摘要:

AbstractIn our previous light microscopic studies (Oka et al., Brain Res. 367:341–345, '86; Oka and Ichikawa, J. Comp. Neurol. 300:511–522, '90), we reported that there are at least two types of terminal nerve (TN) cells based on cell size and immunoreactivity: type I cells had large cell bodies, while type II cells had smaller cell bodies. Type I TN cells were immunoreactive to gonadotropin‐releasing hormone (GnRH) and may be the major source of GnRH‐immunoreactive fibers that are widely distributed throughout the brain. Type if TN cells, on the other Hand, were not immunoreactive to GnRH. In the present paper, we examined the cytology and synaptology of these two types of TN cells with electron microscopy. Type I TN cell bodies were found to have morphological characteristics similar to those of other peptide‐synthesizing neurons and are likely to be actively synthesizing GnRH. The frequent occurrence of coated vesicles close to the plasma membrane of the cell body was suggestive of membrane retrieval following exocytosis of the vesicular contents from the cell surface. Neighboring TN cells were either in direct juxtaposition with one another or made specialized “glomeruloid” cell‐to‐cell contacts; these specializations may be relevant for nonsynaptic intercellular communications among the TN cells. Within these glomeruloid complexes, the somatic processes of TN cells received inputs from two types of synaptic terminals: one containing only spherical synaptic vesicles and another containing a small number of dense‐cored vesicles in addition to the spherical synaptic vesicles. Axosomatic synapses were rare on type I TN cell bodies. In contrast, type II TN cell bodies had morphological characteristics similar to those of neurons in other brain regions. These receive axosomatic inputs from synaptic terminals containing only spherical synaptic vesicles and those with a small number of dense‐cored vesicles in addition to the spherical synaptic vesicles. Thus, each type of TN cell has unique fine structural characteristics which may correlate to their diffe

ISSN:0092-7317    

DOI:10.1002/cne.903040202

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

年代:1991

数据来源: WILEY

摘要:

AbstractEarly development of fungiform papillae on the fetal rat tongue was examined: (1) to determine whether morphogenesis of the taste bud‐bearing fungiform papillae is induced by nerve and (2) to study the growth pattern of the two sensory nerves that innervate the papilla. The papillae first appear on the 15th day of gestation (E15; E1 is the day when the dam is sperm positive) in rows parallel to the midline sulcus. There appears to be a medial‐lateral and an anterior‐posterior gradient in the sequence of papilla differentiation. The epithelium of the early papilla resembles a multilayered placode topped by a flattened surface periderm. Close examination of the peridermal cells at the apex of the papillae reveals that the cells have fewer surface microvilli and their cytoplasm is more electron opaque than that of similar cells in interpapillary regions. The basal cells in the placode‐like epithelium differ from those in interpapillary regions in that they are postmitotic and have more mitochondria. At later stages, the papilla acquires a mesenchymal core and nerves grow into the core. Results from organ culture experiments of tongue fragments taken from E14 fetuses indicate that morphogenesis of fungiform papillae is initiated in the absence of sensory nerve influence, but the nerve exerts a trophic effect on their maintenance. The two sensory nerves of the tongue, the chorda tympani and the lingual branch of the trigeminal nerve, enter the tongue mesenchyme at E14 and grow toward the epithelium. By E15 the chorda tympani branches have reached the developing fungiform papillae, by E16 many have entered the papilla, and by E17 they have penetrated the epithelium at the papilla apex. Their fibers are associated exclusively with the cells at the papilla apex, where the taste bud will develop. The trigeminal nerve ramifies beneath the surface of the entire epithelium by E15. Later, it, too, sends branches into fungiform papillae; these ascend along the trunk of the chorda tympani and at E17 terminate in the connective tissue core around the chorda tympani field. The results are compatible with the notion that the tongue epithelium exerts a general tropic effect on growing axons of both sensory nerves, and the epithelial cells of the fungiform papilla apex exert a similar effect to which only the chorda tympani axons are res

ISSN:0092-7317    

DOI:10.1002/cne.903040203

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

年代:1991

数据来源: WILEY

摘要:

