摘要:

AbstractThe migration and ultimate domain invasion of postmitotic lateral reticular nucleus (LRN) neurons were followed in embryonic day 15–20 (E15‐E20)rat embryos, by using a horseradish peroxidase (HRP) in vitro axonal tracing method. All of the LRN axons elongate and neuronal somata migrate via the subpial or marginal migratory stream (mms), circumnavigating the ventrolateral aspect of the medulla at the glial endfeet level. They reach the ventral midline at E16, bypass it, and begin to settle in their final territory at E17. At E18 the LRN anlage is fully formed, and at E19‐E20 its cells have finished their migration and are rapidly differentiating. Comparison of these sequential steps with their counterparts in the development of the inferior olive (ION) and external cuneatus (ECN) brings to light the essential role of the neuroepithelial cells of the interolivary commissure (the “floor plate”). This zone is likely to act as (1) a chemoattractant for the growth cones of the LRN, ION, and ECN, and (2) a decision‐making center, which instructs the somata of these neurons to cross the midline or not, ultimately governing the crossed or uncrossed pattern of their projection to their common target, the cerebellum. Finally, the ontogeny of the LRN and ECN provides a most surprising example, even unique in the central nervous system, of long‐distance, neurophilic migration that conveys neuronal cell bodies contralaterally to the side on which the

ISSN:0092-7317    

DOI:10.1002/cne.902940102

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe dorsomedial telencephalon of lepidosirenid lungfishes has been interpreted in two divergent ways: earlier investigators regarded it as a subpallial (septal) structure; more recently, it has been reinterpreted as the medial pallium (hippocampus). To resolve this question, we identified parameters that are conclusive in their association with either the medial pallium or the septum in anamniotes. The present study examines the position of ependymal thickenings and the distribution of acetylcholinesterase (AchE) in the cerebral hemispheres of the African lungfishProtopterus, the Australian lungfishNeoceratodus, and the amphibian speciesXenopusandAmbystoma. In addition, projections from the hypothalamus (paraventricular organ) to the telencephalon are investigated inProtopterus.Ependymal specializations are located dorsally and ventrally in the lateral ventricles of amphibians, but laterally and medially in lungfishes. InProtopterus, the paraventricular organ projects to the medial telencephalic hemisphere, but not to the dorsal roof. High levels of AchE are present in restricted neuropil regions of the medial hemisphere and in the ventral and ventrolateral telencephalon, but they are lacking in the dorsal roof. Intensely AchE‐stained neuronal cell bodies are located in the ventral telencephalon (rostrally) and the dorsomedial telencephalon (at mid‐level). InNeoceratodus, AchE staining is pronounced in the septal area, but absent in the pallium. The terminal nerve proper lacks AchE stain inProtopterus; nerve fibers of the preoptic nerve are AchE‐positive in both lungfish species. InXenopus, AchE staining of fibers and terminals is restricted to the subpallium (medial septum, tuberculum olfactorium, striatum, nucleus accumbens, and medial amygdala); cell bodies are AchE positive in parts of the subpallium and rostral pallium.Comparison of cytological, histochemical, and “connectional” parameters substantiates the interpretation that the dorsomedial telencephalon of lungfishes represents asubpallial, but not a “medial pallial” structure. The dorsomedial part of the lepidosirenid telencephalon corresponds to the septum in the most plesiomorphic living lungfish,Neoceratodus forsteri, but it differs considerably from the dorsomedial telencephalon (medial pallium)

ISSN:0092-7317    

DOI:10.1002/cne.902940103

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe present investigation used stable area‐specific, neuronal properties instead of Nissl stain to delineate the boundaries of the nucleus hyperstriatalis caudal c (HVc) in the telencephalon of the adult male canary. Immunocytochemical procedures combined with retrograde tracing labeled a large population of perennial long‐projecting neurons that contain estrogen receptors in the canary HVc. The HVc area defined by the distribution of these neurons was congruent with the HVc area defined in Nissl‐stained sections during the breeding period. The HVc area defined in Nissl‐stained preparations showed an extensive seasonal change in size, confirming previous results Nottebohm:Science, 214:1368–1370, '81. In contrast, the HVc area defined by the distribution of the estrogen receptor containing long‐projection neurons showed little or no seasonal change in size. Because these neurons are permanent, the HVc seems to be of rather constant size year round. The internal morphology of the HVc, however, undergoes seasonal alterations, which are reflected in changes in size of the HVc area distinguishable in Nissl‐stained sections. The combination of cytoarchitectural criteria of Nissl‐stained preparations with area‐specific cytochemical and hodological markers to delineate the boundaries of a brain nucleus might give new insights in the partitioning and neural plastici

ISSN:0092-7317    

DOI:10.1002/cne.902940104

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe somatotopically and functionally organized electrosensory system of gymnotiform teleosts provides a model for the study of the formation of ordered nerve connections. This paper describes the development of the major electrosensory nuclei within the hind‐ and midbrain. All three main electrosensory nuclei‐the electrosensory lateral line lobe (ELL), dorsal torus semicircularis (torus), and tectum‐grow by adding cells at their caudolateral borders. Toral and tectal germinal zones arise from lateral ventricular outpocketings that either completely or partially close by maturity. In the ELL before day 5 postspawning, germinal cells form from an initial periventricular germinal zone, then migrate to the caudolateral border of the hindbrain and begin dividing. The ELL grows from two main germinal zones, one for the medial segment, and one for the three lateral tuberous segments. Within each ELL germinal zone, newly formed cells arise from two areas: granular cells arise from a ventral subzone, pyramidal cells are generated more dorsally. Granular cells remain in situ, whereas pyramidal cells may migrate rostromedially. Cells begin differentiating as soon as they are formed. Spherical and pyramidal cells send ascending axons into the internal plexiform layer by day 14–18 and the ELL gradually begins to assume its mature laminar appearance.The ELL grows caudally, preceding the caudal lobe of the cerebellum, which will eventually lie over and fuse with it. Primary electrosensory afferents enter the ELL by day 6: incoming afferents form four fascicles within the ELL, suggesting the formation of separate ELL segments. Unlabelled projections between labelled fields from a single nerve branch filled with HRP on day 7 suggest that somatotopic order is already present at this early age.In the periphery, receptor addition is unordered, occurring along nerve branch pathways. Meanwhile the ELL adds cells in an orderly fashion at its caudolateral border. This suggests that primary afferents shift position caudally with growth to maintain their somatotopic relationships. Because all three central nuclei are in topographic register and grow by adding cells caudally, during growth ELL efferents to the torus and toral efferents to the tectum may utilize pessive mechanisms, such as fiber‐fiber interactions, to gu

ISSN:0092-7317    

DOI:10.1002/cne.902940105

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

年代:1990

数据来源: WILEY

摘要:

AbstractIntersegmental descending neurons (DNs) link the insect brain to the thoracic ganglia. Iontophoresis of cobalt or fluorescent dyes reveals DNs as uniquely identifiable elements, the dendrites of which are situated within a characteristic region of the lateral deutocerbrum. Here we demonstrate that DNs occur as discrete groups of elements termed DN clusters (DNCs). A DNC is a characteristic combination of neurons that arises from a multiglomerular complex in which the main components of each glomerulus are a characteristic ensemble of sensory afferents. Other neurons involved in the complex are local interneurons, heterolateral interneurons that connect DNCs on both sides of the brain, and neurons originating in higher centers of the brain. We describe the structure, relationships, and projections of eight DNs that contribute to a descending neuron cluster located ventrally in the lateral deutocerebrum, an area interposed between the ventral antennal lobes and the laterally disposed optic lobes. We have named this cluster the GDNC because its most prominent member is the giant descending neuron (GDN), which plays a cardinal role in the midleg “jump” response and which is implicated in the initiation of flight. The GDN and its companion neurons receive primary mechanosensory afferents from the antennae, terminals of wide‐ and small‐field retinotopic neurons originating in the lobula, and endings derived from sensory interneurons that originate in leg neuropil of the thoracic ganglia.We demonstrate that DNs of this cluster share morphological and functional properties. They have similar axon trajectories into the thoracic ganglia, where they invade functionally related neuropils. Neurons of the GDNC respond to identical stimulus paradigms and share similar electrophysiological characteristics. Neither the GDN nor other members of its cluster show spontaneous activity. These neurons are reluctant to respond to unimodal stimuli, but respond to specific combinations of visual and mechanosensory stimulation. These results suggest that in flies groups of morphologically similar DNs responding to context‐specific environmental cues may cooperate in moto

ISSN:0092-7317    

DOI:10.1002/cne.902940106

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe distribution of cells that express mRNA encoding the androgen (AR) and estrogen (ER) receptors was examined in adult male and female rats by using in situ hybridization. Specific labeling appeared to be largely, if not entirely, localized to neurons. AR and ER mRNA‐containing neurons were widely distributed in the rat brain, with the greatest densities of cells in the hypothalamus, and in regions of the telencephalon that provide strong inputs to the hypothalamus. Thus large numbers of heavily labeled cells were found in the medial preoptic and ventromedial nuclei, each of which is thought to play a key role in mediating the hormonal control of copulatory behavior, as well as in the lateral septal nucleus, the medial and cortical nuclei of the amygdala, the amygdalohippocampal area, and the bed nucleus of the stria terminalis. Heavily labeled ER mRNA‐containing cells were found in regions known to be involved in the neural control of gonadotropin release, such as the anteroventral periventricular and the arcuate nuclei, but only a moderate density of labeling for AR mRNA was found over these nuclei. In addition, clearly labeled cells were found in regions with widespread connections throughout the brain, including the lateral hypothalamus, intralaminar thalamic nuclei, and deep layers of the cerebral cortex, suggesting that AR and ER may modulate a wide variety of neural functions. Each part of Ammon's horn contained AR mRNA‐containing cells, as did both parts of the subiculum, but ER mRNA appeared to be less abundant in the hippocampal formation. Moreover, AR and ER mRNA‐containing cells were also found in olfactory regions of the cortex and in both the main and accessory olfactory bulbs. AR and ER may modulate nonolfactory sensory information as well since labeled cells were found in regions involved in the central relay of somatosensory information, including the mesencephalic nucleus of the trigeminal nerve, the ventral thalamic nuclear group, and the dorsal horn of the spinal cord. Furthermore, heavily labeled AR mRNA‐containing cells were found in the vestibular nuclei, the cochlear nuclei, the medial geniculate nucleus, and the nucleus of the lateral lemniscus, which suggests that androgens may alter the central relay of vestibular and auditory information as well. However, of all the regions involved in sensory processing, the heaviest labeling for AR and ER mRNA was found in areas that relay visceral sensory information such as the nucleus of the solitary tract, the area postrema, and the subfornical organ. We did not detect ER mRNA in brainstem somatic motoneurons, but clearly labeled AR mRNA‐containing cells were found in motor nuclei associated with the fifth, seventh, tenth, and twelfth cranial nerves. Similarly, spinal motoneurons contained AR but not ER mRNA. Nor was ER mRNA detected in Purkinje cells of the cerebellum, the pontine gray, or inferior olive, all of which harbor AR mRNA, although the parvicellular part of the dentate (lateral cerebellar) nucleus had clearly labeled ER mRNA‐containing neurons. The density of labeling in other parts of the brainstem tended to be greatest in those regions that have the strongest connections with the hypothalamus like the midbrain periaqueductal gray, the peripeduncular nucleus, and the locus coeruleus.Although no absolute sexual dimorphisms in the distributions of AR and ER mRNA‐containing cells were found, more subtle quantitative differences between levels of AR and ER mRNA in certain regions of the male and female rat brain cannot be ruled out. In at least a few regions, there appeared to be differences in either the number of cells expressing each receptor mRNA. or in the relative density of labeling over certain cell groups. Whether or not both receptors are contained within individual neurons remains to be demon‐ strated; however. The remarkable overlap between the distributions of AR and ER mRNA containing neurons suggests that such coexpression is indeed possibility and that the two receptor systems may interact to differentially activate overlapping sets of genes in a variety

ISSN:0092-7317    

DOI:10.1002/cne.902940107

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

年代:1990

数据来源: WILEY

摘要:

AbstractWe have shown previously that some enkephalin, substance‐P, and serotoninergic neurons in the medullary raphe and adjacent reticular formation project to the spinal cord in the opossum. In the present study we have combined the retrograde transport of True Blue and immunofluorescence histochemistry to determine whether methionine enkephalin or substance‐P containing bulbospinal neurons are serotoninergic. Furthermore, we have used the same immunofluorescence protocol to determine whether spinal axons cocontain the same substances.Neurons that immunostained for both enkephalin and serotonin were observed in many brainstem nuclei. However, those that projected to the spinal cord were limited to the nuclei raphe magnus and obscurus, and the ventral part of nucleus reticularis gigantocellularis, pars ventralis. Neurons that immunostained for both substance P and serotonin were fewer in number, but some of the ones in the above nuclei and within the nucleus raphe pallidus, projected to the spinal cord.Spinal axons exhibiting both enkephalin‐ and serotonin‐like immunoreactivity were observed in the superficial laminae of the dorsal horn, lamina X, and the intermediolateral cell column, whereas those showing both substance‐P and serotonin‐like immunoreactivity were seen primarily in lamina X, the intermediolateral cell column, and the ventral horn. Some of the axons in the ventral horn were in close apposition to presumed motoneurons. Comparison of the above results with those obtained from previous studies of bulbospinal projections has allowed us to infer the origins of axons that innervate different spi

ISSN:0092-7317    

DOI:10.1002/cne.902940108

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe postnatal dendritic maturation of small field type 1 (SF1), medium field type 1 (MF1) and type 2 (MF2), and large field type 1 (alpha) ganglion cells in the rabbit retina was compared qualitatively and quantitatively. Dendritic tree structure was revealed by intracellular injection of the fluorescent dye Lucifer yellow, and the stained cells were then morphologically separated on the basis of soma area, dendritic field size, total dendritic length, number of nodes, and mean internodal distance. Cells in the visual streak and an area inferior to the streak were sampled from retinae between birth and adulthood.The dendrites of all studied classes of rabbit ganglion cells were extensively covered by short spine‐like appendages. As in cat retina, many dendritic spines disappeared by the end of the third postnatal week, at which stage the adult dendritic form could be recognised. However, there was differential loss in the number of spines from the dendrites of the four cell classes. In both the streak and inferior retina, adult SF1 cells had the same number of spines/dendritic unit length througout postnatal life, whereas MF1 and MF2 ganglion cells lost at least half of their number of spines/unit dendritc length by maturity. Alpha ganglion cells lost virtuallyalltheir dendritic spines by adulthood. In both retinal locations, there were small changes in the number of nodes (dendritic branch points) of small field and medium field ganglion cells but alpha cells lost between 70 to 80% of their nodes by adulthood. The dendrites of ganglion cells with contrasting morphology thus undergo differential remodelling during postnatal maturation. The completion of the period of dendritic remodelling coincided with the first appearance of adult receptive field organisation, suggestion, suggesting that structural remodelling, in particular that involving dendritic spines, may be associated with the development of the cell's synaptic circuitry.The dendrites of neighbouring postnatal ganglion cells in the rabbit retina also grow by different amounts; the increase in dendritic tree area, total dendritic length, and mean internodal distances of alpha cells exceeded that of small field and medium field cells in corresponding retinal positions. This implies that retinal dendrites elongate by active growth rather than by “passive stretchin

ISSN:0092-7317    

DOI:10.1002/cne.902940109

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe relationship between structure and function of the projections of single identified primary cutaneous axons was investigated by recording cord dorsum potentials at 4 sites in response to electrical stimulation of the single axon and visualizing the boutons of the axon stained by intracellular injection of horseradish peroxidase. The rostrocaudal extent of boutons differed from fiber to fiber ranging from 4.14–11.50 mm; their location in the dorsal horn also varied in agreement with the known somatotopy of the presynaptic neuropil and dorsal horn neurons. Rostrocaudal distributions of cord dorsum potentials and boutons of individual fibers revealed good agreement. Cord dorsum potential amplitude and length of the spinal projection were positively correlated with number of boutons, but no correlation with bouton density was found. The spinal projection of afferents innervating slowly adapting type 1 mechanoreceptors exhibited a greater rostrocaudal extent (mean: 8.48 mm) than those innervating rapidly adapting mechanoreceptors (i. e., hair follicle and field receptors: mean: 5.87 mm). Although the mean total number of boutons was greater for axons with slowly adapting receptors (7,250/fiber) than for axons of rapidly adapting receptors (4,677/fiber), no differences in the longitudinal density of boutons (boutons/mm) were observed. Likewise, summed amplitudes of cord dorsum potentials at the 4 recording electrodes were larger for SA1 afferents than for those of field and hair follicle afferents. A major role for the number of boutons in determining these differences is supported by the finding that the calculated average contributionper boutonto cord dorsum potentials (expressed as an amplitude coefficient a) was similar for slowly and rapidly adapting afferents. No evidence was found for regions in which boutons did not contribute to the cord dorsum potentia

ISSN:0092-7317    

DOI:10.1002/cne.902940110

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe differentiated cytology across subregions of the rat subfornical organ (SFO) prompted our hypothesis that ultrastructural features of capillary endothelial cells would vary topographically and quantitatively within this small nucleus. We used electron microscopic and computer‐based morphometric methods to assess fine structural dimensions of the capillary endothelium in four distinct subregions of the SFO from Long‐Evans and homozygous Brattleboro rats. Three types of capillary were present. Type III capillaries (resembling those of endocrine glands) had an average wall thickness of 0.17 μm, 54% thinner than those of Type I and II capillaries. Pericapillary spaces around Type III capillaries measured 56 μm2, 100% larger than for Type I vessels (resembling those of skeletal muscle). Only Type III capillaries contained fenestrations (9 per μm2of endothelial cell) and were the predominant type of capillary in central and caudal subregions of the SFO. Type I capillaries, prevalent in the transitional subregion between the central and rostral parts of the SFO, had 10 cytoplasmic vesicles per μm2of endothelial cell area, a number not different from that of Type III capillaries but 3× the frequency found in Type II vessels. Type II capillaries (those typical of “blood‐brain barrier”endothelium) had low vesicular density (3 per μm2), no fenestrations, and no pericapillary spaces. Luminal diameters and the densities of mitochondria and intercellular junctions were not different among capillary types or subregions in the SFO. Furthermore, there were no morphometric differences for any capillary dimensions between Long‐Evans and Brattleboro rats. These studies reveal quantitative differences among capillary networks in four distinct compartments of the rat SFO and provide morphometric dimensions for the three types of capillary existing in this cerebra

ISSN:0092-7317    

DOI:10.1002/cne.902940111

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

年代:1990

数据来源: WILEY