ISSN:0092-7317    

DOI:10.1002/cne.903550102

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

年代:1995

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903550103

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe birth of a neuron initiates a series of ontogenetic events, e. g., neuronal migration and differentiation. The outcomes of these events are neurons that successfully integrate into the cortical circuitry and neurons that are unsuccessful and ultimately die. The present study determined whether there is a relationship between the generation and death of cortical neurons.The decrease in the density of postmigratory neurons (heavily labeled by a single injection of [3H]thymidine) during normal development was used as an index of neuronal death. The survival indices of neurons varied with their times of origin. Neurons born from gestational day (G) 15 to G18 had the highest rates of survival. In contrast, the earliest and latest generated neurons (i. e., those born on G12‐G13 and those born on G19‐G21, respectively) had the lowest survival rates.The role of neuronal death in the formation of cortical patterns was determined by assessing the survival of neurons in the barrels and septa of somatosensory cortex. No differences in the survival index were determined for neurons in the C‐row barrels and adjacent septa with a particular time of origin.The survival rate of projection and local circuit neurons was determined with a doublelabeling technique. One label, [3H]thymidine, was used to determine the time of origin of the neurons. The second label was used to identify the chemical or hodological characteristics of a neuron; projection neurons were labeled either by retrograde transport of horseradish peroxidase or by glutamate immunohistochemistry, and local circuit neurons were immunohistochemically identified with an antibody directed against gamma‐aminobutyric acid (GABA) antibody. The survival rate for projection neurons (labeled by either technique) was as much as twice that for GABA‐immunoreactive local circuit neurons.Thus, the death of cortical neurons is related to their time of origin. Although neuronal death is not important for sculpting cortical patterns, death does selectively affect neurons with a specific hodological

ISSN:0092-7317    

DOI:10.1002/cne.903550104

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

年代:1995

数据来源: WILEY

摘要:

AbstractEfferent axons from area V2 to the middle temporal area (MT) were anterogradely labeled byPhaseolus vulgaris‐leucoagglutinin (PHA‐L) or biocytin and analyzed in serial reconstructions. Five of seven reconstructed axons had three arbors (each<200 μm in diameter) in layers 3–4, separated by 200–600 jLm. Two axons terminated in what was apparently a single focus in layers 3–4. Of 15 additional single arbors analyzed, 12 were concentrated in layers 3–4, and measured 200–250 μm across at their widest point. Three of these arbors were more columnar in shape (about 400 μm in diameter), and extended from layer 4 toward layer 1. This system differs in several features from MT‐projecting axons originating from V1. Namely, V2 axons terminating in MT are thinner (∼ 1. 0 μm vs. 3. 0 gm), their terminal specializations are more delicate, and their arbors are concentrated in layer 4 and overlying layer 3, with no collaterals to layer 6. These differences may reflect the distinctive neuronal populations giving rise to these two connectional systems (different sizes of pyramidal neurons in layer 3 of V2, and a mix of pyramidal and spiny stellate cells in area V). Differences may have implications for timing factors; that is, impulses from V1, subserved by large‐caliber axons, may arrive in MT coincidentally with indirect connections via V2 to MT. Another consideration may be the functional architecture of MT. Regularly spaced clusters of neurons have been described in MT which have similar directionality preferences. The interarbor spacing of cortical efferents is consistent with a columnar organization, but the laminar specificity may indicate recruitment of different combinations of postsynaptic populations b

ISSN:0092-7317    

DOI:10.1002/cne.903550105

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe human anterior cingulate cortex is distinguished by the presence of an unusual cell type, a large spindle neuron in layer Vb. This cell has been noted numerous times in the historical literature but has not been studied with modern neuroanatomic techniques. For instance, details regarding the neuronal class to which these cells belong and regarding their precise distribution along both ventrodorsal and anteroposterior axes of the cingulate gyrus are still lacking. In the present study, morphological features and the anatomic distribution of this cell type were studied using computer‐assisted mapping and immunocytochemical techniques. Spindle neurons are restricted to the subfields; of the anterior cingulate cortex (Brodmann's area 24), exhibiting a greater density in anterior portions of this area than in posterior portions, and tapering off in the transition zone between anterior and posterior cingulate cortex. Furthermore, a majority of the spindle cells at any level is located in subarea 24b on the gyral surface. Immunocytochemical analysis revealed that the neurofilament protein triplet was present in a large percentage of these neurons and that they did not contain calcium‐binding proteins. Injections of the carbocyanine dye DiI into the cingulum bundle revealed that these cells are projection neurons. Finally, spindle cells were consistently affected in Alzheimer's disease cases, with an overall loss of about 60%. Taken together, these observations indicate that the spindle cells of the human cingulate cortex represent a morphological subpopulation of pyramidal neurons whose restricted distribution may be associated with functionally distinct ar

ISSN:0092-7317    

DOI:10.1002/cne.903550106

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe present investigation examines the role of intercellular, relationships in the guidance of neuronal migration in embryonic rat cervical spinal cord. A “U‐shaped” group of cholinergic neurons, was first detected on embryonic days (E) 15. 5–16 surrounding the ventral proliferative zone. At these stages, no cholinergic cells were observed in the dorsal spinal cord, but by E17, many of the “U‐shaped” group of cholinergic cells appeared to have translocated dorsally, to become the cholinergic dorsal horn cells seen in older animals. Between E16 and E17, these choline acetyltransferase (ChAT)‐immunoreactive cells displayed primitive processes oriented dorsoventrally, suggesting migration along that axis. Two early forming substrates present in embryonic spinal cord have been implicated in the guidance of other populations of migrating neurons: glial cells organized in radial arrays and commissural axons aligned along the dorsoventral axis. Involvement of the commissural fibers with cholinergic cell migration seems more likely because the fibers and the translocation pathway have similar orientations. In double‐labeling immunocytochemical studies of E15. 5–17 spinal cord, some immature ChATcontaining neurons were directly adjacent to commissural fibers, as identified by SNAP/TAG‐1 immunoreactivity. The temporal and spatial coincidence of developing cholinergic neurons and commissural axons is consistent with the hypothesis that these neurons could use commissural fibers as migratory guides. In addition, conventional electron micrographs were examined to determine if immature neuronal profiles were physically apposed to commissural axons. Immature neurons with leading and trailing processes oriented dorsally and ventrally, respectively, were embedded within and aligned along bundles of commissural fibers or along other similarly oriented neurons. This direct apposition of immature cells to the surfaces of commissural axons and other bipolar neurons is consistent with the hypothesis that the “U‐shaped” group of cholinergic neurons may use commissural axons and other cohort neurons for guidance du

ISSN:0092-7317    

DOI:10.1002/cne.903550107

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

年代:1995

数据来源: WILEY

摘要:

AbstractAn electron microscopic analysis of cell islands in layer II of the entorhinal cortex from rhesus monkeys was made to determine the ultrastructural features of these unique neuronal clusters. The rostral, intermediate, and caudal divisions of the entorhinal cortex were selected for electron microscopic examination. In the rostral division, neurons were grouped together in prominent clusters, often with 10 or more contiguous somata. Somatic and dendrosomatic appositions were frequent, without intervening cellular processes or specialized junctions. Somata were relatively small, typically 10–15 μm in diameter, with oval or circular nuclei that were euchromatic and contained nucleoli. Small nuclear infoldings were commonly seen. A thin shell of perikaryal cytoplasm contained numerous organelles. Axosomatic synapses were infrequent, with a mean of only 1. 0 synapse per neuron per thin section. The neuropil contained numerous synapses, and myelinated axons were seen infrequently. In the intermediate division, somatic appositions were rarely observed. Somata were relatively large, typically 15–20 μm in diameter, and displayed a moderate amount of cytoplasm. Axosomatic synapses were relatively common, with a mean of 3. 3 synapses per neuron per thin section. In the caudal division, neurons were typically grouped in clusters of two to three contiguous somata. Neurons were about 15 μm in diameter and displayed a moderate amount of cytoplasm. Axosomatic synapses were of moderate frequency, with a mean of 2. 5 synapses per neuron per thin section. The neuropil in the caudal division displayed a relatively high frequency of myelinated axons.Our analysis of three regions of the entorhinal cortex revealed significant differences in the frequency of somatic appositions and axosomatic synapses, and in certain ultrastructural features of the somata and neuropil. These results showed that cell islands in layer II of the entorhinal cortex display regional morphologic differences. The paucity of symmetric axosomatic synapses in the rostral division may correlate with this region's vulnerability in certain di

ISSN:0092-7317    

DOI:10.1002/cne.903550108

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

年代:1995

数据来源: WILEY

摘要:

AbstractHypotransferrinemic (Hp) mice have a point mutation or small deletion in the transferrin (Tf) gene, resulting in defective splicing of precursor Tf mRNA. Hp animals produce 1% of normal Tf levels and require supplemental serum or purified Tf for survival. Because of the lack of endogenous brain Tf, we examined regional and cellular distributions of iron and iron regulatory proteins (Tf and ferritin) in selected brain regions of Hp mice. The regional distribution of iron, Tf, and ferritin in Hp brain was similar to normal except for the pattern of iron staining in hippocampus. The cellular distribution of iron, ferritin, and Tf was similar between Hp and normal animals. The predominant cell type, staining for Tf and iron was oligodendrocytes. Qualitative observations suggest that the number of cells staining for iron was similar between Hp and normal mice, whereas the number of Hp Tf‐positive cells was reduced. Ferritin immunostaining was similar in both cases. However, ferritin‐positive cells were preominantly astrocytes, an observation unique to mice among species studied previously. Western blot analysis revealed that Tf present in HP brain was of exogenous origin (from supplemental injections). Presumably, Tf transports the iron found in Hp oligodendrocytes. These data demonstrate that, despite reduced endogenous Hp brain Tf, iron and plasma Tf migrate or are transported to the appropriate cells (oligodendrocytes), bringing into question the role of endogenous brain Tf in extracellular iron transp

ISSN:0092-7317    

DOI:10.1002/cne.903550109

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

年代:1995

数据来源: WILEY

摘要:

AbstractA light microscopic immunocytochemical approach has been used to examine the distribution and maturation of γ‐aminobutyric acid‐ (GABA) containing cells in rat medial prefrontal cortex (mPFC) at progressive postnatal stages. Between P1 and P5, labeled cells in the cortical plate show less differentiated morphological characteristics when compared to cells in the deeper laminae. By P10, however, most labeled cells in superficial laminae show more differentiated characteristics with some having a distinctive multipolar appearance. Between P1 and P5, there is a significant increase (50%) in the density of GABA‐containing cells in the superficial laminae, while concurrently there is an overall decrease in the subjacent deeper laminae. As the cortex continues to expand, there is a corresponding decrease in the density of GABA‐immunoreactive cells in the outer two‐thirds of the cortical mantle until approximately P15, stabilizing at 20–25 cells/100,000 μm2for all laminae. Between P1 and P15, there is also a significant increase (133%) in the average size of labeled cells, followed by a gradual decrease of 30% between P15 and P41. During P1–7, there is a marked increase in the density of labeled axosomatic terminals in both the superficial (200%) and deep laminae (116%). In the superficial layers, however, the density of labeled terminals again increases by 86% between P12 and P18. In general, the present findings are consistent with the idea that there is a progressive maturation of the intrinsic GABAergic system in rat mPFC in a classic “inside‐out” pattern, and this involves extensive postnatal changes occurring during the fi

ISSN:0092-7317    

DOI:10.1002/cne.903550110

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

年代:1995

数据来源: WILEY

摘要:

AbstractMossy cells of the hippocampal dentate gyrus were analyzed through postnatal development. At birth, a few thorny excrescences were found on the proximal dendrites of mossy cells, whereas distal dendrites displayed pedunculate spines. Thorny excrescences increased in number and complexity until the third month. After that age, the complexity of thorny excrescences is so great that an increase in spine density can be seen only in electron microscopic preparations. An increase in the number of pedunculate spines per unit length of distal dendrite was detected via light microscopy during the first 9 postnatal months. The somata and dendrites of mossy cells displayed adult‐like characteristics after the ninth postnatal month.Mossy fiber terminals at birth frequently displayed immature ultrastructural characteristies and formed synapses with dendritic shafts and spines. At later postnatal ages and in adults, axospinous synapses were found almost exclusively. This is consistent with the postnatal development of the complex spines of the mossy cells.Axons of mossy cells were generally confined to the hilus in our 150 ‐μm‐thick sections, where they gave rise to several collaterals. The axon terminals from these collaterals formed asymmetric synapses with dendrites and dendritic spines in the hilar region of the dentate gyrus. These data provide the first anatomical evidence that hilar mossy cells of the primate dentate gyrus have excitatory projections similar to their equivalent cell type in subprimates.The present study indicates that mossy cells of the dentate gyrus are in a more advanced stage of development at birth and mature faster than similar neurons of the human hippocampus. This may represent a faster maturation of hippocampal circuitry in nonhuman primates compared to that in the

ISSN:0092-7317    

DOI:10.1002/cne.903550111

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

年代:1995

数据来源: WILEY