摘要:

AbstractThe numbers of 1) dorsal root ganglion cells in the 2nd spinal segment, 2) ventral horn cells in the 2nd spinal segment, 3) Purkinje cells of the cerebellum, and 4) neurons in the nucleus glomerulosus were counted and correlated with age and size in the guppy,Lebistes. The findings were that the neuronal numbers in all these areas increased throughout much of the life of the animal. These data, combined with the previously demonstrated increases in retinal neurons in goldfish and sensory and spinal neurons in stingrays, suggest that neurons are added to many areas of the nervous system of fish as the animal ages and grows. In this respect, the nervous systems of fish differ from the nervous systems of other vertebrates. We offer the suggestion that the comparatively greater ability of fish to regenerate their nervous system after injury may be related in part to their ability to add neurons to various parts of the nervous system throughout life.

ISSN:0092-7317    

DOI:10.1002/cne.901940202

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe California newtTaricha torosamanufactures tetrodotoxin, a blocker of voltage‐sensitive sodium channels and therefore of action potentials. The newt's own nervous system is insensitive to this toxin. Grafting an embryonic eye to the newt from a tetrodotoxin‐sensitive species, the Mexican axolotl, blocks action potentials in the retinal ganglion cells of the transplanted eye. Neuroanatomical and electrophysical techniques demonstrate that while such ganglion cells are incapable of firing impulses, they develop normally, grow axons to the host tectum, terminate in the appropriate neuropil layers, form synapses, and project to the tectum retinotopically. Furthermore, they develop these apparently normal projections even in competition with electrically active axons from a host

ISSN:0092-7317    

DOI:10.1002/cne.901940203

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractEye primordia from the Mexican axolotl or the California newt were transplanted into hosts of either species. These “third” eyes often developed an optic nerve that penetrated the host brain and made one of three central projections: bilateral to the dorsal thalami, tecta, and basal optic nuclei; ipsilateral to the same areas; or ipsilateral into the cord. The type of projection made by a transplanted eye seemed to depend on where its nerve first entered the brain. The optic fibers that reached the visual centers of the midbrain were organized retinotopically in the optic tectum and mediated visually‐guided beh

ISSN:0092-7317    

DOI:10.1002/cne.901940204

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractUsing the anterograde degeneration technique, we examine the tangential organization of a thalamofugal axon population (class I of Frost and Caviness, ′80) whose terminations are preferentially distributed to the middle tier (located in layers III and/or IV) of three radially separated tiers of thalamic projections to the neocortex. Less extensive data are also presented on the tangential organization of thalamofugal axon populations (class II of Frost and Caviness, ′80) that do not terminate preferentially in the middle tier, but that are otherwise heterogeneous with respect to their radial pattern of intracortical termination.The projections of class I axons are distributed to all neocortical fields with the possible exception of fields 13, 25, and 35. The class I projections to a given cortical field (with the possible exception of the cortex of the second somatosensory representation) originate in only one thalamic nucleus. The class I projections of an individual thalamic nucleus form a cortical representation of the nucleus that constitutes a “first order line‐to‐line” (topologic) transformation of the nuclear volume. The ensemble of class I projections forms a cortical representation of the corresponding thalamic regions that constitutes a “second order line‐to‐line” (non‐topologic) transformation of the thalamic volume.Class II axons project to all neocortical fields. Class II and class I projections contrast in that the class II projections of multiple thalamic nuclei overlap in the tangential plane of any given sector of the cortex. While the class II projections of the intralaminar nuclei and the widely projecting ventromedial nucleus are known to be topologically organized, the tangential organization of class II projections arising in other nuclei is in

