Biomedical subjects

D K Ryugo

Publications and source records attributed to D K Ryugo.

At least 55 records · Page 3Linked to original sources

PubMed1987

Hair cell innervation by spiral ganglion neurons in the mouse.

Horseradish peroxidase (HRP) was injected extracellularly into the auditory nerve of adult mice so that the enzyme could infuse individual spiral ganglion neurons. Forty-two well-stained neurons were reconstructed through serial sections from their cell bodies to peripheral terminations in the organ of Corti with the aid of a light microscope and drawing tube. No neuron was observed to innervate both inner and outer hair cells (IHCs and OHCs). Previous observations from neonatal mammals that reported that IHCs and OHCs were innervated by the same neuron are thus presumed to describe a transient developmental phenomenon. Two populations of spiral ganglion neurons were determined on the basis of the differences in receptor innervation. The type I neurons innervated exclusively IHCs by way of thick (1-2 microns) radial fibers, whereas the type II neurons innervated only OHCs by way of thin (approximately 0.5 micron) outer spiral fibers. Certain features of the peripheral process in the vicinity of the cell body were highly correlated with fiber type. This pattern of separate innervation of IHCs and OHCs by type I and type II neurons, respectively, may represent the general plan of afferent organization for the adult mammalian cochlea.

Animals↗

PubMed1986

A monoclonal antibody labels type II neurons of the spiral ganglion.

Tissue from mature rat and cat cochleas was stained with basic dyes in order to distinguish between the cell bodies of type I and II spiral ganglion neurons. This same tissue was then stained with protargol, or processed immunocytochemically using a monoclonal neurofilament antibody, RT-97. Type II neurons were intensely stained, whereas type I neurons were not. We conclude that type II neurons can be clearly distinguished by their abundant neurofilament content.

Animals↗

PubMed1986

The central projections of intracellularly labeled auditory nerve fibers in cats: an analysis of terminal morphology.

The axons of physiologically characterized spiral ganglion neurons (type I) were stained throughout their arborizations in the cochlear nucleus by the intracellular injection of horseradish peroxidase (HRP). The tips of the axonal branches were marked by distinct swellings, ranging in size and shape from small boutons to large perisomatic ramifications. Electron microscopic analysis of such swellings revealed ultrastructural features characteristic of primary auditory synapses, consistent with the hypothesis that terminal swellings identifiable in the light microscope represent presynaptic endings. On the basis of light microscopic differences in size, these endings were organized into three categories. Endings of relatively small size (terminal boutons, free endings, boutons with filopodia, string endings, and small complex endings) composed 94% of all terminal endings. Within this category of small endings, there were predictable variations in relative size and regional distribution that related to the spontaneous discharge rate (SR) of the fiber. The endings of low and medium SR fibers (SR less than or equal to 18 spikes/second) were smaller on average than those of high SR fibers (SR greater than 18 spikes/second). Furthermore, there were more endings arising from the ascending branch than from the descending branch when comparing fibers of the low and medium SR group with those of the high SR group. There were not, however, obvious morphological features of this ending category that correlated with the characteristic frequency (CF, the pure tone frequency to which the neuron is most sensitive). A second category contained medium-sized complex endings, most of which formed axosomatic contacts. This category composed 4% of the population and was found in close proximity to the perikarya of globular, octopus, and spherical cells. The endings from low and medium SR fibers were smaller on average than those from high SR fibers. These endings did not vary in their parent branch distribution with respect to fiber SR, nor did they exhibit morphological features that correlated with fiber CF. The third category contained large complex endings (endbulbs of Held) and composed 2% of the ending population. Within the anteroventral cochlear nucleus, these large, complex endings made axosomatic contact with spherical cells in the anterior division and with globular cells in the posterior division. There were no systematic variations in ending size or branch distribution that correlated with fiber SR. There was, however, a relationship between ending size and fiber CF such that fibers having CFs below 4 kHz gave rise to the largest endbulbs.

Action Potentials↗

PubMed1985

The dorsal cochlear nucleus of the mouse: a light microscopic analysis of neurons that project to the inferior colliculus.

In the mouse dorsal cochlear nucleus (DCN), all members of a distinct class of large multipolar neurons were shown to project to the contralateral inferior colliculus by using retrograde horseradish peroxidase techniques. Typically, these multipolar neurons have the largest cell bodies in the nucleus and are distributed in layers II, III, and IV. Each contains a round, pale nucleus with a prominent nucleolus and conspicuous Nissl bodies. In Golgi preparations, however, two types of large cells could be distinguished on the basis of dendritic characteristics. Pyramidal cells form relatively flattened, slablike dendritic fields whose alignment contributes to the laminar organization of the DCN. They represent 75-80% of the large cell population and are found in layer II and the superficial region of layer III. Giant cells represent the other type of large multipolar neuron and are distributed in the deeper regions of layer III and in layer IV. Their ellipsoidal dendritic fields are formed by long and relatively unbranched dendrites that project across the laminae. The differences in dendritic morphology imply that each cell class segregates its afferent input in distinct ways and subserves different auditory functions.

