摘要:

AbstractThe sheath around the roots of the sixth abdominal ganglion in the yentral nerve cord of the crayfish consists of concentric layers of thin glial processes alternating with wide clefts containing filamentous connective tissue. Regions of each glial lamella are perforated by single, short, tubular channels: the trans‐glial channels. In thin plastic sections examined in the electron microscope, the channels appear as slits that are 240 Å wide and 450–550 Å long which traverse glial lamellae less than 1,500 Å thick. Branched tubular channels cross glial sheets that are thicker than 1,500 Å. The thickest glial wrap is adaxonal; it closely encapsulates individual axons and its cell membrane is separated from the axolemma by a collagen‐free space of only 150 Å. The adaxonal glial cytoplasm contains unique, three‐dimensional networks of interconnected tubules. Separate tubular lattices occur along these thicker processes.In replicas of freeze‐fractured sheaths, the outer half of the plasma membrane belonging to the thin glial sheets exhibits many volcano‐like protrusions which represent cross fractures through the necks of trans‐glial channels. Corresponding depressions on the inner half of these membranes are sites where the plasma membrane invaginates to form the channels. Although some channels are randomly dispersed, others are lineraly positioned in restricted areas across successive glial layers. The number of channels is far more readily appreciated in replicas than in thin sections. The average frequency of channels is 16 per μ2(range 8 to 33) in normal roots and does not differ significantly from the average of 13 per μ2in proximal stumps of roots fixed three to four weeks after the roots were cut. The channels are not precisely aligned from one glial layer to the next but do appear to coincide approximately with the adaxonal tubular lattice. The combination of trans‐glial channels and adaxonal tubular lattices may provide a complex conduit that could facilitate a rapid, passive flow of electrolytes and nutrients across the nerve sheath to the axonal surface. Horseradish peroxidase solutions bathing the ventral roots enter the trans‐glial channels, extracellular clefts and finally the tubular lattices. This distribution supports the proposed role of the channels in a rapid extracellular passage of solutes. The channel profiles have a range of forms consistent with the supposition that they are not static but continually reforming.There are indications that, proximal to the cut, the areas of glial plasma membrane with channel profiles contain more junctional complexes between regenerating cells than between glial cells of normal sheaths. The channel profiles and aggregates of particles belonging to junctions are closely associated when they occupy the sam

ISSN:0092-7317    

DOI:10.1002/cne.901670102

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractThe differentiation of Purkinje cells and their relationship to other components of the developing cerebellar cortex were analyzed by the Golgimpregnation method and by electron microscopy in human specimens of various pre‐ and postnatal ages. The three stages of Purkinje cell maturation that have been previously recognized in other species are also evident in man: thefirststage occupies primarily the fourth fetal month (12–16 weeks); thesecondstage lasts through the fifth, sixth and seventh fetal months (16–28 weeks); thethirdstage extends throughout the remaining period of intrauterine life and the first postnatal year and continues at a slow rate thereafter. During the first stage, Purkinje cells are distributed in a layer, several rows deep. Their bipolar somas are relatively smooth and have only a few processes at the apical and basal cell poles. In the 3‐month period of the second stage, Purkinje cells become gradully organized into a single row. Their somas become invested with additional randomly oriented dendritic processes and numerous somatic spines (pseudopodia). The first morphologically well‐defined synapses appear on the Purkinje cell somatic spines and on their immature dendritic shafts at the beginning of the second stage and become more prominent during the period from 18 to 24 weeks. In the third stage, the dendritic arbor becomes flattened in the plane transverse to the folium and somatic spines disappear. Spines appear on the secondary and tertiary dendrites between the twenty‐fourth and twenty‐eighth fetal weeks and continue to increase in number during the entire third stage as new dendritic branches develop. These observations indicate that cellular maturation and synaptogenesis in the primate cerebellum differ from these events in non‐primate species, with respect to time of birth, in the relative duration of each phase and in the total time necessary for neuronal differentiation. The protracted time of differentiation and the slow growth of Purkinje cell dendrites in man may be due to the numerically complex relationships existing between granule and Purkinje cells. It is probably not simply a reflection of the larger size of human Purkinje cells and

ISSN:0092-7317    

DOI:10.1002/cne.901670103

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractPrevious investigators have reported an increase in numbers of amacrine synapses in the inner plexiform layer (IPL) of the rat retina following light deprivation, and an increase in amacrine along with a decrease in bipolar synapses following light damage. Since there are several points of disagreement between the published reports on this subject we undertook a more detailed study of the effects of light deprivation and light damage on the retina.Four groups of eight male albino rat pups (14 days old) were raised for eight weeks under different conditions: (1) unsutured, bright light reared (UB); (2) bilaterally lid‐sutured, bright light reared (SB); (3) unsutured, low light reared (UL); and (4) bilaterally lid‐sutured, dark reared (SD). The intensity of the light given the UL group was equated with that striking the corneas of the SB group.Light microscopy showed that the retinas of the SB as well as the UB groups had almost complete degeneration of the outer retinal layers, indicating that even low intensity light, when continuous, causes severe retinal damage. The SD group was thicker in many of the retinal layers compared to the UL (control) group.Electron microscopy revealed that there were no significant changes in the incidences ofanytype of synapse in the IPL following light deprivation or light damage when averaged over total depth. This is in contradiction to the reports of other investigators. However, when the IPL was analyzed by levels, the incidence of amacrine‐ganglion synapses was significantly greater (p<0.05) in groups UB and SD, but only in the outer third of the IPL. Thus, extensive postnatal plasticity of IPL synapses in the rat retina did not occur under our experimental conditions. We found, at best, only limited effects which were confined to the amacrine‐ganglion s

ISSN:0092-7317    

DOI:10.1002/cne.901670104

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractThe neuronal organization of the motor cortex of a 19‐month old child with Down's syndrome (mongolism) has been studied with the rapid Golgi method. This congenital syndrome, also known as 21 Trisomy is caused by a chromosomal abnormality consisting of the presence of an extra chromosome in the group 21. Various structural abnormalities have been found in the dendritic spines (postsynaptic structures) of the pyramidal neurons of the motor cortex of this child. The axo‐spinous synapses of these neurons are considered to be altered by these spine abnormalities. In addition, a peculiar form of intrinsic vacuolar change affecting the dendrites and scattered neuronal fragmentation and necrosis have also been found. At least three different types of abnormality involving the spines — (the unusually long spine, the very short spine and a reduction in the number of spines) — are recognized among the pyramidal cells of the motor cortex. It is postulated herein: that a basic anomaly, possibly related to the genetic disorder affects primarily some cortical neurons which undergo progressive degenerative changes terminating in cell fragmentation and death. The different spine abnormalities are considered to represent various developmental stages of the common genetic anomaly. These changes might be structural correlates of the motor incoordination and mental retardation which are characteristic of this genetic disorder, but, final conclusions should await the investigation of other cases with this or similar methods capable of demonstrating the normal as well as the abnormal structural organization of the human cerebral

ISSN:0092-7317    

DOI:10.1002/cne.901670105

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractThe distribution of labeled cells was investigated in the brain of the ring dove one hour after administration of3H‐estradiol. Major areas of concentration of labeled cells were found in (1)the preoptico‐strial region: nucleus preopticus medialis and nucleus interstitialis of the dorsal olfactory projection, (2)the basal hypothalamic region: nucleus hypothalamicus posterior medialis and nucleus inferior, (3)the amygdaloid region: nucleus taeniae and adjacent portions of the archistriatum, and (4)the midbrain: substantia grisea surrounding the nucleus mesencephalicus lateralis, pars dorsalis. The findings support the phylogenetic homologies between the avian nucleus interstitialis of the stria dorsal olfactory projection and the mammalian nucleus interstitialis of the stria terminalis, the avian nucleus hypothalamicus posterior medialis and the mammalian nucleus ventromedialis hypothalami, as well as the avian nucleus inferior and the mammalian nucleus infundibularis‐premammillaris ventralis. The results also suggest that the nucleus taeniae and adjacent portions of the archistriatum correspond to the nucleus medialis and other more differentiated labeled areas of the mammalian amy

ISSN:0092-7317    

DOI:10.1002/cne.901670106

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractThe present study is an electron microscope analysis of the rami communicantes and its purpose is to determine the functional categories of unmyelinated axons in these nerves. Our findings indicate that the grey rami of segments T7, T8, or T9in the cat consist of approximately 5,000 unmyelinated axons and 20 myelinated axons, and that these axons are post‐ganglionic sympathetics. Although the numbers are new data, this conclusion confirms classic work. The white rami from the same segments contain approximately 3,200 unmyelinated axons and 1,600 myelinated axons. 80–90% of the myelinated axons are preganglionic sympathetics and the remainder are presumably sensory. This conclusion is also in confirmation of classic work. The new conclusions are that approximately 30% of the unmyelinated axons are preganglionic sympathetics, approximately 60% seem to be post‐ganglionic sympathetics and the surprisingly small remainder may be se

ISSN:0092-7317    

DOI:10.1002/cne.901670107

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901670101

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY