摘要:

AbstractInjections of HRP‐WGA in four cytoarchitectonic subdivisions of the posterior parietal cortex in rhesus monkeys allowed us to examine the major limbic and sensory afferent and efferent connections of each area. Area 7a (the caudal part of the posterior parietal lobe) is reciprocally interconnected with multiple visual‐related areas: the superior temporal polysensory area (STP) in the upper bank of the superior temporal sulcus (STS), visual motion areas in the upper bank of STS, the dorsal prelunate gyrus, and portions of V2 and the parieto‐occipital (PO) area. Area 7a is also heavily interconnected with limbic areas: the ventral posterior cingulate cortex, agranular retrosplenial cortex, caudomedial lobule, the parahippocampal gyrus, and the presubiculum. By contrast, the adjacent subdivision, area 7ip (within the posterior bank of the intraparietal sulcus), has few limbic connections but projects to and receives projections from widespread visual areas different than those that are connected with area 7a: the ventral bank and fundus of the STS including part of the STP cortex and the inferotemporal cortex (IT), areas MT (middle temporal) and possibly MTp (MT peripheral) and FST (fundal superior temporal) and portions of V2, V3v, V3d, V3A, V4, PO, and the inferior temporal (IT) convexity cortex. The connections between posterior parietal areas and visual areas located on the medial surface of the occipital and parieto‐occipital cortex, containing peripheral representations of the visual field (V2, V3, PO), represent a major previously unrecognized source of visual inputs to the parietal association cortex. Area 7b (the rostral part of the posterior parietal lobe) was distinctive among parietal areas in its selective association with somatosensory‐related areas: S1, S2, 5, the vestibular cortex, the insular cortex, and the supplementary somatosensory area (SSA). Like 7ip, area 7b had few limbic associations. Area 7m (on the medial posterior parietal cortex) has its own topographically distinct connections with the limbic (the posterior ventral bank of the cingulate sulcus, granular retrosplenial cortex, and presubiculum), visual (V2, PO, and the visual motion cortex in the upper bank of the STS), and somatosensory (SSA, and area 5) cortical areas.Each parietal subdivision is extensively interconnected with areas of the contralateral hemisphere, including both the homotopic cortex and widespread heterotopic areas. Indeed, each area is interconnected with as many areas of the contralateral hemisphere as it is within the ipsilateral one, though less intensively. This pattern of distribution allows for a remarkable degree of interhemispheric integration.These findings provide evidence that each major subdivision of posteriorparietal cortex has a unique set of reciprocal connections with limbic and sen‐sory areas in both hemispheres. For the most part, each parietalsubdivision, rather than being a site of multimodal convergence, receives input from only one sensory modality, though often from different channels of information within that modality. For example, the two streams of visual information tra‐ditionally linked to pattern and motion seem to converge in both areas 7a and 7ip. The areal parcellation of parietal cortex byits afferent and efferent con‐nections provides an anatomical foundation for a parallel processing model of higher cor

