Biomedical subjects

F H Willard

Publications and source records attributed to F H Willard.

8 recordsLinked to original sources

PubMed1999

Distribution of unipolar brush cells and other calretinin immunoreactive components in the mammalian cerebellar cortex.

We have compared the distribution of unipolar brush cells (UBCs) in the cerebellum of Brazilian opossum (Monodelphis domestica), mouse, guinea pig, rabbit, cat, and Rhesus monkey, using an antiserum to calretinin which is present in those cells. The morphology and calretinin staining intensity of the UBCs remains constant across species. As a general trend, in all species studied, UBCs are particularly enriched in the vestibulocerebellum. Interspecies differences, however, were noted in the distribution of UBCs across other regions of the cerebellar cortex. A major variation involves the extent of the UBC-rich region of the ventral portion of the paraflocculus. The distribution of UBCs in non-vestibular vermal folia also varies substantially. UBCs are deployed in more or less distinct parasagittal zones in the vermis of the opossum, rabbit, cat, and macaque. The density of UBCs decreases progressively from medial to lateral portions of the same folium and is lowest in the lateral, posterior portions of the cerebellar hemispheres (crus II) and in the dorsal portion of the paraflocculus. In cat and macaque, the decrease in the density of UBCs across the intermediate cortex is more gradual than in the other species. The data indicate that the UBCs play a more prominent role in the modulation of sensorimotor transformations in carnivores and primates than in smaller mammals and should not be considered a vestigial form of neuron. In addition to the UBCs, calretinin antibody distinctly stains the following neurons in different species: granule cells and parallel fibers in all species except rabbit and cat; Golgi cells, especially in rat and macaque; Lugaro-like cells, especially in mouse, rat, and macaque; basket cells in macaque; subsets of mossy fibers in all species; and subsets of climbing fibers in all species but guinea pig. Usually, the distribution of UBCs is related to that of calretinin stained granule cells and mossy fibers.

Animals↗

PubMed1986

The development and migration of large multipolar neurons into the cochlear nucleus of the North American opossum.

We have studied the maturation of the inferior colliculus and cochlear nuclei of the North American opossum with particular emphasis on the large multipolar neurons of the cochlear nucleus. These neurons include the principal and giant cells of the dorsal cochlear nucleus (DCN) and the large neurons of the ventral cochlear nucleus (VCN), all of which can be labelled by horseradish peroxidase (HRP) injections into the contralateral inferior colliculus (IC). The size of these neurons, their characteristic Nissl patterns, and their labelling density after injections into the IC render them distinguishable from other neurons in this nuclei, even in young animals. In Nissl-stained sections of newborn opossums, a band of horizontally oriented neurons can be identified dorsomedial to the vestibular nerve root. This band extends from an apparent cytogenetic zone close to the sulcus limitans, to, but not within, the presumptive cochlear nucleus. Between birth and estimated postnatal day 22 (EPND 22) the band shifts laterally, eventually becoming incorporated into the cochlear nucleus. Many neurons in this band have perinuclear caps of Nissl substance similar to those present in the principal cells of the adult DCN. Injections of HRP into the IC as early as EPND 5 (17 days after conception) labelled neurons in the band referred to above but not in the presumptive cochlear nucleus. By EPND 15, labelled cells were clustered mainly within the nucleus proper. Most of these cells were located in the DCN, but a few were scattered in the dorsocentral VCN. Consistent labelling of small neurons in VCN was not obtained until sometime later. From EPND 15 to EPND 20 most of the labelled cells in DCN reoriented in the vertical plane, aligned in layer II, and differentiated into principal neurons. Some, however, remained deep to layer II and differentiated into giant neurons. The heavily labelled cells in VCN differentiated into large neurons. Our results suggest that the large multipolar neurons of the nucleus are generated in a cytogenetic zone medial to the rhombic lip and that they subsequently migrate laterally, in a band, to reach their adult locations in the nucleus. It is during this migratory stage that their axons reach the inferior colliculus.

Animals↗

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↗

PubMed1984

Collateral innervation of the inferior colliculus in the North American opossum: a study using fluorescent markers in a double-labeling paradigm.

The innervation of the opossum inferior colliculus was investigated using the retrograde transport of fluorescent markers in a double-labeling paradigm. True Blue was injected into one inferior colliculus while Nuclear Yellow was placed into the other. Many single-labeled neurons were found in all of the brainstem and cortical areas previously labeled by comparable injections of HRP. When the two injections of fluorescent markers were bilaterally symmetrical within the inferior colliculi, double-labeled neurons were numerous in the medial and lateral superior olivary nuclei. Only a few double-labeled neurons were found in the auditory cortex (AC), the dorsal nucleus of the lateral lemniscus (DNLL), the nucleus reticularis gigantocellularis pars ventralis (RGcv), and the dorsal column nuclei (DColN) and the spinal trigeminal complex (TrS). These data suggest that two patterns of innervation are seen for afferent fibers from regions with bilateral connections to the IC. The first pattern, typified by projections from AC, DNLL, RGcv, the DColN and TrS, primarily consists of neurons with unilaterally directed axons, extending to either the ipsilateral or contralateral IC. The second pattern, typified by projections from LSO and MSO, displays a great number of neurons whose axons apparently innervate both inferior colliculi, presumably through a process of axon collateralization. The bilateral projection of axons from individual neurons in these two nuclei possibly reflects their involvement in the processing of sensory information from the two cochleas and may represent at least one pathway whereby binaural information is relayed to both inferior colliculi.

Animals↗

PubMed1984

The neuronal types and the distribution of 5-hydroxytryptamine and enkephalin-like immunoreactive fibers in the dorsal cochlear nucleus of the North American opossum.

The opossum dorsal cochlear nucleus is divided into four layers distinguishable either on the basis of differential distribution of neuron types or by neuropil organization. We have used Nissl, Golgi and protargol stained preparations to examine these components. Four types of neurons (excluding granule cells) are seen. The principal neurons have large cell bodies arranged in a sheet defining layer II, their apical dendrites extend dorsally to form an elaborate arbor in layer I and their basal dendrites pass ventrally into layer III. Round cells are found throughout layers I and II. Their densely packed dendritic domains feature thick spine encrusted dendrites that have many recurrent branches. Giant neurons have large perikarya scattered throughout layers III and IV and long thick dendrites that radiate throughout the nucleus. Small multipolar neurons (stellate cells) are found throughout the nucleus. The more superficial ones have small perikarya whereas those found in deeper layers tend to be large. All four layers of the nucleus may be clearly differentiated in protargol stained sections. Layer I has small, thin fibers in parallel array, layer II has a mixture of fibers with an apparent random orientation, layer III has large diameter vertically oriented fibers, and layer IV has fibers of similar diameter but deposed horizontally. Immunohistochemical techniques have been used to identify specific fiber systems in the neuropil of the dorsal cochlear nucleus. Fibers containing 5-hydroxytryptamine (5-HT) immunoreactivity were prevalent in layers I, III and IV but sparse in layer II. Fibers containing enkephalin (ENK)-immunoreactivity were prevalent in layer I and II with only a few scattered fibers in the deeper layers. Isolated clusters of 5-HT and ENK immunoreactive fibers in layer II were found around principal neuron somata; similar clusters in the deep layers were located around the somata of giant neurons. The wide distribution of 5-HT immunoreactive fibers suggests they may be involved in a general regulation of activity in this nucleus; conversely the more circumscribed distribution of ENK immunoreactive fibers would suggest a restricted involvement of this fiber system with a specific feature of information processing.

Animals↗

PubMed1983

The auditory brainstem nuclei and some of their projections to the inferior colliculus in the North American opossum.

Afferent projections to the inferior colliculus in the North American opossum have been examined using the retrograde transport of horseradish peroxidase. Projections to primarily the contralateral inferior colliculus arise in the dorsal and ventral cochlear nuclei, the auditory nerve nucleus and the spinal trigeminal nucleus pars caudalis, while ipsilateral projections arise in the superior paraolivary nucleus, the ventral nucleus of the trapezoid body, the ventral nucleus of the lateral lemniscus, the paralemniscal nucleus, the deep layer of the superior colliculus and the parabrachial nucleus. Bilateral projections to the inferior colliculus originate within the dorsal column nuclei, the nucleus reticularis gigantocellularis pars ventralis, the lateral and medial superior olivary nuclei, the dorsal nucleus of the lateral lemniscus and the auditory cortex. Nissl, fiber and Golgi-stained preparations were used to study the neuronal organization of those auditory nuclei with projections to the inferior colliculus. Anterograde axonal degeneration and transport techniques revealed that the inferior colliculus is innervated differentially by the dorsal and ventral cochlear nucleus, the superior olivary complex and the auditory neocortex. Axons from the contralateral dorsal cochlear nucleus and the ipsilateral superior olivary complex innervate both the central nucleus and external cortex, whereas those from ventral cochlear nucleus and contralateral, superior olivary complex project to only the central nucleus. Projections from auditory cortex form the complement of those from the cochlear nuclei and superior olivary complex, that is, they terminate in a thin band overlying the dorsal cortex and the superficial layer of external cortex. Our results have been compared with those obtained from eutherian mammals and it is clear that there are striking similarities in neuronal organization and connectivity. Since the opossum is born 12 days after conception and has an extended development in an external pouch, it may be suited for developmental studies of the mammalian auditory connections and the behaviors dependent of them.

Aging↗

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↗

PubMedDate not supplied

Osteopathic medicine.

Osteopathic physicians are licensed physicians practicing in all 50 states. This article describes the philosophy of Osteopathic Medicine and reviews the objective support for it. Special emphasis is placed on somatic, visceral, and psychologic interaction. Specific examples of Osteopathic Manipulative Therapy (OMT) are also described.

Humans↗