摘要:

AbstractThe organization of interconnections between the mediodorsal nucleus of the thalamus (MD) and the orbital and medial prefrontal cortex and the agranular insular cortex in the monkey was studied by retrograde and anterograde tracing techniques. In addition to the magnocellular and parvicellular divisions of MD, three other subdivisions can be recognized on the basis of myeloarchitecture, cytoarchitecture, and connections. The first two of these represent a parcellation of the magnocellular division into a lateral, fiber‐richMD pars fibrosaand a medial, poorly myelinatedMD pars paramedianaadjacent to the midline. The third is a small, poorly myelinated area located at the caudomedial and dorsal edges of MD; it is referred to asMD pars caudodorsalis.MD pars fibrosa is reciprocally interconnected primarily with areas 11, 12 and 13 in the central and lateral part of the orbital cortex. There is a general organization within this projection, with the rostrocaudal axis of the cortex represented from dorsal to ventral in the pars fibrosa, and the mediolateral cortical axis represented from medial to lateral. Cells that project to area 12 also extend laterally into the adjacent pars parvicellularis. MD pars paramediana is more heavily interconnected with the caudal and medial portions of the orbital region, particularly the agranular insular areas and the caudal parts of areas 13 and 14. Cells that project to two caudal areas, 13a and Iad, do not fit with the general organization, in that they are located in the dorsomedial parts of the pars fibrosa and pars paramediana, where they overlap with cells that project to area 14. The pars fibrosa and pars paramediana receive inputs from areas of the ventral forebrain such as the amygdala, piriform (olfactory) cortex, and entorhinal cortex, which project directly to the orbital and agranular insular cortex, and entorhinal cortex, which project directly to the orbital and agranular insular cortex, as well as from the ventral pallidum.MD pars caudodorsalis is reciprocally interconnected with areas 14, 24, and 32 on the medial surface of the prefrontal cortex. In this part of the nucleus the dorsoventral axis of the medial prefrontal cortex is represented from caudal to rostral in the thalamus. The amygdala and other ventral forebrain structures do not send fibers into the pars caudodorsalis, even though some of these structures project directly to the medial prefrontal cortex.Ventral to MD, and separated from it by the internal medullary lamina, a small region was recognized that appears to be comparable to the anteroventral part of the submedial nucleus previously defined in the rat and cat. This region receives input from the piriform cortex and is interconnected with orbital cortical area 13a. © 1993 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903370102

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

年代:1993

数据来源: WILEY

摘要:

AbstractAscending auditory efferents in birds terminate mainly within Field L2, a cytoarchitectonically distinct region of the caudomedial telencephalon. The organization of Field L2, and that of its flanking regions, L1 and L3, was investigated with 14C‐2‐deoxyglucose (14C‐2‐DG), cytochrome oxidase, and both retrograde and anterograde tracing techniques.Field L2 was found to contain a high concentration of cytochrome oxidase. Following auditory stimulation, 14C‐2‐DG autoradiography revealed that Field L2 consists of two adjacent but seemingly discontinuous zones, designated Field L2a, which lies ventromedially, and Field L2b, which lies dorsolaterally.Termination of thalamic efferents: The thalamic auditory nuclei ovoidalis (Ov) and semilunaris parovoidalis (SPO) project predominantly upon Field L2, and possibly sparsely upon L1, L3 and the overlying hyperstriatum ventrale (HV). Ov subnuclei project upon L2a and SPO projects predominantly upon L2b. The topography of the projections is inverted along the ventromedial‐to‐dorsolateral axis of L2, and is in accord with an inverted tonotopic representation of frequencies; high frequencies (<3.5 kHz) being found in the more ventromedial parts of L2a, and low frequencies and broad band responses in L2b.Intra‐ and extratelencephalic connections: Field L2a also receives a substantial projection from HV, but the efferent projections of L2a appear confined to adjacent “neostriatal” regions. The subsequent projections of L2b were not identified in this study. L1 and L3 project predominantly to the dorsal neostriatum (Nd) caudolateral to Field L, and have fewer projections to the caudomedial paleostriatum and anterior hyperstriatum accessorium. Nd projects massively upon the ventromedial nucleus of the intermediate archistriatum (Aivm), which has bilateral projections upon the caudomedial telencephalon and is the origin of a major descending pathway having dense terminations surrounding the ovoidalis complex (Ov and SPO), MLd, the lateral lemniscal nuclei, and sparse terminations within SPO itself.It is suggested that within the telencephalon the major components of the auditory pathway consist of cell groups which collectively correspond to the populations of neurons found within the auditory cortex of mammals.

ISSN:0092-7317    

DOI:10.1002/cne.903370103

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

年代:1993

数据来源: WILEY

摘要:

AbstractLittle information is available concerning the pelvic visceral afferent system, in view of its terminal location in the spinal cord and its associated transmitter substances in the rat. By utilizing an immunostaining method to examine the transneuronal neurotransmitter depletion resulting from peripheral sensory nerve injury, the spinal projections of primary afferent fibers containing calcitonin gene‐related peptide (CGRP) and originating from pelvic viscera were studied in the lumbosacral spinal cord of the rat. After unilateral or bilateral pelvic nerve section, CGRP immunoreactivity in the lumbosacral spinal cord was decreased greatly in the sacral parasympathetic nucleus (SPN), the dorsolateral fasciculus, the medial border of the dorsal horn, the dorsal gray commissure (DGC), and the intermediate gray connecting the SPN and DGC. Fine structural analysis showed that the CGRP‐immunoreactive terminals made synaptic contact with dendrites and, rarely, with somata. Although there was some incidence of a synaptic contact between a CGRP‐IR terminal and a vesicle‐containing profile, definite evidence of axo‐axonal synapse has not been confirmed. These data indicate that CGRP‐containing pelvic visceral primary afferent fibers project to autonomic areas of the lumbosacral spinal cord by way of the pelvic nerve and make synaptic contact with dendrites and somata. © 1993 Wil

ISSN:0092-7317    

DOI:10.1002/cne.903370104

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe abnormal location of large numbers of neurones is characteristic of genetic mutations which impair the migratory processes of developing nerve cells. Nevertheless, the presence of small amounts of ectopic neurones is a fairly common finding even in normal adult animals. The first aim of this study was to investigate a series of features of ectopic Purkinje cells in normal adult rats and particularly to assess whether these cells are still capable of interacting with their normal afferents. Several displaced Purkinje cells, identified by anti‐D28K calbindin immunolabelling as well as by typical morphological features, were present in the brainstem and cerebellum of all the examined animals. Two distinct morphological types of such cells could be recognized: (1) noncortical Purkinje cells, located in several areas of the dorsal brainstem and cerebellum, characterised by poorly developed and randomly oriented dendrites; and (2) cortical Purkinje cells, exclusively located in the dorsal cochlear nucleus, characterised by large dendritic trees oriented along parasagittal planes. Tracing experiments, in whichPhaseolus vulgarisleucoagglutinin (PHA‐L) was injected into the inferior olive, revealed that several ectopic Purkinje cells, belonging to both types, were contacted by the terminal arbours of olivary axons, structurally similar to cerebellar climbing fibres.On the basis of the observation that ectopic Purkinje cells were more frequent in the dorsal cochlear nucleus than in any other of the examined regions, we tested the hypothesis that this nucleus might represent a particularly favourable environment for the survival and development of Purkinje cells. By grafting embryonic cerebellar tissue in the fourth ventricle, only minimal migration of Purkinje cells into the recipient parenchyma was observed when the transplant was placed on the brainstem surface caudal to the cochlear nucleus. By contrast, when the graft was apposed to the latter nucleus, large numbers of Purkinje cells migrated and developed in its superficial layers. These Purkinje cells passed through all the different phases which characterise the normal ontogenesis of this neuronal population and finally developed mature structural features similar to those displayed by cortical ectopic Purkinje cells.This study demonstrates that at least some of the ectopic Purkinje cells receive their physiological olivary input. This fact indicates that Purkinje cells are able to attract olivary axons and establish specific connections, even if they are displaced in an abnormal environment. In addition, we show that the dorsal cochlear nucleus represents a particularly favourable environment for the survival and the development of Purkinje cells. © 1993 Wiley‐Li

ISSN:0092-7317    

DOI:10.1002/cne.903370105

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe rostral ventromedial medulla contains two classes of physiologically defined neurons, on‐cells and off‐cells, that are implicated in nociceptive modulation. In a continuing effort to detail the neural circuitry that underlies the activity of these two distinct neuronal types, the three‐dimensional somatodendritic morphology of on‐ and off‐cells was studied in the cat and the rat.Following physiological characterization with intracellular recording, on‐ and off‐cells were injected with horseradish peroxidase and sectioned in the coronal plane. Their somatodendritic arborizations were reconstructed with the aid of a computerized three‐dimensional reconstruction program.There were no differences between on‐ and off‐cells in any somatodendritic feature analyzed. On‐ and off‐cells possess dendritic arbors that are elongated in the mediolateral axis relative to the dorsoventral and rostrocaudal axes. In the rat, the average dendritic extent was more than 1,400 μm mediolaterally but only about 800 μm in either the dorsoventral or rostrocaudal axis. All somatic and dendritic measures were greater for both cat cells than for any rat neuron. Dendrites and their tips were located predominantly in regions lateral to the soma. The center of total dendritic length was usally located within 150 μm of the soma, most frequently ventral and lateral to the soma.The present results demonstrate that the dendritic domains of neurons in the nuclei raphe magnus and reticularis paragigantocellularis pars alpha are not contained within cytoarchitechtonic boundaries. On‐ and off‐cell dendrites are interdigitated throughtout the mediolateral extent of the rostral ventromedial medulla. Since on‐ and off‐cell dendritic domains occupy a restricted rostrocaudal plane, afferents to the rostral ventromedial medulla that are confined to a single coronal plane and those that collateralize at several levels are likely to play different roles in the control of on‐and off

ISSN:0092-7317    

DOI:10.1002/cne.903370106

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

年代:1993

数据来源: WILEY

摘要:

AbstractWe used tritiated amino acids to study projections to the basilar pons from prestriate cortices in 18 rhesus monkeys to determine how connectional and functional heterogeneity of these regions are reflected in corticopontine circuitry. Fibers travelled with those from other parasensory associative cortices before terminating in the pontine nuclei. Prelunate projections were derived from area 19 (OA) at the medial convexity (including areas V3 and PO) and from the lateral convexity dorsal to the caudal tip of the Sylvian fissure (including areas DP and the dorsal part of area V4d). Pontine projections also arose from area 19 (OA), and areas TF, TL, and TH in the posterior aspect of the parahippocampal gyrus. No pontine projections arose from the prelunate convexity ventral to the caudal tip of the Sylvian fissure (ventral part of area V4d and area V4v), area TEO, the inferior temporal gyrus, or the lateral ventral temporal region. Terminations in the pons were distributed in the dorsolateral and lateral nuclei, and the lateral part of the peripeduncular nucleus. Medial convexity injections produced more extensive rostrocaudal pontine labeling, as well as terminations in the extreme dorsolateral nucleus and the nucleus reticularis tegmenti pontis. Dorsal prelunate injections had additional terminations in the ventral pontine nucleus. Posterior parahippocampal gyrus injections resulted in discrete label in the lateral and dorsolateral nuclei.Corticopontine projections destined for the cerebellum appear to be derived from extrastriate areas concerned mainly with visual spatial parameters, visual motion, and the peripheral field of vision, but not from areas subserving visual object identification and the central field of vision. Pontine afferents from the posterior parahippocampal gyrus may facilitate a cerebellar contribution to visual spatial memory, particularly when invested with motivational valence. © 1993 Wiley‐Liss,I

ISSN:0092-7317    

DOI:10.1002/cne.903370107

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn an attempt to estimate the relative importance of the various afferent systems impinging on the oculomotor regions of the posterior cerebellar vermis of rhesus monkeys in quantitative terms, we made small injections of the retrograde tracers fast blue, fluorogold, and cholera toxin into different parts of a region of the posterior vermis, spanning lobuli VI through VIII. We found that the vast majority of cells retrogradely labeled by injections of lobulus VII and its vicinity lay in the pontine nuclei (PN), the nucleus reticularis tegmenti pontis (NRTP), and subnuclei a and b of the medial accessory olive. The remaining retrogradely labeled cells were distributed among a number of other brainstem nuclei or regions including the paramedian pontine reticular formation (PPRF).A quantitative analysis showed that the projection from the NRTP to the posterior vermis was focused on lobulus VII. While the projection from the PN as a whole demonstrated a preference for the more caudal parts of the posterior vermis, a closer look at the different regions of the PN revealed that cells located in the dorsal parts of the PN showed the same preference for lobulus VII as cells in the NRTP.The dorsal PN are a major gateway for cortical input to the cerebellum, related to visual processing and visually guided eye movements. Conversely, the NRTP, likewise involved in visually guided eye movements, is much more dependent on subcortical afferents. The observed convergence of input derived from the dorsal PN and the NRTP in oculomotor lobulus VII therefore suggests that a major function of this part of the vermis might be the integration of cortical and subcortical signals important for visually guided eye movements. © 1993 Wiley‐Liss,I

ISSN:0092-7317    

DOI:10.1002/cne.903370108

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

年代:1993

数据来源: WILEY

摘要:

AbstractFibers containing acetylcholine (ACh) form distinct patches in the dorsal intermediate gray layer (IGL) of the cat superior colliculus (SC). Although these patches are known to overlap several afferent projections to SC, it is not known whether they are associated with specific postsynaptic cell groups. We have examined the relationship of these ACh fiber patches to specific efferent cell groups by combining retrograde transport of horseradish peroxidase (HRP) with choline acetyltransferase (ChAT) immunocytochemistry. Successful HRP injections were made into the predorsal bundle (PB), the tecto‐pontine‐bulbar pathway (TPB) and the cuneiform region (CFR), the inferior olive (IO), the dorsolateral pontine gray nucleus (PGD), and the pedunculopontine tegmental nucleus (PPTN). The distribution of HRP‐labeled neurons which project to these targets was mapped by a computer‐based microscope plotter.Distinct clusters of HRP‐labeled neurons in the IGL were seen after three injections into the mesencephalic reticular formation that involved the caudal TPB and cuneiform region (CFR), and after one injection into the medial accessory nucleus of IO. As many as seven clusters of labeled neurons were found in some sections through the caudal one‐half of SC after the TPB/CFR injections. Each cluster consisted of 3‐20 cells, all of which were small to medium in size. In sections also tested for ChAT, the cell clusters in the TPB/CFR cases were found to overlap precisely the ACh patches in the IGL. In addition, SC neurons projecting to the IO formed clusters above the ChAT patches and in the intermediate white layer (IWL) of SC. None of the other HRP injections produced any obvious cell clusters in the deep layers of SC. These results are the first to show that specific cell groups, distinguished by size and projection site, form clusters that match the patch‐like innervation of cholinergic afferents to SC. This modular organization may correspond to saccade‐related cells that have also been reported to be organized into clusters in the cat SC. © 1

ISSN:0092-7317    

DOI:10.1002/cne.903370109

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn the present study we describe the characteristics of the chandelier cells in the rat entorhinal cortex and subicular complex by using the Golgi method and combined Golgi‐electron microscopic techniques. In the entorhinal cortex, chandelier cells were frequently stained in layers II/III. Two types of axonal complexes were noted. One had a preferential horizontal orientation and gave rise to terminals located in the upper portion of layers II/III. The second type of chandelier cell axon was observed in the medial entorhinal area, innervating the entire extent of layers II/III. In the subicular complex, chandelier cells were frequently stained in the parasubiculum, whereas only a few cells were found in the presubiculum. In both subfields, chandelier cell axons were restricted to layers II/III. In the subiculum, most chandelier cells were present in the stratum radiatum, giving rise to a descending axon that branched in the stratum pyramidale. Both the size and morphological features of the chandelier cell terminal portions were found to be region‐specific.Electron microscopically, the cell body and dendrites of gold‐toned chandelier cells displayed typical features of nonpyramidal cells, such as the presence of nuclear infoldings, symmetric and asymmetric synapses on the cell body, and moderate numbers of axon terminals covering the smooth dendritic surface. Five gold‐toned chandelier cell axonal complexes were analyzed at the fine structural level. In all parahippocampal regions, gold‐labeled axon terminals formed symmetric contacts with axon initial segments. Our results demonstrate the presence, morphological characteristics, and target selectivity of identified chandelier cells in the parahippocampal region of the rat. Together with previous data, these results suggest a wide distribution of this specialized type of cortical interneuron and indicate that it is a constant and essential component of inhibitory circuits in the cerebral cortex. The possible significance of chandelier cells for the circuits linking several subfields of the hippocampal formation is discussed. © 1993 Wile

ISSN:0092-7317    

DOI:10.1002/cne.903370110

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe developmental regulation of neurotransmitter synthesis has been extensively studied and appears in many cases to depend on electrical activity. The central nervous system of theXenopusembryo and young larva is an attractive subject for such studies, since action potentials first elicited fromXenopusspinal neurons at the time of closure of the neural tube are long in duration and calcium‐dependent. Moreover, cells exhibit spontaneous elevations of intracellular calcium during this early period as a consequence of calcium influx through voltage‐dependent channels, which induces calcium release from intracellular stores. Since the early differentiation ofXenopusspinal neurons in dissociated cell culture parallels development in vivo, we have examined the maturation of γ‐aminobutyric acid (GABA) immunoreactivity in cultured neurons and explored its dependence on spontaneous calcium influx at early stages of development. We find that specific GABA immunoreactivity develops in spinal neurons in dissociated cell culture with the same time course previously defined in vivo. Additionally, this process requires calcium influx that occurs spontaneously through voltage‐dependent channels. The appearance of GABA immunoreactivity is blocked by transcriptional inhibitors. The early appearance of GABA raises the possibility that it may play additional roles at early stages of development. © 1993 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903370111

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

年代:1993

数据来源: WILEY