AbstractAbout half of the motor neurons produced by some neural centers die during the course of normal development. It is thought that the size of the target muscle determines the number of surviving motor neurons. Previously, we tested the role of target size in limiting the number of survivors by forcing neurons to innervate a larger target (Sohal et al., '86). Results did not support the size‐matching hypothesis because quail trochlear motor neurons innervating duck superior oblique muscle were not rescued. We have now performed the opposite experiment, i.e., forcing neurons to innervate a smaller target. By substituting the embryonic forebrain region of the duck with the same region of the quail before cell death begins, chimera embryos were produced that had a smaller quail superior oblique muscle successfully innervated by the trochlear motor neurons of the duck. The number of surviving trochlear motor neurons in chimeras was significantly higher than in the normal quail but less than in the normal duck. The smaller target resulted in some additional loss of neurons, suggesting that the target size may regulate neuron survival to a limited extent. Failure to achieve neuron loss corresponding to the reduction in target size suggests that there must be other factors that regulate neuron numbers during developmen

ISSN:0092-7317    

DOI:10.1002/cne.903040204

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe distribution of the calcium binding protein calretinin (protein 10) was examined in the rat forebrain by immunohistochemistry. The main and accessory olfactory bulbs had immunoreactive label in granule, periglomerular, and mitral cells. Positive fibers were noted in the external plexiform and granule cell layers, glomeruli, and in the molecular layer of the anterior olfactory nucleus. The cerebral cortex contained calretinin label in nonpyramidal bipolar cells. Cells in the substantia nigra compacta and ventral tegmental area were also calretinin positive as were nigrostriatal and mesolimbic projections (caudate‐putamen, nucleus accumbens). In the hippocampus, interneurons were stained in all the subfields of the CA1‐CA4 regions. In the thalamus, many positive cells were observed in the periventricular, reticular, lateral habenula, and reunions nuclei. Calretinin immunoreactive cells were particularly abundant in the lateral mamillary and septofimbrial nuclei. Several fiber tracts were also revealed, i.e., the lateral olfactory tract, mamillothalamic tract, fasciculus retroflexus, optic tract, and stria medullaris. These results demonstrate a distinct distribution of calretinin within cell bodies and fib

ISSN:0092-7317    

DOI:10.1002/cne.903040205

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe distribution of cells containing mRNA encoding cholecystokinin was studied in the rat central nervous system by in situ hybridization histochemistry.Cholecystokinin mRNA containing neurons were considerably more numerous than the cholecystokinin‐like immunoreactive neurons detected by immunocytochemistry even after cholchicine pretreatment and appeared to be heavily, moderately, or lightly labeled. Such neurons were present in the olfactory bulb, olfactory nuclei, layers II–III and V–VI of the cerebral cortex, amygdaloïdnuclei, subiculum, hippocampus, claustrum, endopiriform nucleus, several hypothalamic nuclei, most of the thalamic nuclei, ventral tegmental area, substantia nigra, interfascicularis nucleus, linearis rostralis, central gray, Edinger‐Westphal nucleus, superior and inferior colliculi, parabrachial nucleus, reticular formation, raphe nuclei, and spinal trigeminal nucleus.This distribution partly confirmed and partly extended the previous immunohistochemical descriptions. Several brain areas such as the thalamus and the colliculi contain cholecystokinin mRNA but are devoid of perikarya exhibiting cholecystokinin‐like immunoreactivity. The cerebral cortex and the hippocampus present a far higher density of cholecystokinin mRNA containing cells, including pyramidal neurons, than of perikarya containing cholecystokinin‐like immunoreactivity.These results suggest that cholecystokinin or cholecystokinin‐related peptides could have a functional role in numerous cerebral pathways including long projections such as cortical or thalam

ISSN:0092-7317    

DOI:10.1002/cne.903040206

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis is a quantitative study of the motoneuronal population of the rat's common peroneal nerve following severe crush injury of the sciatic nerve or its component branches. The crush was performed unilaterally under anesthesia for 60 seconds with hemostat jaws covered with tubing to form a smooth, 2 mm long, injured zone. Recovery from injury was allowed for 14 to 188 days. It was measured behaviorally using the sciatic functional index (SFI) and electrophysiologically by comparing the conduction velocity and amplitudes of evoked muscle action potentials prior to injury, and again after injury just before the nerve was labeled with horseradish peroxidase (HRP), and/or its wheat germ agglutinin conjugate (WGA‐HRP), 48–72 hours before sacrifice. The motoneurons were retrogradely labeled on both sides so that the uninjured side might serve as a control. On the injured side the nerves were labeled either distal or proximal to the crush site, The tibialis anterior muscles on both sides were removed and weighed. Spinal segments L2 to L6 were cut in serial, frozen cross‐sections. HRP reaction products were formed using TMB as the chromogen. The normal peroneal nerve was found to contain 634 ± 26 motoneurons (22 cases). The number of motoneurons labeled 5–15 mm distal to the injury site (22 cases) was 535 ± 69 or 84.4% of normal. In 12 cases in which the nerve was labeled 5 mm proximal to the injury normal population numbers (648 ± 30) were found. These counts demonstrated that the unlabeled 15.6% in the distal labeled cases had not vanished as a result of cell death. Instead, the unlabeled group was composed mainly of small motoneurons whose axons probably had not regenerated distal to the crushed zone. Mean soma size of injured neurons increased to maximum 3–6 weeks after injury and then gradually decreased in size over the following weeks to nearly normal values. This transient increase in size was due to two factors: (1) soma swelling in response to axonal injury, and (2) absence of many small motoneurons, presumably γ‐motoneurons, which were either incapable of, or prevented from, regenerating beyond the injury zone long after larger motoneurons had reinnervated their targets. SFI scores, muscle weights, and amplitude ratios of evoked potentials recovered to control values by 70–80 days post‐injury. Conduction velocities remained 20–25% below normal at the end of 80 days. These data suggest that because all motoneurons survived injury, it is possible for all of them to reinnervate their original targets under certain conditions providing that proper pat

ISSN:0092-7317    

DOI:10.1002/cne.903040207

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe central‐peripheral transitional zones of rat dorsolateral vagal rootlets are highly complex. Peripheral nervous tissue extends centrally for up to several hundred micrometers deep to the brainstem surface along these rootlets. In some instances this peripheral nervous tissue lacks continuity with the peripheral nervous, system (PNS) and so forms an island within the central nervous system (CNS). In conformity with the resulting complexity of the CNS‐PNS interface, segments of vagal axons lying deep to the brainstem surface are myelinated by one or moreintercalatedSchwann cells, contained in peripheral tissue insertions or islands, at either end of which they traverse an astroglial barrier. Intercalated Schwann cells are thus isolated from contact or contiguity with the Schwann cells of the PNS generally. They are short, having a mean internodal length of around 60% of that of the most proximal Schwann cells of the PNS proper, which lie immediately distal to the CNS‐PNS interface and which are termedtransitionalSchwann cells. The thickness of the myelin sheaths produced by intercalated Schwann cells is intermediate between that of transitional Schwann cells and that of oligodendrocytes myelinating vagal axons of the same calibre distribution. This is not due to limited blood supply or to insufficient numbers of intercalated Schwann cells, the density of which is greater than that of transitional Schwann cells. These factors are unlikely to restrict expression of their myelinogenic potential. Nevertheless, the regression data show that the setting of the myelin‐axon relationship differs significantly between the two categories of Schwann cell. Thus, the myelinogenic response of Schwann cells to stimuli emanating from the same axons may differ between levels along one and the same nerve bundle. Mean myelin periodicity was found to differ between sheaths produced by intercalated and by transitional Schwan

ISSN:0092-7317    

DOI:10.1002/cne.903040208

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

年代:1991

数据来源: WILEY

摘要:

AbstractMotor fibers of the accessory celiac and celiac vagal branches are derived from the lateral columns of the dorsal motor nucleus of the vagus nerve. These branches also contain sensory fibers that terminate within the nucleus of the tractus solitarii. This study traces the innervation of the intestines by using the tracer cholera toxin‐horseradish peroxidase. In 53 rats, the tracer was injected into either the stomach, duodenum, jejunum, terminal ileum, cecum, or ascending colon.With all cecal injections, prominent retrograde labeling of cell bodies occurred bilaterally in the lateral columns of the dorsal motor nucleus of the vagus nerve above, at, and below the level of the area postrema. Dendrites of laterally positioned neurons projected medially and rostrocaudally within the dorsal motor nucleus of the vagus nerve and dorsomedially into both the medial subnucleus and parts of the commissural subnucleus of the nucleus of the tractus solitarii. Sensory terminal labeling occurred in the dorsolateral commissural subnucleus at the level of the rostral area postrema and the medial commissural subnucleus caudal to the area postrema. Additionally, there was sensory terminal labeling within a small confined area of the dorsomedial zone of the nucleus of the tractus solitarii immediately adjacent to the fourth ventricle at a level just anterior to the area postrema. Stomach injections labeled motoneurons of the medial column of the entire rostrocaudal extent of the dorsal motor nucleus of the vagus nerve and a sensory terminal field primarily in the subnucleus gelatinosus, with less intense labeling extending caudally into the medial and ventral commissural subnuclei. Dendrites of gastric motoneurons project rostrocaudally and mediolaterally within the dorsal motor nucleus of the vagus nerve and dorsolaterally within the nucleus of the tractus solitarii. They are most pronounced at the level of the rostral area postrema where many dendrites course dorsolaterally terminating primarily within the subnucleus gelatinosus.Injections of the duodenum labeled a small number of the cells within the medial aspects of the dorsal motor nucleus of the vagus nerve. Jejunal, ileal, and ascending colon injections labeled cells sparsely within the lateral aspects of the dorsal motor nucleus of the vagus nerve bilaterally. No afferent terminal labeling was evident after injection of these areas of the bowel.The dorsal vagal complex has a prominent viscerotopography: the dorsal motor nucleus of the vagus nerve has a mediolateral organization corresponding to end‐organ innervation; the nucleus of the tractus solitarii has a rostrocaudal axis of visceral representation with some overlap corresponding to rostrocaudal positioning along the alimentary canal and mediolateral separation of terminals within the nucl

