show the general orientation of the maps. Lesions within the dorsomedial pure crossed crescent show that fibers in this crescent arise from retinal areas close to the optic disc, near the site of the early fetal fissure. Localized injections of horseradish peroxidase into the optic tract show the relationships of the several maps in terms of the retinal distribution of retrogradely labeled retinal ganglion cells. They show that axons of large and small cells map ventrolaterally in the tract while intermediate sizes map dorsomedially. They confirm that the crossed map is displaced relative to the uncrossed map.It is suggested that the optic tract develops by fibers taking a position in the tract in accordance with their time of arrival at the chiasm. The several maps are displaced because they develop sequentially and the optic tract can be read as a developmental record, the most dorsomedial axons being the o

ISSN:0092-7317    

DOI:10.1002/cne.902110405

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe potential for the transformation of the normal microglial cell to a lipid phagocyte was studied by light and electron microscopy in the brains of rodents and by light microscopy only in primates. All were subjected to some form of hypoxia‐ischemia and the microglial response was examined in regions of selective neuronal destruction (SND) so that infarction was deliberately excluded. In vivo perfusion‐fixation was employed in all animals and light microscopic examination was carried out on paraffin‐ and sometimes celloidin‐embedded material. Semithin plastic sections from several regions of the rodent brains were used for light microscopy but ultrastructural studies were confined to the hippocampus.In all animals the microglia were activated and transformed into rod cells exhibiting phagocytic properties but only a minority gave rise to lipid phagocytes. Blood vessels were normal in all animals and no hematogenous elements were identified in the parenchyma. As neuronal ghosts could be identified for up to 3 weeks it was concluded that the capacity of the microglia for phagocytic activity was

ISSN:0092-7317    

DOI:10.1002/cne.902110406

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe source of the lipid phagocytes that occupy a cerebral infarct has been determined by light and electron microscopy in the brains of rodents and by light microscopy only in the brains of primates. The infarcts (in neocortex, hippocampus, and thalamus) were the consequence of hypoxiaischemia of various types. Hemorrhagic infarcts were excluded. After in vivo perfusion‐fixation, paraffin‐ and celloidin‐embedded material was used for light microscopy. Semithin plastic sections from the neocortex and thalamus were studied with the light microscope and ultrastructural studies were confined to the same regions.In all animals after about 2 days there was evidence of phagocytic activity in the fibroblasts in the adventitia of the remaining large vessels and also proliferation by mitotic division. At 5‐7 days fibroblasts appeared to migrate from the vessels in a semifluid or fluid milieu and to give rise to typical phagocytes. These increased in size and number but signs of degeneration became apparent after 10 days and they had largely disappeared by 32 days. Smooth muscle cells and pericytes showed evidence of degeneration and phagocytic activity was never seen in the

ISSN:0092-7317    

DOI:10.1002/cne.902110407

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe present study uses a spinal cord isolation procedure to remove extrinsic axons but leave intrinsic axons intact. The isolation is done by sectioning the spinal cord in two places and then cutting all dorsal roots between the two sections. The axons that survive the isolation procedure are thought to be propriospinal axons. Following isolation, approximately one‐third of the axons in sacral tracts of Lissauer in the rat survive. Thus approximately one‐third of the axons in sacral tracts of Lissauer in the rat are propriospinal. Proportionately more myelinated than unmyelinated axons are lost. There are approximately equal numbers of surviving axons in the medial as opposed to the lateral part of the tract. This implies that there is, as yet, no morphological basis for dividing the tract into medial and lateral halves. The fact that the number of propriospinal axons in the tract of Lissauer has been quantitated offers more precision in our thinking about the organization of the dorsal h

ISSN:0092-7317    

DOI:10.1002/cne.902110408

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe present study was undertaken to provide an explanation for previous autoradiographic results suggesting a several times higher rate of synthesis of glycoconjugates per unit volume of hypothalamic glia than of neurons. Volume densities, specific surfaces (surface:volume ratios), and relative surfaces (contribution of the surface of a tissue element to the total surface of the tissue) were assessed.Neuronal elements occupy about 74% and glial elements about 8% of the total volume. The specific surface, i.e., the amount of plasma membrane per unit volume of structure, is more than 30 times higher in the neuropil than in the neuronal perikaryal fraction. The largest specific surface is found with (unmyelinated) axons and astroglial processes. The specific surface of the average astrocyte is about twice that of the average neuron. If the surface of the entire cell is considered in relation to the perikaryal volume only, this ratio is about seven times as large for glial cells as for neurons. It follows that an astrocyte perikaryon has to renew a several times larger plasma membrane than a neuron, which can account for the above differences in perikaryal synthesis rates of glycoconjugates.

ISSN:0092-7317    

DOI:10.1002/cne.902110409

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThis study examines the connections underlying the vestibulocollic system in the adult pigeon by using retrogradely transported horseradish peroxidase (HRP) to identify neck muscle motoneurons in one set of animals, and transneural anterograde transport of tritiated proline‐fucose to delineate the descending medial (MVST) and lateral (LVST) vestibulospinal tracts in a second set of animals. Correlations of location and distribution of HRP‐labeled motoneurons and autoradiographically labeled fiber tracts and terminal fields were performed between the two sets of experiments.The right biventer cervicis and complexus neck muscles were subdivided into rostral and caudal halves in ten animals and HRP injected into only half of one of the two muscles in each experiment. Following a 16–48‐hour survival, the brain was fixed by intracarotid catheterization and perfusion and the HRP in the brain sections reacted with the tetramethylbenzidine (TMB) blue reaction process. Three groups of HRP‐labeled motoneurons were identified in the ipilateral ventral horn of the upper cervical spinal cord: a ventromedial and ventrolateral group within lamina VIII innervating the biventer cervicis and the more rostral part of the complexus muscle, and a dorsolateral group of motoneurons within lamina VII innervating the caudal part of the complexus muscle. The dorsolateral motoneurons with their HRP‐labeled axons leaving the cord through the dorsal root are homologous to the spinal accessory nucleus of mammals. Labeled motoneurons were also noted in the ipsilateral medulla adjacent to the medial longitudinal fasiculus (ELM) in a location previously identified as the hy‐poglossal nucleus. Additional experiments were performed in which HRP was injected directly into the base of the tongue. The resultant HRP‐labeled hypoglossal motoneurons were separate and dorsolateral to the collic motoneurons.Descending vestibulospinal projections from one vestibular labyrinth were identified autoradiographicalry (ARG) by transneural anterograde transport of3H‐proline‐fucose injected into the left labyrinthine endolytine endolymph in five animals. Heavily labeled MVST fibers were observed crossing the midline of the brain to enter and descend in the contralateral ELM. Labeled MVST fibers were noted to leave the contralateral FLM and surround the previously identified collie motoneurons in the medulla with intense terminal fields suggestive of synaptic contact. Labeled MVST fibers in the contralateral ventral funiculus of the cord were also noted to innervate the HRP‐identified ventromedial and ventrolateral cervical motoneurons, but not the dorsolateral motoneurons in lamina VII. Ipsilateral (left) descending MVST and LVST fibers were less heavily labeled at all levels in the medulla and upper cervical cord. Labeled ipsilateral (left) vestibulospinal fibers were also observed to leave the lateralmost aspect of the left ventrolateral funiculus in the upper cervical cord to terminate among left ventrolateral motoneurons. Our findings are compared and contrasted with previous studies of ves

ISSN:0092-7317    

DOI:10.1002/cne.902110410

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902110411

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY