摘要:

AbstractEarlier small‐angle X‐ray diffraction studies have indicated that central and peripheral nerve myelins may be significantly different structurally, although relatively few examples for each system and for individual species have been examined. In order tounderstand better the intra‐ and inter‐system relationships, this study has developed more extensive information for a single species: six cases centrally and ten peripherally, featuring cranial nerves and a few others of the human nervous system. Peripheral myelin spacings (membrane pair thicknesses) are relatively similar, 184.4 ± 1.40 Å, and the ratios of diffraction peak height intensities of the second to fourth orders are also closelybunched: 1.85 ± 0.216. Central myelin spacings and intensity ratios are distinctly different and more variable: spacings 160.3‐165.8 A and intensity ratios 2.81‐4.46. It appears that within a given species or between closely related (e.g., mammalian) species peripheral myelins possess relatively invariant structures, though significant spacing declines are encountered for both systems as phylogenetic relationships become more distant. The observed greater variability of CNS structures within a singlespecies may correspond to known compositional differences between CNS regionsor result from observational difficulties. In any case there is a marked discontinuity between the myelin structures of CNS

ISSN:0092-7317    

DOI:10.1002/cne.901770102

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractScanning along human acoustovestibular nerves from cross‐sections closely proximal to the brain to locations distinctly peripheral thereto, by means of small‐angle X‐ray diffraction, has disclosed transitional junctions at which the myelin structure typical of central nervous system (CNS) axons gives way to one characteristic of peripheral (PNS) fibers. The junctions correspond to regions along the nerves, previously recognized histologically, at which the satellite cells responsible for axon myelination change character, from the oligodendrocytes of the CNS to the Schwann cells of the PNS. Thus the structural discontinuity between the CNS and PNS myelins can be ascribed to differences in the biosynthetic processes of the respective satellite cells. Junctions of this kind are to be expected in all cranial and spinal roots near the locations where they leave th

ISSN:0092-7317    

DOI:10.1002/cne.901770103

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractVisual response properties of single neurons in the superior colliculus of golden hamsters reared from birth to adulthood in total darkness were compared to those of normal hamsters. Directional selectivity, speed preferences, and receptive field organization in dark‐reared hamsters were essentially the same as those found in normally reared animals. Subtle neurophysiological effects of visual deprivation were indicated by the longer latencies of “on” responses to flashed spots of light in the dark‐reared animals. Also, in the visually deprived animals three cells were encountered which changed their responses from phasic to tonic as the size of the visual stimulus was increased. In normally reared animals all cells responding to stationary stimuli showed only phasic responses regardless of spot size. Behaviorally, dark‐reared animals could not be distinguished from normal animals on the basis of visual orienting and following tests. It was concluded that in the golden hamster visual experience during development has a minimal role in the induction or maintenance of the normal functional development of the superior c

ISSN:0092-7317    

DOI:10.1002/cne.901770104

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractThe onset and sequence of cell death in the lateral motoneurons of the lumbar spinal cord of the chick embryo was studied between 4 and 18 days of incubation by light and electron microscopy. The naturally occurring degeneration of a few motoneurons begins already on day 4 of incubation, but the cell loss becomes much more frequent from day 5.5 to day 9, during which 40% of the neuron population degenerates. In the light microscope, the degenerating neurons are seen to undergo shrinkage and condensation. Ultrastructurally, two types of degeneration can be recognized. In the first, termedType I, the polyribosomes are dissociated and appear free in the cytoplasm. Ribosomes also become detached from rough endoplasmic reticulum, although small pieces of cisternae of rough endoplasmic reticulum are still recognizable. Most of the mitochondria are vacuolized. These changes are accompanied by the appearance of a pyknotic nucleus which contains condensed chromatin masses. The most characteristic feature in what we termType IIdegeneration is the striking dilatation of the endoplasmic reticulum, the nuclear envelope and the Golgi apparatus. Ribosomes still form distinctly rosette‐like polyribosomes. A few mitochondria show signs of degeneration. The nuclear profile in most cells of this type is rounded whereas the chromatin is becoming condensed. In the late stages of Type II degeneration, the dilated membrane systems break down into numerous vesicles some of which still have ribosomes attached. Only late in the sequence of Type II degeneration do polyribosomes then dissociate to free monoribosomes. The degeneration process in both types leads finally to cell death and complete cellular breakdown: the entire process being due to an autolytic mechanism. The nuclear envelope breaks down and the nuclear content becomes mixed with lytic cytoplasm. The dying cell finally either condenses into one big globule or several smaller fragmented globules. All the globular debris are highly osmiophilic and compact. Only at this stage of breakdown is the cell debris phagocytozed by radial ependymal processes and mononuclear leukocytes. The entire degenerative process in these immature neurons is strikingly rapid.In the case of induced cell death by removal of the limb bud on day 2.5, we found that both types of degeneration described above also occur in the peripherally deprived lateral motor column (LMC). The only obvious difference is that limb bud removal increases thespeedand thenumberof cells undergoing degeneration. By day 10, about 90% of the neuron population in the deprived LMC have completely disappeare

ISSN:0092-7317    

DOI:10.1002/cne.901770105

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractDevelopment of the ventral roots in thecaudal halfof the chick lumbar spinal cord (segments 26‐29) was studied by electron microscopy. The ventral root fibers at 4, 5, 6, 7, 8, 9, and 13 days of incubation and at 1, 10 days and 5 weeks post‐hatching were counted either from photomontages or directly in the electron microscope.In the chick, most, if not all, the fibers in the caudal ventral roots studied here probably arise from axons of motoneurons in the lateral and medial motor columns. At four days of incubation, there is an average of 800 axons per segment. The number increases very rapidly reaching a peak of 5,500 axons at day 5.5 In other words, by day 5.5 all the axons of motoneurons hav ealready reached the ventral root region. Between days 6 and 9, the number dreastically declines to 2,200 axons poer segment, a 57% reduction in ventral root fibers. After day 9, there is only aminor and rather slow additional loss of axons, reaching 1, 700 in the 13‐day embryo and 1,500 in the 1‐day post‐hatching chick. In brief, during embryonic development about 71% of the axons are depleted in the ventral roots.Quantitatuve comparisons ofMotoneuronsin the lateral motor column (LMC) of segments 26‐29 with theaxon countsfrom the same segments have demonstrated: (a) that there is a massive natural cell loss in this region between days 5.5 and 9 amounting to 53%; (b) that axons are lost to the same extent as the motoneurons during this period, Resulting in a close to 1:1 relationship between the two by day 9.When horseradish peroxidase (HRP) was injected into the limb‐buds of 5‐day embryos, prior to the onset of massive cell death, virtually all motoneurons in the LMC were found to contain the HRP reaction product. Since approximately 50% of the cells present on day 5 typically degenerate by day 9, this finding, coupled with the observed close correspondence between axon and cell counts, strongly indicates that all motoneurons, even those destined to die, normally innervate the leg.Ultrastructural changes of motoneuron axons undergoing spontaneous degeneration in the ventral root were also described. The degenerating axons are found in the ventral root as early as the fourth day of incubation, although the number at this time is very low. More massive degeneration occurs between 5.5 and 9 days of incubation. The increrased number of degenerating axons in the ventral root during this period is in agreement with the increased number of degenerating cell bodies in the spinal lateral motor column at these same stages. Between day 4 and day 9, the degenerating axons are characterized by the presence of numerous vesiculated structures, membrane‐bounded autophagic vacuoles, membranous lamellar figures and electron dense bodies in focal, swollen portions of the axon, as well as the disruption of the axolemma. The degeneration process seems to be due to progressive autolysis with the final axonal remnants being phagocytozed by the surrounding Schwann cells and some mononuclear leukocytes. Approximately 60% of the ventral root fibers completely disappear within three to four days, leaving very little evidence of axonal debris. We have found no differences in the details of axonal degeneration of ventral roots from limbbud removal embryos. The spontaneous degeneration of axons continues even after hatching but on a much reduced scale. The post‐hatching degeneration is evidenced by the loosening of myelin sheath, shrinking of th axoplasm, an increase in both multivesicular bodies and lamellated dense bodies, and the disintergration of neurofilamen

ISSN:0092-7317    

DOI:10.1002/cne.901770106

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractThe differentiation of motoneurons following early limb‐bud ablation was studied in chick embryos from four days to hatching. Following the removal of the normal targets of these cells about 90% of the neurons in the lateral motor column (LMC) of segments 23–29 (lumbar) were found to disappear. By counting degenerating cells it was shown that virtually all of the cell loss could be accounted for by cell death, rather than impaired proliferation or enhanced migration away from the LMC. Quantitative comparisons of cell death between the peripherally deprived and the control, non‐deprived side demonstrated that limb‐bud removal not only enhanced the 50% natural cell death known to occur in this system, but also greatly accelerated the whole process. By stage 30 (6.5‐7 days) 75% of the final cell loss had occurred on the deprived side, whereas only 40% of the final cell loss had occurred on the control side. In both cases, however, cell death was confined to the period of limb innervation. Axon counts of the peripherally deprived ventral root showed that all the deprived neurons initially had sent an axon out of the spinal cord. Most of these, however, became caught in a neuroma before reaching the site of limb attachment. Though no synapses were found in the neuroma the axons were shown to be able to transport HRP back to the spinal cord. Before they began to degenerate, the deprived LMC motoneurons developed dendritic processes and these were able to form synapses with axons in the prospective lateral white matter. In early stages, frequent axo‐glial “synapses” were observed in the prospective lateral white matter of both deprived and control sides of the spinal cord. Since by stage 36 (day 10) these had virtually all disappeared, it was suggested that synapse formation in this region of the spinal cord may initially be under few constraints. In late stages (i.e., after day 8) it was noted that there were frequently signs of axonal degeneration in the lateral white matter on both sides of the spinal cord, suggesting a retrograde transneuronal degeneration initiated by the earlier cell death of motoneurons. Electron microscopic examination of the deprived LMC cells at different stages prior to degeneration failed to uncover any obvious differences between them and control cells on the non‐deprived side of the spinal cord.By histochemical and neurochemical methods the cholinergic enzymes acetylcholinesterase and choline acetyltransferase were found to develop normally up until the onset of frank degeneration in the deprived motoneurons, on day 5 or 6. After this the enzymes decreased at a rate comparableto the morphological loss of motoneurons by cell death.On the basis of these various lines of evidence, it is argued that all the motoneurons in the LMC have a remarkable intrinsic capacity toinitiatedifferentiation and that neurons experimentallydeprived of their normal target are no differen

ISSN:0092-7317    

DOI:10.1002/cne.901770107

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractThe efferent projections of the globus pallidus (GP) and entopeduncular nucleus (EP) in the rat were studied using autoradiographic and horseradish peroxidase (HRP) histochemical techniques. Following stereotaxic injections of3H‐leucine into EP, transported label was observed in the lateral part of the ventromedial nucleus (VM) of the thalamus, and more laterally, in the ventrolateral aspect of the ventral lateral‐ventral anterior thalamic complex (VALv). Selective accumulation of autoradiographic grains was also found in the parafascicular nucleus (Pf) and in the lateral habenular nucleus. HRP injections into the thalamus confirmed the entopeduncular projections to these nuclei. Comparison of grain distribution in the thalamus after3H‐leucine injections into EP and the zona reticulata of the substantia nigra (Clavier et al., '76) indicates that there is considerable overlap between nigral and EP projections to both VM and Pf. The nigrothalamic and entopedunculothalamic projections to VM and VALv are discussed with reference to the possibility that in the rat these nuclei are homologous to specific nuclei within the ventral lateral‐ventral anterior complex in primates.Injections of3H‐leucine into GP resulted in major accumulations of autoradiographic grains in the medial part of the subthalamic nucleus and the substantia nigra. Light and diffuse labelling was also observed in the dorsal thalamus. However, a consistent feature of the GP injections was that they appeared to result in diffusion of isotope to the reticular nucleus of the thalamus, and in view of the widespread thalamic projections of this nucleus, the label in dorsal thalamus could not be positively attributed to pallidal efferents. HRP injections throughout the thalamus failed to produce reactive cells in the GP. These experiments provided no firm support therefore for a recent suggestion that there are extensive projections from the globus pallidus to the thalam