ISSN:0092-7317    

DOI:10.1002/cne.903040209

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

年代:1991

数据来源: WILEY

摘要:

AbstractAnterograde and retrograde transport methods have been used to analyze the projection of the superior colliculus upon the dorsal lateral geniculate nucleus in 19 mammalian species. Our retrograde findings reveal that tectogeniculate neurons are relatively small, and lie dorsally within the superficial gray. These small tectogeniculate neurons are spatially related to a dense tier of W‐cell retinal input.Our anterograde tracing results show that tectogeniculate axons are visuotopically distributed to small‐celled regions of the lateral geniculate in all nineteen species. In the majority of these species, the small‐celled, tectally innervated regions of the lateral geniculate lie adjacent to the optic tract and contain W‐cell‐like neurons. Our findings suggest that neuroanatomical demonstration of the tectogeniculate projection is a relatively simple and straightforward way of revealing regions of the lateral geniculate which contain W‐cells. This is true even in species in which the lateral geniculate lacks obvious cellular laminae, and in regions of the lateral geniculate where W‐cells are few in number.The present data are especially interesting in light of the cortical projections of tectally innervated, small‐celled regions of the lateral geniculate to the patches or puffs within layer III of area 17. Since these regions of small‐celled geniculocortical axons are co‐extensive with zones (“blobs”) rich in cytochrome oxidase, it might be that information carried over the tectogeniculate circuitry plays an important role in the funct

ISSN:0092-7317    

DOI:10.1002/cne.903040210

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe have studied the ability of primary afferent neurones to proliferate within the grey matter of the dorsal horn following the degeneration of other, nearby, afferent fibres. The peripheral branches of primary afferents have the capacity to regenerate successfully over long distances, and we have examined the possibility that when they are so doing, the neurones' status changes to facilitate greatly the sprouting of afferent fibres within the dorsal horn.“Spared root” preparations (rhizotomies of L3, L4, L6, S1, and the caudal half of L5, sparing the rostral half of the L5 dorsal root) were made in adult rats. In some animals (acute preparations) the distribution of the central terminals of the spared root was assessed by labelling the sciatic nerve with WGA‐HRP at the time of the rhizotomies. In other animals (chronic preparations, symmetrical bilateral spared roots were made and the sciatic nerve on one side was concomitantly crushed to trigger regrowth of the peripheral branches of these axons. Eight to 10 weeks later the sciatic nerves on both sides were labelled with HRP‐WGA.In the acute preparations the reaction product was found in a limited rostrocaudal and mediolateral region of the dorsal horn. In lamina II (the lamina of densest labelling the labelled terminals occupied an average of 1.17 ± 0.21 mm2. In chronic preparations, the area of labelled terminals on the side of the uncrushed sciatic nerve was 1.34 ± 0.28 mm2(not significantly different from acute animals). However, the labelled area on the side of the crushed sciatic nerve was significantly greater, averaging 2.17 ± 0.14 mm2. Hence, primary afferent nerve fibres show greatly enhanced sprouting within the grey matter of the dorsal horn of the spinal cord when two conditions are fulfilled; 1) vacant synaptic sites are created by the degeneration of other primary afferent fibres; and 2) the peripheral branches of the axons are actively re

ISSN:0092-7317    

DOI:10.1002/cne.903040211

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

年代:1991

数据来源: WILEY