摘要:

AbstractCross sections from the trigeminal alveolar nerve of the lower jaw in the cichlidTilapia mariaewere examined by electron microscopy. The nerve fibers are arranged in groups with a core of unmyelinated and small myelinated axons, surrounded by myelinated axons of varying sizes. The core contains large bundles of unmyelinated axons collectively ensheathed by circumferentially located Schwann cells, as well as smaller bundles of unmyelinated axons partly separated from each other by Schwann cell processes. Among the unmyelinated axons, occasional scattered profiles resembling growth cones are seen. The total number of axons in this tooth‐related nerve increases from approximately 1,500 to 5,000, as the animals grow in length from 4.5 to 21.5 cm. Some 24–49% of the axons are unmyelinated. The myelinated axons have maximum diameters of 1.0–3.0 μm, depending on body size. Most myelinated axons have diameters less than 1.0 μm and the smallest ones reach down to 0.3 μm. These results show that there is a continual addition of axons to the alveolar nerve of the lower jaw inTilapia mariaeand that the critical diameter for myelination in this peripheral nerve is similar to that typically found in the mamma

ISSN:0092-7317    

DOI:10.1002/cne.902720302

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

年代:1988

数据来源: WILEY

摘要:

AbstractLight microscopic autoradiography of [3H]quinuclidinyl benzilate (QNB) binding sites was used to study the distribution of muscarinic acetylcholine receptors in the mouse, rat, guinea pig, and rabbit cerebellar cortex. In the mouse, the laminar distribution of grain density was similar throughout the cortex, with slightly higher levels over lobules IX and X. The highest [3H]QNB labeling was present over the granule cell layer, and low levels were observed over the molecular layer. In the rat, the general distribution was similar to that of the mouse in that the granule cell layer was most densely labeled and the highest concentration of [3H]QNB binding sites was present in lobules IX and X of the archicerebellum. In these lobules, however, the laminar distribution of grain density was reversed so that the molecular layer was more densely labeled than the granule cell layer. In addition, several discrete columns of elevated grain density traversed the granule cell layer in caudal regions of lobule IX. The distribution of [3H]QNB binding sites in the guinea pig cerebellum was similar to that of the rat in that the molecular layer of lobules IX and X was again more intensely labeled than other cerebellar regions. In the remaining lobules, grain density was equal over the granule cell and molecular layers. In the rabbit cerebellar cortex, slightly higher grain density was observed in the granule cell layer than in the molecular layer. In lobules IX and X and in the hemisphere of X, the Purkinje cell layer was most densely labeled; parasagittal columns of very high grain density were present over the molecular layer of several cortical regions, including lobules I, II, III, IV, V, IX, X, and the hemispheres of IX and X.Since muscarinic receptors have previously been found on blood vessels, there is a possibility that some proportion of receptor labeling may be localized to these structures. Microvessels and capillaries in each of the species examined were more numerous in the granule cell layer than in the molecular layer and white matter. The distribution of blood vessels in many cerebellar lobules of mice, rats, and guinea pigs corresponded quite closely to the general distribution of [3H]QNB binding sites. Unique patterns of labeling in lobules IX and X were not accompanied by corresponding patterns of blood vessel distribution, however. In the mouse, there was a slight increase in muscarinic receptor density observed in the archicerebellum, with no corresponding increase in the density of blood vessels. In the rat and guinea pig, the highest receptor densities in the archicerebellum were observed in the molecular layer rather than in the granule cell layer, a reversal of the laminar pattern in the remaining lobules. There was no corresponding reversal in laminar microvessel density in this region. In addition, columnar patterns of elevated grain density, observed in the cerebellar vermis of rats, guinea pigs, and rabbits, were not accompanied by corresponding patterns of increased microvessel density. It is concluded that, although some proportion of paleo‐ and neocerebellar muscarinic receptors may be localized to microvessels and capillaries, the unique patterns of [3H]QNB binding sites in the archicerebella of all four species, plus the discrete columns of high grain density observed in the rat, guinea pig, and rabbit, may reflect the presence of neuronal receptor

ISSN:0092-7317    

DOI:10.1002/cne.902720303

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe development of neuropeptide and neurotransmitter‐related immunoreactivities in the rat olfactory bulb were investigated immunohistochemically by using antisera raised against substance P (SP), cholecystokinin‐8 (CCK), neurotensin (NT), leucine‐enkephalin or methionine‐enkephalin‐Arg6‐Gly7‐Leu8(ENK), somatostatin (SOM), neuropeptide Y (NPY) and tyrosine hydroxylase (TH).Results obtained for the adult olfactory bulb confirmed previous observations, except for SP‐like immunoreactive (SP‐IR) granule cells in the main olfactory bulb (MOB) and NT‐IR neurons around the modified glomerular complex (MGC) (Teicher et al., Brain Res.194:530‐535, 1980).SP‐, CCK‐ and NT‐IR neurons were observed in the MOB of the rat fetus. SP‐IR neurons also appeared in the accessory olfactory bulb (AOB). Among them, NT‐IR neurons in the MOB and SP‐IR neurons in the AOB were observed on embryonic day 16. SP‐ and CCK‐IR neurons in the MOB appeared on embryonic day 18. Most of these neurons were presumed to be projecting neurons. SOM‐, NPY‐, ENK‐ and TH‐IR neurons appeared in the newborn rats. The number and intensity of immunostaining of these neurons continued to increase with age, producing the adult pattern, except for NT‐IR neurons in the MGC and SP‐IR neurons in the mitral cell layer of the AOB, which were mor

ISSN:0092-7317    

DOI:10.1002/cne.902720304

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

年代:1988

数据来源: WILEY

摘要:

AbstractPutative glycinergic neurons in the larval tiger salamander retina were localized by a comparative analysis of high affinity3H‐glycine uptake and glycine‐like immunoreactivity (Gly‐IR) at the light microscopic level. Commonly labeled neurons include at least three types of amacrine cell (Type IAd, Type IAb, Type IIAd; distinquished by soma location and dendritic ramification), cell bodies in the ganglion cell layer (GCL), and rarely observed Type II (inner) bipolar cells. With the increased resolution provided by Gly‐IR, we identified a Type IAa amacrine cell, two types of Type IIAd amacrine cells, and Gly‐IR interplexiform cells. Gly‐IR axons in longitudinal sections of the optic nerve indicate the presence of Gly‐IR ganglion cells. The percentage of labeled somas in the inner nuclear layer (INL) compared to all cells in each layer was similar for the two methods: 30‐40% in INL 2 (middle layer of somas), 30–40% in INL 3 (inner layer of somas), and about 5% in the GCL. Labeled processes were found throughout the full thickness of the inner plexiform layer (IPL), but with a much denser band in the proximal half (sublamina b). The only major difference between the two methods (3H‐glycine uptake vs. Gly‐IR) was that Type I (outer) bipolar cells were labeled only by3H‐glycine uptake; these cells were more lightly labeled with silver grains than cell bodies in either INL 2 or INL 3. Postembed labeling of 1 μm Durcupan plastic sections for Gly‐IR showed the same pattern, but with much higher resolution, as obtained with 10 μm cryostat sections. This study indicates extensive colocalization of labeling by both probes in INL 2, INL 3, the IPL, and the GCL. We conclude that Gly‐IR can serve as a valid and reliable marker for glycine‐containing neurons in this retina and suggest that glycine serves as a transmitter for several morphologically distinct types of amacrine cell, an interplexiform cell, and perhaps a small percentage of Type II b

ISSN:0092-7317    

DOI:10.1002/cne.902720305

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe subcellular distribution of two molluscan neuropeptides, the small cardioactive peptides A and B (SCPAand SCPB), has been determined in two identifiedAplysiabuccal ganglion neurons, B1 and B2. These neurons were previously shown to synthesize and release these neuropeptides. B1 and B2, identified by their size and location within the ganglion, were labeled by intrasomatic injection of an electron‐dense particulate marker (ferritin or Imposil) permitting the unequivocal identification of their somata and proximal processes in thin sections. The somatic cytoplasm of both neurons had a conspicuous population of large dense‐core vesicles along with a smaller number of compound vesicles and small lucent vesicles. All three vesicle types are found in the neurites within the neuropil and proximal axon in the esophageal nerve. Immunoreactivity was localized on the surface of thin sections by the indirect immunogold method. The primary antiserum was shown to recognize both SCPAand SCPBafter the neuropeptides had been immobilized on protein‐coated nitrocellulose membranes by means of glutaraldehyde, the primary fixative used to immobilize SCPAand SCPBin situ. SCP immunoreactivity was present in the lumens of the dense‐core vesicles distributed throughout the cytoplasm of B1 and B2 and in dense‐core regions of the Golgi apparatus in the somatic cytoplasm. Taken together with biochemical evidence that B1 and B2 synthesize and release SCPs, these data suggest that the neuropeptides are sequestered into the protein secretory pathway of B1 and B2, a distribution that supports the notion that the SCPs function physiologically as neurotransmitters or neurom

ISSN:0092-7317    

DOI:10.1002/cne.902720306

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe method of transganglionic transport of horseradish peroxidasewheat germ agglutinin conjugate (HRP‐WGA) was used to determine the location within the monkey trigeminal ganglion of the primary afferent neurons that innervate the cornea, and the brainstem and spinal cord termination sites of these cells. In each of four animals, Gelfoam pledgets were saturated with 2% HRP‐WGA in saline and applied to the scratched surface of the central cornea for 30 minutes. Postmortem examination of the corneal whole mounts revealed that the tracer solution remained confined to approximately the central one‐fourth of the cornea with no spread into the peripheral cornea or limbus. Seventy‐two to 96 hours after tracer application, 126–242 labeled cell bodies were observed in the medial region of the ipsilateral trigeminal ganglion. The majority of neurons were concentrated in an area of the ganglion that lay directly caudal to the entering fibers of the ophthalmic nerve, but smaller numbers of cells lay somewhat more laterally, near the region where the ophthalmic and maxillary nerves come together. A very small number of neurons in one animal innervated the cornea by sending their fibers into the maxillary nerve. HRP‐WGA‐labeled terminal fields were present to some extent in all four major rostrocaudal subdivisions of the ipsilateral trigeminal brainstem nuclear complex (TBNC), but the size of the terminal fields and the intensity of labeling differed markedly from one level of the TBNC to the next. Labeled fibers projected heavily to the transitional zone between caudal pars interpolaris and rostral pars caudalis (i.e., the “periobex” region of the TBNC) and moderately to the trigeminal main sensory nucleus, pars oralis, and caudal pars caudalis at the level of the pyramidal decussation. Remaining areas of the TBNC, including rostral pars interpolaris and the midlevel of pars caudalis, received few, if any, corneal afferent projections. Occasional labeled fibers were observed in the dorsal horn of C1 and in the rostral half of C2. It is hoped that data generated in the current investigation of nonhuman primates will contribute to a better understanding of the neural substrates that subserve corneal sensation and the blink

ISSN:0092-7317    

DOI:10.1002/cne.902720307

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

年代:1988

数据来源: WILEY

摘要:

AbstractThese experiments examine which morphological features of axon terminals and their synaptic glomeruli are determined by afferent axons, and which by their targets. In normal, adult hamsters, electron microscopy reveals that, with respect to multiple ultrastructural features, the terminals and synaptic glomeruli of retinal afferent axons in the dorsal lateral geniculate nucleus differ from those of ascending auditory and somatosensory afferents in the medial geniculate and ventrobasal nuclei, respectively. These features include: (1) the location of specific sensory axon terminals on the somata and dendrites of their targets neurons, (2) the constitutents of the glomeruli and their synaptic relationships, (3) the number of specific sensory terminal boutons per glomerulus, (4) bouton size, (5) the number of dendritic and somatic appendages contacted by each bouton, and (6) the mitochondrial morphology of the specific sensory afferent boutons.In order to ascertain which of these features are determined by afferent axons and which by their targets, we subjected newborn Syrian hamsters to surgical procedures known to produce permanent, abnormal retinal projections to the main thalamic auditory (medial geniculate) and somatosensory (ventrobasal) nuclei. When the animals were adults, we examined the terminals and synaptic glomeruli of abnormal retino‐auditory and retino‐somatosensory axons that were anterogradely labeled by intraocular injection of horseradish peroxidase. With respect to all of the preceding features except mitochondrial morphology, the terminals and synaptic glomeruli of retino‐medial geniculate and retino‐ventrobasal axons more nearly resembled those of normal, auditory and somatosensory afferent axons, respectively, than they did those of normal, retino‐lateral geniculate axons.These results demonstrate that the differentiation of all the features that we have examined, except mitochondrial morphology, is determined by factors in target neurons or their environment. This finding suggests that the differentiation of morphological features involved incontactsamong neurons (including the type, number and size of interconnected neuronal elements and the loci at which they contact each other) is responsive to interactions among the connected elements, or between neural elements and their environment (e.g., glia, extracellular matrix), whereas the differentiation of structures reflectingintrinsic functionsof individual neuronal elements is not responsive to such int

ISSN:0092-7317    

DOI:10.1002/cne.902720308

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe morphology, ultrastructure, and principal synaptic input of longspined neurons located in the inner plexiform layer of the medial cortex in three related species of lizards is described.Golgi impregnations have been used to define the external morphology of these neurons and their axonal trajectories. Their most striking characteristic is the presence of very long spines or “microdendrites” especially abundant on the distal dendritic segments. Axons have ascendent trajectories, pass through the cell layer, and ramify in the outer plexiform layer. Combined Golgi‐electron microscopy as well as standard electron microscopy permitted the definition of the ultrastructure of these neurons. Timm and sulfide‐osmium methods permitted the detection and characterization of their principal synaptic input (i.e., zinc‐containing boutons).Gamma aminobutyric acid (GABA)‐immunostained sections in one of the species studied allowed the identification of GABA‐immunoreactive somata which had the same morphology and ultrastructure as long‐spined neurons; these GABAwimmunoreactive somata and their processes were found in the same location as long‐spined neurons. This suggests that at least some long‐spined polymorphic neurons are GABA‐ergic and presumably inhibitory.Finally, the neurobiological significance of these long‐spined neurons is discussed and briefly compared with that of similar neurons of the hilus of the fa

ISSN:0092-7317    

DOI:10.1002/cne.902720309

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe timing, magnitude, and spatial distribution of neuron elimination was studied in the dorsal lateral geniculate nucleus of 57 rhesus monkeys (Macaca mulatta) ranging in age from the 48th day of gestation to maturity. Normal and degenerating cells were counted in Nissl‐stained sections by using video‐enhanced differential interference contrast optics and videooverlay microscopy.Before embryonic day 60 (E60), the geniculate nucleus contains 2,200,000 ± 100,000 neurons. Roughly 800,000 of these neurons are eliminated over a 40‐ to 50‐day period spanning the middle third of gestation. Neurons are lost at an average rate of 300 an hour between E48 and E60, and at an average rate of 800 an hour between E60 and E100. Very few neurons are lost after E100, and as early as E103 the population has fallen to the adult average of 1,400,000 ± 90,000. Degenerating neurons are far more common in the magnocellular part of the nucleus than in the parvicellular part. In 20 of 29 cases, the number of neurons is greater on the right than on the left side. The right‐left asymmetry averages about 8.5% and the difference is statistically significant (X2= 38, p<.001).The period of cell death occurs before the emergence of cell layers in the geniculate nucleus, before the establishment of geniculocortical connections, and before the formation of ocular dominance columns (Rakic, 76). Most important, the depletion of neurons in the geniculate nucleus begins long before the depletion of retinal axons. The number of geniculate neurons is probably a key factor controlling the number of the retinal cells that survive

ISSN:0092-7317    

DOI:10.1002/cne.902720310

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe primary locomotory apparatus in the three larval stages of the lobster,Homarus americanus, are paddlelike structures on the thoracic appendages called exopodites, which beat almost continuously. Consequently their power and return‐stroke muscles are examples of highly active but short‐lived neuromuscular systems. The muscles, which are well vascularized, are of the fast type with 2‐3‐μm sarcomere lengths and 6 thin filaments surrounding a thick one. The most striking feature, however, is the large volume of mitochondria making up 40‐50% of the fiber. They appear as simple cylinders packed several layers deep along the periphery of the fiber and as large, multibranched forms distributed throughout the fiber and subdividing it into smaller units. The motor innervation to the return‐stroke muscle is via 3 excitatory axons, which generate large junctional potentials and twitch contractions. The muscle is densely populated with large neuromuscular synapses, most of which have a well‐defined active site or dense bar denoting the site of transmitter release. Altogether this motor system is specialized for prolonged activity. Atrophy of the neuromuscular system occurs by the late larval third stage. The muscle fibers lose their identity, fuse, and become vacuolated. The myofibrils condense and erode and the mitochondria are lost. Atrophy of motor innervation is gradual with individual axons dropping out. The largest axon providing most of the innervation is the first to degenerate. Early degenerative changes affect the axon and neuromuscular terminals but not the synaptic contacts, dense bars, and vesicles, which appear intact. Continued atrophy in the postlarval fourth stage reduces the exopodites to vestiges. Thus the returnstroke muscle of the larval exopodites in which muscle fiber and motoneurons are identifiable permits study of the interaction between a neuron and its target muscle undergoing programme

ISSN:0092-7317    

DOI:10.1002/cne.902720311

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

年代:1988

数据来源: WILEY