ISSN:0092-7317    

DOI:10.1002/cne.901770108

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractPurkinje cell degeneration (pcd), an autosomal recessive mutation in the mouse, causes the postnatal death of virtually all cerebellar Purkinje cells during the third and fourth postnatal week. We have compared the postnatal development of normal andpcdmutant Purkinje cells. The early deviations from normal development involve primarily the perikaryonal polysomes and endoplasmic reticulum. Many of the mutant Purkinje cells retain abnormally the basal accumulation of polysomes, a finding which permits the identification of affected animals at postnatal day 15, one week prior to the onset of behavioral abnormalities. In addition, the affected Purkinje cells possess unusual configurations of endoplasmic reticulum with associated electron‐dense particles similar to but larger than ribosomes, mature and forming intracisternal A particles and nematosomes. Before thepcdPurkinje cells degenerate they appear to receive all their appropriate synaptic contacts. Some disruption, however, of parallel fiber: Purkinje spine synaptogenesis occurs at late stages of development. Some spines lack presynaptic elements, postsynaptic thickenings are present along the dendritic shafts and parallel fibers appear to make synaptic contacts directly onto the shafts. The spectrum of early morphological changes that has been observed inpcdmutant Purkinje cells is thus far unique to this cerebellar abnormalit

ISSN:0092-7317    

DOI:10.1002/cne.901770109

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractIn the present study the size of large samples of cells and the relative frequency of Y‐cells were measured in the lateral geniculate nucleus of monocularly‐deprived and reverse‐sutured cats. Due to deprivation large cells shrink more than smaller cells. This shrinkage is irreversible even over two years of reverse suture although over the same time the animals showed a remarkable pattern discrimination ability, which, in these animals, depends on the integrity of the geniculo‐cortical system. Physiologically, a significant increase in the probability of recording Y‐cells in the early‐deprived laminae of the LGNd was found after a reverse suture. The relative frequency of Y‐cells in the earlydeprived layers and in the late‐deprived layers was almost equal and not different from normal, although after the early deprivation by itself only 20% Y‐cells were found in the deprived layers. The latter results confirm our previous observation (Sherman et al., '72). The increase in the number of recorded Y‐cells following a reverse suture after monocular deprivation is accompanied by only small changes in the distribution of cell sizes in the LGNd. The number of very large cells in the early‐deprived layers was increased but the mean cell size remained unaltered after long forced usag

ISSN:0092-7317    

DOI:10.1002/cne.901770110

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY

摘要:

AbstractThe effects of undernutrition on the developing cerebellum were studied in 30‐day‐old rats undernourished from birth byrestricting access to the lactating mother. These animals showed a significant reduction in cerebellar weight when compared with well‐nourished controls. Quantitative studies of the cerebeller vermis revealed a 34.2% reduction in total area, with the densityof both granule cells and Purkinje cells increased. Network analysisof Golgi‐Cox preprations indicated a significant increase in the density of dendritic fields of Purkinje cells, although there was a 37% decrease in overall network size, due to reduction inthe total number of dendritic segments, and a reduction in the length of distal segments. Topological analysis indicated that the network had developed by terminal branching, as in normal animals, butwithsome deviation from the usual purely random branching pattern.All the observed modifications may be accounted for in terms of alterations in protein synthesis and DNA synthesis ocurring in undernourished animals. This leads to alterations in the extent of the intereuronal matrix, a rdduction in the number of granule cells and direct effects in Purkinje cell metabolism, all of which influence dendritic development, although the relative impotance of each of these factors awaits precise def

ISSN:0092-7317    

DOI:10.1002/cne.901770111

出版商:The Wistar Institute of Anatomy and Biology    

年代:1978

数据来源: WILEY