摘要:

AbstractWhile the somatotopic organization of many central systems is well characterized, that of peripheral sensory neurons has not been adequately defined. This is especially true for the trigeminal ganglion. By applying HRP subcutaneously at each of 14 sites and also intramuscularly, it is possible to determine whether the location of sensory neurons within the ganglion reflects their peripheral projections.There is no discernible somatotopic organization of neurons in the ophthalmic lobe. However, the location of maxillary neurons in the maxillo‐mandibular lobe is organized with the most posterior cells projecting to sites closest to the ganglion and with neurons located more anteriorly projecting to progressively more distant sites. There is a less well defined organization in the superior‐inferior axis of the ganglion, and none along its proximal (root) to distal axis.Mandibular exteroceptive neurons are found primarily in the anterior region of the maxillo‐mandibular lobe, while mandibular proprioceptive cells are located in the proximo‐central part of this lobe. In most cases there is a considerable scattering of horseradish peroxidase (HRP)‐filled neurons. Projections to contralateral ganglia, the trigeminal motor nucleus, and the trigeminal motor nucleus, and the trigeminal mesencephalic nucleus were also examined.Cytologically, the hatchling trigeminal consists of two interspersed types of neurons: large, lightly staining and smaller, darkly staining cells. Previous experiments have proved that these two cell types do not correspond to each of the embryonic precursorsof trigeminal neurons, the neural crest and placodal cells. In this study HRP was found localized in both classes of neurons following injection at all sites, including jaw‐closing muscles. This indicates that the dual cytology is not correlated with either distribution of peripheral fibers or exteroceptive vs. proprioceptive functions. The possibilities that the two types of neurons may have different central projections and/or may be related to visceral vs. somatic afferent functions ar

ISSN:0092-7317    

DOI:10.1002/cne.901900302

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

年代:1980

数据来源: WILEY

摘要:

AbstractHorseradish peroxidase (HRP) has been injected into periocular, upper beak, or lower jaw tissues of chick embryos aged 6–8 days of incubation. Subsequent mapping of the distribution of labeled neurons in the trigeminal ganglion indicates that the somatotopic organization of neurons is essentially identical to that found after hatching.At these stages most labeled cells are in the distal parts of the bilobed ganglion. There is no indication that any of these neurons, most but not all of which are derived from epidermal placodes, establish any erroneus projections. Most of the proximo‐central or core neurons, which are of neural crest origin, are immature at these stages. On the eighth day of development, by which time the embryo is responsive to tactile stimulation of the beak, few of these core cells have established projections to more distal (rostral) periocular or upper beak areas or to the lower jaw. In contrast, injection of HRP above the eye results in labeling of many of the core neurons. This suggests that there is an asymmetry in the time of neurite outgrowth from core neurons that is correlated with their peripheral projections but not with their time of terminal mitosis.Following injection of HRP into temporal periocular tissues, most of the core cells in the maxillo‐mandibular lobe contain peroxidase. This is probably due to uptake by growth cones emerging along the maxillary ramus.Examination of contralateral trigeminal ganglia indicates that the transmedian projections of these sensory fibers form later in development. Branches of the mandibular motor nerve extend throughout the lower jaw and presumptive jaw‐closing muscle anlagen, as evidenced by incorporation of HRP into motoneurons of the trigeminal

ISSN:0092-7317    

DOI:10.1002/cne.901900303

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

年代:1980

数据来源: WILEY

摘要:

AbstractThalamic fibers in the cortex ofPseudemysturtles were studied with the electron microscope to determine the type of synaptic vesicle they contain, the type of membrane differentiation they form, and the type of processes they contact. Following unilateral removal of the thalamus, all degenerating thalamic axon terminals are located in the outer third of the molecular layer in the rostral half of general cortex. In the middle of this zone they constitute as much as 25% of all vesicle‐containing profiles. The degenerated terminals appear as electron opaque profiles, most commonly with a uniform opacity. They contain round agranular vesicles and form synapses with asymmetrical membrane differentiations. They synapse mainly on dendritic spines containing mitochondria and/or membranous sacs, although some thalamic fibers contact small clear spines, dendrites, and, rarely, cell bodies. Counts show that 86% of degenerated contacts are on dendritic spines and 14% on dendritic shafts. The spines probably all belong to the dendrites of the pyramidal cells, whose somata are located in the deep cellular layer. The dendritic shafts and somata are most likely those of the aspinous stellate neurons located in the molecular layer. Although these stellate cells are not sufficiently numerous to form a cell “layer,” each transverse section through thalamic recipient cortex contains about nine of these cells and they occur in a ratio of 1:37 to pyramidal cells in the underlying main cell layer. We have calculated that in a rectangular solid of turtle cortex whose dimensions are 1 mm × 1 mm × the depth from pial surface to the underlying ventricle, there are 5.2 million thalamic fiber contacts (all in the outer 100 μm), 15,000 pyramidal neurons in the main cell layer, and 400 stellate cells in the molecular layer. Of the 5.2 million thalamic synapses, 0.7 million contact stellate cells and 4.5 million contact pyramidal cells. Thus each stellate cell in the molecular layer receives on the average 1,800 thalamic fiber contacts, while each pyramidal cell receives only 300 thalamic fiber synapses on the distal portion of its dendrites. The calculations lead to the conclusion that individual stellate cells receive at least six times more thalamic fiber synapses than individual pyramidal cells in turtle cortex. We suggest that the stellate cells in the thalamic input zone are inhibitory and that each thalamic volley not only excites efferent pyramidal cells but is also a powerful activator of inhibitory inte