Animals↗

PubMed1985

Progress in low-LET heavy particle therapy: intracranial and paracranial tumors and uveal melanomas.

The Harvard Cyclotron Laboratory in collaboration with the Department of Radiation Medicine of the Massachusetts General Hospital and the Retina Service of the Massachusetts Eye and Ear Infirmary provides low-LET heavy particle therapy with 160 MeV protons. The improved dose distribution of protons results from their physical characteristics. A total of 965 patients have been treated as of December 31, 1984. Dose is expressed in units of cobalt gray equivalent (CGE) which is the dose in Gy multiplied by the RBE (1.1) for modulated protons relative to 60Co radiation. Sixty-seven patients with chordomas or low-grade chondrosarcomas of the base of skull or cervical spine have received proton treatment. Forty-three of these patients have been followed for at least 8 months with a median follow-up of 27 months. The median dose is 69 CGE. The 3-year actuarial local control rate is 89%. Seven patients with gliomas, eight with craniopharyngiomas, and six with meningiomas have also received proton radiation treatments. A total of 615 patients with uveal melanomas have received a median dose of 70 CGE in five fractions. Tumor regression has been seen in 94% with 66% having vision of 20/100 or better.

Actuarial Analysis↗

PubMed1984

The central projections of intracellularly labeled auditory nerve fibers in cats.

The central projections of physiologically characterized auditory nerve fibers were studied in the cochlear nuclei of adult cats after intracellular staining with horseradish peroxidase (HRP). This technique consistently labels only the type I spiral ganglion neurons which contact inner hair cells in the cochlea (Liberman and Oliver, '84). The central axon of each type I neuron bifurcates in the cochlear nucleus to form an ascending branch and a descending branch. The characteristic frequency (CF) of a fiber corresponds to the dorsoventral position of these major branches and their collateral ramifications within the nucleus. Fibers of low CFs are distributed ventrally, and fibers of increasing CF are distributed progressively more dorsally. In some cases, the collateral branches deviate from this tonotopic arrangement, particularly in (1) the octopus cell region of the posteroventral cochlear nucleus, (2) the zone of bifurcations of the auditory nerve fibers, and (3) the anterior, dorsal, and lateral margins of the ventral cochlear nucleus. Spontaneous discharge rate (SR) is related to the complexity of the axon arbor, especially along the ascending branch. Fibers of low and medium SR exhibit more axonal branch points and longer collateral lengths than do those with high SR. Six of 37 labeled fibers fail to innervate the dorsal cochlear nucleus, a feature apparently unrelated to CF or SR.

Afferent Pathways↗

PubMed1984

Intracellular marking of physiologically characterized cells in the ventral cochlear nucleus of the cat.

In the cat ventral cochlear nucleus, separate neuronal classes have been defined based on morphological characteristics; physiologically defined unit types have also been described based on the shape of post-stimulus-time-histograms in response to tone bursts at characteristic frequency. The aim of the present study was to address directly the issue of how morphological cell types relate to physiological unit types. We used intracellular injections of horseradish peroxidase to stain individual neurons after their response characteristics were determined by intracellular recordings. The maintenance of a continuous negative resting potential, the correspondence of the calculated position of the electrode tip at the time of injection to the location of the stained neuron, and the similarity of response properties collected before and after the injection provide evidence that the injected, stained, and recovered neuron corresponds to the functionally defined unit. In the region around the nerve root in the anteroventral cochlear nucleus, two " primarylike " and one " primarylike with notch" units were "bushy" cells. "Bushy" cells are characterized by primary dendrites arising from one hemisphere of the soma and ramifying repeatedly to produce their bushy dendritic arbor. In this same region, the "chopper" and two "on" units were also "bushy" cells. In the posteroventral cochlear nucleus, the "chopper" unit was a "stellate" cell and the "on" unit was an "octopus" cell. These results are partially consistent with previous conclusions based on correlations established between the regional distribution of physiological unit types and morphological cell types. More importantly, they confirm and extend recent intracellular marking data (Rhode et al., ' 83b ). If our classification schemes have functional significance, we are left with the conclusion that the distinction between "bushy" and "stellate" cells in the auditory nerve root region of the ventral cochlear nucleus does not correspond in any simple way to distinctions between physiological unit types. More than one morphological cell type can exhibit the same particular response patter, and the same morphological cell type can exhibit several different response patterns.

