摘要:

AbstractThe positions of the crossed and uncrossed optic axons of distinct diameter classes has been examined in the optic tract of the adult cat. In addition, the retinal origin of axons occupying different positions within the tract has been studied. Since the position of a fibre within the optic tract reflects its time of arrival during development, we have used axonal position as an indicator of age and have related this to the chiasmatic pathway choice of the axons.Cats were either monocularly enucleated, to reveal the position and diameter of surviving crossed and uncrossed optic axons in semithin and thin sections, or implants of horseradish peroxidase (HRP) were placed so as to retrogradely label the ganglion cells giving rise to axons within the deep (early arriving), or superficial (later arriving) parts of the tract selectively. This was accomplished by either (1) surgically implanting HRP into the superficial portion of the optic tract, via a transbuccal approach, or (2) making such a transbuccal transection of the superficial fibres, followed by intracerebral injections of HRP to retrogradely label the surviving, deeper, optic axons from their target nuclei.The deep parts of the optic tract contain fine and medium, crossed and uncrossed axons arising from mainly medium sized cells in the contralateral nasal and the ipsilateral temporal retina; there is a clear line of decussation. In contrast, the superficial parts of the tract contain mainly fine diameter axons arising from small cells in the whole contralateral retina, and a small proportion of large diameter axons arising from large, alpha cells in the whole contralateral retina and in the ipsilateral temporal retina.The likelihood that axons from the temporal retina will project contralaterally therefore increases as development proceeds, since these axons are found in the superficial parts of the tract only. This suggests that a time‐dependent signal that weakens with age is responsible for directing early arriving optic axons from the temporal retina to take an exclusively uncrossed cours

ISSN:0092-7317    

DOI:10.1002/cne.903060402

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

年代:1991

数据来源: WILEY

摘要:

AbstractPrevious studies have mapped the visuotopic organization of visual areas from V1 through V4 in the occipital cortex and of area TE in the temporal cortex, but the cortex in between, at the occipito‐temporal junction, has remained relatively unexplored. To determine the visuotopic organization of this region, receptive fields were mapped at 1,200 visually responsive sites on 370 penetrations in the ventral occipital and temporal cortex of five macaques. We identified a new visual area, roughly corresponding to cytoarchitectonic area TEO, located between the ventral portion of V4 and area TE. Receptive fields in TEO are intermediate in size between those in V4 and TE and have a coarse visuotopic organization. Collectively, receptive fields in TEO appear to cover nearly the entire contralateral visual field. The foveal and parafoveal representation of TEO is located laterally on the convexity of the inferior temporal gyrus, and the peripheral field is represented medially on the ventral surface of the hemisphere, within and medial to the occipitotemporal sulcus. Beyond the medial border of TEO, within cyteoarchitectonic area TF, is another visually responsive region, which we have termed VTF; this region may also have some crude visual topography. Bands of constant eccentricity in TEO appear to be continuous with those in V2, V3v, and V4. The upper field representation in TEO is located adjacent to that in ventral V4, with a representation of the horizontal meridian forming the boundary between the two areas. The lower field representation in TEO is located just anterior to the upper field but is smaller. In contrast to the orderly representation of eccentricity in TEO, we found little consistent representation of polar angle, other than the separation of upper and lower fields. The results of injecting anatomical tracers in two animals suggest that TEO is an important link in the pathway that relays visual information from VI to the inferior temporal cortex. TEO is thus likely to play an important role in pattern perceptio

ISSN:0092-7317    

DOI:10.1002/cne.903060403

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

年代:1991

数据来源: WILEY

摘要:

AbstractSerotoninergic projections from the dorsal and median raphe nuclei to the area dentata of the hippocampal formation terminate mainly in the molecular layer and hilus, respectively. Consequently, a reduction in the density of the hilar serotoninergic plexus is seen by immunocytochemistry 2 weeks after lesions of the median raphe nucleus. Hippocampal serotonin concentration and serotonin high affinity uptake are also significantly reduced. Six weeks after lesion, surviving serotoninergic axons form a dense band in the inner molecular layer of the dorsal area dentata, a region that usually contains a sparse serotoninergic plexus. Moreover, serotoninergic fibers traverse the molecular layer and pass through the granule cell layer to reinnervate the hilus. Serotonin concentration and high affinity uptake have recovered to near normal levels by 6 weeks postlesion. Changes in the anatomical distribution of the area dentata serotoninergic plexus have not been reported in cases in which serotoninergic sprouting follows axotomy of serotoninergic projections. Thus direct lesions of serotoninergic neurons can produce a homotypic compensatory response that is qualitatively different from that generated by axotomy. The mechanistic basis for this reorganization is unclear, but the apparent extension of serotoninergic axon collaterals toward the hilus suggests that the denervated hilar neuropil is guiding reinnervation. Finally, anatomical evidence from animals studied 10 weeks postlesion suggests that the compensatory proliferation of serotoninergic axons observed 6 weeks after median raphe lesion is a transient event.

ISSN:0092-7317    

DOI:10.1002/cne.903060404

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

年代:1991

数据来源: WILEY

摘要:

AbstractPresumptive catecholamine (CA) neurons in the opossum midbrain were identified by tyrosine hydroxylase immunohistochemistry. In the midline, small to moderate numbers of CA cells were present in the rostral third of the nucleus raphe dorsalis and throughout the nucleus linearis. Ventrolaterally, such cells were observed in the deep tegmental reticular formation, in all subnuclei of the ventral tegmental area, and in the three subdivisions of the substantia nigra. The CA cells in these areas conform to the dopamine cell groups, A8, A9, and A10 as described in the rat. In several areas there appeared to be no separation between the CA neurons belonging to cytoarchitecturally different nuclei. In order to determine which CA neurons gave rise to striatal projections, the neostriatum was injected with True Blue (TB), and sections through the midbrain were processed for tyrosine hydroxylase (TH) and visualized by immunofluoroscence. Neurons containing both TB and TH were observed in each of the CA cell groups mentioned above. The distribution of these cells confirmed organizational features that may be unique to the opossum's substantia nigra. In addition, different patterns of labeling resulted from caudate versus putamen injections, suggesting a rudimentary medial to lateral topography in the organization of nigrostriatal projections. Although our results suggest that the organization of midbrain CA neurons in the opossum is similar to that in placental mammals, it is clear that differences exist.

ISSN:0092-7317    

DOI:10.1002/cne.903060405

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

年代:1991

数据来源: WILEY

摘要:

AbstractAlz‐50 is a monoclonal antibody recognizing a 68 kilodalton protein that is abundant in Alzheimer's disease (AD) but not detectable by immunoblotting methods in normal brains. When used for immunohistochemistry in AD cortex, Alz‐50 recognizes large numbers of neurofibrillary tangles (NFT), neuritic plaques, and some neurons that show no evidence of neurofibrillary degeneration by conventional histopathological staining methods, Alz‐50 immunoreactivity is described at the light and electron microscopic levels in the hypothalamus of brains obtained at autopsy from normal and AD subjects. Alz‐50 immunoreactivity in the rat hypothalamus is also described. A well‐defined population of Alz‐50 immunoreactive hypothalamic neurons was identified in both the normal human and rat. At the light microscopic level in the normal human, immunoreactive neurons were most concentrated in the periventricular region, but were also scattered throughout the arcuate nucleus (ARC), lateral hypothalamic area, and tuberal region. Immunoreactive fibers were seen in the periventricular region, dorsal division of the ventromedial nucleus (VMNd), ARC, and external layer of the median eminence (ME). In the rat, reactive neurons were seen only in the periventricular region, and reactive fibers were seen in the periventricular zone, medial preoptic nuclear complex, suprachiasmatic nucleus, VMNd, ARC, and external layer of the ME. Ultrastructurally, all immunoreactivity in the normal human and rat hypothalamus was associated with intraneuronal vesicles. In the AD hypothalamus, Alz‐50 identified numerous senile plaques and NFT in addition to the cells and fibers that were stained in the normal brains. Immunoreactive plaques and NFT were most numerous in regions previously reported to undergo neurofibrillary degeneration. At the ultrastructural level, the immunoreactivity in the AD hypothalamus was associated with filaments as well as vesicles. The significance of the selective staining of a specific population of vesicles by Alz‐50 is unknown; however, the present results suggest that it is independent

ISSN:0092-7317    

DOI:10.1002/cne.903060406

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe connectivity pattern of the laminar, principal, and magnocellular nuclei of the frog torus semicircularis (TS) was investigated. A small amount of horseradish peroxidase was injected focally into individual divisions of the TS and anterograde and retrograde transport patterns were observed. Results of our tracing study showed that these divisions of the TS possessed distinct innervation patterns. The principal nucleus appeared to be the primary input port of the TS receiving extensive inputs from all caudal brainstem auditory nuclei bilaterally, but especially from the contralateral dorsal medullary nucleus and the ipsilateral superior olivary and lateral lemniscus nuclei. Descending projection to this nucleus was limited to that from the posterior thalamic nucleus. In contrast, the laminar nucleus, but even more markedly the magnocellular nucleus, received extensive descending inputs from numerous structures in the dorsal thalamus and less pronounced ascending afferents from caudal brainstem auditory nuclei. Similar to the afferent connection patterns, the efferent projections originating from these three toral divisions differed substantially. The principal nucleus gave restricted ascending projections, limited mainly to the caudal region of the posterior thalamic nucleus, a region important in processing spectral information of complex sounds, and the pretectal gray. Its descending projection was also somewhat restricted, being limited to the superior olivary and lateral lemniscus nuclei. The laminar nucleus and especially the magnocellular nucleus gave robust descending as well as ascending projections; these nuclei serve as the main output paths for the TS and provide the main routes by which auditory input reaches the central thalamic nucleus, a structure previously shown to be involved in temporal information processing.

ISSN:0092-7317    

DOI:10.1002/cne.903060407

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

年代:1991

数据来源: WILEY

摘要:

AbstractAxonal projections from hypothalamic nuclei to the basal forebrain, and their relation to cholinergic projection neurons in particular, were studied in the rat by using the anterograde tracerPhaseolus vulgaris‐leucoagglutinin (PHA‐L) in combination with choline acetyltransferase (ChAT) immunocytochemistry. Discrete iontophoretic PHA‐L injections were delivered to different portions of the caudal lateral hypothalamus, as well as to various medial hypothalamic areas, including the ventromedial, dorsomedial, and paraventricular nuclei, and anterior hypothalamic and medial preoptic areas. The simultaneous detection of PHA‐L‐labeled fibers/terminals and ChAT‐positive neurons was performed by using nickel‐enhanced diaminobenzidine (DAB) and nonenhanced DAB as chromogens. Selected cases were investigated at the electron microscopic level.Ascending hypothalamic projections maintained an orderly lateromedial arrangement within the different components of the medial forebrain bundle, as well as with respect to their terminal projection fields (e.g., within the bed nucleus of the stria terminalis and lateral septal nucleus). The distribution pattern of hypothalamic inputs to cholinergic projection neurons corresponded to the topography of ascending hypothalamic axons. Axons originating from neurons in thefar‐lateral hypothalamusreached cholinergic neurons in a zone that extended from the dorsal part of the sublenticular substantia innominata (SI) caudolaterally, to the lateral portion of the bed nucleus of the stria terminalis rostromedially, encompassing a narrow band along the ventral part of the globus pallidus and medial portion of the internal capsule. Axons originating from cells in themedial portion of the lateral hypothalamusreached cholinergic cells primarily in more medial and ventral parts of the SI, and in the magnocellular preoptic nucleus and horizontal limb of the diagonal band nucleus (HDB). Axons frommedial hypothalamic cellsappeared to contact cholinergic neurons primarily in the medial part of the HDB, and in the medial septum/vertical limb of the diagonal band complex. Electron microscopic double‐labeling experiments confirmed contacts between labeled terminals and cholinergic cells in the HDB and SI. Individual hypothalamic axons established synapses with both cholinergic and noncholinergic neuronal elements in the same regions. These findings have important implications for our understanding of the organization of afferents to the basal forebrain cholinergic

ISSN:0092-7317    

DOI:10.1002/cne.903060408

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

年代:1991

数据来源: WILEY

摘要:

AbstractLarge retinal ganglion cells in the tilapid cichlid fishOreochromis spilurus(standard length 15–54 mm) were filled with horseradish peroxidase and studied in flatmounts. Three types, with distinct patterns of dendritic stratification, formed spatially independent, nonrandom mosaics.One type (about 0.3% of all ganglion cells) resembled the outer (off) alpha cells of mammals. They were very large, with thick primary dendrites and large, sparsely branched planar trees in the outer part of the inner plexiform layer (IPL). About 300 were arrayed regularly across each retina, their exact number and spacing depending on its size. Their somata were often displaced into the IPL, even where neighbours in the mosaic were orthotopic. Another type (0.8%) resembled the inner (on) alpha cells of mammals. These had slightly smaller somata that wereneverdisplaced and smaller trees in the middle layers of the IPL. About 800 were arrayed uniformly and regularly across each retina. A rarer type (0.06–0.08%) had two planar trees: one forming a coarse mosaic in the outer part of the inner plexiform layer (co‐planar with the trees of outer alpha‐like cells) and another in the outer plexiform layer. These “biplexiform” cells were smaller and rounder than alpha‐like cells andalwaysdisplaced. The dendrites were finer and less tapered. Cells in which we could identify an outer plexiform tree failed to cover the retina completely, but were nonrandomly distributed.We draw three main conclusions: (1) some nonmammalian vertebrates have separate inner and outer mosaics of large ganglion cells like those of mammals, (2) the vertical displacement of ganglion cell somata can vary widely within a single mosaic and may thus be functionally irrelevant, and (3) biplexiform ganglion cells exist in fish but differ in morphology from the biplexiform types described in some othe