ISSN:0092-7317    

DOI:10.1002/cne.901900304

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

年代:1980

数据来源: WILEY

摘要:

AbstractAmong the Reptilia the morphology of the trigeminal (V) motor nucleus is a rather good indicator of the sophistication of jaw kinetics. As it becomes more complex, the nucleus shifts ventrolaterally and becomes divisible into subnuclear groups. The cottonmouth moccasin, a pit viper with very finely developed jaw musculature and kinetics, has a very large V motor nucleus. It is divisible into three subnuclei: the ventral and intermediate, containing predominantly large neurons (40–60 μm), and the dorsal subnucleus, containing only small neurons (20 μm).Ultrastructural study has indicated that these subnuclei can also be characterized according to the types of boutons synapsing on the cells. The soma of neurons in the ventral and intermediate subnuclei have up to 50% of their profile covered with clusters of boutons. The neurons of the dorsal subnucleus usually have only one cluster of two to three boutons per profile. Both cell types have more boutons containing spherical vesicles in axo‐dendritic synapses than those containing flattened vesicles, and approximately equal numbers of these boutons in axosomatic contacts. However, the small cells have proportionately more boutons containing spherical vesicles synapsing on them.Boutons similar to those described in mammalian spinal cord were identified in the snake V motor nucleus. Small terminals containing spherical (S) or flattened (F) vesicles and terminals associated with postsynaptic cisternae (C) or with dense bodies (T) are commonly found in the ventral and intermediate subnuclei. C‐ and T‐boutons are rare in the dorsal subnucleus. Large terminals with multiple active sites and postsynaptic dense bodies (M) and their associated, small, preterminal boutons (P) were not observed in the snake V motor nucleus. Boutons containing only large granular vesicles (G) were also not observed.We suggest that the ventral and intermediate subnuclei consist of α‐ and possibly β‐motoneurons and the dorsal subnucleus contains γ‐motoneurons. This anatomical segregation of function may be important to the physiology of ophidian mastication, which is quite different from that of mammals. However, there do exist several morphological similarities to mammals, suggesting that the snake brainstem may be a good model for comparative structure–f

ISSN:0092-7317    

DOI:10.1002/cne.901900305

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

年代:1980

数据来源: WILEY

摘要:

AbstractHorseradish peroxidase (HRP), injected intramuscularly, specifically labeled motoneurons innervating antagonistic jaw muscles in the cottonmouth mocassin,Agkistrodon piscivorus piscivorus. Adductor mandibulae profundus, part 3a, motoneurons were localized in the lateral regions of the ventral and intermediate subnuclei of the trigeminal (V) motor nucleus. These were large cells containing fine, granular reaction product characteristic of α‐motoneurons. Small cells, which contained large coarse reaction granules characteristic of γ‐motoneurons were localized in a separate cluster in the lateral regions of the dorsal subnucleus of the V motor nucleus. Depressor mandibulae motoneurons were localized in the ventromedial regions of the facial (VII) motor nucleus, primarily in the caudal half. Cell sizes ranged from 30–50 μm in diameter and HRP staining characteristics were variable, indicating a mixed population of motoneuron functional types without the segregation noted in the V motor nucleus.Boutons which made synaptic contact with labeled somata or processes were classified according to morphological type and their frequency of appearance. Boutons containing spherical vesicles (S‐, C‐, T‐) were distributed similarly on motoneurons of both muscles, but more F‐boutons, those with flattened vesicles, synapsed on the adductor motoneurons.Comparison of snake bouton distribution with that in mammalian spinal cord indicates that synaptology on all these motoneurons are remarkably similar. The more frequent occurrence of C‐boutons, those with a subsynaptic cistern, on reptilian motoneurons may indicate a stronger intrasegmental input, as determined from mammalian de

ISSN:0092-7317    

DOI:10.1002/cne.901900306

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

年代:1980

数据来源: WILEY

摘要:

AbstractElectron microscopic examination of the bases of adult rod and cone outer segments (rhesus monkey, ground squirrel, and grey squirrel) has led to a new model of disc morphogenesis. In this model the disc surfaces and disc rims develop by separate mechanisms and from separate regions of the membrane of the inner face of the cilium. This membrane is alternately specified into regions that will form either the disc surfaces or the disc rims. The disc surfaces develop by an evagination or outpouching of the ciliary membrane. The two surfaces of an evagination, scleral and vitreal, each form one of the surfaces of adjacent discs. The disc rim is initially specified as a region of ciliary membrane between adjacent disc‐surface evaginations. This region grows bilaterally around the circumferences of adjacent discs, zippering together the apposed surfaces to form the rim and completed disc. At the same time it seals the plasma‐membrane edges of the evaginations, which have become detached from the surfaces. Incisures form in rod discs by infolding of the rim and surfaces together, and they begin to form before the rim is completed around the disc perimeter. When a number of new discs are developing simultaneously the ciliary membrane at the base of an outer segment consists of a stack of rim forming and surface forming growth points. This model provides, in addition, for the continuous renewal of outer‐segment plasma membrane. It also establishes a developmental basis for the structural uniqueness of the disc rim. Finally, it indicates an evolutionary relationship between the discs of vertebrate visual cells and the membrane specializations of invertebrate visual

ISSN:0092-7317    

DOI:10.1002/cne.901900307

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

年代:1980

数据来源: WILEY

摘要:

AbstractNeurosecretory neurons of the hyperosmotically stressed hypothalamo‐neurohypophysial system have been a useful model with which to demonstrate interrelationships among perikaryal lysosomes, agranular reticulum‐like cisterns, endocytotic vacuoles, and the axoplasmic transport of acid hydrolases and horseradish peroxidase. Supraoptic neurons from normal mice and mice given 2% salt water to drink for 5–8 days have been studied using enzyme cytochemical techniques for peroxidase and lysosomal acid hydrolases. Peroxidase‐labeling of these neurons was accomplished by intravenous injection or cerebral ventriculocisternal perfusion of the protein as previously reported (Broadwell and Brightman, '79).Compared to normal controls, supraoptic cell bodies from hyperosmotically stimulated mice contained elevated concentrations of peroxidase‐labeled dense bodies demonstrated to be secondary lysosomes and acid hydrolase‐positive and peroxidase‐positive cisterns either attached or unattached to secondary lysosomes. These cisterns were smooth‐surfaced and 400–1,000 A wide. Their morphology was similar to that of the agranular reticulum. Some of the cisterns contained both peroxidase and acid hydrolase activities. The cisterns probably represent an elongated form of lysosome and, therefore, are not elements of the agranular reticulum per se. By virtue of their direct connections with perikaryal secondary lysosomes, these cisterns may provide the route by which acid hydrolases and exogenous macromolecules can leave perikaryal secondary lysosomes for anterograde flow down the axon. Very few smooth‐surfaced cisterns were involved in the retrograde transport of peroxidase within pituitary stalk axons from normal and salt‐treated mice injected intravenously with peroxidase. Peroxidase undergoing retrograde transport was predominantly in endocytotic structures such as vacuoles and cupshaped organelles, which deliver this exogenous macromolecule directly to secondary lysosomes for degradation in the cell body.These observations extend our previously reported findings in the axon to the cell body and suggest that agranular reticulum‐like cisterns in the perikaryon, like those in the axon, may be part of the lysosomal system rather than associated with the agranular reticulum. A diagram summarizing the lysosomal system of organelles and proposed transport of acid hydrolases and peroxidase in neurosecretory neurons specifically and in neurons

ISSN:0092-7317    

DOI:10.1002/cne.901900308

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe configuration of somatosensory relay nuclei and termination of spinothalamic fibers were studied in the dorsal thalamus of a prosimian primate (Galago senegalensis) using Nissl, Klüver and Barrera ('53), Weil ('45), and Fink and Heimer ('67) methods. The ventral posterolateral nucleus (VPL) is divided into medial and lateral parts (VPLmand VPLl, respectively) by a sheet‐like lamina of fibers. Spinothalamic input to Galago VPL is somatopically arranged; input from the forelimb terminates in VPLmand that from hindlimb in VPLl. In addition, preterminal debris in caudal VPL is dense and organized into “parcellated bursts” (terminology of Mehler, '69). Consequently, the nature of the spinothalamic debris in VPL ofGalagois similar to that reported for higher primates (Mehler et al., '60). Located dorsomedial to the rostral extension of VPL is a zone of large, deeply staining cells designated as the ventral intermediate nucleus (Vim). Following hemisection at either cervical or lumbar spinal cord levels, preterminal debris, independent of that coursing into VPL, enters the Vim. This substantiates the presence of an intermediate nucleus (i.e., Vim) between VPL and the more rostral ventral lateral nucleus.In the medial thalamic region, axonal degeneration is located in the central lateral nucleus (CL) and in the densocellular and the multiform portions of the dorsomedial nucleus. Only fibers of passage are identified in the centre median, the paracentral and the subparacentral nuclei. The posterior nuclear group (PO) inGalagois divided into medial and lateral parts designated as POmand POl, respectively. In addition, PO contains three distinct nuclei: 1) the magnocellular (MC) portion of the medial geniculate nucleus; 2) the nucleus limitans (Lim); and 3) the suprageniculate nucleus (SG). Following spinal cord hemisection, preterminal debris is located throughout the POmand around cells of the MC. Lim and SG contain no discernible degeneration. Preterminals are also found in a group of cells designated as the caudal part of the central lateral nucleus

