摘要:

AbstractThis study examines the distribution and morphological characteristics of glutamic‐acid‐decarboxylase‐like (GAD)‐ and parvalbumin‐like (PA)‐immunoreactive structures in the olfactory bulb of the human adult.GAD‐immunoreactive somata occurred in the glomerular layer, the external granule cell layer, the more superficial portion of the external plexiform layer, and the internal granule cell layer. The cells were small‐ to mediumsized. Demonstration of lipofuscin pigment revealed the presence of unpigmented as well as pigmented neurons, thus suggesting the existence of two subpopulations of GAD‐positive neurons. GAD‐immunoreactive puncta and/or fibers were mainly seen in the periglomerular region and the internal granule cell layer. All other layers of the bulb, as well as the intrabulbar portion of the anterior olfactory nucleus, displayed considerably less of these puncta and/or fibers. The olfactory nerve layer remained practically clear of immunoreactive material.PA‐immunoreactive somata occurred in the glomerular layer and both the external and internal granule cell layer. Only a small number of immunoreactive nerve cells were encountered within the white matter or the olfactory tract. Most PA‐positive neurons displayed characteristics of short axon cells whereas a few others resembled van Gehuchten cells. All of the PA‐immunoreactive neurons were devoid of lipofuscin pigment. Immunoreactive puncta and fibers were present in all layers though predominating in the periglomerular region, the olfactory nerve layer, and the internal granule cell layer. The intrabulbar portions of the anterior olfactory nucleus did not show any

ISSN:0092-7317    

DOI:10.1002/cne.902910102

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe developmental stage at which a neuron becomes committed to a neurotransmitter phenotype is an important time in its ontogenetic history. The present study examines when choline acetyltransferase (ChAT) is first detected within each of four different subsets of cholinergic neurons previously identified in the cervical enlargement of the spinal cord: namely, motor neurons, partition cells, central canal cluster cells, and dorsal horn neurons. By examining the temporal sequence of embryonic development of these cholinergic neurons, we can infer the relationships between ChAT expression and other important developmental events.ChAT was first detected reliably on embryonic day 13 (E13) by both biochemical and immunocytochemical methods, and it was localized predominantly within motor neurons. A second group of primitive‐appearing ChATpositive cell was detected adjacent to the ventricular zone on E14. These neurons seemed to disperse laterally into the intermediate zone by E15, and, on the basis of their location, were tentatively identified as partition cells. A third group of primitive ChAT‐immunoreactive cells was detected on E16, both within and around the ventral half of the ventricular zone. By E17, some members of this “U”‐shaped group appeared to have dispersed dorsally and laterally, probably giving rise to dorsal horn neurons as well as dorsal central canal cluster cells. Other members of this group remained near the ventral ventricular zone, most likely differentiating into ventral central canal cluster cells.Combined findings from the present study and a previous investigation of neurogenesis (Phelps et al.:J. Comp. Neurol. 273: 459–472, '88), suggest thatpremitoticprecursor cells have not yet acquired the cholinergic phenotype because ChAT is not detectable untilafterthe onset of neuronal generation for each of the respective subsets of cholinergic neurons. However, ChAT is expressed in primitive bipolar neurons located within or adjacent to the germinal epithelium. Transitional stages of embryonic development suggest that these primitive ChAT‐positive cells migrate to different locations within the intermediate zone to differentiate into the various subsets of mature cholinergic neurons. Therefore, it seems likely that spinal cholinergic neurons are committed to the cholinergic phenotype at pre‐ or early migratory stages of their development. Our results also hint that the subsets of cholinergic cells may follow different migration routes. For example, presumptive partition cells may use radial glial processes for guidance, whereas dorsal horn neurons may migrate along nerve fibers of the commissural pathway. Cell‐cell interactions along such diverse migratory pathways could play a role in determining the different morphological, and presumably functional, phenotypes expressed by spinal ch

ISSN:0092-7317    

DOI:10.1002/cne.902910103

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe tectum mesencephali of salamanders shows a morphology that has long been considered primitive when compared with that of frogs. The alternative hypothesis is that the salamander brain is secondarily simplified. In order to test these two hypotheses, the cytoarchitecture of the tectum and the projections of tectal neurons were studied in 11 species of salamanders. Application of the Golgi method reveals three major morphological types. Type 1 has a very wide dendritic arborization mostly confined to the deep fiber layers, and somata are always located within the most superficial part of the periventricular gray matter. Type 2 possesses a wide to medium‐size dendritic arborization. In subtype 2a the somata are located in the uppermost part of the gray, and dendrites always reach the uppermost layer of retinal afferents; in subtype 2b the somata are found in deeper parts of the gray, and dendrites arborize in the deeper layers of retinal afferents; and in subtype 2c the somata are also located in deeper parts, but the wide dendritic arborization is confined to deep fiber layers. Type 3 shows the narrowest dendritic arbors that always reach the upper two tectal fiber layers. The somata are found at any depth of the gray matter.HRP experiments reveal a correlation between morphological differences and the projections of tectal neurons. Type 1‐ and type 2c‐like cells constitute the uncrossed tecto‐bulbo‐spinal tract, whereas type 1‐ and type 2a‐like cells and migrated large spindle‐shaped cells(Salamandra)constitute the crossed tecto‐bulbo‐spinal tract. Type 3‐like neurons project to thalamic, pretectal and isthmc termination sites.The HRP experiments also demonstrate the existence of two classes of mesencephalic trigeminal cells.A comparison shows that salamanders and frogs possess very similar functional and morphological types of tectal cells. However, tectal cells of salamanders show a “juvenile” morphology, and the number of migrated cells is about 10 times higher in frogs compared to salamanders. Both phenomena are seen as the result of secondary simplification of brain structures in the

ISSN:0092-7317    

DOI:10.1002/cne.902910104

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

年代:1990

数据来源: WILEY

摘要:

AbstractPyramidal neurons in the mouse SmI cortex were labeled by the retrograde transport of horseradish peroxidase (HRP) injected into the ipsilateral MsI cortex. Terminals of the local axon collaterals of these neurons (CC terminals) were identified in SmI, and their distribution and synaptic connectivity were examined. To avoid confusion, terminals in SmI cortex labeled by the anterograde transport of HRP injected into MsI were eliminated by lesioninduced degeneration. Lesions of MsI were made 24 hours after the injection of HRP; postlesion survival time was 4 days.Most CC axon terminals occurred in layers III and V where they formed asymmetrical synapses. Of 139 CC synapses in layer III and 104 in layer V, approximately 13% were formed with dendritic shafts. Reconstruction of 19 of these dendrites from serial thin sections showed them to originate from both spiny and nonspiny neurons. Most synapses of CC terminals (about 87%) were onto dendritic spines. In contrast, White and Keller (1987) demonstrated that terminals belonging to the local axon collaterals of corticothalamic (CT) projection cells synapse mainly with dendritic shafts of nonspiny neurons: 92% onto shafts, the remainder onto spines. The distribution of asymmetical synapses onto spines and dendritic shafts was analyzed for neuropil in layers III, IV, and V. Depending on the layer, from 34 to 46% of the asymmetrical synapses in the neuropil were onto dendritic shafts. Results showing that CC and CT terminals form proportions of axodendritic vs. axospinous synapses that differ from each other, and from the neuropil indicate that local axon collaterals are highly selective with regard to their postsynaptic elements.

ISSN:0092-7317    

DOI:10.1002/cne.902910105

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

年代:1990

数据来源: WILEY

摘要:

AbstractDespite the putative role of opioids in disorders of the developing human brainstem, little is known about the distribution and ontogeny of opioid‐ specific perikarya, fibers, terminals, and/or receptors in human fetuses and infants. This study provides baseline information about the quantitative distribution of opiate receptors in the human fetal and infant brainstem. Brainstem sections were analyzed from three fetuses, 19‐21 weeks gestation, and seven infants, 45‐68 postconceptional weeks, in whom the postmortem interval was ≤12 hours. Opiate receptors were localized by autoradiographic methods with the radiolabelled antagonist3H‐naloxone. Computer‐based methods permitted quantitation of3H‐naloxone binding in specific nuclei, as well as three‐dimensional reconstructions of binding patterns. High3H‐naloxone binding corresponds primarily to sensory and limbic nuclei, and to nuclei whose functions are known to be influenced by opioids, e.g., trigeminal nucleus (pain), nucleus tractus solitarii and nucleus parabrachialis medialis (cardiorespiration), and locus coeruleus (arousal). The regional distribution of opiate receptors as determined by3H‐naloxone binding is similar in human infants to that reported in human adults and animals and corresponds most closely to that of mu receptors. We found, however, that opiate receptor binding is high in the fetal and infant inferior olive, in comparison to low binding reported in this site in adult humans, primates, and rodents. In addition, opiate receptors are sparse in the fetal and infant substantia nigra, as in reports of the adult human substantia nigra, compared to moderate densities reported in primates and rodents. By midgestation, the regional distribution of3H‐naloxone binding in human fetuses is similar, but not identical, to that in infants. Highest3H‐naloxone binding occurs in the inferior olive in fetuses at midgestation, compared to the interpeduncular nucleus in infants. Tritiated naloxone binding quantitatively decreases in virtually all nuclei sampled over the last trimester, but not to the same degree. The most substantial binding decrease (two‐ to fourfold) occurs in the inferior olive and may reflect programmed regressive events, e.g., neuronal loss, during its development. Definitive developmental trends in3H‐naloxone binding occurs in the inferior olive in fetuses at midgestation, compared to the interpeduncular nucleus in infants. Tritiated naloxone binding quantitatively decreases in virtually all nuclei sampled over the last trimester, but not to the same degree. The most substantial binding decrease (two to fourfold) occurs in the inferior olive and may reflect programmed regressive events, e.g., neuronal loss, during its development. Definitive developmental trends in3H‐ naloxone binding are not observed in the postnatal period studied. The heterogeneous distribution of opiate binding in individual brainstem nuclei underscores the need for volumetric sam

