摘要:

AbstractAnterograde and retrograde tracing techniques have been used to study the uncrossed retinal projection in neonatal pigmented and albino Syrian hamsters. The total number of retinal ganglion cells projecting ipsilaterally peaks at postnatal days 2–4 (P2–P4) and declines to adult values by P12. The change in cell numbers has a similar time course in albino and pigmented animals. Although the population of uncrossed cells in the temporal retina of albino hamsters is always less than that in pigmented hamsters, no difference between the colour phases was found for the population of uncrossed cells in nasal retina. Differential cell death also contributes to the adult albino decussation pattern in hamsters: The relative loss of cells from temporal retina in albinos (72%) is greater than that in pigmented animals (56%). The additional loss in albinos does not appear to depend on binocular interactions: The same proportion (30%) of uncrossed cells is “rescued” from death by neonatal monocular enucleation in both colour phases.Flat‐mount preparations showing the distribution of uncrossed fibres reveal that a distinct focus of terminals emerges in rostral superior colliculus, which is topographically appropriate for a binocular mapping, at the peak of uncrossed ganglion cell numbers (P4). Comparison of uncrossed terminal distributions and ganglion cell death reveals considerable refinement of the terminals prior to the main phase of cell death. Monocular enucleations performed some time after birth have a greater effect on uncrossed terminal distributions than on cell death. These observations suggest that independent mechanisms may be involved in the regulation of terminal distributions and of cell numbers in the developing uncrossed retinal pathways. © 1995 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903570202

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractWe have examined the projection from the lateral superior olive (LSO) to the inferior colliculus (IC) in the ferret, with particular interest in the laterality of the projection and in the effects of unilateral cochlear removal in infancy. Large or small deposits of the retrograde tracer wheat germ agglutininhorseradish peroxidase (WGA‐HRP) were made in the IC of anesthetized adult ferrets that either were normally hearing or had been unilaterally deafened in infancy (P5 or P25). After 2 days, the ferrets were perfused, and frontal sections of the brainstem were treated with tetramethyl benzidine. For large deposits of WGA‐HRP, equal numbers of labelled neurons were found evenly spread through both LSOs. Smaller deposits of WGA‐HRP produced four results that contrasted with previous reports on the cat. First, many more labelled neurons were found in the contralateral than in the ipsilateral LSO. Second, the relative number of labelled neurons in each LSO was independent of whether the deposits were in the ventral or in the dorsal IC. Third, the total number of labelled LSO neurons was independent of whether the deposits were in the ventral or in the dorsal IC. Fourth, the proportion of ipsilateral to contralateral labelled neurons was slightly higher in the medial LSO than in the lateral LSO. Ventral IC deposits resulted in more labelled neurons in the medial LSO, and dorsal IC deposits resulted in more labelled neurons in the lateral LSO, as expected. Neonatal cochlear removal did not change any of these results. We conclude that, in the ferret, the organization of the crossed and uncrossed projections from the LSO to the IC differs from that of the cat, and any similarity with the optic chiasm is not obvious. © 1995 Wiley‐L

ISSN:0092-7317    

DOI:10.1002/cne.903570203

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe organization of neurons and fibers in the cochlear nuclei of the alligator lizard (Gerrhonotus multicarinatus) was examined with light and electron microscopy. In this species, much is known about the anatomy and physiology of the inner ear including the cochlear nerve, but little is known about the synaptic connections of cochlear fibers on second‐order neurons. These data will help to develop general principles addressing the cellular organization of the vertebrate auditory system.Subdivisions of the cochlear nuclei were defined on the basis of their histologic appearance and neuronal composition. Neuron classes were proposed from their light microscopic and ultrastructural features. Nucleus magnocellularis medialis consists of a homogeneous population of neurons called “lesser ovoid” cells. Nucleus magnocellularis lateralis consists of “greater ovoid” and “small” cells. Nucleus angularis lateralis consists of “spindle” cells. Lastly, nucleus angularis medialis contains a population of large neurons called “duckhead” and “multipolar” cells, and a population of smaller neurons called “bulb” and “agranular” cells.These neuron populations are differentially innervated by tectorial and free‐standing cochlear fibers that are associated with separate frequency ranges. All neuronal populations except agranular cells were observed to receive synaptic input from cochlear nerve fibers. In nucleus magnocellularis medialis and nucleus angularis medialis, primary afferents form both chemical and electrical synapses with resident neurons. These observations imply that acoustic information is synaptically processed in fundamentally distinct ways in the cochlear nuclei of alligator lizards and distributed along separate neural circuits. Thus, the characteristic structural and functional dichotomy of the alligator lizard inner ear is extended to central auditory pathways by way of cochlear nerve