ISSN:0092-7317    

DOI:10.1002/cne.901900309

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe topographic arrangement and cytoarchitecture of cells in the ventral posterolateral nucleus (VPL) of a prosimian primate (Galago senegalensis) were studied using horseradish peroxidase (HRP) and Golgi impregnation techniques. Following cortical implants of HRP, reactive neurons in VPL are organized into medially concave lamellae which extend through the dorsoventral and rostrocaudal dimensions of the nucleus. After implant in forelimb and hindlimb areas of motor‐sensory cortex, labeled cells are confined to the medial (VPLm) and lateral (VPLl) portions of VPL, respectively. HRP‐positive cells in the ventral part of each lamella are organized into clusters which correspond to the clusters of cells and “parcellated‐bursts” of preterminal debris previously described in bushbaby VPL (Pearson and Haines, this volume). HRP‐reactive cells in the ventral intermediate nucleus (Vim) are evenly distributed as contrasted to the tightly clustered groups of somata in the adjacent VPL. This evidence argues in favor of the presence of Vim in dorsal thalamus of this prosimian.Golgi impregnations reveal two main types of relay cells inGalagoVPL. Type I cells have multiangular somata, straight distal dendrites, and primary dendritic branch points which are free of appendages. Type II cells have rounded somata, sinuous distal dendrites, and clusters of appendages located at primary branch points. Intermediate cells (i.e., cells with morphological features in between types I and II) are also present in VPL. Comparison of tufted Golgi impregnated cells with neurons labeled with HRP shows definite similarities in somata size and shape, and in the orientation of proximal dendrites. This evidence corroborates the relay nature of the tufted neurons in VPL. Relay cells inGalagoVPL have morphological features which are similar to those of relay cells in lateral and medial geniculate nuclei of cat and primate.Type III cells have small round somata, radiate dendrites with elaborate appendages, and axons which appear to be intrinsic to VPL. Consequently, these cells are considered to be interneurons in the VPL ofGalago. Glial‐like neurons (type IV cells) were also observed. These have beaded dendritic processes similar to those which presumably represent presynaptic boutons in other species. Consequently, these cells are also assumed to function intrinsical

ISSN:0092-7317    

DOI:10.1002/cne.901900310

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe effects of the indolic neurotoxins 5,6‐ and 5,7‐dihydroxytryptamine (5,6‐DHT; 5,7‐DHT) on the enteric nervous system were examined. 5,6‐DHT, in moderate dosage, 40 mg/kg, decreased uptake of tritiated 5‐hydroxytryptamine (3H‐5‐HT) but not that of tritiated norepinephrine (3H‐NE). However, selectivity of the neurotoxins for enteric serotonergic rather than adrenergic axons was enhanced by pretreating animals with desmethylimipramine to inhibit the catecholamine uptake mechanism. When this was done, 5,7‐DHT was found to prevent the development of 5‐HT histofluorescence (following injection of L‐tryptophan) without affecting histofluorescence of NE. In contrast, 6‐hydroxydopamine virtually abolished NE histofluorescence and uptake of3H‐NE without affecting development of 5‐HT histofluorescence or uptake of3H‐5‐HT. Electron microscopy revealed that 5,7‐DHT induced dose‐dependent lesions of axonal varicosities in the enteric nervous system. Early lesions, 1–4 hours following injection, resembled cytolysosomes and consisted of membrane enclosed regions of opaque cytoplasm containing synaptic vesicles. Affected varicosities contained a mixed population of large dense cored (∼120nm) and small lucent vesicles (∼70nm) but none exhibited pre‐ or postsynaptic membrane specializations. After 24 hours terminals degenerated and were engulfed by surrounding supporting cells. It is concluded that peripheral serotonergic neurons resemble central serotonergic neurons in susceptibility to the toxic effects of indolic neurotoxins. These neurotoxins are useful anatomical

ISSN:0092-7317    

DOI:10.1002/cne.901900311

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

年代:1980

数据来源: WILEY