摘要:

AbstractA new cell type is described in silver‐impregnated sections of the rat cerebellar cortex, uniformly distributed through all the cerebellar folia. The soma is rather small, roughly pyriform, vertically oriented, and squeezed, in a sandwich‐like manner, between the Purkinje cell somata. One or two thick dendrites arise from the upper pole of the cell body and course through the entire molecular layer, dividing into a few, slightly oblique, branches that can reach the pia mater. These dendrites are covered with irregularly distributed spines. Some more slender dendrites emerge from the lower part of the cell body, or from the proximal trunk of a molecular dendrite, and spread tortuously for a short distance in the upper granular layer. A thick initial segment emerges directly from the soma or from the proximal portion of a dendrite, the axon winding then horizontally through or just above the Purkinje cell layer. During this horizontal course it gives off vertically oriented beaded branches ascending through the major part of the molecular layer. These branches, rather closely spaced, occupy different parasagittal planes, separated by about 10 to 30 μm. This axonal arborisation can thus be compared with a candelabrum. The peculiar three‐dimensional spread of the axonal collaterals suggests a functional relationship between these branches and the dendritic trunks of neighbouring Purkinje cells. A comparative analysis of the morphological differences between this candelabrum interneuron and the other corticocerebellar interneurons found in the vicinity of the ganglionic layer confirms the specificity of this new cell class. © 1994 Wiley‐

ISSN:0092-7317    

DOI:10.1002/cne.903390202

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe describe with a variant of the Golgi method a new type of neuron that is prominently represented in the granular layer of the mammalian vestibulocerebellum but is presently neglected in all major accounts on the cerebellum. These neurons, here termed unipolar brush cells, are intermediate in size between granule cells and Golgi cells. They typically have a thin and presumably myelinated axon, and a single and stubby dendrite whose tip forms a tightly packed group of branchlets resembling a paintbrush. The branchlets often intertwine with the digitiform claws of granule cell dendrites and are occasionally approached by Golgi cell dendrites, indicating that the unipolar brush cells may share the input of the other granular layer neurons. Branchlets of neighboring unipolar brush cells converging into the same neuropil island also occur. The brush‐like tip of the unipolar cell engulfs one or two mossy fiber rosettes to form an extensive synapse that appears to close recurrent loops involving the vestibular nuclei. Positive feedback in these loops could help to explain several motor responses and drive mechanisms of extended duration that are controlled by the ventral cerebellum. © 1994 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903390203

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe intrahippocampal distribution of axon collaterals of individual CA3 pyramidal cells was investigated in the rat. Pyramidal cells in the CA3 region of the hippocampus were physiologically characterized and filled with biocytin in anesthetized animals. Their axonal trees were reconstructed with the aid of a drawing tube. Single CA3 pyramidal cells arborized most extensively in the CA1 region, covering approximately two‐thirds of the longitudinal axis of the hippocampus. The total length of axon collaterals in the CA3 region was less than in CA1 and the axon branches tended to cluster in narrow bands (200–800 μm), usually several hundred microns anterior or posterior to the cell body. The majority of the recurrent collaterals of a given neuron remained in the same subfield (CA3a, b, or c) as the parent cell. CA3a neurons innervated predominantly the basal dendrites, whereas neurons located proximal to the hilus (CA3c) terminated predominantly on the apical dendrites of both CA1 and CA3 cells. Two cells, with horizontal dendrites and numerous thorny excrescences at the CA3c–hilus transitional zone, were also labeled and projected to both CA3 and CA1 regions. All CA3 neurons projected some collaterals to the hilar region. Proximal (CA3c) neurons had numerous collaterals in the hilus proper. One CA3c pyramidal cell in the dorsal hippocampus sent an axon collateral to the inner third of the molecular layer. CA3c pyramidal cells in the ventral hippocampus had extensive projections to the inner third of the dentate molecular layer, as well as numerous collaterals in the hilus, CA3, and CA1 areas, and several axon collaterals penetrated the subiculum. The total projected axon length of a single neuron ranged from 150 to 300 mm. On the basis of the projected axon length and bouton density (mean interbouton distance: 4.7 μm), we estimate that a single CA3 pyramidal cell can make synapses with 30,000–60,000 neurons in the ipsilateral hippocampus. The concentrated distribution of the axon collaterals (“patches”) indicates that subpopulations of neurons may receive disproportionately denser innervation, whereas innervation in the rest of the target zones is rather sparse. These observations offer new insights into the physiological organization of the CA3 pyramidal cell network. © 1994 W

ISSN:0092-7317    

DOI:10.1002/cne.903390204

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

年代:1994

数据来源: WILEY

摘要:

AbstractImmunohistochemical techniques were used to study the distributions of glutamic acid decarboxylase (GAD) and γ‐aminobutyric acid (GABA) in pigeon forebrain and midbrain to determine the organization of GABAergic systems in these brain areas in birds. In the basal ganglia, numerous medium‐sized neurons throughout the striatum were labeled for GABA, while pallidal neurons, as well as a small population of large, aspiny striatal neurons, labeled for GAD and GABA. GAD+ and GABA+ fibers and terminals were abundant throughout the basal ganglia, and GABAergic fibers were found in all extratelencephalic targets of the basal ganglia. Most of these targets also contained numerous GABAergic neurons. In pallial regions, approximately 10‐12% of the neurons were GABAergic. The outer rind of the pallium was more intensely labeled for GABAergic fibers than the core. The olfactory tubercle region, the ventral pallidum, and the hypothalamus were extremely densely labeled for GABAergic fibers, while GABAergic neurons were unevenly distributed in the hypothalamus. GABAergic neurons and fibers were abundant in the dorsalmost part of thalamus and the dorsal geniculate region, while GABAergic neurons and fibers were sparse (or lightly labeled) in the thalamic nuclei rotundus, triangularis, and ovoidalis. Further, GABAergic neurons were abundant in the superficial tectal layers, the magnocellular isthmic nucleus, the inferior colliculus, the intercollicular region, the central gray, and the reticular formation. GABAergic fibers were particularly abundant in the superficial tectal layers, the parvocellular isthmic nucleus, the inferior colliculus, the intercol‐licular region, the central gray, and the interpeduncular nucleus. These results suggest that GABA plays a role as a neurotransmitter in nearly all fore‐ and midbrain regions of birds, and in many instances the observed distributions of GABAergic neurons and fibers closely resemble the patterns seen in mammals, as well as in other vertebrates. © 1994 Wile

ISSN:0092-7317    

DOI:10.1002/cne.903390205

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

年代:1994

数据来源: WILEY

摘要:

AbstractWithin the basal forebrain, γ‐aminobutyric acid (GABA)‐synthesizing neurons are codistributed with acetylcholine‐synthesizing neurons (Gritti et al. [1993] J. Comp. Neurol. 329:438–457), which constitute one of the major forebrain sources of subcortical afferents to the cerebral cortex. In the present study, descending projections of the GABAergic and cholinergic neurons were investigated to the lateral posterior hypothalamus (LHp) through which the medial forebrain bundle passes and where another major forebrain source of subcortical afferents is situated. Retrograde transport of cholera toxin b subunit (CT) from the LHp was combined with immunohistochemical staining for glutamic acid decarboxylase (GAD) and choline acetyl transferase (ChAT) using a sequential peroxidase‐antiperoxidase (PAP) technique.A relatively large number of GAD+ neurons (estimated at ∼ 6,200), which represented>15% of the total population of GAD+ cells in the basal forebrain (estimated at ∼ 39,000), were retrogradely labeled from the LHp. These cells were distributed through the basal forebrain cell groups, where ChAT+ cells are also located, including the medial septum and diagonal band nuclei, the magnocellular preoptic nucleus, and the substantia innominata, with few cells in the globus pallidus. In these same nuclei, a small number of ChAT+ cells were retrogradely labeled (estimated at ∼ 800), which represented only a small percentage (15%) and the ChAT+ neurons a very small proportion (∼ 2%). The relative magnitude of the GABAergic projection suggests that it may represent an important inhibitory influence of the descending efferent output from the basal forebrain and preoptic‐anterior hypothalamic regions. This influence could suppress the activity of neurons in the posterior lateral hypothalamus that are involved in establishing the vegetative, somatomotor, and electrocortical components of the waking state and b

ISSN:0092-7317    

DOI:10.1002/cne.903390206

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

年代:1994

数据来源: WILEY

摘要:

AbstractRecent reports have indicated that analysis of changes in the staining characteristics of gonadotropin‐releasing hormone (GnRH) neurons and characterization of morphological plasticity of the related structural framework may help to elucidate the physiological mechanisms involved in neuroendocrine control of mammalian reproduction. Whether comparative studies will facilitate this process or simply elucidate species‐specific mechanisms is not yet clear. The present study was performed in order to begin analysis of GnRH neurons in a seasonally breeding species that exhibits an unusually long ovulatory luteinizing hormone (LH) surge. To this end, light microscopy and image analysis were used to characterize distribution and morphology of GnRH neurons in 15 adult male and female ponies. Samples were collected in the middle of the normal ovulatory season. Unipolar, bipolar, and multipolar GnRH neurons were organized in a loosely defined continuum that extended from the medial septum to tuberoinfundibular areas in the medial basal hypothalamus (MBH). Most cells were bipolar, and the majority of neurons were located in the MBH. Fiber projections to the median eminence included presumptive pathways similar to those previously described in other species. Image analysis of cell size indicated that cells in the MBH were larger than those in preoptic areas and GnRH neurons in both of these locations were larger than neurons in rostral areas of the medial septum. Results from this experiment suggest that the large population of MBH GnRH neurons in the equine species is likely to be of primary importance to reproductive function, whereas cells in other areas are fewer and smaller. Further work is needed to characterize morphological characteristics that may be related to physiological fluctuations in reproductive function of the equine species. © 1994 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903390207

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe cat's visual cortex is immature at birth and undergoes extensive postnatal development. For example, cells of layers 2 and 3 do not complete migration until about 3 weeks after birth. Despite the importance of dendritic growth for synaptic and functional development, there have been few studies of dendritic development in the cat's visual cortex to correlate with numerous studies of functional and synaptic development. Accordingly, we used the Golgi method to study the development of the dendrites of layer 3 pyramidal cells in the visual cortex of a series of cats ranging in age from 2 days to 3 years. Blocks of visual cortex were impregnated by the Golgi‐Kopsch method and sectioned in the tangential plane. Layer 3 pyramidal cells were drawn with a camera lucida and analyzed by Sholl diagrams and vector addition. In kittens<1 week old, these cells were very immature, with only an apical dendrite and no basal dendrites. Basal dendrites appeared during the second week. By 2 weeks, all of the basal dendrites had emerged from the soma, but they had few branches and were tipped with growth cones. By 4 weeks, they had finished branching but continued to grow in length until, by 5 weeks, they reached their adult size. Examination of the basal dendritic fields in the tangential plane revealed that the dendritic fields were more elongated at 2 weeks than at later ages, perhaps because of their smaller size. The distribution of dendritic field orientations was uniform at all ages except 3 and 4 weeks, when there was a preponderance of fields oriented in the rostrocaudal direction. Because dendritic growth and branching occurred very rapidly over a period that precedes and overlaps with the peak periods of synaptogenesis and of sensitivity to the effects of early visual experience, they may depend on afferent visual activity. The early emergence of primary dendrites, however, suggests that this process is independent of afferent activity. The coincident timing of dendritic branching with the presence of dendritic growth cones suggests that branching may occur at growth cones. © 1994 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903390208

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

年代:1994

数据来源: WILEY

摘要:

AbstractSome effects on auditory brainstem connections of long (1–2.3 years) survival following unilateral cochlear removal in infant and adolescent ferrets were examined by making multiple injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) in either the left or the right inferior colliculus (IC). Previous studies have shown that, in normal adult ferrets, about 50 times as many cochlear nucleus (CN) neurons project to the contralateral as to the ipsilateral IC. Right cochlear removal at P25 increased, within 30 days, the number of retrogradely labeled left CN neurons projecting to the left ipsilateral IC by 17% (from n = 235 to n = 275), relative to normals. In this study, longer survival (3 months to 1 year) after right cochlear removal at P25 resulted in larger increases (38–47%; n ≈ 100) in the number of neurons labeled in the left CN after injections of WGA‐HRP in the left IC. No change occurred in the number of neurons labeled in the right CN. Taken together, the results of these experiments show that the ratio of the number of labeled neurons in the left CN to that in the right CN increases progressively with survival time out to the maximum time tested (1 year). In contrast to these results, we have previously reported that right cochlear removal at P90 did not change the number of neurons projecting from the left CN to the left IC after 90 days of survival. However, in this study, very long survival (2–3 years) following right cochlear removal at P90 resulted in an increased (51%, from n = 235 to n = 355) number of left CN neurons labeled by WGA‐HRP injections into the left IC, relative to normals. The increased number of labeled neurons included neurons throughout each division of the CN and all of the principal morphological types. In a separate series of experiments involving long survival (1‐2 years), right cochlear removal at P25 or P40 did not significantly change the number of neurons in either CN retrogradely labeled by injections of WGA‐HRP in the right IC, or the ratio between the number of neurons labeled in each CN. Long survival following cochlear removal at P25–P90 did not result in any loss of neurons in the ipsilateral CN or in any shrinkage of CN neurons further than the 10–20% seen at a shorter survival time (90 days). These results show that at least one pathway within the auditory brainstem continues to be changed in later life following either early or late cochlear removal. They provide a possible anatomical basis for long‐term changes seen in sensory systems following lesions of the sense organs of mature animals.

ISSN:0092-7317    

DOI:10.1002/cne.903390209

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

年代:1994

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903390201

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

年代:1994

数据来源: WILEY