Animals↗

PubMed1984

Effects of sensory deprivation on the developing mouse olfactory system: a light and electron microscopic, morphometric analysis.

Closure of the nostril by electrocauterization on postnatal day (PN) 1 or 2 was used to study effects of olfactory deprivation on developing olfactory epithelium (OE) and bulb (OB) in CD-1 mice. No damage was observed in OE sections 1 or 3 days after closure, and at PN 30 no difference was found in the number of OE receptors between closed and open sides. Odor deprivation and a decrease in functional activity in experimental bulbs was evident from deoxyglucose autoradiographs at PN 21 and PN 30. At PN 30 deprived bulbs appeared smaller than nondeprived bulbs. Nissl stains revealed normal cytoarchitecture, but a protargol stain demonstrated fewer intraglomerular dendrites in deprived bulbs. At PN 30, volumes of deprived bulbs were 26% smaller than nondeprived bulbs. The volume of each bulbar lamina was 13 to 35% smaller than the comparable nondeprived lamina except for the ventricular/subependymal zone which was not significantly different between bulbs. Volumes of bulbs contralateral to the closed naris and the volumes of their laminae were not significantly different from control bulbs, suggesting no hypertrophy of nondeprived laminae. Deprivation did not affect the number of mitral cells seen at PN 30, their nuclear size, or their number of nucleoli. Lateral olfactory tract cross-sectional area was also unaffected by deprivation. Mitral cell perikaryal size, however, was smaller in deprived bulbs. Soma surface areal density of deprived mitral-to-granule cell synapses in deprived bulbs was 65% of the nondeprived density, while the density of granule-to-mitral cell synapses was only 46% of the nondeprived density. It is concluded that neonatal naris closure brings about a functional deprivation of the OB without receptor degeneration. Neonatal olfactory deprivation affects the perikaryal surface area but not the number of mitral cells. Also, deprivation markedly affects the reciprocal synapses between mitral and granule cells. Olfactory sensation thus appears necessary for normal development of OB neurons and synapses.

Animals↗

PubMed1982

Morphology of primary axosomatic endings in the anteroventral cochlear nucleus of the cat: a study of the endbulbs of Held.

The central axons of Type I spiral ganglion neurons travel in the auditory nerve and terminate in the cochlear nucleus. The ascending branches of these axons innervate the anteroventral cochlear nucleus and give rise to large axosomatic endings, called the endbulbs of Held, and smaller boutons. This paper reports a study of the endbulbs of Held, stained by horseradish peroxidase and variants of the Golgi method in kittens 2, 5, 10, 20, and 45 days postnatal and adult cats. Endbulbs tend to fall into two extreme groups with some endbulbs having an intermediate appearance; consequently, we have defined three descriptive stages of endbulbs that are conceived of as representing a developmental sequence. One group of endbulbs is found mostly in kittens younger than 10 days postnatal and is similar to the classic description of endbulbs by Ramón y Cajal ('09). The other extreme group of endbulbs is found mostly in adult cats. In these cases, the parent axonal trunk divides into several thick, gnarled branches that in turn branch again, sometimes repeatedly. These branches display irregular varicosities and form a cup-shaped arborization into which the postsynaptic cell body nestles. A chronology of postnatal endbulb development has been inferred from the relative proportions of the different endbulb stages at various ages. Maturation transforms the endbulb of Held from a large, spoon-shaped swelling having many filipodia into an elaborate tree with broad trunks and many smaller branches. Some implications of the proposed development sequence are discussed.

Aging↗

PubMed1982

Hair-cell innervation by spiral ganglion cells in adult cats.

A horseradish peroxidase technique was used to trace the peripheral terminations of two types of ganglion cells in adult cats. It was found that large, usually bipolar ganglion cells end on inner hair cells and small, usually pseudomonopolar ganglion cells end on outer hair cells. Thus, a virtually complete segregation of afferent neural inputs from the two types of hair cells was directly confirmed.

Animals↗

PubMed1981

Differential afferent projections to the inferior colliculus from the cochlear nucleus in the albino mouse.

The axonal projections from the cochlear nuclear complex to the inferior colliculus (IC) were examined using the retrograde transport of horseradish peroxidase. Thin sheets of neurons in the dorsal and ventral cochlear nuclei were found to project axons in a topographic fashion to restricted laminae of the central nucleus of the IC; the dorsal cochlear nucleus was also found to project axons to the external cortex. No projections were detected from the cochlear nuclear complex to the dorsal cortex of the IC.

Afferent Pathways↗

PubMed1978