ISSN:0092-7317    

DOI:10.1002/cne.903570204

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractAnterograde transport of horseradish peroxidase was used to map the initial projection patterns of motor and sensory axons innervating the wing of the chick embryo. Injections which resulted in labeling large numbers of motor and sensory axons, separately or in combination, were used to define the time course of innervation and to visualize the progressive morphogenesis of the peripheral nerve pattern. Motor axons emerged from the spinal cord and accumulated near the ventromedial border of the myotome where they remained for up to 16 hours before growing into the plexus region and limb bud. Despite the known later time of sensory neuron production, the first sensory axons projected to the wing at the same time as motor axons. When axons first entered the wing bud, they were distributed in two loosely organized sheets of axon fascicles, one projecting to dorsal muscle mass, the other to ventral muscle mass. The width of the sheets was between one‐third to one‐half the width of the wing bud, and this distance was more than twice the diameter of the proximal nerve trunks measured at stage 28. In the proximal limb the basic pattern of peripheral nerves emerged gradually from stages 26 to 28. During these stages, the loosely organized sheets of axonal fascicles seen at younger stages were progressively transformed into several coherent nerve trunks and muscle nerves extended from common nerve trunks. The implication of these observations is that many outgrowing axons appear not to follow preformed pathways corresponding to the mature peripheral nerve branching pattern. This pattern may instead result from axonal recognition of cues within a largely undifferentiated limb bud, and from the subsequent bundling together of loosely organized axon fascicles. These events occur concurrently with limb growth and differentiation. © 1995 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903570205

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe development and distribution of neuronal projections to the developing chick wing was studied using anterograde transport of horseradish peroxidase (HRP). Small injections of HRP were made into motor or sensory neuronal populations in order to visualize individual axons and their associated growth cones. Motor growth cones were observed in different regions of the embryo at different stages, in a proximal‐to‐distal pattern of distribution which paralleled the process of axon outgrowth and nerve formation. Different growth cone morphologies were associated with differing regions of the developing projection. In the spinal nerves, axons destined for the limb were unbranched and terminated in simply shaped growth cones. As axons approached the developing limb and entered the plexus region, their growth cones became more complex and larger primarily because of widening, and they sometimes branched, producing processes which could extend tens of microns from a tricorne branch point on the parent axon. Both motor and sensory fibers showed similar morphological changes in the plexus region. A distinctively shaped growth cone expanded on its leading edge was observed, sequentially apparent in the distal spinal nerves, in the plexus region, in the loosely organized axonal sheets projecting to the uncleaved dorsal or ventral muscle masses, and where muscle nerves diverged from nerve trunks and within muscle nerves. It is likely that some of these are transitional growth cones preparing to branch, because complex and branched growth cones were also observed in these regions. Branched axons oriented along the anteroposterior axis were similarly observed in the plexus region and distal to the plexus when axons first projected to the limb bud. At somewhat older stages when the basic peripheral nerve branching pattern had formed, motor growth cones were observed in common nerve trunks and in individual muscle nerves, but they were no longer found in the plexus region. Branched axons were likewise restricted to these peripheral Imations. Taken together, these observations suggest that one of the ways in which axons navigate is by exploration in the form of growth cone widening, and in some cases terminal bifurcation which may produce axon branches. Selection of the most appropriately directed growth cone process and/or precocious axonal branches may be one of the ways in which axons respond to specific growth cues which guide axons into the limb bud. Alternatively, this precocious branching may be an early neurotrophic response to developing muscle and play no significant role in axon navigation. © 1995 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903570206

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractAxon navigation during vertebrate limb innervation has been shown to be associated with position‐dependent changes in size and complexity of the axon growth cones, and sometimes with bifurcation of terminal growth cones and axon branching (Hollyday and Morgan‐Carr, companion paper). We have further examined axon branching and asked whether it extends to the projection of collaterals to different nerves. Injections of horseradish peroxidase or DiI were made into individual peripheral nerves in the wings of chick embryos at stages 28–35, and the trajectories of solidly labeled axons were traced proximally from the injection site in tissue sections. During stages when the peripheral nerves were first forming in the shoulder region, collaterals of retrogradely labeled axons were frequently observed to project into uninjected nerves proximal to the injection site. These two‐nerve collaterals were formed by a small percentage of axons in a high percentage of the embryos studied and could occur in both motor and sensory axons. Two‐nerve collateral projections were observed between nerves separated along both the proximodistal and anteroposterior axes of the limb, but they were limited in spatial extent to nerves supplying adjacent limb regions and were never seen between nerves projecting to widely disparate regions of the limb. Collaterals were not seen at the plexus projecting to both dorsal and ventral pathways. The apparent frequency of two‐nerve collaterals was found to decline progressively from stage 28–29 to stage 32; no two‐nerve collaterals were seen in the proximal wing at stage 33 and older. The mechanism of their elimination is presently unknown. These observations suggest that some axon branching seen during outgrowth is sufficiently divergent to result in axon collaterals which project to two different peripheral nerves. Presumably, two‐nerve collaterals reflect both the neuron's ability to branch and some imprecision in the axonal guidance mechanisms. Together these give rise to minor errors in projection which are subsequently removed. © 19

ISSN:0092-7317    

DOI:10.1002/cne.903570207

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractTheStrongyloides stercoralisinfective larva resumes feeding and development on receipt of signals, presumably chemical, from a host. Only two of the anterior sense organs of this larva are open to the external environment. These large, paired goblet‐shaped sensilla, known as amphids, are presumably, therefore, the only chemoreceptors. Using three‐dimensional reconstructions made from serial electron micrographs, amphidial structure was investigated. In each amphid, cilialike dendritic processes of 11 neurons extend nearly to the amphidial pore; a twelfth terminates at the base of the amphidial channel, behind an array of lateral projections on the other processes. A specialized dendritic process leaves the amphidial channel and forms a complex of lamellae that interdigitate with lamellae of the amphidial sheath cell. This “lamellar cell” is similar to one of the “wing cells” or possibly the “finger cell” ofCaenorhabditis elegans. Each of the 13 amphidial neurons was traced to its cell body. Ten neurons, including the lamellar cell, connect to cell bodies in the lateral ganglion, posterior to the nerve ring. The positions of these cell bodies were similar to those of the amphidial cell bodies inC. elegans. Therefore, they were named by usingC. elegansnomenclature. Three other amphidial processes connect to cell bodies anterior to the nerve ring; these have no homologs inC. elegans. A map allowing identification of the aimphidial cell bodies in the living worm was prepared. Consequently, laser ablation studies can be conducted to determine which neurons are involved in the infective process. © 1995