ISSN:0092-7317    

DOI:10.1002/cne.902870402

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe have examined the circuitry connecting the posterior parietal cortex with the frontal lobe of rhesus monkeys. HRP‐WGA and tritiated amino acids were injected into subdivisions 7m, 7a, 7b, and 7ip of the posterior parietal cortex, and anterograde and retrograde label was recorded within the frontal motor and association cortices. Our main finding is that each subdivision of parietal cortex is connected with a unique set of frontal areas. Thus, area 7m, on the medial parietal surface, is interconnected with the dorsal premotor cortex and the supplementary motor area, including the supplementary eye field. Within the prefrontal cortex, area 7m's connections are with the rostral sector of the frontal eye field (FEF), the dorsal bank of the principal sulcus, and the anterior bank of the inferior arcuate sulcus (Walker's area 45). In contrast, area 7a, on the posterior parietal convexity, is not linked with premotor regions but is heavily interconnected with the rostral FEF in the anterior bank of the superior arcuate sulcus, the dorsolateral prefrontal convexity, the rostral orbitofrontal cortex, area 45, and the fundus and adjacent cortex of the dorsal and ventral banks of the principal sulcus. Area 7b, in the anterior part of the posterior parietal lobule, is interconnected with still a different set of frontal areas, which include the ventral premotor cortex and supplementary motor area, area 45, and the external part of the ventral bank of the principal sulcus. The prominent connections of area 7ip, in the posterior bank of the intraparietal sulcus, are with the supplementary eye field and restricted portions of the ventral premotor cortex, with a wide area of the FEF that includes both its rostral and caudal sectors, and with area 45. All frontoparietal connections are reciprocal, and although they are most prominent within a hemisphere, notable interhemispheric connections are also present.These findings provide a basis for a parcellation of the classically considered association cortex of the frontal lobe, particularly the cortex of the principal sulcus, into sectors defined by their specific connections with the posterior parietal subdivisions. Moreover, the present findings, together with those of a companion study (Cavada and Goldman‐Rakic):J. Comp. Neurol. This issue have allowed us to establish multiple linkages between frontal areas and specific limbic and sensory cortices through the posterior parietal cortex. The net‐works thus defined may form part of the neural substrate of parallel distrib‐uted processing in the cerebral

ISSN:0092-7317    

DOI:10.1002/cne.902870403

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe spectra of fiber and axon diameter, myelin sheath thickness, fiber density, and g ratio of the optic nerve were analyzed for the strain‐13 guinea pig, an animal extensively utilized in the investigation of experimental disorders of demyelination. Our detailed analytical study of the normal guinea pig optic nerve provides the basis for comparison to disease states and the morphology of other species. As in the rat, mouse, and chipmunk, fiber diameters in the guinea pig were unimodal, but dissimilar to the trimodal fiber spectra of the cat and primate. The predominance of medium‐sized fibers (0.80–2.00 μm), common to most species, contributed to the larger mean fiber diameter (1.45 μm) of the guinea pig optic nerve, in which small fibers (0.50 μm or less) were infrequent and fibers larger than 5.00 μm in diameter, seen in the cat and primate, were absent. While myelin sheath thickness increased with axon diameter in the guinea pig, as in other species, a g ratio of 0.81 in the guinea pig was greater than in most mammals. Since conduction velocity is dependent on axon size, as well as myelin properties, the relatively larger mean axon diameter of the guinea pig optic nerve (1.18 μm) may compensate for the decrease in its m

ISSN:0092-7317    

DOI:10.1002/cne.902870404

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe chick brain is a useful model system for studying the ontogeny and phylogeny of neural circuitry, especially that of the visual system. In this study the distribution of cells and processes showing GABA‐like immunoreactivity (GABA+) in the diencephalon and mesencephalon of the posthatch chick was determined immunohistochemically with a polyclonal antibody to GABA and compared with the results of similar studies in mammals. Most of the small GABA+ cells were found in the chick visual centers such as the nucleus lateralis anterior, suprachiasmatic nucleus, ventral lateral geniculate, optic tract, dorsolateralis anterior pars lateralis, lentiformis mesencephali, ectomammillary nucleus, area pretectalis, and the optic tectum. Large GABA+ cells were found in the following nuclei: reticularis superior, posteroventralis thalami, subpretectalis, isthmi pars magnocellularis, interstitiopretectosubpretectalis, mesencephalicus lateralis pars dorsalis. These large cell‐containing nuclei receive projections from visual or auditory centers. GABA+ axons were found throughout the diencephalon and mesencephalon but were especially prominent in the ansa lenticularis, fasciculus medialis longitudinalis, and optic tract. The distribution of GABA+ cells in the chick is more widespread than in rodents and exhibits an increased association with the visual centers suggesting a correlation with the specialized visual requirements of the b

ISSN:0092-7317    

DOI:10.1002/cne.902870405

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe second‐ and third‐order auditory nuclei in the brainstem of the chicken, nucleus magnocellularis (NM) and nucleus laminaris (NL), receive afferents that are immunoreactive to gamma‐aminobutyric acid (GABA). In order to investigate the source(s) of these GABAergic afferents, we examined the distribution, morphology, and connectivity of GABAergic neurons in and adjacent to NM and NL in chicks from 7 days of incubation to 12 days posthatch. Immunocytochemical techniques revealed the presence of approxi‐mately 150 GABA‐labeled neurons within the neuropil surrounding NM and NL on each side of the brainstem. Most of these neurons are located between NM and NL and along the lateral border of NM. GABAergic neurons are mul‐tipolar; their thick dendritic processes branch extensively and give rise to several thin, secondary processes. Frequently, the GABA‐labeled processes arbo‐rize within NM or NL. The morphology of these non‐NM/NL neurons was investigated further with Golgi impregnation and specific neuronal markers (antisera to microtubule‐associated protein). Our observations suggest that a considerable portion of GABAergic input to NM and NL originates from local GABAergic neurons.In order to determine other possible sources of GABAergic input to NM and NL, we injected tracers unilaterally into NM/NL. A small number (20–30)of neurons were retrogradely labeled in the trapezoid body, almost exclusively ipsilaterally. No labeled cells were found in other regions of the brainstem, except for the contralateral NM, Unilateral injections of horseradish‐peroxi‐dase‐labeled wheat germ agglutinin into the paraflocculus revealed only minor terminal labeling in the lateral region of NL bilaterally. The number and dis‐tribution of GABAergic terminals in NM and NL appeared normalafter transection of the

ISSN:0092-7317    

DOI:10.1002/cne.902870406

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe present study investigated the ventral medullary distribution of enkephalin‐immunoreactive neurons that project to the intermediolateral cell column and the relationship of these neurons to substance P–immunoreactive neurons. Neurons that projected to the intermediolateral cell column were identified by the presence of rhodamine‐labeled microspheres within the neuronal cell body after an injection of the microspheres into the intermediolateral cell column of the third thoracic spinal cord segment. Enkephalin‐ and substance P‐immunoreactivities were identified by dual‐color immunohistochemistry. Enkephalin‐immunoreactive neurons that projected to the intermediolateral cell column were present in the raphe magnus, the nucleus reticularis magnocellularis pars alpha, the paragigantocellular reticular nucleus, and the parapyramidal region. These neurons were present throughout the rostrocaudal extent of each of these nuclei. However, in the raphe magnus the greatest number was present at more rostral levels of the nucleus. The morphology and distribution of enkephalin‐immunoreactive neurons that projected to the intermediolateral cell column were similar to those of enkephalin‐immunoreactive neurons that were not observed to contain rhodamine‐labeled microspheres. Substance P– and enkephalin‐immunoreactive neurons that projected to the intermediolateral cell column were present in similar distributions in each of the nuclei studied, except the raphe magnus. The raphe magnus contained more enkephalin‐ than substance P–immunoreactive neurons at rostral levels and more substance P‐immunoreactive neurons than enkephalin‐immunoreactive neurons at caudal levels. Coexistence of substance P‐ and enkephalin‐immunoreactivities in ventral medullary neurons that projected to the intermediolateral cell column was rarely seen. These studies support the hypothesis that ventral medullary enkephalinergic neurons project to the intermediolateral cell column where they could act to modulate

ISSN:0092-7317    

DOI:10.1002/cne.902870407

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe superficial and intermediate gray layers of the superior colliculus are heavily innervated by fibers that utilize the neurotransmitter acetylcholine. The distribution, ultrastructure, and sources of the cholinergic innervation of these layers have been examined in the cat by using a combination of immunocytochemical and axonal transport methods. Putative cholinergic fibers and cells were localized by means of a monoclonal antibody to choline acetyltransferase (ChAT).ChAT immunoreactive fibers are distributed throughout the depth of the superior colliculus, with particularly dense zones of innervation in the upper part of the superficial grey layer and in the intermediate grey layer. Within the superficial grey layer, the fibers form a continuous, dense band, whereas within the intermediate grey layer the fibers are arranged in clusters or patches. Although the patches are present throughout the rostrocaudal extent of the superior colliculus, they are most prominent in middle to caudal sections.The structure of the ChAT immunoreactive terminals was examined electron microscopically. The appearance of the terminals is similar in the superficial and intermediate grey layers. They contain closely packed, mostly round vesicles, and form contacts with medium‐sized dendrites that exhibit small, but prominent postsynaptic densities; a few of the terminals contact vesicle‐containing profiles.To identify the sources of the cholinergic input to the superior colliculus, injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) were made in the superior colliculus and the sections were processed to demonstrate both the retrograde transport of WGA‐HRP and ChAT immunoreactivity. Neurons containing both labels were found in the parabigeminal nucleus, and in the lateral dorsal and pedunculopontine tegmental nuclei of the pontomesencephalic reticular formation. Almost every cell in these nuclei that contained retrograde label was also immunoreactive for ChAT.The similarities between the laminar distributions of the ChAT terminals and the terminations of the pathway from the parabigeminal nucleus (Graybiel:Brain Res. 145:365–374, '78) support the view that the latter nucleus is a source of the cholinergic fibers in the superficial grey layer. The possibility that the pedunculopontine tegmental nucleus is a source of cholinergic fibers in the deep layers was tested by examining the distribution of labeled fibers following injections of WGA‐HRP into this region of the tegmentum. Patches of labeled terminals were found in the intermediate grey layer that resemble in distribution the patches of ChAT immunoreactive fibers in this layer. Only a sparse distribution of labeled terminals was found in the other layers. These results suggest that there are at least two distinct sources of the cholinergic innervation of the superior colliculus: the parabigeminal nucleus for the superficial grey layer and the pedunculopontine tegmental nucleus for the intermediate grey layer. Other potential sources of cholinergic input to the superior colliculus include ChAT immunoreactive neurons that were observed in the present study in the superficial layers of the superior colliculus itself and the cholinergic cells of the lateral dorsal tegmental nucleus that project to the superior colliculus.Since the pontomesencephalic reticular formation is known to have extensive connections with efferent pathways of the basal ganglia, in a final series of experiments the relationships between the cholinergic pathways from the tegmentum to the superior colliculus and the projections of substantia nigra pars reticulata were explored. Injections of WGA‐HRP were madeinto the substantia nigra pars reticulata and alternate sections were processed for either HRP histochemistry or ChAT immunocytochemistry. Within the superior colliculus, the nigrotectal terminals form patches that are approxi‐mately equal in number and aligned with the patches of ChAT immunoreac‐tive processes. Within the tegmentum, extensive overlap was found between the ChAT immunoreactive cells in the pedunculopontine tegmental nucleus and the terminal field of substantia nigra pars reticulata. These results suggest that there is a close association between the cholinergic innervation of the intermediate grey layer and the nigral outflow of

ISSN:0092-7317    

DOI:10.1002/cne.902870408

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe bag cells of the marine molluscAplysiaare well‐characterized neuroendocrine cells that initiate egg laying, but the natural stimulus triggering bag‐cell activity has not been determined. As a first step toward identifying central neurons that might provide synaptic or neurohormonal input onto the bag‐cell network, antibodies specific for alpha‐bag‐cell peptide (α‐BCP) were generated. This peptide belongs to a small family of structurally related peptides that can elicit bag‐cell activity in vitro. Antibody specificity was established by immunodot assay and preabsorption studies: immunocytochemical labeling was abolished in each ganglion when the antibodies were preincubated with either α‐BCP‐thyroglobulin conjugate or α‐BCP‐(1–8) but was not affected by preincubation with thyroglobulin or thyroglobulin‐thyroglobulin conjugate. The antibodies specifically labeled the bag cells in the abdominal ganglion and ectopic bag cells in both the abdominal and right pleural ganglia. The ectopic bag cells were similar to conventional bag cells in size and morphology, but varied in number and location among preparations. In the cerebral ganglion, the antibodies labeled a bilaterally symmetrical pair of cell clusters, containing approximately ten cells each, on the dorsal surface of the ganglion. The cerebral cells were smaller than bag cells, were constant in location, and sent their processes into the neuropil rather than the connective tissue sheath. Immunoreactive processes were observed in the neuropils of the cerebral, pleural, and pedal ganglia and among the axons of the cerebropedal, cerebropleural, and pleurovisceral connectives. No immunoreactive cell bodies were observed in the buccal or pedal ganglia. Identical patterns of labeling were observed inAplysia californica, A. Brasiliana, andA. Dactylomela.The distribution of immunoreactive cell bodies within the circumesophageal ganglia of all three species thus parallels the distribution of receptive sites for the in vitro induction of bag‐cell activity by atrial gland peptide B, a peptide structurally related to α‐BCP. These observations suggest that the immunoreactive cells identified in these studies, or a subset of them, may be involved in the physiological induction of bag‐cell activity. Since low doses of α‐BCP have additional inhibitory actions on the bag cells, however, it is possible that the identified cells could play a more complex role

ISSN:0092-7317    

DOI:10.1002/cne.902870409

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn the process of disk renewal in retinal cone outer segments (COSs), apical displacement of disks must be coupled to systematic reductions in disk area and perimeter in order to retain overall conical geometry. We have quantified these changes in disk area and perimeter segment lengths by morphometric analyses of cross sections of fully formed disks taken from basal to apical ends of COSs. Specifically excluded from these analyses are data arising from partial or incomplete disks within the COS, which do not conform to the conical geometry and which constitute a minor fraction of the COS disk population. Thus, our results address the long‐range pattern of structural changes affecting the major population of disks along the length of the COS. Our data indicate that decreases in total disk margin length associated with apical displacement of fully formed disks are due to decreases in the length of the margin opposite the cilium, i.e., the open margin segment. In contrast, the average length of the closed margin segment remains constant or increases slightly in the apical direction.The open margins of frog COS disks have recently been shown to possess a distinctive lattice of membrane‐associated components (Fetter and Corless:Invest. Ophthalmol. Vis. Sci. 28:646–657, '87). We have also examined COSs by the freeze‐fracture, deep‐etch technique for evidence of a mechanism whereby measured changes in open margin length may be accommodated while maintaining the overall organization of the open margin segments. In regions of membrane continuity between open margins and the COS plasma membrane, we have observed elevated ridges on the plasma membrane that (1) tend to lie parallel to the open margin segments, (2) have a similar axial spacing, (3) occasionally demonstrate interconnecting filaments similar to those of the open margin lattice, and (4) appear to have a particulate substructure. The mechanism proposed for reducing open margin length involves tangential displacement of the lateral edges of the open margin lattice to the adjacent plasma membrane. These shifted lattice domains initially give rise to the plasmalemmal ridges, which subsequently disassemble, and whose components become redistributed in the COS plasma membrane. These structural features of COS open margins suggest several revisions of our earlier model of disk morphogenesis (Corless and Fetter:J. Comp. Neurol. 257:24–38, '87), which was based on the margin structure of ROS disks alone.Eckmiller (J. Cell Biol. 105:2267–2277, '87) has recently proposed that partial disks observed within the COS represent sites of new disk formation. We evaluate the consequences of partial disk geometries for local remodelling of the open margin lattice and briefly outline an alternative interpretation of the partial COS disks that is fully consistent with available morph

ISSN:0092-7317    

DOI:10.1002/cne.902870410

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

年代:1989

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902870401

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

年代:1989

数据来源: WILEY