ISSN:0092-7317    

DOI:10.1002/cne.903060409

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

年代:1991

数据来源: WILEY

摘要:

AbstractWhen a peripheral nerve is severed and left untreated, the most likely result is the formation of an endbulb neuroma; this tangled mass of disorganized nerve fibers blocks functional recovery following nerve injury. Although there are several different approaches for promoting nerve repair, which have been greatly refined over recent years, the clinical results of peripheral nerve repair remain very disappointing. In this paper we compare the results of a collagen nerve guide conduit to the more standard clinical procedure of nerve autografting to promote repair of transected peripheral nerves in rats and nonhuman primates.In rats, we tested recovery from sciatic nerve transection and repair by (1) direct microsurgical suture, (2) 4 mm autograft, or (3) entubulation repair with collagen‐based nerve guide conduits. Evoked muscle action potentials (MAP), were recorded from the gastrocnemius muscle at 4 and 12 weeks following sciatic nerve transection. At 4 weeks the repair group of direct suture demonstrated a significantly greater MAP, compared to the other surgical repair groups. However, at 12 weeks all four surgical repair groups displayed similar levels of recovery of the motor response.In six adult maleMacaca fascicularismonkeys the median nerve was transected 2 cm above the wrist and repaired by either a 4 mm nerve autograft or a collagen‐based nerve guide conduit leaving a 4 mm gap between nerve ends. Serial studies of motor and sensory fibers were performed by recording the evoked MAP from the abductor pollicis brevis muscle (APB) and the sensory action potential (SAP) evoked by stimulation of digital nerves (digit II), respectively, up to 760 days following surgery. Evoked muscle responses returned to normal baseline levels in all cases. Statistical analysis of the motor responses, as judged by the slope of the recovery curves, indicated a significantly more rapid rate of recovery for the nerve guide repair group. The final level of recovery of the MAP amplitudes was not significantly different between the groups. In contrast, the SAP amplitude only recovered to the low normal range and there were no statistically significant differences between the two groups in terms of sensory recovery rates.The rodent and primate studies suggest that in terms of recovery of physiological responses from target muscle and sensory nerves, entubulation repair of peripheral nerves with a collagen‐based nerve guide conduit over a short nerve gap (4 mm) is as effective as a standard nerve autograft. Furthermore, preliminary results show that entubulation repair with this material can support axon regeneration and maturation over a nerve gap distance of at least

ISSN:0092-7317    

DOI:10.1002/cne.903060410

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe examined the effects of loss of monocular retinal activity 2‐deoxyglucose (2‐DG) uptake in the adult rat geniculostriate system. Of particular interest was whether the influence of the normally functioning eye changed during long‐term contralateral retinal silence. Group 1 rats were subjected to short‐term (24 hours) and group 2 rats to long‐term (21–90 days) monocular tetrodotoxin (TTX) blockade, and metabolic activity was assessed during exposure to square‐wave gratings. Group 1 rats exhibited patterns of cortical glucose utilization commensurate with complete monocular loss of retinal activity: minimal 2‐DG uptake in contralateral monocular area 17 and dorsal lateral geniculate nucleus (LGN), and a bilateral depression in the binocular regions; 2‐DG uptake was highest in the monocular regions fed by the stimulated normal eye (in both area 17 and the LGN) and these regions appeared unaffected by the monocular blockade. After repeated injections of TTX (group 2), metabolic activity in binocular area 17 and binocular LGN increased bilaterally relative to the metabolically active monocular regions contralateral to the normal eye. Group 3 rats were monocularly TTX‐injected for 30 or 60 days, and, 24 hours before 2‐DG, all retinal activity was eliminated by means of binocular TTX injections or binocular enucleation. Glucose utilization in the binocular regions of both area 17 and the LGN in these rats was depressed to levels seen in monocular area 17 after complete and recent loss of activity from the contralateral eye, indicating that the metabolic increase which occurred in the binocular regions during long‐term monocular retinal blockade was dependent upon the neuronal processing of retinal information from the non‐TTX eye. We conclude that, in the adult rat, an activity‐dependent, physiologically based shift in ocular influence occurred in the binocular geniculostriate system during long‐term m

ISSN:0092-7317    

DOI:10.1002/cne.903060411

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

年代:1991

数据来源: WILEY