摘要:

AbstractIsthmotectal projections in turtles were examined by making serial section reconstructions of axonal and dendritic arborizations that were anterogradely or retrogradely filled with HRP. Two prominent tectal‐recipient isthmic nuclei–the caudal magnocellular nucleus isthmi (Imc) and the rostral magnocellular nucleus isthmi (Imr)–exhibited strikingly different patterns of organization. Imc cells have flattened, bipolar dendritic fields that cover a few percent of the area of the cell plate constituting the nucleus and they project topographically to the ipsilateral tectum without local axon branches. The topography was examined explicitly at the single‐cell level by using cases with two injections at widely separated tectal loci. Each Imc axon terminates as a compact swarm of several thousand boutons placed mainly in the upper central gray and superficial gray layers. One Imc terminal spans less that 1% of the tectal surface.Imr cells, by contrast, have large, sparsely branched dendritic fields overlapped by local axon collaterals while distally, their axons nontopographically innervate not only the deeper layers of the ipsilateral tectum but also ipsilateral Imc. Imr receives a nontopographic tectal input that contrasts with the topographic tectal input to Imc.Previous work on nucleus isthmi emphasized the role of thecontralateralisthmotectal projection (which originates from a third isthmic nucleus in turtles) in mediating binocular interactions in the tectum. The present results on the two different but overlappingipsilateraltecto‐isthmo‐tectal circuits set up by Imc and Imr are discussed in the light of physiological evidence for selective attention effects and local‐global interactions

ISSN:0092-7317    

DOI:10.1002/cne.902610302

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractTo compare patterns of projections to the inferior colliculus from different sources, injections of [3H]‐leucine were placed in the cochlear nuclei, superior olivary complex, and nuclei of the lateral lemniscus ofPteronotusc parnellii.The results show that the target of the anteroventral cochlear nucleus (AVCN) is the ventral and lateral two thirds of the central nucleus of the inferior colliculus. The binaural pathways from the medial and lateral superior olives (MSO and LSO) project to the same target. The dorsal cochlear nucleus (DCN) projects to the entire central nucleus of the inferior colliculus and does so in a more diffuse manner than does the AVCN. The DCN also sends sparse projections beyond the central nucleus into dorsal parts of the pericentral area. The intermediate (INLL) and ventral (VNLL) nuclei of the lateral lemniscus are relays in pathways that originate in the cochlear nucleus and terminate in the contralateral inferior colliculus. These nuclei also receive indirect input from the contralateral AVCN via the medial nucleus of the trapezoid body. Although nuclei of the lateral lemniscus project most densely to those areas of the inferior colliculus that are also the targets of the AVCN, MSO, and LSO, the nuclei of the lateral lemniscus also send spare projections outside these areas. Many of the pathways just described project in bands, a finding that raises the possibility that the projections parallel the orientation of disk‐shaped cells in the inferior colliculus and raises the question of whether the bands from one source overlap or interdigitate with the bands from another sou

ISSN:0092-7317    

DOI:10.1002/cne.902610303

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe origins and terminations of the amygdaloid connections with the modality‐specific visual cortical areas TEa (anterior TE area), TEp (posterior TE area), TEO, V4, V2, MST (medial superior temporal visual area), MT (middle temporal visual area), and V1 were studied in macaques. These were compared with the amygdaloid connections of a vision‐related polysensory area TG by making cortical injections of horseradish peroxidase (HRP) and incubating the sections with tetramethylbenzidine (TMB) as the chromogen. Both areas TEa and TEp receive a major projection from the lateral basal nucleus and a minor one from the accessory basal nucleus of the amygdaloid complex, whereas these areas send a major projection to the lateral nucleus and a minor one to the lateral basal nucleus. Areas TEO, V4, V2, MST, MT, and V1 receive projections only from the lateral basal nucleus; none of them project to any amygdaloid nucleus. Thus, the amygdalofugal projections are more widespread and more complex than the amygdalopetal projections. These findings indicate that the connections between the amygdaloid nuclei and the visual areas are generally nonreciprocal and underlie the importance of a feedback mechanism from the amygdala to the visual cortical areas in visual information processing. There appears to be a caudorostral (occipitotemporal) gradient in the distribution and density of the amygdaloid projections, which become progressively more widespread and heavier among the progressively more rostral visual areas (from area V1 to area TEa).The amygdaloid connections with area TG are distinctly different from the connections with the visual areas. Area TG is reciprocally connected mainly with the periamygdaloid cortex, and with the lateral, accessory basal, and medial basal nuclei of the amygdala as w

ISSN:0092-7317    

DOI:10.1002/cne.902610304

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractAn antiserum to γ‐aminobutyric acid (GABA) was used in a light and electron microscopic immunocytochemical study to determine the morphology and distribution of GABA‐containing neurons in the rat visual cortex and to ascertain whether all classes of nonpyramidal neurons in this cortex are GABAergic. The visual cortex used for light microscopy was prepared in such a way that the antibody penetrated completely through tissue sections, and in these sections large numbers of GABA immunoreactive neurons were apparent. The labeled neurons could be identified as being either multipolar, bitufted, bipolar, or horizontal neurons. In layers II through Via, GABA immunostained cells were distributed uniformly and accounted for approximately 15% of all neurons, but in layer I all neurons appeared to be immunostained.Electron microscopy of GABA immunostained visual cortex prepared to ensure good fine structural preservation confirmed the presence in layers II through Via of numerous immunoreactive bipolar neurons, both small and large varieties, as well as multipolar and bitufted neurons. Additionally, electron microscopy reveals that astrocytes are frequently GABA immunoreactive.From a correlated light and electron microscopic evaluation of neurons in GABA immunostained visual cortex, it was possible to confirm which kinds of neurons are GABAergic and what proportion of the neuronal population they represent. Thus, from an analysis of some 950 neurons, it was found that pyramidal neurons were never immunoreactive and that except for 20% of the bipolar cell population, all examples of other types of nonpyramidal neurons encountered in this material were GABA immunoreac

ISSN:0092-7317    

DOI:10.1002/cne.902610305

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe brains of seizure‐sensitive (SS) and seizure‐resistant (SR) gerbils were studied with an immunocytochemical method to localize glutamic acid decarboxylase (GAD) to determine whether a defect existed in the inhibitory GABAergic system similar to that which has been reported in animal models of focal epilepsy in which GABAergic cell bodies and terminals are decreased in number. A major difference between the two strains of gerbils was found in the number of GABAergic neurons in the hippocampal formation. Specifically, a paradoxical increase occurred in the number of glutamate decarboxylase (GAD)‐immunoreactive neurons: there were approximately 65% more GABAergic cells within the dentate gyrus and the CA3 region of the hippocampus in the SS gerbils. Furthermore, the density of GAD‐immunoreactive puncta, the light microscopic correlates of synaptic boutons, was greater in the SS animals. Other histological methods were used to determine if the difference between SS and SR gerbils was specific for the GABAergic system. Nissl‐stained preparations showed that the number of granule cells in the dentate gyrus was 20% greater in SS gerbils than in SR gerbils. An examination of some hippocampal afferents, efferents, and intrinsic connections with acetylcholinesterase histochemistry and the Timm's stain for heavy metals demonstrated no differences between the two strains. In addition, Golgi‐stained preparations of the dentate gyrus indicated that the morphology of basket cells did not differ between the two strains nor between the gerbil and the rat.Several brain regions in addition to the hippocampus were studied to determine whether or not the increased number of GAD‐immunoreactive neurons was specific for the hippocampal formation. These regions included the substantia nigra, motor cortex, and nucleus reticularis thalami and were selected because they contain large populations of GABAergic neurons and have been implicated in seizure activity. No differences between the two strains were detected in any of these regions. Therefore, a major morphological difference between the brains of SS and SR gerbils exists in the hippocampal formation of SS gerbils in which an increase occurs in the number of GABAergic neurons and granule cells. If these additional inhibitory neurons act mainly to inhibit other inhibitory neurons, the net effect would be increased disinhibition of the principal excitatory neurons of the hippocampal formation. This could lead to seizure activity within the hippocampal formation and at distant sites through multiple synapti

ISSN:0092-7317    

DOI:10.1002/cne.902610306

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractSurvival of motoneurons in the lateral motor column (LMC) of the chick embryo is known to depend on the periphery. How this dependence relates to the normally occurring death of motoneurons is unknown. Analysis of the time course of LMC cell loss in the absence of varying amounts of limb musculature could help bring about an understanding of this relationship. We undertook this analysis by studying LMC development inwinglesschick embryos. Grossly these embryos lack wings, but we have reported that some of them possess more than 40% of the normal volume of wing bud‐derived muscles (M.E. Lanser and J.F. Fallon, Anat. Rec.217:61–78, 1987). In the present work we compared the time course of LMC development in wingless embryos that possessed varying amounts of wing bud‐derived musculature with that in normal embryos. In normal embryos little cell loss occurs from the brachial LMC prior to day 8 (15% of the: total cell loss). Most of the normal cell loss occurs between 8 and 10 days (62% of the total cell loss). In thewinglessLMC, anywhere from 55% to 70% of the total cell loss occurs before day 8. The death of motoneurons prior to day 8 is proportional to the amount of wing bud musculature eliminated by the mutation. Cell loss after day Bis proportional to the amount of wing bud musculature spared by the mutation. Therefore, when the limb is missing, most motoneurons die before the major period of cell loss even begins in the normal LMC. Counts of dead cells in the LMC also support this conclusion. In addition, curves plotting the rates at which cells are lost from the brachial LMC provide a suggestion that normal cell loss is biphasic and that limb removal enhances primarily the first phase of cell loss. These data suggest that the majority of motoneurons may die for different reasons in the normal and the limb‐deprived LMCs. Overall, the number of motoneurons surviving in the brachial LMC is proportional to the volume of wing bud‐derived muscle present. However, as the muscle volume approaches zero, motoneuron number does not. This suggests that most, but not all, motoneurons depend on limb bud‐derived muscles for survival. Finally, the decreased motoneuron number in thewinglessLMC, when compared to normal after the cell death period, cannot be totally accounted for by the additional loss of cells that occurred during the cell death period in thewinglessLMC. This raises the possibility that limb absence influences the initial formation of the LMC, a possibility that deserves further in

