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Biomedical subjects

R E Foster

Publications and source records attributed to R E Foster.

At least 55 records · Page 3Linked to original sources
PubMed1989

HIV screening and counseling for intravenous drug abuse patients. Staff and patient attitudes.

At least one third of patients enrolled in a methadone maintenance treatment program are willing to comply voluntarily with screening for and counseling about human immunodeficiency virus (HIV). A questionnaire about knowledge, attitudes, and behavior concerning acquired immunodeficiency syndrome was answered anonymously by 79% (46) of the clinical staff and 67% (868) of the enrolled patients. On their own initiative, 21% of the patients had already received voluntary anonymous HIV screening and brief counseling, seldom discussing the result with the staff. Approximately 90% of the staff and a majority of the patients (72%) thought a voluntary HIV screening program should be offered to all patients. Almost all staff (98%), but only 50% of the patients, felt the HIV test results should be known to physicians, nurses, and counselors at the clinic. Few staff members (15%) believed that patients had changed their sex behavior; more (48%) felt that needle sharing was reduced. Patients believed methadone patients in general had changed their sex behavior (49.2%) and reduced needle sharing (62%) to prevent becoming infected. Patients reported statistically significant reductions both in number of sex partners and in personal needle sharing during the past year.

Adult↗
PubMed1987

Age-related responses to influenza vaccination in the Newcastle region during 1983 and 1984.

A study was carried out in Newcastle to assess responses to influenza vaccines in elderly nursing home patients and in younger adults during 1983 and 1984. The decision to vaccinate the elderly subjects was made by their general practitioners. A concurrent randomized placebo-controlled trial of the same vaccine was performed in young adult volunteers. Elderly subjects generally possessed higher levels of pre-existing antibody to the influenzal haemagglutinins that were present in the vaccines than did younger subjects. The highest levels were observed in the 52-63 years' age group. Younger subjects showed significantly greater responses to vaccines compared with elderly subjects (P less than 0.05). Peak responses were noted in the 16-24 years' age group. Of a total of 326 elderly subjects (70% of whom had been vaccinated), six participants, two of whom had been vaccinated, contracted laboratory-proven influenza during 1983. Only one unvaccinated subject of a total of 365 subjects (50% of whom had been vaccinated) contracted influenza during 1984. In both years illness was produced by strain A/Philippines/2/82.

Adolescent↗
PubMed1987

Monitoring the bioenergetics of cardiac allograft rejection using in vivo P-31 nuclear magnetic resonance spectroscopy.

Monitoring human cardiac allograft rejection is currently accomplished by endomyocardial biopsy. Available noninvasive methods for identifying rejection have lacked the necessary sensitivity or specificity, or both, for routine clinical application. In vivo phosphorus-31 (P-31) nuclear magnetic resonance (NMR) spectroscopy has been used for monitoring phosphorus metabolism in both animal models and humans. In the present study this technique was employed as a noninvasive means to assess the bioenergetic processes that occur during cardiac allograft rejection in a rat model. Brown Norway rat hearts were transplanted subcutaneously into the anterior region of the neck of Lewis rat recipients (allografts). Control isografts employed Lewis donors and recipients. Phosphocreatine to inorganic phosphate (PCr/Pi), phosphocreatine to beta-adenosine triphosphate (PCr/ATP beta), beta-adenosine triphosphate to inorganic phosphate (ATP beta/Pi) ratios and pH of the transplanted hearts were monitored using surface coil P-31 NMR spectroscopy (at 4.7 tesla) daily for 7 days. To allow recovery from the compromise induced by the surgical procedure, the measurements obtained on day 2 were taken as a baseline. PCr/Pi was unchanged or increased in the isografts but decreased continually in allografts, with the difference becoming significant by day 4 when compared with levels in day 2 allografts (p less than 0.005) and by day 3 when compared with levels in the isograft group (p less than 0.05). PCr/ATP beta in isografts did not change throughout the study; however, allografts demonstrated a significant decrease as early as day 3 (p less than 0.01), although a significant difference between isografts and allografts did not become manifest until day 4 (p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1986

Oscillatory behavior in inferior olive neurons: mechanism, modulation, cell aggregates.

Inferior olive neurons, in brain slices maintained in vitro, display spontaneous, continuous oscillations of their membrane potential which are consonant with olivary rhythmic activity seen in vivo. This oscillatory behavior was studied with intracellular electrophysiological techniques. The 3-10 Hz rhythmicity of these cells from guinea pigs is tetrodotoxin resistant and dependent on a somatic calcium conductance. The oscillatory behavior can exhibit intrinsic frequency modulation and can be altered by synaptic processes. Synaptic alteration of the oscillatory behavior by afferent sources and extensive electrotonic coupling between cells in local aggregates (shown by Lucifer yellow dye-coupling) provide the substrate for a potent central pattern generator with a well established efferent pathway for control of motor functions.

Animals↗
PubMed1986

The inferior olivary complex of guinea pig: cytoarchitecture and cellular morphology.

The inferior olivary complex (I.O.C.) of the guinea pig can be divided into three primary subdivisions: the principal olive (PO), the medial accessory olive (MAO), and the dorsal accessory olive (DAO). In Nissl-stained preparations, the PO possessed darker staining cells than did the MAO and DAO and was the most densely populated with cells. All neuronal somata in the I.O.C. were oblique-spheroid in profile (mean size: coronal = 18.3 microns, parasagittal = 15.8 microns). Based on Golgi impregnations, it was apparent that inferior olive cells were of two unique radiate-cell types (I and II). Type I neurons had relatively diffuse, sparsely branched dendritic arbors, whereas type II cells had dendrites which were highly branched and massed about the cell body, at times creating complex spirals. Type II cells were further categorized into types IIa and IIb based on geometric variations of the type II dendritic arbors. Indices of branching and tortuosity, together with estimates of dendritic arbor volume, were quite helpful in distinguishing cell types. The cell types were differentially distributed across the subdivisions with type I neurons being encountered in the MAO while type II cells were found in all three subdivisions. Within the neuropil of the I.O.C., three different afferent axonal arbors were identified, as was the presence of dendrites from surrounding reticular formation cells. Neuronal aggregates creating a possible electrical syncytium within the I.O.C. are consistent with the dendroarchitectonics of the cells.

Animals↗
PubMed1986

Ultrastructural effects of pyridostigmine on neuromuscular junctions in rat diaphragm.

Pyridostigmine bromide, a quaternary carbamate, is widely used in treatment of myasthenia gravis and has been suggested for use in prophylaxis against intoxication with irreversible cholinesterase inhibitors. Since there are virtually no anatomical data concerning the neuromuscular toxicity of the drug, this study was undertaken to evaluate the effects of acute and subacute doses of pyridostigmine on the ultrastrucutre of nerve terminals in rat diaphragm neuromuscular junctions (NMJs). Pyridostigmine in a Mestinon-equivalent buffer was administered by single, subcutaneous injection (acute exposure; 10-30 min) or by a subcutaneously implanted Alzet osmotic minipump (subacute exposure; 2, 7 or 14 days). Acute exposure doses ranged from 0.0036 mg/kg to 3.6 mg/kg (0.001-1.0 LD50), while subacute exposure doses ranged from 0.43 to 20 mg of the drug. Both acute and subacute exposures resulted in dose dependent alterations of presynaptic elements in diaphragmatic NMJs, which included disruption of organelles in the axon terminal, regional or total withdrawal of the nerve terminal from postsynaptic junctional folds, and invasion of Schwann cell fingers into the synaptic cleft. These ultrastructural observations suggest that the normal cell-to-cell interactions at diaphramatic NMJs are altered by this "reversible," cholinesterase inhibiting drug.

Animals↗
PubMed1985

Neuromuscular toxicity of pyridostigmine bromide in the diaphragm, extensor digitorum longus, and soleus muscles of the rat.

The neuromuscular junctions from diaphragm, soleus, and extensor digitorum longus (EDL) muscles of male albino rats were assessed for morphological alterations following acute (30-min) and subacute (2-day) exposure to pyridostigmine bromide in Mestinon-equivalent buffer. These muscles were selected to compare the effects of the drug on muscles of different fiber type composition. The diaphragm has approximately equal numbers of type I and type II fibers while the soleus and EDL possess primarily type I and type II fibers, respectively. Pyridostigmine was administered to each acute-exposure animal by a single subcutaneous injection of 0.36 mg/kg pyridostigmine and to each subacute-exposure animal by a subcutaneously implanted osmotic minipump containing 10 mg/ml pyridostigmine. Both treatments resulted in whole blood cholinesterase (ChE) depression of approximately 60-70% as determined by radiometric assay. Control animals received only Mestinon-equivalent buffer. Both acute and subacute exposures resulted in morphological alteration of the neuromuscular junctions (NMJs) of all three muscles, although considerable variation in the extent of damage occurred even within individual NMJs. The most frequently observed presynaptic alterations were mitochondrial damage and partial withdrawal of nerve terminal branches (partial denervation). Post-synaptic changes included occasional rarefaction of mitochondrial matrices and disruption of the myofibrillar organization in small numbers of subjunctional sarcomeres. The data indicate that acute or subacute exposure to pyridostigmine bromide at a whole blood ChE depression of 60-70% results in similar alterations to the NMJs of three muscles with substantially different fiber type compositions. Although the severity of the damage varies from fiber to fiber, the variability appears random and not related to a specific fiber type or dosage regimen.

Animals↗
PubMed1983

Freeze-fracture ultrastructure of developing and adult non-myelinated ganglion cell axolemma in the retinal nerve fibre layer.

The ultrastructure of non-myelinated ganglion cell axolemma in the retinal nerve fibre layer from developing and adult rats was examined by freeze-fracture electron microscopy. The axolemma of fibres from neonatal (2-8 days) rats had a moderate density (510-556/micrometers 2) of intramembranous particles (IMPs) on the P-fracture face, while there was a low density (101-146/micrometers 2) of particles on the E-fracture face. Particle density on the P-face increased with development, such that by 28 days the density of IMPs was 1281/micrometers 2. Adult fibres had a high (1741/micrometers 2) density of particles on the P-face. On the E-face, the density of IMPs did not change substantially throughout development, and remained less than 225/micrometers 2 at all ages. Mean particle diameters were compiled for P- and E-fracture faces at the various developmental ages and were greatest in fibres from adult animals. P-face particle density of non-myelinated axons in the retinal nerve fibre layer changed at approximately the time that myelination occurred in distal (optic nerve) segments of these axons. The alteration in membrane structure during development of non-myelinated axons in the retinal nerve fibre layer suggests that conduction properties may also change with development.

Animals↗
PubMed1982

Rat optic nerve: freeze-fracture studies during development of myelinated axons.

This freeze-fracture study examines the development of myelinated fibers in the rat optic nerve. Axolemma of optic nerve fibers were studied before, during, and after myelination. At birth, the optic nerve is composed entirely of non-myelinated (premyelinated) axons, while in the adult, virtually all fibers acquire compact myelin. Myelination begins at 6-8 days postparturition and proceeds rapidly, such that by 28 days of age approximately 85% of the axons are myelinated. The axolemma of premyelinated fibers from 2-day-old animals exhibits an asymmetrical partitioning of intramembranous particles (IMPs) between E- and P-fracture faces; the E-face had approximately 125 particles/micron2 and the P-face approximately 550 particles/micron2. Particle densities for premyelinated axolemma from 8, 12, 14, 16, and 28-day-old nerves were similar to those observed at 2 days. Beginning at 8-12 days postnatal, definitive association between oligodendroglial processes and axons (termed 'ensheathed' fibers) was observed. At the time of glial ensheathment, there was a 50-100% increase in the number of P-face particles; in contrast, the E-face did not display an overall increase in particle density. In certain regions, however, localized aggregations of E-face particles were observed. IMPs on P-faces of ensheathed axons had a greater mean particle size and higher percentage of 'large' (greater than 9.6 nm) particles than did IMPs on the corresponding fracture face of premyelinated fibers. Myelinated axons from 14-16 day optic nerves displayed several differences from adult myelinated fibers. The P-face of the internodal axolemma had approximately 45% fewer particles than that of adult internodal membrane, and the percentage of large IMPs on the P-face of the younger internodal membrane was approximately 50% of the value for adult internodal axolemma. E-faces of internodal axolemma from 14-16-day-old and adult animals had equivalent IMP densities and size distributions. The nodal region of myelinated axons from 14-16-day-old rats had fewer large particles on both E- and P-faces than did adult fibers, though particle densities on both fracture faces were similar for the two age groups. These studies demonstrate a clear reorganization of axon membrane structure concomitant with axo-glial ensheathment, followed by continued gradual axolemmal changes as myelination progresses.

Aging↗
PubMed1982

Spatial heterogeneity of the axolemma of non-myelinated fibers in the optic disc of the adult rat. Freeze-fracture observations.

This freeze-fracture study examined the structure of the axolemma of non-myelinated fibers in the optic disc region of the adult rat. Spatially heterogeneous patterns of intramembranous particles (IMPs) were observed on the E-fracture faces; particle distribution patterns ranged from clusters of 4-7 IMPs to linear arrays of particles 1-3 IMPs wide that apparently encircle the axon. These bands of particles displayed a periodicity of approximately 0.16 micrometers. The present findings demonstrate that, in specialized regions, the axolemma of non-myelinated fibers not in the region of synapses can exhibit distinct spatial heterogeneity.

Animals↗
PubMed1982

Rat optic nerve: electrophysiological, pharmacological and anatomical studies during development.

Changes in conduction properties and in morphology were studied during rat optic nerve growth from birth (when no myelin is present and the glia have not differentiated) to adulthood (when the optic nerve is essentially 100% myelinated). Myelination begins around the sixth postnatal day and proceeds rapidly so that 85% of the fibers are myelinated at 28 days of age. Mean diameter of optic nerve axons remains about 0.2 micron for the first week and then increases rapidly if the fiber is being myelinated. Those axons not being myelinated remain about 0.2-0.3 micron in diameter. At birth the compound action potential has a single negative peak and a conduction velocity of about 0.2 m/s. The increase in conduction velocity prior to myelination is considerably greater than can be accounted for on the basis of increase in axonal diameter. There is no clear step increase in the velocity of the shortest latency peak correlated with the onset of myelination. During myelination the compound action potential develops multiple short latency components, which evolve into the adult-like 3 component compound action potential by 3-4 weeks of age. Durations of the relative refractory period and supernormal period decrease as age increases, but are not related to myelination in a simple manner. Sodium appears to be the only significant carrier of inward current at all ages. A measureable calcium conductance is not present at any age. Voltage-dependent potassium conductance contributes to the compound action potential at all ages, but the response to 4-aminopyridine in rapidly conducting fibers is apparently smaller than that in slowly conducting fibers. These results show that conduction can occur before myelination or the differentiation of glial cells. Moreover, changes in conduction velocity do not depend entirely on myelination or increases in axonal size. Finally, these results suggest a reorganization of axonal membrane properties during the development of rat optic nerve.

Animals↗
PubMed1981

Laminar organization of efferent cells in the parietal cortex of the Virginia opossum.

The size, shape and laminar position of efferent neurons in the parietal cortex of the Virginia opossum were identified using the method of retrograde transport of horseradish peroxidase (HRP). Injection of HRP into the spinal cord, dorsal column nuclei or pontine nuclei leads to labeling of cells in layer V and occasionally in layer VI, while a large injection of HRP in the dorsal thalamus labels many cells in layer VI, with fewer cells in layer V. HRP injections in the SSM cortex label cells in layers II-VI of ipsilateral and contralateral cortical areas. However, the majority of these cortico-cortical cells are found in the supragranular layers. Examination of the size, shape and laminar position of retrogradely labeled layer V neurons after injections in each of these areas suggests that none of these features can be used to predict accurately the projection target of individual neurons. We conclude that the laminar organization of efferent cells of the opossum parietal cortex is very similar to that seen in the neocortex of other mammals, despite the complete coalescence of somatic sensory (SI) and motor (MI) areas in the opossum.

Animals↗
PubMed1981

Freeze-fracture ultrastructure of rat C.N.S. and P.N.S. nonmyelinated axolemma.

The axolemma of nonmyelinated fibres from the corpus callosum and cerebellar cortex (C.N.S.) and the vagus nerve (P.N.S.) was investigated with freeze-fracture electron microscopy. The major observations of this study are as follows: (1) there is a highly asymmetrical distribution of intramembranous particles between the E- and P-fracture faces in both C.N.S. and P.N.S. fibres; (2) the total number of particles on the P-faces of all axonal types studied is considerably greater than that on the E-face; (3) the number of particles on the E-faces of C.N.S. axons is greater than that on the E-faces of P.N.S. axons; and (4) the percentage of large (greater than 9.6 nm) particles is greater on the E-face than on the P-face regardless of the axon studied. The results are compared with previous freeze-fracture investigations on the nodal and intermodal membranes of myelinated fibres.

Animals↗
PubMed1980

Reorganization of the axon membrane in demyelinated peripheral nerve fibers: morphological evidence.

Cytochemical staining of demyelinated peripheral axons revealed two types of axon membrane organization, one of which suggests that the demyelinated axolemma acquires a high density of sodium channels. Ferric ion-ferrocyanide stain was confined to a restricted region of axon membrane at the beginning of a demyelinated segment or was distributed throughout the demyelinated segment of axon. The latter pattern represents one possible morphological correlate of continuous conduction through a demyelinated segment and suggests a reorganization of the axolemma after demyelination.

Animals↗
PubMed1980

Development of the axon membrane during differentiation of myelinated fibres in spinal nerve roots.

Previous studies by a number of workers have shown that the axon membrane in normal mature myelinated fibres is highly differentiated, with the nodal axolemma exhibiting characteristics different to those of the internodal axolemma. However, the development of this axolemmal heterogeneity has not been previously explored. In the present study we used cytochemical methods to examine the development of nodal axolemma during the differentiation of myelinated fibres in rat spinal roots. The staining properties characteristic of normal nodal membrane appear in the axon, at gaps between Schwann cells, before the development of mature compact myelin or well defined paranodal axon--Schwann cell specializations close to the region of nodal axolemmal differentiation. These results are consistent with the hypothesis that the axon membrane differentiates into nodal and internodal regions before, or early in the process of, myelination, and suggest that the differentiation of the axon membrane may provide a signal demarcating the region to be covered by the myelin-forming cell.

Animals↗
PubMed1980

Lysophosphatidyl choline-induced focal demyelination in the rabbit corpus callosum. Electron-microscopic observations.

Under electrophysiological control, a focal demyelinating lesion can be produced in the corpus callosum of the rabbit by slow pressure injection of a 1% solution of lysophosphatidyl choline (LPC). Light- and electron-microscopic examination of the LPC demyelinated corpus callosum indicates that many axons remain structurally intact after LPC injection. In addition, some axons show early signs of remyelination. Our results indicate that small diameter, central nervous system myelinated axons can be focally demyelinated with LPC. Furthermore, our procedure for producing demyelination in the corpus callosum is particularly suitable for combined anatomical and electrophysiological study of small demyelinated axons.

Animals↗