ISSN:0092-7317    

DOI:10.1002/cne.902910106

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

年代:1990

数据来源: WILEY

摘要:

AbstractRetrograde and anterograde transport of tracers, electrophysiological recording, somatotopic mapping, and histochemical and immunological techniques have all revealed a parasagittal parcellation of the cerebellar cortex, including its efferent and many of its afferent connections. In order to establish whether the different compartments share a common organizational plan, a systematic comparative analysis of the patterns of parasagittal zonation in the cerebellar cortex of the rat has been undertaken, by using the parasagittal compartmentation of zebrin I+ and zebrin I‐Purkinje cells as revealed by monoclonal antibody Q113 as a reference frame. The distribution of mossy fiber terminals originating from the lower thoracic‐higher lumbar spinal cord was compared to the distribution of zebrin I bands. Three‐dimensional reconstructions from alternate frontal sections processed either for the anterograde transport of tracer or for zebrin I immunoreactivity reveal that the limits of the spinocerebellar terminal fields in the granular layer correlate well with the boundaries of some, but not all, zebrin I compartments in the molecular layer above. This leads to a subdivision of the zebrin I compartments into spinal receiving and spinal nonreceiving portions. In lobules II and VIII, the spinocerebellar terminal fields assume different positions relative to the zebrin I compartments in the ventral compared to the dorsal faces. Thus, each longitudinal compartment may be further divided transversely into subzones, each receiving a specific combination of mossy fiber afferents. The further subdivision of zebrin I compartments by mossy fiber terminal fields increases the resolution of the topography to such a point that anatomical compartment widths become compatible with the width of the microzones and the patches identified by electrophysiological me

ISSN:0092-7317    

DOI:10.1002/cne.902910107

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

年代:1990

数据来源: WILEY

摘要:

AbstractRecent studies of visually elicited orienting in the frogRana pipienssuggest that tectofugal signals important in this behavior relay in the midbrain tegmentum before descending to the spinal cord. They also suggest that the high degree of topographic organization displayed by the retinotectal projection may be less characteristic of other tectal afferent and efferent pathways. To explore these possibilities, we have studied patterns of retrograde and anterograde labelling following multiple and single injections of horseradish peroxidase into the tectum.We have found that the midbrain tegmentum is major terminal zone for tectal efferent projections. Our material also provided a description of the boundaries of other structures which project to and receive input from the tectum. With this background, we studied topographic organization by analyzing for each structure the distribution of labelling following multiple injections, and comparing it with the label distribution following single injections at tectal loci with known visual field input. Multiple injections produced patchy anterograde and retrograde labelling in the nucleus isthmi, with the number of patches corresponding to the number of tectal sites injected. Single injections produced labelling in restricted regions of the nucleus isthmi, the location of which varied systematically with the location of the tectal injection site. In all other structures studied, labelling was more evenly distributed following multiple injections. In none of these structures could we detect systematic variations in the location of labelling associated with variations in the location of single tectal injection sites, and the labelling following single injections was frequently coextensive with that following multiple injections. We also found no evidence that there exist structures which project to or receive input from particular tectal regions and not others.We conclude that there exist adequate neuroanatomical substrates for a tectotegmentospinal pathway believed to be important for visually elicited orienting in the frog. We also conclude that a high degree of topographic organization is more the exception than the rule in considering tectal connections generally in the frog. Topographic organization was readily apparent in connections related to the nucleus isthmi but not in connections related to any other nonretinal structure.

ISSN:0092-7317    

DOI:10.1002/cne.902910108

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe normal adult rat corpus callosum contains numerous axonal profiles that are immunoreactive for the high molecular weight subunit of the neurofilament triplet (NF‐ H). NF‐H immunoreactivity develops gradually during the first 2 postnatal weeks. The expression of NF ‐ H immunoreactivity is almost completely suppressed in rats rendered hypothyroid by neonatal treatment with propylthiouracil. To ensure that the cytoskeletal deficit was due to a shortage of thyroid hormones rather than to unspecific, toxic effects of propylthiouracil, hypothyroid animals kept on the propylthiouracil diet were given restorative thyroxine injections daily. Such animals express NF‐H at normal levels. This suggests that the callosal axons may be arrested at an immature stage of development. The immaturity of the hypothyroid corpus callosum can also be revealed by a comparison of the myelin content in the corpus callosum between normal rats, hypothyroid rats, and hypothyroid rats under thyroxine therapy. Hypothyroid rats are severely deficient in myelin, and again this deficit can be corrected by postnatal thyroxine treatment. During normal callosal development, there is a progressive spatial restriction of the transcallosal projection that creates in the adult patches of callosally projecting cortex interposed by acallosal regions. Given the structural immaturity of the hypothyroid callosal axons, it was interesting to investigate the state of development of their topography. For this purpose, multiple injections of wheat germ agglutinin‐horseradish peroxidase were made into the occipital and parietal cortices of adult hypothyroid animals. In normal rats, the majority of visual callosally projecting cells are located in three groups–in area 18b, at the boundary of area 17 and 18a, and in the lateral portion of area 18a. Within these areas projecting cells are concentrated in layers IIhyphen;III, Va, and Vc‐VIa. The callosal axon terminals are concentrated in these same regions, with a laminar distribution as far as the somata plus layer I. In the midportion of areas 17 and 18a, fewer callosal cells are found, and they occupy mainly layers Vchyphen;VIa, as is the case for terminals in these same areas. In the parietal cortex, callosal cells and terminals are disposed in vertical arrays alternating with almost empty zones. Most are concentrated in layers III and V. The topography of the callosal axon terminal fields is unaffected by hypothyroidism. However, there is a dramatic redistribution of the callosally projecting cell somata. Although these adopt the same radial distribution as seen in the normal animals, they are now arranged in continuous tangential laminae throughout both visual and somatosensory areas, and the normal acallosal patches are absent. This arrangement resembles the situation in the early neonate where the somata of callosally projecting cells are also arranged in continuous tangential laminae. The progressive restriction of callosal projection domains has been thought to occur through selective axon elimination. It therefore appears that hypothyroid animals retain inappropriate immature callosal projections due to the thyroid hormone dependence of the normal eliminati

ISSN:0092-7317    

DOI:10.1002/cne.902910109

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

年代:1990

数据来源: WILEY

摘要:

AbstractQuantitative electron microscopy has been used to study the number of callosal axons in the corpus callosum of normal and hypothyroid rats during postnatal development. At birth, the normal corpus callosum contains 4.4 × 106axons. This number increases to 11.4 × 106by 5 days of age (P5) and then, in contrast to cats and primates, remains constant until at least P60, the oldest age examined. The number of axons in the corpus callosum of hypothyroid animals is not significantly different from the values observed in normal rats at all ages studied, although the callosal axons of hypothyroid rats remain structurally immature. As extensive elimination of callosal axons has been shown to occur in normal rats past P5, we conclude that new callosal processes grow through the corpus callosum past this age that compensate numerically for the loss. Moreover, as the number of callosally projecting neurons seems to be higher in hypothyroid rats than in normal controls, it seems that the constant axon number derives from more parent neurons, and thus that there are more axon collaterals per callosal neuron in a normal animal than in a hypothyroid one. Taken together, these data indicate that although hypothyroidism does not alter the total number of callosally projecting axons, it interferes with the normal processes that define or sculpt the projection fields, thereby leading to a numerically normal projection with abnormal topograph

ISSN:0092-7317    

DOI:10.1002/cne.902910110

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

年代:1990

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902910101

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

年代:1990

数据来源: WILEY