摘要:

AbstractBilateral interactions between the right and left sides of the vocal control pathway of three avian species, the budgerigar(Melopsittacus undulatus), the zebra finch(Poephila guttata), and the canary(Serinus can‐arius), were compared by using microstimulation. Stimulation of the neo‐striatal nucleus, hyperstriatum ventrale pars caudale (HVc), caused a constant‐latency increase in neural activity of the tracheosyringeal (ts) nerve. This nerve supplies the avian vocal organ, the syrinx.Unilateral stimulation of HVc in budgerigars caused equal responses in both right and left ts nerves, whereas in canaries and zebra finches, much larger responses with lower thresholds and shorter latencies were evoked in the ipsilateral ts nerve than in the contralateral ts nerve. Furthermore, contralateral responses in the oscines were seen only at high rates of stimulation, whereas ipsilateral responses could be evoked by a single stimulus pulse.Simultaneous bilateral stimulation of HVc in budgerigars evoked a greater than linear summation of responses on each ts nerve, evidence for convergence of ipsi‐ and contralateral inputs onto the same set of motor neurons. No such summation was detected in zebra finches or canaries.The bilateral distribution of excitation within the song control pathway of budgerigars should lead to coactivation of bilaterally paired muscles on each side of the syrinx. This type of interaction should ensure that the two sides of the parrot syrinx operate as parts of a unitary, or single‐voiced, syrinx. In contrast, the two sides of the song control pathway in canaries and zebra finches are almost completely isolated from each other, and are thus free to act independently. This type of organization lends itself to the separate control of simultaneously produced, harmonically unrelated sound elements by the two independent sound sources present in the songbird's two‐vo

ISSN:0092-7317    

DOI:10.1002/cne.902120402

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractDescending spinal projections were investigated in the turtlePseudemys scripta elegansfollowing injections of horseradish peroxidase and/or radioactive wheat germ agglutinin into the spinal cord at various levels. Using various planes of section the cells of origin in the brainstem, cerebellum, and diencephalon were characterized according to their size, dendritic tree, and precise location.Projections to levels as far caudal as the lumbar spinal cord were found to arise from medial and lateral rhombencephalic reticular fields, including the perihypoglossal complex, the nucleus raphe inferior, and the locus coeruleus; from certain subdivisions of the vestibular complex (ipsi‐lateral subnucleus (subn.) ventrolateralis, contralateral subn. veritrome‐dialis, and possibly subn. tangentialis); from the motor trigeminal nucleus; from the contralateral red nucleus, the ipsilateral nucleus (n.) interstitialis of the fasciculus longitudinalis medialis (flm) and from the hypothalamus. Fibers to high cervical levels arose from neurons within the dorsolateral and superior vestibular nuclei, the lateral cerebellar nucleus, the mesen‐cephalic trigeminal nucleus, and from neurons of the optic tectum. Low cervical and thoracic spinal levels were reached by fibers from the torus semicircularis n. laminaris, the n. of the flm, the medial cerebellar nucleus as well as from the n. vestibularis inferior and the principal and descending trigeminal n

ISSN:0092-7317    

DOI:10.1002/cne.902120403

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractAscending spinal projections were investigated in turtlePseudemys scripta elegansfollowing injections of radioactive amino acids into the spinal cord at various levels. Experiments using S35‐methionine were most successful in demonstrating various mesodiencephalic target areas.Ascending projections from lumbar and cervical segments terminated predominantly in caudal and lateral reticular fields including the perihy‐poglossal complex. These spinal regions also projected for a lesser extent to rostrolateral and caudomedial reticular fields and to the nucleus (n.) raphe inferior. Afferents terminated consistently within the peritoral region, the optic tectal layers, the mesodiencephalic periventricular white matter, and the ovalis complex. Occasional labeling was noted in the diencephalic white matter adjacent to the optic tract, the n. supraopticus, and in the n. commissuralis anterior. Projections to the so‐called rostrolateral perirotundal complex following high cervical injections were less prominent following low cervical and lumbar injections. Cervical afferents terminated in a variable manner in the vestibular complex, the torus semicircularis n. centralis, the mesodiencephalic periventricular gray (griseum centrale, n. intersti‐tialis commissuralis posterior and hypothalamic areas), the n. suprapedun‐cularis, and the n.

ISSN:0092-7317    

DOI:10.1002/cne.902120404

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe mitral cell in the olfactory bulb of the goldfish was examined by means of light microscopy, high‐voltage electron microscopy, and conventional electron microscopy.Mitral cells are located rather diffusely throughout the glomerular and plexiform layers. They do not make their own discrete layer. The cell bodies are rounded or triangular, and are about 10–25 μm in diameter. In Golgi‐impregnated material, thick cylindrical dendrites can be seen arising from the cell bodies and branching in the glomerular layer. Dendritic branches of some cells make two or more rather compact tufts, while the dendrites of other cells intermingle loosely with one another.In semithin and thin sections, darkly stained nodules appear to be scattered diffusely in the glomerular layer without clustering into discrete spheres, which are characteristic of the mammalian glomerulus. Hence, instead of the glomerulus, the “glomerular area” is defined as an area consisting of darkly stained nodules with rather pale granular regions surrounding them. Branches of mitral cell dendrites in the glomerular area consist of cylindrical shafts and irregular appendages arising from them. The shafts appear in the pale granular region and the appendages are found in the darkly stained nodules.Synapses can be found on all parts of the mitral cell: the soma, axon hillock, axon initial segment, thick dendritic stems, and dendritic branches. The abundance of synapses seems to vary considerably from part to part, and is highest on the dendritic branches in the glomerular area. The mitral cell is postsynaptic to olfactory nerve terminals and granule cell dendrites, and presynaptic to granule cell dendrites and some processes of unknown origin. Olfactory nerve terminals make asymmetrical synapses specifically on the appendages of the dendritic branches. Of the synapses on the shafts of the mitral cell dendritic branches in the glomerular area, 90% are with granule cell dendrites. Of the synapses between two different kinds of processes 30% are mitral‐to‐granule asymmetrical synapses, 20% are granule‐to‐mitral symmetrical synapses, and 50% are reciprocal pairs. Gap junctions and mixed synapses are also seen on branches of mitral cell dendrites.Features of the goldfish mitral cell are compared with those of the mammal. The differences in neuronal organization between the olfactory bulbs of teleosts and mam

ISSN:0092-7317    

DOI:10.1002/cne.902120405

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe effects of a variety of developmental manipulations on the distribution of the callosal pathway to visual cortex were examined by using the Fink Heimer technique in adult rats. First, the callosal projections in albino and pigmented rats were compared and found to be similar. The callosal pathway was limited in area 17 to a region adjoining its lateral border with area 18a. Second, dark‐reared rats were found to have normal callosal projections. Third, rats bilaterally enucleated at birth had expanded callosal inputs within area 17. Fourth, monocular enucleation at birth produced an expanded callosal pathway to area 17 contralateral to the enucleation and normal callosal projections to the opposite hemisphere. The expanded callosal inputs after enucleation showed a patchy distribution and usually avoided the most medial part of area 17. Fifth, a reduction in the callosal projections to the area 17/18a border was found after neonatal unilateral optic tract lesions. Sixth, expanded callosal inputs to area 17 were found following unilateral thalamic lesions at birth. The abnormal projection occupied mainly layers IV and III.The results of the different experiments indicate that the detailed distribution of the visual callosal projection within area 17 depends heavily on the organization of the retinogeniculocortical pathways to each hemispher

ISSN:0092-7317    

DOI:10.1002/cne.902120406

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractUsing wheat germ agglutinin‐conjugated horseradish peroxidase (WGA‐HRP) and the fluorescent dyes true blue and nuclear yellow, we have reex‐amined the time of arrival at the retina of the centrifugal fibers from the contralateral isthmo‐optic nucleus (ION), and have followed, quantitatively, the appearance and fate of other neurons that can be retrogradely labeled from the ipsilateral and contralateral eyes.The earliest age at which ION neurons can be retrogradely labeled is on the ninth day of incubation; the cells labeled at this stage are located in the ventrolateral part of the nucleus on the contralateral side. Over the course of the next 48 hours of development more and more cells can be labeled in a distinct ventrolateral to dorsomedial progression within the nucleus. Since this labeling sequence parallels the time course of generation of the ION neurons it is suggested that the axons of the first ION cells to be generated are the first to reach the contralateral retina, and that in this system there is a close relationship between the time that neurons withdraw from the cell cycle and the time that their axons reach their target area.In addition to the neurons in the ION, about 1,500 cells outside of the nucleus can be retrogradely labeled by WGA‐HRP injected into the contra‐lateral eye in posthatched chicks. This is slightly less than half the number of “ectopic isthmo‐optic neurons” that can be similarly labeled on the 13th day of incubation (when the ION is numerically complete). The reduction in the number of ectopic ION neurons occurs over the same period as the phase of naturally occurring cell death in the ION itself–between the 13th and 17th days of incubation. Long‐term labeling experiments with true blue indicate that the disappearance of about 53% of the ectopic ION cells is due to their death rather than the elimination of axon collaterals. In their morphology the ectopic neurons resemble the cells in the ION at early stages in their development, and there is indirect evidence that the ectopic ION neurons which survive also receive an input from the optic tectum through the‐tecto‐isthmal tract. On these and other grounds it is suggested that the ectopic neurons are indeed “misplaced” ION cells.Between the tenth and 13th days of incubation a small and rather variable number of neurons (58–178) was retrogradely labeled from theipsilateraleye. Of these neurons with aberrant, ipsilaterally projecting axons, an average of just under 30 lay within the interior of the ION, about 33 were along its borders, and 38 were observed scattered among the ectopic ION cells. Double labeling experiments indicate that early in their development some of these neurons have axon collaterals which project to the contralateral eye. In a large number of animals injected with WGA‐HRP after the 17th day of incubation, only a single neuron was seen in the interior of the ipsilateral ION, but, on average, about nine labeled neurons were found along its borders and about 20 were ectopically placed.The numbers of ectopic ION neurons and ION cells with ipsilaterally projecting axons that we have observed are substantially higher than those reported in a previous study (Clarke and Cowan, '76) in which it was also suggested the both classes of cells were effectively eliminated between the 13th and 17th days of incubation. The observed differences are attributable to the greater sensitivity of the WGA‐HRP method when used with the chromogen tetramethyl benzidine. It is now clear that although cells in the ION with aberrantly projecting axons (or axon collaterals) may be selected against during the later stages of development, the fate of the ectopic ION neurons is not significantly different from that of the cells in the ION itself, but since they lie outside the nucleus their dendritic processes are not subject t

ISSN:0092-7317    

DOI:10.1002/cne.902120407

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe spiny collaterals of the Mauthner axon were reinvestigated in the tench (Tinea tineaL.) with the electron microscope and special staining procedures. These collaterals, as demonstrated by intraaxonal labelling with lucifer yellow, are more or less regularly spaced (100–300 μm) and make synaptic contacts with processes of spinal motoneurons and interneurons. The unrnyelinated tips of the collaterals are further characterized by the following structural features: (1) an electron‐dense undercoating of the axolemma, (2) a positive Prussian blue reaction of the inner surface of the axolemma following ferric ion‐ferrocyanide staining (Waxman and Quick, '78a), (3) expanded extracellular spaces which react specifically to inorganic phosphate, metallic ions, and diaminobenzidine. All these properties are known to be shared by the axolemma of central and peripheral nodes of Ranvier. Previous studies from this laboratory have shown that the nerve impulse is propagated along the Mauthner axon in a saltatory mode. Since classical nodal gaps could not be identified within the myelin sheath of this giant fiber, it is concluded on the basis of the present findings that the unrnyelinated tips of the spiny collaterals represent nodal equivalents, and thus provide the morphological substrate for the saltatory propagation of the nerve impulse along the Mauthner axon. The typical latency steps, as demonstrated in the latency plot of the longitudinal current signals (Greeff and Yasargil, '80), and the distances between the identified membrane specializations at the axon collaterals are consistent with this conc

ISSN:0092-7317    

DOI:10.1002/cne.902120408

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe normal fine structure of the deep dorsal horn (laminae IV, V, and VI) of the lumbosacral spinal cords of adult Macaque monkeys was examined. Axonal profiles with rounded synaptic vesicles (R) constitute about one‐fourth of the total synaptic population in lamina IV and gradually increase in number to comprise more than a third of the synaptic population in lamina VI. Conversely, profiles with flattened vesicles (F) make up two‐thirds of the synaptic population in lamina IV and slightly more than half in lamina VI. Axons which form the central profile (C) of synaptic glomeruli are more common in laminae IV and V than in lamina VI, and constitute about 5% of the total synaptic population. Profiles with large granular vesicles (LGV) are relatively uncommon in all the deep laminae.The vast majority of synaptic contacts are axodendritic. Axoaxonal synapses are formed between F, and R or C profiles, the F profile being the presynaptic component.It is concluded that there are both light and electron microscopic morphological differences among the deep laminae, as well as between the deep laminae and the superficial laminae of the spinal cord. Therefore, it appears that Rexed's original schema for laminar organization of the dorsal horn in the cat is also applicable to that of the monkey. In view of the relative paucity of LGV profiles in the deep dorsal horn, it is suggested that synapses in these laminae which contain monoamines or peptides are more likely to be associated with clear synaptic vesicles than granular synaptic vesic

ISSN:0092-7317    

DOI:10.1002/cne.902120409

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe projections of dorsal root axons to the deeper laminae (IV, V, and VI) of the Macaque spinal cord were examined by the use of experimentally induced degeneration following dorsal rhizotomy or by injection of dorsal root ganglia with tritiated amino acids followed by light and electron mi‐croscopic autoradiography.Following dorsal rhizotomy, neurofilamentous degeneration of synaptic profiles occurs in each of the three deep laminae, more commonly in laminae IV and V than in lamina VI. The neurofilamentous degeneration is seen both in central glomerular (C) profiles and in many of the round vesicle (R) profiles. Neurofilamentous degeneration occurs as early as 18 hours following rhizotomy and the degenerating terminals are most numerous at 3–4 days postrhizotomy. None are seen after 7 days survival. The neurofilamentous profiles form axodendritic and, occasionally, axosomatic synapses with neurons of the dorsal horn. They are also seen to be postsynaptic to flat vesicle (F) profiles in axoaxonal synapses.A second type of degeneration, electron‐lucent degeneration, is seen in laminae V and VI, and only occasionally in lamina IV. The lucent degeneration occurs somewhat later after rhizotomy than does the neurofilamentous degeneration and reaches its peak at 5 days postrhizotomy. No lucent terminals are seen after 7 days survival. Electron‐dense degeneration, so common in lamina II, is not seen in the deeper dorsal horn.Autoradiographic techniques show that both C and R terminals are labelled in the deeper dorsal horn. Both of these terminals form axodendritic synapses and a significant number are found to be postsynaptic in axoaxonal synapses.Most of the C terminals degenerate following rhizotomy or are labelled following injection of the parent dorsal root ganglia with tritiated amino acids. Approximately one‐fifth of the R profiles are derived from dorsal roots. F profiles do not appear to be of dorsal root origin in any case.It is concluded that neurofilamentous alterations represent the degeneration of larger‐diameter (Aβ) axons which distribute to the deeper dorsal horn and that electron‐lucent degeneration represents the termination of Aδ fibers. Electron‐dense degeneration thought to represent the termination of nonmyelinated axons (C fibers) in the superficial dorsal horn is not seen in the deeper dorsal horn and it is concluded that C fibers do not project to t

ISSN:0092-7317    

DOI:10.1002/cne.902120410

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902120411

出版商:Alan R. Liss, Inc.    

年代:1982

数据来源: WILEY