ISSN:0092-7317    

DOI:10.1002/cne.901940205

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe intracortical distributions of the thalamic projections to a large number of neocortical fields are studied by the anterograde degeneration method in the mouse. The basic radial distribution of terminating thalamofugal axons is uniform throughout the mouse cortex and is essentially the same as that encountered in other mammalian species. Terminating axons are concentrated in three tiers: an outer tier in layer I, a middle tier in layers IV and/or III, and an inner tier in layer VI. In most fields, terminating axons also extend, to some extent, into layer V. Variations are encountered from field to field, particularly in the density and degree of divergence of projections and in the radial extent of individual tiers with respect to cytoarchitectonic layers.In accord with other studies, the thalamic projections to each field appear to be composed of two general axon classes. Class I axons terminate densely in the middle tier, seem to be of large caliber, and often have collaterals to the other tiers. Class II axons do not terminate densely in the middle tier and seem to be of small caliber. Terminating class II axons may be distributed to one or more tiers and may be concentrated in the inner and/or outer tiers. The thalamic projection to each field has its origin in multiple nuclei. All thalamic nuclei projecting to the neocortex appear to have class II projections and many also have class I projections.Patterns of degeneration in the cortex associated with lesions in different positions in many nuclei suggest that thalamic relay neurons are organized along “lines of projection”–neurons in the same line projecting to the same tangentially restricted cortical region. The neurons of origin of class I and class II axons are intermixed along the lines of proje

ISSN:0092-7317    

DOI:10.1002/cne.901940206

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe development of the human lateral geniculate nucleus has been studied on Nissl‐ and silver‐stained sections from 61 fetal human brains collected during normal autopsy procedures. The age of the fetuses, which ranged from 16 to 40 (newborn) weeks was determined by comparing crown‐to‐rump lengths and body weights to the values published by Streeter (′20).The development of the human lateral geniculate nucleus is remarkably similar to the described for the rhesus monkey (Rakic, ′77). As a result of the late growth of the pulvinar, the human lateral geniculate nucleus is displaced and rotated such that, at around week 24, the nucleus has come to lie along the ventrolateral border of the thalamus. The cellular laminae that characterize the adult nucleus are formed over a 3‐week period of time beginning around the 22nd week of gestation. More caudal parts of the nucleus laminate first. During this same period of time, the optic disc representation in laminae 4 and 6 is also formed.Throughout most of the development of the human lateral geniculate nucleus, individual rows of cells can be seen extending across the nucleus. Although such rows of cells are best seen before the nucleus laminates, in older laminated nuclei the rows of cells are oriented either perpendicular or oblique, but never parallel, to the plane of the laminae. Previous findings in both the monkey (Rakic, ′77) and human (Hickey and Guillery, ′79) suggest it is possible that these rows of cells can be used to define the lines of projection through the nucleus. Incoming optic tract fibers run along, rather than perpendicular to, th

ISSN:0092-7317    

DOI:10.1002/cne.901940207

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe effects of monocular lid‐suture deprivation on development were evaluated by measurement of cell sizes in the lateral geniculate nuclei of six deprived and three normally reared galagos. In all animals autoradiographic demonstration of the retino‐thalamic projections from one eye was used to define the lamination and distinguish the monocular from the binocular segment of the nucleus. Our results indicate that monocular deprivation significantly affects cell growth in both the binocular and monocular geniculate segments, with the greater change occurring in the binocular segment, suggesting that both visual experience and binocular competitive interactions influence geniculate cell growth in these primates. In animals forced to use their deprived eye for 2 months or more by reverse suturing, disparity of cell sizes is reduced in the monocular segment, while differences in binocular segment cell sizes are maintained. Our results also show that monocular deprivation with or without later reverse suture has an unequal influence on different geniculate layers, such that cells in laminae 4 and 5 are not as severely affected as the remaining layers. This differential influence could relate either to the unique pattern of projection of these layers to cortex or to functional differences between lay

ISSN:0092-7317    

DOI:10.1002/cne.901940208

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractDistribution of cerebellothalamic neurons projecting to the ventral nuclei of the thalamus was examined in the cat, using the horseradish peroxidase (HRP) method.After injections of HRP within the lateral or ventrolateral portions of the ventroanterior and ventrolateral nuclear complex of the thalamus (VA‐VL), neurons labeled retrogradely with HRP were seen contralaterally in the cerebellar nuclei; many of them were situated in the nucleus interpositus anterior and nucleus interpositus posterior, and a moderate number of them were located in the nucleus lateralis. Labeled neurons in the nucleus interpositus posterior were observed mainly in the medial and ventral portions of the nucleus. On the side ipsilateral to the injections, a few labeled neurons were seen in the nucleus interpositus anterior, nucleus interpositus posterior, and nucleus lateralis. Virtually no labeled neurons were found in the nucleus medialis of the cerebellum.After HRP injections into the medial or dorsomedial portions of the VA‐VL, many labeled neurons were found contralaterally in the ventral and ventrolateral portions of the nucleus interpositus posterior, as well as in the nucleus lateralis, especially in its ventral and lateral portions. On the side ipsilateral to the injections, labeled neurons in the nucleus lateralis and nucleus interpositus posterior were small in number. In the nucleus medialis only a few labeled neurons were found bilaterally in the caudal levels of the nucleus.After HRP injections centered on the ventromedial nucleus of the thalamus, many labeled neurons occurred bilaterally in the caudal portions of the nucleus medialis, with a slight contralateral preponderance, and contralaterally in the lateral and ventral portions of the nucleus lateralis. A few labeled neurons were also seen contralaterally in the ventrolateral and lateral portions of the nucleus interpositus posterior, and ipsilaterally in the nucleus latera

ISSN:0092-7317    

DOI:10.1002/cne.901940209

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe motor nucleus of the opossum trigeminal nerve consists of a main body and a small dorsomedial cell cluster. The cell bodies form a unimodal population with areas that range from 150–2700 μm2. Golgi impregnations reveal that each neuron has three to six primary dendrites which radiate in all planes from the cell body. Within 300 μm from the soma, the primary dendrites divide into secondary branches and these, in turn, bifurcate into thinner distal dendrites. The overall diameter of the dendritic tree often extends as much as 1 mm, with a rare branch leaving the confines of the nucleus to enter the neighboring reticular formation. Somatic and dendritic spines are often present and are either sessile or complex appendage forms.The perikarya and initial dendritic trunks of trigeminal neurons are contacted by four types of presynaptic terminals which cover more than 40% of the membrane. Most endings are 1–3 μm long and contain either spherical (S) or pleomorphic (P) synaptic vesicles. Another, less common, type of bouton is marked by large dense‐core (DC) vesicles. Approximately 8% of the terminals on trigeminal cell bodies are large (2–5 μm) with spherical synaptic vesicles and are always associated with a subsynaptic cistern (C‐boutons). These terminals very often interdigitate with adjacent synaptic endings. S‐, P‐, and C‐boutons synapse on the dendritic tree of trigeminal neurons in the following characteristic pattern: proximal dendrites (greater than 5 μm in diameter) are contacted by all three types of terminals; intermediate‐sized dendrites (between 2.5 and 5.0 μm in diameter) are most often contacted by S‐boutons although P‐boutons are also present; and small, distal dendrites (less than 2.5 μm in diameter) are almost always contacted by S‐ boutons. Both S‐ and P‐boutons contact spines.In order to determine the ultrastructural identity of some of the major afferent systems to the trigeminal motor nucleus, adult opossums were subjected to two different types of lesions. Three and 5 days subsequent to lesions which destroyed most of the trigeminal mesencephalic nucleus, degenerating terminals containing spherical vesicles were found. These endings were S‐boutons on more distal parts of the dendritic tree while on the cell body and proximal dendrites they were C‐boutons. Seven days after a mesencephalic lesion, expanded glial processes approximated the trigeminal cell membrane. Two days subsequent to lesions which transected commissural fibers from the contralateral trigeminal complex, degenerating S‐ and P‐boutons were found in contact with intermediate and dis

ISSN:0092-7317    

DOI:10.1002/cne.901940210

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe peroxidase‐antiperoxidase (PAP) technique is used to determine the cellular localization of tyrosine hydroxylase in the human fetal nervous system. Antiserum to trypsin‐treated tyrosine hydroxylase from the bovine adrenal medulla can be detected immunocytochemically in peripheral sympathetic neurons in the 8‐mm (5‐week) fetus, but can not be detected in the central nervous system until later stages of development. The cytological features and distribution of the neuronal perikarya and processes labeled for the enzyme are similar to those of the catecholaminergic neurons previously identified by histofluorescence. These findings indicate that specific neurons in the human fetus have at least one of the enzymes necessary for the biosynthesis of catecholamines and that cross‐species reactivity exists between antiserum produced to the bovine tyrosine hydroxylase and huma

ISSN:0092-7317    

DOI:10.1002/cne.901940211

出版商:Alan R. Liss, Inc.    

年代:1980

数据来源: WILEY