Using simulated patients to teach family practice residents to manage patients by telephone.
Explore the source record for details and available documents.
Family Practice↗
Biomedical subjects
R C Dunn
Publications and source records attributed to R C Dunn.
A morphometric study of the effects of maturation and aging on synaptic patterns in the spinal trigeminal nucleus of the cat.
Morphometric methods have been used to study the synaptic and terminal patterns in cat trigeminal nucleus, pars interpolaris, during development and aging. Ages 1, 3, 6, 11, 16, 21, 27, 110, 600 days and 8 and 11 years were studied. Both proportions and densities (number per unit area) of certain terminals and synapses showed significant changes with age. Axoaxonic synapses especially showed two major periods of increase (3-6 days and 21-27 days). The values of most parameters increased in the 21-27 day period to peak levels and then decreased gradually with age. The results indicate two separate critical synaptogenic periods of development and a loss of synaptic elements in aging. Factors contributing to these changes are discussed as is the potential for plasticity in the different afferents at each period.
Age Factors↗
The postnatal development of corticotrigeminal projections in the cat.
The postnatal development of corticotrigeminal projections was studied in kittens following 3H-amino acid injections into the face area of the primary somatosensory cortex. Corticofugal axons grow into the brainstem and form the pyramidal tract prenatally. Corticotrigeminal projections begin to develop at the end of the first postnatal week. The earliest corticotrigeminal axons grow out of the pyramidal tract caudally and project into laminae III-V of the spinal trigeminal (Vs) nucleus caudalis. During the second postnatal week, corticotrigeminal axons grow out of the pyramidal tract in a caudal to rostral sequence and project up to the ventromedial borders of Vs-interpolaris, Vs-oralis, and to the principal trigeminal nucleus. Corticotrigeminal axons pause at the periphery of these nuclei for 1-2 days before penetrating the trigeminal neuropil and forming terminal arborizations in a centripetal direction. Coincident with the development of cortical projections to the principal trigeminal nucleus, some of the labeled axons which were in lamina III of Vs-caudalis project into lamina I and terminate. This sequence of development of corticotrigeminal projections closely parallels, albeit at a later time, the sequence of formation of the trigeminal nuclei, suggesting that the temporal sequence of cytogenesis of trigeminal neurons may be a factor which regulates their order of innervation by afferents. Corticotrigeminal projections develop bilaterally and, during the second postnatal week, are relatively equal in density in the ipsilateral and contralateral nuclei. Many of the ipsilateral corticotrigeminal projections are lost, however, after the second postnatal week, so that by the fourth postnatal week, corticotrigeminal projections are mainly contralateral and adultlike in their distribution. It remains to be determined whether the transience of ipsilateral corticotrigeminal projections is due to selective elimination of axon collaterals or to neuronal death.
Animals↗
The corticotrigeminal projection in the cat. A study of the organization of cortical projections to the spinal trigeminal nucleus.
The projection from the cerebral cortex to the spinal trigeminal nucleus has been studied light microscopically in adult cats. Both orthograde degeneration and orthograde intra-axonal labeling techniques have been applied. Our results indicate that the projection from the coronal gyrus (face area of primary somatosensory cortex) to the spinal trigeminal complex is somatotopically organized. In subnucleus caudalis this somatotopy is organized dorsoventrally and appears to match the somatotopic distribution of the divisional trigeminal afferents. Hence cortical fibers originating from the posterior coronal gyrus (upper representation) project ventrolaterally into caudalis where division I trigeminal afferents terminate. Likewise cortical fibers from the anterior coronal gyrus (jaw and tongue representation) terminate dorsomedially in caudalis to overlap with division III trigeminal afferents. In contrast, the distribution of corticofugal afferents to the rostral spinal trigeminal subnuclei (pars interpolaris and oralis) is organized mediolaterally. Therefore in these subnuclei the cortical projection does not appear to overlap the dorsoventral lamination of the divisional trigeminal afferents. In addition, our results suggest that the cortical projection to subnucleus caudalis includes fibers which terminate in the marginal zone (lamina I) and its extensions into the spinal trigeminal tract (the interstitial cells of Cajal). We have been unable to document a projection from the proreate gyrus to the spinal trigeminal complex.
Animals↗
Sensorimotor cortical projections to the marginal zone of the trigeminal subnucleus caudalis.
An ultrastructural investigation of the marginal zone (lamina I) of the spinal trigeminal subnucleus caudalis was carried out in 7 adult cats at 30 h through 7 days after ablations of face area of the contralateral sensorimotor cortex. Corticofugal boutons were observed to undergo electron-dense degeneration in the marginal zone beginning 4 days after the cortical lesion. These boutons were small (1--2 micrometers), widely dispersed and made synaptic contacts onto small dendrites or dendritic spines. These new observations indicate that cortical inhibition and facilitation of ascending orofacial sensation may be mediated in part by a direct pathway to the marginal zone.
Animals↗
Surgical decompression after cerebral hemispheric stroke: indications and patient selection.
Decompressive craniotomy has a place in acute hemispheric infarctions. Patient selection should be guided by CT to exclude those with huge dominant hemispheric lesions that make reasonable neurologic recovery unattainable. Intracranial pressure monitoring should reduce the severity of neurologic sequelae by providing earlier, more timely operative intervention.
Brain Edema↗
Anterior encephalocele.
Eighteen cases of anterior encephalocele treated at the University of Malaya Hospital between 1970 and 1980 are discussed, and the literature concerning this defect is reviewed. A detailed analysis of the microscopic abnormalities present in the surgical specimens is included, along with the relevant radiographic and demographic data. Anterior encephalocele is more common in Southeast Asia than elsewhere. The possible ethnographic and geographic implications are presented, as well as a discussion of the relevant embryology, in attempting to define possible etiologies for this malformation. The author's surgical approach to the repair of this defect and reasons for preferring a transcranial, intradural approach are described. Potential complications are enumerated.
Adult↗
Unusual CT-dense posterior fossa epidermoid cyst: case report.
Explore the source record for details and available documents.
Adolescent↗
Spinal epidural neoplasia. A 15-year review of the results of surgical therapy.
The outcome following decompressive laminectomy and spinal irradiation has been evaluated in 104 consecutive patients with epidural metastatic neoplasia, using broad criteria for successful outcome. Of patients so treated, 33% were benefited, while 23% became worse. Both tumor histology and the preoperative neurological status were important factors in determining the response to this therapy. The authors review the surgical and radiotherapeutic literature in the treatment of this condition, and conclude that there is no clearly established superiority of laminectomy followed by irradiation over radiotherapy alone. Specific indications for surgery exist if prior histological confirmation of malignancy is lacking, if there is neurological deterioration during radiotherapy, or if there are recurrent symptoms referable to a previously irradiated metastasis. Surgery is also indicated if facilities for prompt administration of radiotherapy are unavailable.
Aged↗
Intracerebral hemorrhage and acute hypertension.
Explore the source record for details and available documents.
Acute Disease↗
Synapse development within the spinal trigeminal nucleus.
Pars interpolaris of the spinal trigeminal nucleus of kittens has been studied with the electron microscope at birth and at several subsequent ages during the first month of life. Attention has been given to ultrastructural maturational changes that occur in this neuropil, especially events in synaptogenesis. The results of this investigation include the following observations: (1) the neuropil, even at the earliest ages studied (three-hour-old kittens), is strikingly mature, necessitating a quantitative assessment in order to determine subtle developmental changes in synaptic patterns; (2) the number of axoaxonic contacts at birth are few, and their emergence is essentially a postnatal phenomenon; (3) it appears that the immature Gray type II or symmetrical synapse possesses distinct cleft material and dense, parallel membrane specializations. Synaptic vesicle accumulation at this contact appears to occur after the membrane specializations have formed. A previous study by Kerr26 has shown a reduced potential for primary afferent reorganization with the spinal trigeminal nucleus when kittens are subjected to trigeminal rhizotomy after three days of age. Our observations on the development of axoaxonic synaptic arrangements in the neonatal period may provide an explanation for these earlier results.
Age Factors↗
Axoaxonic synaptogenesis in neonatal kitten spinal trigeminal nucleus.
Explore the source record for details and available documents.
Age Factors↗
Calcium regulation of nuclear pore permeability.
The nuclear envelope is an integral part of the structural framework of the nucleus, and is involved in organizing intranuclear events. It serves as a selective barrier, actively transporting proteins required for normal nuclear function and exporting RNA. The movement of molecules across the nuclear envelope is critical for cellular homeostasis, and it allows cells to respond to external events. The only known pathway for direct communication between the cytoplasm and the nucleoplasm of a cell is through the nuclear pore complex. In the past decade, rapid advances have been made in elucidating the structure and function of the nuclear pore complex. Yet, researchers are just beginning to identify some of the regulatory mechanisms controlling transport through the pore complex. The nucleus is surrounded by a Ca2+ storage compartment, which sequesters and releases Ca2+ in response to intracellular second messengers, Recent evidence suggests that the nuclear Ca2+ store may indirectly regulate passive diffusion through the nuclear pore complex. The evidence for Ca2+ regulation of the nuclear pore complex will be discussed, along with the introduction of the simplest, testable model to describe the observations.
Animals↗
Low-density lipoproteins inhibit endothelium-dependent relaxation in rabbit aorta.
The vascular endothelium, in response to pulsatile flow and vasoactive agents including acetylcholine, secretes the endothelium-derived relaxing factor (EDRF), a substance which regulates vascular tone. Recent interest in EDRF has focused on its possible dysfunction in atherosclerosis. In animal models of the disease, endothelium-dependent relaxation is markedly reduced. The continuous exposure of the endothelium in hyperlipidaemia to high concentrations of low-density lipoprotein (LDL), a known atherogenic risk factor, may explain this dysfunction. Here, we demonstrate that pathophysiological concentrations of LDL directly inhibit endothelium-dependent relaxation. Chemically modified LDL, in contrast, is inactive, implying that the inhibition is through a receptor-dependent mechanism.
Acetylcholine↗
Domain formation in thin lipid films probed with near-field scanning optical microscopy.
High-resolution near-field scanning optical microscopy (NSOM) fluorescence and topographic images of L-alpha-dipalmitoylphosphatidylcholine (DPPC) monolayers doped with a fluorescent dye are presented. DPPC monolayers are deposited onto mica substrates from the air-water interface at several surface pressures using the Langmuir-Blodgett technique. Sub-diffraction limit phase domain structures are observed in both fluorescence and topographic NSOM images of the lipid films. The morphology of the resulting monolayers depends strongly on the surface pressure and composition of the subphase used in the film transfer. Mechanisms for lipid domain formation and growth are discussed.
1,2-Dipalmitoylphosphatidylcholine↗
Near-field scanning optical microscopy studies of L-alpha-dipalmitoylphosphatidylcholine monolayers at the air-liquid interface.
The phase structure in L-alpha-dipalmitoylphosphatidylcholine-20 mol% fluorescent 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate Langmuir monolayers dispersed on a 2 M sucrose solution subphase is studied with near-field scanning optical microscopy (NSOM). Cantilevered NSOM probes operating in a tapping-mode feedback or an optical interferometric feedback mode are capable of tracking the air-sucrose solution interface. At the micrometre scale, the NSOM fluorescence images reveal lipid domain features similar to those observed previously in supported Langmuir-Blodgett (LB) monolayers. At the submicrometre scale, the small nanometric lipid islands seen in LB films are not observed at the air-sucrose interface. This supports a mechanism in which domain formation in LB films can be induced by means of the transfer process onto the solid support. Progress towards extending these studies to films at the air-water interface using the optical interferometric feedback method is also discussed.
1,2-Dipalmitoylphosphatidylcholine↗