ISSN:0092-7317    

DOI:10.1002/cne.903570208

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractTo evaluate effective means for delivering exogenous neurotrophins to neuron populations in the brain, we compared the distribution and transport of brain‐derived neurotrophic factor (BDNF), nerve growth factor (NGF), and neurotrophin‐3 (NT‐3) following intracerebral delivery. Rats received an injection of radioiodinated or unlabeled neurotrophin into the lateral ventricle and were killed humanely after 1.5–24 hours. Other rats received continuous infusion of unlabeled neurotrophin into the lateral ventricle, the striatum, or the hippocampus for 3–14 days. The neurotrophins were detected by autoradiography or immunohistochemistry. There were striking differences between BDNF, NGF, and NT‐3 in their penetration through brain tissue. These differences occurred regardless of the site or method of delivery, but were most pronounced following a bolus intracerebroventricular (ICV) injection. After ICV injection, NGF was widely distributed in tissues around the ventricles and at the surface of the brain, whereas the penetration of BDNF into brain tissue was distinctly less than that of NGF, and the penetration of NT‐3 was intermediate. An ICV injection of NGF produced prominent but transient labeling of cells that contain the low‐affinity NGF receptor, whereas an injection of BDNF prominently labeled the ventricular ependyma. During ICV infusion (12 g/day), the distribution of BDNF was no greater than that observed after a 12‐g bolus injection. A sixfold increase in the amount of BDNF infused (72 g/day) produced a more widespread distribution in the brain and doubled the depth of penetration into periventricular tissues near the cannula. Corresponding to their differences in penetration, NGF was retrogradely transported by basal forebrain cholinergic neurons after ICV or intrastriatal delivery, whereas NT‐3 was transported by a few basal forebrain neurons after ICV delivery, and BDNF was rarely detected in neurons after ICV delivery. Delivery of BDNF directly to the striatum or the hippocampus labeled numerous neurons in nuclei afferent to these structures. In situ hybridization studies confirmed that the high‐affinity BDNF receptor (TrkB) was much more widely expressed in neurons than was the high‐affinity NGF receptor (TrkA). Moreover, mRNA for truncated forms of TrkB was expressed at high levels in the ependyma, the choroid epithelium, and the gray matter. It is likely that binding of BDNF to TrkB, which appears to be more abundant and ubiquitous than TrkA, restricts the diffusion of BDNF relative to that of NGF.

ISSN:0092-7317    

DOI:10.1002/cne.903570209

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractDirect projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter and the external anal sphincter muscles were examined in the rat by the tract‐tracing methods utilizing retrograde transport of cholera toxin B subunit and anterograde transport of biotinylated dextran amine. The dorsolateral pontine tegmental region, corresponding to the micturition reflex center of Barrington, was confirmed to send bilaterally, with an ipsilateral dominance, projection fibers to the spinal parasympathetic nucleus (inferior intermediolateral nucleus). The micturition reflex center of Barrington, however, did not seem to send many projection fibers to the ventral horn of the lumbosacral cord segments, whereas the region immediately ventral to the micturition reflex center of Barrington was found to send bilaterally, with a contralateral dominance, projection fibers to the dorsolateral group of pudendal motoneurons in both the male and female rats. In the female rat, the dorsolateral group of pudendal motoneurons are comprised primarily of motoneurons that innervate the external urethral sphincter muscle. The dorsomedial group of pudendal motoneurons, which contain motoneurons that innervate the external anal sphincter and the bulbocavernosus muscles, did not seem to receive major projections from the dorsolateral pontine tegmental regions. It was also observed that the locus coeruleus sent some projection fibers bilaterally to the spinal parasympathetic nucleus but only a few to the ventral horn of the lumbosacral cord segments. Thus, the present results indicate that the dorsolateral group of pudendal motoneurons containing those innervating the external urethral sphincter muscle receive pontospinal projection fibers mainly from the dorsolateral pontine tegmental region immediately ventral to the micturition reflex center of Barrington. © 1995 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903570210

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractMonocular enucleations were done in ferret embryos before or during the earliest stages of development of the retinofugal pathway (E23‐E26). The effects on the development of the uncrossed pathway from the surviving eye were assessed on embryonic day 30. This stage was chosen for two reasons: (1) we show that in normal development a substantial uncrossed component from the temporal crescent has developed by E30; and (2) the pathway cannot yet have been affected by the cell death that normally occurs in the retina in the perinatal period. Using DiI labelling from either the temporal crescent or the optic nerve head, we have shown that such early enucleations prevent the formation of the uncrossed pathway from the temporal crescent of the surviving eye. Enucleation at E23/24, before or during the period when the first axons reach the chiasm, prevents the formation of the uncrossed projection. The axons that would normally take an uncrossed course stall lateral to the midline of the optic chiasm. At E26, when many axons have reached the optic chiasm, but none yet come from the temporal crescent, enucleation causes a dramatic reduction in the uncrossed projection, and the complete abolition of the normal uncrossed pathway from the temporal crescent. This demonstrates that there is a requirement for an interaction between the axons of the two eyes at the optic chiasm to establish the normal formation of the uncrossed pathway at the optic chiasm. © 1995 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903570211

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY