摘要:

AbstractThe retinal projection to the superior colliculus can be made abnormally dense by inducing a “compressed” retinal projection into a subnormal tectal volume, or abnormally spares by monocular enucleation early in development. Any or all of the features of cell number, axonal arbor, dendritic arbor, and synaptic density could potentially be adjusted to compensate for such variations in the convergence of one cell population on another. We have examined the consequences of neonatal partial tectal ablation or monocular enucleation for synaptic length, density, and relative numbers of synapse classes in the superficial gray layer of the hamster superior colliculus.Monocular enucleation resulted in a reduction of synaptic density in the superficial gray layer of the colliculus ipsilateral to the remaining eye. This decrease in density was entirely accounted for by a reduction of the number of synapses with round vesicles, large asymmetric terminal specializations, and pale mitochondria characteristic of retinocollicular terminals (RLP synapses). There was no compensatory increase in any other synaptic class. RLP synapses were larger in monocular enucleates.Partial tectal ablation had no effect on synaptic density, nor on the relative proportions of different synaptic types. Synapses of the RLP class were slightly smaller than normal. These results suggest that synaptic density is normally at a maximum that cannot be altered by increases in potential input. However, density may be reduced by decreasing the number of inputs. Terminal classes do not appear to compete with each other within the collicular volume, suggesting that postsynaptic cells control both the classes and numbers of their potential inp

ISSN:0092-7317    

DOI:10.1002/cne.903300402

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

年代:1993

数据来源: WILEY

摘要:

AbstractAs nuclei in the central nervous system develop, neurons actively migrate from their site of generation to their permanent residence. This study examines the spatiotemporal sequence of the migration of neurons to the principal sensory nucleus of the trigeminal nerve (PSN) of the rat. Tritiated thymidine autoradiography and bromodeoxyuridine immunohistochemistry were used to examine the spatiotemporal patterns of migration of PSN neurons born on gestational day (G) 12 (early‐generated neurons) and of those born on G14 (late‐generated neurons). The final residence of early‐ and late‐generated neurons was determined by injecting a thymidine analog into a pregnant rat on G12 or G14 and sacrificing the pups on postnatal day (P) 30. Early‐ and late‐generated neurons were distributed medially and laterally, respectively. The schedule of the migration of PSN neurons was also determined. A few pioneer neurons born on G12 reached the PSN by G14; however, the last of the neurons born on G12 arrived in the PSN by G18. The migration of neurons born on G14 was completed 2–6 days later than that of the early‐generated neurons. The path followed by migrating neurons was delineated by radial glial fibers. These processes were identified in the developing metencephalon by RAT‐401 immunohistochemistry. Radial glial fibers extended from the lateral part of the ventricular zone through the tegmentum and the PSN to the surface of the metencephalon external to the sensory tract of the trigeminal nerve. RAT‐401‐immunoreactive processes were detected during the period of neuronal migration, but disappeared by P5. Thus, the migration of PSN neurons follows an inside‐to‐outside sequence, which apparently is organized by radial glial fibers. The inside‐to‐outside sequence of neuronal migration directly opposes the outside‐to‐

ISSN:0092-7317    

DOI:10.1002/cne.903300403

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe early development of the principal sensory nucleus of the trigeminal nerve (PSN) was examined to determine whether spatiotemporal patterns of synaptogenesis coincide with patterns in neuronal generation, migration, and death. The morphogenesis of PSN neurons during the period from G16 to P14 was studied with a Golgi method. Prenatally, PSN neurons had dendrites that extended into the sensory tract of the trigeminal nerve (s5), and from as early as G18, these dendrites were studded with spines. The dendrites in the s5 degenerated or regressed in the early postnatal period so that the s5 was free of dendrites by P14. The development of anti‐synapsin I immunoreactivity was traced from G14 to P10. Immunoreactive puncta (synaptic boutons) appeared in the medial third of the s5 transiently between G18 and P5. On the other hand, puncta in the PSN did not appear until G20, at which time they were confined to the lateral margin of the PSN. By P0, puncta were distributed throughout the PSN. Cytochrome oxidase activity in the PSN was low and unpatterned prenatally. Postnatally, cytochrome oxidase activity intensified and a segmented pattern of barreloids appeared in the ventral PSN on the day of birth. By P5, the complete pattern of barreloids, spanning the full width of the ventral PSN, was evident. The development of cytochrome oxidase activity in the PSN followed the lateral‐to‐medial gradient of synaptogenesis revealed by the development of synapsin 1 immunoreactivity. This gradient is opposite of that for neuronal generation, migration, and death. Moreover, the s5 serves as a transient synaptic

ISSN:0092-7317    

DOI:10.1002/cne.903300404

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe overproduction and subsequent death of neurons is a common phenomenon in the developing vertebrate central nervous system (CNS). We tested the hypothesis that the survival of a neuronal subpopulation is related to its time of origin. Neuronal survival was examined in a well‐defined CNS structure, the principal sensory nucleus of the trigeminal nerve (PSN) of the rat. The changes in the total number of PSN neurons and in the numbers of early‐ and late‐generated neurons (i.e., neurons heavily labeled by a single injection of [3H]thymidine on G12 or G14, respectively) between gestational day (G) 16 and postnatal day (P) 10 were determined. The total number of neurons in the PSN rose prenatally to a maximum of 40,600 on G18.5. The increase in neuronal number correlates to the period of migration. More than half of the neurons that successfully migrated to the PSN were lost by P10. The patterns for the changes in the numbers of early‐ and late‐generated neurons were similar; however, there were significant differences between the two subpopulations. The maximum number of early‐generated neurons (4,250) was attained on G18.2 and subsequèntly 58.9% of these neurons were lost. In contrast, the maximum number of late‐generated neurons (5,050) was attained on G20.0 and 66.6% of these neurons were lost by P10. Therefore, it appears that the survivability of early generated neurons is greater than for late‐generated neurons. This enhanced survivability presumably results from a competitive advantage that early‐generated neurons have for forming synapses or gaining access to trophic factor(s) that are

ISSN:0092-7317    

DOI:10.1002/cne.903300405

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

年代:1993

数据来源: WILEY

摘要:

AbstractNeurons in areas 17/18a and 17/18b of mouse cerebral cortex were labeled by the retrograde transport of horseradish peroxidase (HRP) transported from severed callosal axons in the contralateral hemisphere. Terminals of the local axon collaterals of labeled neurons (intrinsic terminals) were identified in the border regions of area 17 with areas 18a and 18b, and their distribution and synaptic connectivity were determined. Also examined were the synaptic connections of extrinsic callosal axon terminals labeled by lesion‐induced degeneration consequent to the severing of callosal fibers. A postlesion survival time of 3 days was chosen because by this time the extrinsic terminals were all degenerating, whereas the intrinsic terminals were labeled by horseradish peroxidase.Both intrinsic and extrinsic callosal axon terminals occurred in all layers of the cortex where, with rare exception, they formed asymmetrical synapses. Layers II and III contained the highest concentrations of intrinsic and extrinsic callosal axon terminals. Analyses of serial thin sections through layers II and III in both areas 17/18a and 17/18b yielded similar results: 97% of the intrinsic (1,412 total sample) and of the extrinsic (414 total sample) callosal axon terminals synapsed onto dendritic spines, likely those of pyramidal neurons; the remainder synapsed onto dendritic shafts of both spiny and nonspiny neurons. Thus, the synaptic output patterns of intrinsic vs. extrinsic callosal axon terminals are strikingly similar. Moreover, the high proportion of axospinous synapses formed by both types of terminal (97%) contrasts with the proportion of asymmetrical axospinous synapses that occurs in the surrounding neuropil where about 64% of the asymmetrical synapses are onto spines. This result is in accord with previous quantitative studies of the synaptic connectivities of callosal projection neurons in mouse somatosensory cortex, and lends additional weight to the hypothesis that axonal pathways are highly selective for the types of elements with which they synaps

ISSN:0092-7317    

DOI:10.1002/cne.903300406

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

年代:1993

数据来源: WILEY

摘要:

AbstractImmunoreactivity for calcitonin gene‐related peptide (CGRP) has been observed in both adult and embryonic rat motoneurons. However, the developmental pattern of CGRP expression in motoneurons has not been systematically examined and the role of CGRP in neuromuscular development is poorly understood. We have mapped the ontogeny of CGRP‐like immunoreactivity in three motoneuron pools of the rat lumbar spinal cord from birth through adulthood. Immunoreactivity was uniformly high in lateral horn motoneurons (the retrodorsolateral nucleus) of males and females at all ages examined. The majority of motoneurons of the dorsolateral nucleus also were positive throughout postnatal development although the percentage of positive motoneurons was slightly higher in males than in females. In contrast, virtually no motoneurons of the spinal nucleus of the bulbocavernosus, located in the medial ventral horn, were positive for CGRP in neonatal rats. CGRP‐like immunoreactivity was delayed in this nucleus until approximately postnatal day 6 in males and day 27 in females. Because these three motoneuronal nuclei are differentially sensitive to early androgen and differ with respect to the timing of several developmental milestones, these observations have implications for the regulation and possible roles of CGRP in developing motor sy

ISSN:0092-7317    

DOI:10.1002/cne.903300407

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe auditory epithelium in birds and mammals consists of a postmitotic population of hair cells and supporting cells. Unlike mammals, birds can regenerate their auditory epithelia after trauma. Recent evidence indicates that supporting cells undergo mitosis after acoustic trauma, suggesting that supporting cells may transdifferentiate into hair cells. The goals of this study were to (1) characterize the responses of hair cells and supporting cells to acoustic trauma, and (2) determine whether hair cell loss is a prerequisite for generation of new hair cells. Chicks were exposed to an octave‐band noise and their inner ears assayed with fluorescence or scanning electron microscopy. In one area of the basilar papilla, defined as the center of the lesion, extensive hair cell degeneration occurred. Expanded supporting cells obliterated degenerating hair cells and invaded spaces normally occupied by hair cells. Aggregates of DNA were found within the basilar papilla, suggesting that hair cell death and disintegration may occur within the epithelium. The epithelial sheet appeared structurally confluent at all times examined. Supporting cells exhibited altered apical contour in distal regions of the basilar papilla, where hair cell damage was mild or inconspicuous. Four days after noise exposure, newly generated hair cells were found in the center of the lesion and in the distal areas, where no hair cell loss could be detected. The results suggest that supporting cells may play an important role in maintenance and repair of the traumatized basilar papilla and raise the possibility that production of new hair cells is not dependent on hair cell loss in the immediate vicinit

ISSN:0092-7317    

DOI:10.1002/cne.903300408

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe organization of projections from the anterior thalamic nuclei to the cingulate cortex was analyzed in the rat by the anterograde transport ofPhaseolus vulgaris‐leucoagglutinin.The rostral part of the anteromedial nucleus projects to layers I, V and VI of the anterior cingulate areas 1 and 2, layers I and III of the ventral orbital area, layers I, V and VI of area 29D of the retrosplenial area, and layers I and V of the caudal part of the retrosplenial granular and agranular areas. In contrast, the caudal part of the anteromedial nucleus projects to layer V of the frontal area 2, and layers I and V of the rostral part of the retrosplenial granular and agranular areas. The interanteromedial nucleus projects to layers I, III and V of the frontal area 2, layer V of the agranular insular area, and layers I, V and VI of area 29D. The anteroventral nucleus projects to layers I and IV of the retrosplenial granular area, whereas the anterodorsal nucleus projects to layers I, III and IV of the same area. Projections from the anteroventral and anterodorsal nuclei were, furthermore, organized such that their ventral parts project to the rostral part of the retrosplenial granular area, whereas their dorsal parts project to the more caudal part.The results suggest that the anterior thalamic nuclei project to more widespread areas and laminae of the cingulate cortex than was previously assumed. The projections are organized such that the anteromedial and interanteromedial nuclei project to layer I and the deep layers of the anterior cingulate and retrosplenial cortex, whereas the anteroventral and anterodorsal nuclei project to the superficial layers of the retrosplenial cortex. These thalamocortical projections may play important roles in behavioral learning such as discriminative avoidance behavio

ISSN:0092-7317    

DOI:10.1002/cne.903300409

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

年代:1993

数据来源: WILEY

摘要:

AbstractMicroinjection of cholinergic agonists in a dorsolateral part of the mesopontine tegmentum has been shown to induce a rapid eye movement (REM) sleep‐like state. Physiological evidence indicates that not only acetylcholine but also various amine transmitters, including those implicated in behavioral state regulation, affect neuronal activity in this region of the pontine reticular formation. In the present study, sources of select aminergic and cholinergic inputs to this REM sleep induction zone were identified and quantitatively analyzed by using fluorescence retrograde tracing combined with immunofluorescence in the rat.In addition to previously demonstrated cholinergic projections from the pedunculopontine and laterodorsal tegmental nuclei, the REM sleep induction zone received various aminergic inputs that originated in widely distributed regions of the brainstem and hypothalamus. Serotoninergic afferents represented a mean of 44% of all aminergic/cholinergic source neurons projecting to the REM sleep induction zone, which was comparable to the mean percentage of 39% represented by cholinergic afferent neurons. The serotoninergic afferents originated from the raphe nuclei at all brainstem levels, with heavier projections from the pontine than from the medullary raphe nuclei. Unexpectedly, an additional major serotoninergic input was provided by serotoninergic neurons in the nucleus prosupralemniscus (B9). Noradrenergic afferent neurons represented a mean of 14% of all aminergic/cholinergic source neurons, which was only about one‐third of the mean percentage of either cholinergic or serotoninergic source neurons. These noradrenergic projection neurons were located not only in the locus ceruleus (8%) but also in the lateral tegmentum, including the A5 (4%) and A7 (2%) cell groups. Histaminergic neurons in the tuberomammillary hypothalamic nucleus represented a minor group of afferent neurons (3%), and a still smaller input came from adrenegic C1 neurons. The pattern of these transmitter‐specific afferent connections appeared to be similar regardless of the longitudinal level within the REM sleep induction zone.The present results are consistent with previous behavioral and physiological evidence for a role of the pontine REM sleep induction zone in triggering REM sleep. The regulation of REM sleep induction would be best understood in terms of a state‐dependent interplay of cholinergic, serotoninergic, and other inputs all acting convergently upon neurons in the REM sleep‐inducing region of the pontine reticular

ISSN:0092-7317    

DOI:10.1002/cne.903300410

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

年代:1993

数据来源: WILEY

摘要:

AbstractRecent studies have demonstrated an important contribution of the A5 noradrenergic cell group of the rostral medulla in the regulation of nociceptive messages at the level of the spinal cord. These noradrenergic controls parallel those arising from the serotonin‐containing neurons of the nucleus raphe magnus. In the present study, we used postembedding immunogold staining to identify GABA‐immunoreactive terminals that synapse upon identified spinally projecting noradrenergic neurons of the A5 cell group in the rat. A5 projection neurons were identified by Fluoro‐Gold transport from the spinal cord; sections containing retrogradely labelled cells were then immunoreacted for tyrosine hydroxylase (TH) to identify the catecholamine‐containing, presumed noradrenergic, neurons. Double‐labelled A5 cells were intracellularly filled with Lucifer Yellow (LY) and then the LY was photo‐oxidized to an electron‐dense product.Seven intracellularly filled TH‐immunoreactive projection neurons were studied with postembedding immunocytochemistry. Each A5 neuron received a significant GABA‐immunoreactive terminal input. Out of a pooled total of 151 terminal profiles found in apposition to intracellularly labelled somatic and dendritic profiles, 31 (20.5%) were GABA‐immunoreactive. The proportion of GABA‐immunoreactive terminals that contacted somatic profiles (12/72; 17%) was similar to the proportion that contacted TH‐labelled dendritic profiles (19/79; 24%). There was a discernible synaptic specialization in about 50% of the labelled terminals that contacted the TH projection neuron. Both symmetric and asymmetric synaptic specializations were found. Labelled terminals contained round or pleimorphic vesicles, but not flat vesicles; many also contained dense‐core vesicles.Our results indicate that noradrenergic neurons of the A5 cell group, which contribute to both antinociceptive and cardiovascular controls through their projection to the spinal cord, are regulated by local GABAergic, presumably inhibitory, mechanisms. Whether the initiation of A5 neuron activity results from a lifting of tonic GABAergic inhibitory control, as has been proposed for the neurons of the nucleus raphe magnus,

ISSN:0092-7317    

DOI:10.1002/cne.903300411

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

年代:1993

数据来源: WILEY