ISSN:0092-7317    

DOI:10.1002/cne.902610307

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have used an antibody to glutaraldehyde fixation complexes of γ‐amino butyric acid (GABA) to stain the developing central nervous system ofXenopus laevisembryos. Neuronal somata, growth cones, axons, and dendrites were found with GABA‐like immunoreactivity. Transmission electron microscope (TEM) observations were made of axons and synapses. By observation of the earliest stages of differentiation of neurons, seven classes of putative GABAergic interneurons were discerned. (1) Ascending neurons are first stained in the hindbrain at stage 26 and later extend caudally in the spinal cord. They have ascending ipsilateral axons. (2) Midhindbrain reticulospinal neurons are first stained at stage 25 and develop as a compact group with descending ipsilateral and contralateral axons, (3) Vestibular complex commissural neurons are first stained at stage 29/30 in a dorsal position near the entry of the seventh and eighth cranial nerves. They have ventral commissural axons that descend contralaterally and their somata form a compact mass. (4) Rostral hindbrain commissural neurons are first stained at stage 33/34 just rostral to the entry of the trigeminal nerve. They each have a decussating projection. (5). Rostral midbrain neurons are first stained in the midbrain at stage 29/30 and are later associated with prominent dorsal and ventral commissures. (6) Optic tract and (7) rostral forebrain neurons are found in the forebrain associated with strongly stained axon tracts.The direction of axonal growth from its earliest stages was distinct for each class of hindbrain and spinal cord ne

ISSN:0092-7317    

DOI:10.1002/cne.902610308

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe methods of transganglionic transport of horseradish peroxidase (HRP) and horseradish peroxidase–wheat germ agglutinin (HRP‐WGA) were used to determine the location within the trigeminal ganglion of the primary afferent neurons that innervate the rat central cornea, and the brainstem and spinal cord termination sites of these cells. In each of 18 animals, solutions of HRP or HRP‐WGA were applied to the scarified corneal surface and allowed to infiltrate into the corneal epithelium and stroma for 15 minutes. Postmortem examination of the corneal whole mounts from the experimental animals, and of corneas and neural tissues from several control animals, showed that the HRP/HRP‐WGA remained confined to the central cornea with no spread into adjacent intra‐ or extraorbital tissues.HRP‐labeled corneal afferent somata were located in the dorsal part of the ophthalmic region of the ipsilateral trigeminal ganglion. The central fibers of the corneal afferent neurons projected very heavily to interstitial nuclei of Cajal in the spinal tract of V at the level of caudal pars interpolaris and rostral pars caudalis, lightly to the pars caudalis/C1 transition zone, and sparsely to the dorsal horn of spinal cord segments C1‐C3. The trigeminal main sensory nucleus, pars oralis, the rostral three‐fourths of pars interpolaris, and an extensive midregion of pars caudalis were totally devoid of reaction product. Terminal fields in Caudal pars caudalis and in the spinal cord dorsal horn were concentrated largely in the outer half of lamina II, with lesser accumulations in lamina I, the deeper half of lamina II, and in lamina III.The present study demonstrates for the first time by means of an anatomical tracing procedure the brainstem termination sites of corneal afferent neurons in the rat. The patchy, discontinuous nature of the corneal afferent projection to the caudal trigeminal brainstem nuclear complex (TBNC), and the total lack of corneal projections to rostral subdivisions of the TBNC, provide an exception to the general rule of trigeminal organization in which most areas of the head and face are represented as continuous columns throughout the rostrocaudal extent of the i

ISSN:0092-7317    

DOI:10.1002/cne.902610309

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractFollowing intraocular injection in adult rats of125I‐labeled wheat germ agglutinin (I‐WGA), the ultrastructural distribution of label in the superior colliculus and lateral geniculate was examined by electron microscope auto‐radiography. Three days after injection, 5.4% of the label in the lateral geniculate was associated with neuronal perikarya, and 3.6% was associated with glial perikarya. The corresponding figures for the superior colliculus were 5.1% and 0.8%. When the data were expressed as number of grains per μm2cytoplasm, there was no statistically significant difference between the grain density over neuronal or glial cytoplasm in either the lateral geniculate or the superior colliculus, A statistical analysis of the distance between the silver grains and the cell membranes showed that in both neurons and glia, the observed labeling was the product of internalized I‐WGA and not the result of scatter from the neuropil or from label bound to the surface of the cells. These results indicate that much of the WGA released from axons and axon terminals is not confined to a specific “transsynaptic” pathway, but produces a generalized labeling of nearby cells, much like a microinjection of WGA int

ISSN:0092-7317    

DOI:10.1002/cne.902610310

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902610301

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY