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Biomedical subjects

R F Miller

Publications and source records attributed to R F Miller.

At least 271 records · Page 15Linked to original sources
PubMed1990

Cytomegalovirus in the lungs of patients with AIDS. Respiratory pathogen or passenger?

A total of 166 consecutive clinical episodes of pneumonitis in patients with acquired immune deficiency syndrome (AIDS) or antibody positive for human immune deficiency virus (HIV) were investigated for evidence of cytomegalovirus (CMV) infection in their lungs and at peripheral sites to determine the pathogenicity of this virus in the lung and its relationship to peripheral CMV shedding. Evidence of CMV infection was sought in bronchoalveolar lavage (BAL) fluid, blood, saliva, and urine using a specific monoclonal antibody to antigens produced by CMV-infected cells within 24 h. Although CMV was detected in 31 (19%) of BAL fluid specimens, in only six episodes was this the sole pathologic finding. In the remaining episodes either another infectious agent, Kaposi's sarcoma, or lymphoid interstitial pneumonitis was found or no pathogen was detected. None of the patients were given specific anti-CMV treatment, and all but two recovered, including those patients in whom CMV was the sole finding at BAL. The presence of peripheral shedding of CMV did not have any significance in mortality or morbidity. Our findings are in direct contrast to those in recipients of allogeneic bone marrow transplants, in whom CMV pneumonitis is associated with a high mortality. We postulate that this difference is because AIDS patients cannot mount the destructive immune response to CMV in the lung, which we believe to be the basis of the pathology seen in the former group. We conclude that CMV is not a pathogen in the lungs of patients with HIV infection, and we suggest that its presence at this site does not warrant specific therapy in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1990

The physiology of substance P in the rabbit retina.

The neuropeptide substance P (SP) has been localized to amacrine and ganglion cells in the rabbit retina. We have examined the effects of SP and related peptides on rabbit retinal neurons using bath application and intra- and extra-cellular electrophysiological methods in an in vitro retina eyecup preparation. Substance P, at concentrations as low as 25 nM, moderately excited most brisk ganglion cells. SP excited some ganglion cells directly during cobalt block of synaptic transmission. Intracellular recordings from amacrine cells demonstrated that some, but not all, were depolarized by SP; pharmacological evidence suggested GABAergic amacrines were probably among those sensitive to SP. SP did not affect horizontal cells or the ERG, suggesting that the effects of this peptide are confined to the inner retina. The effects of SP were strongly potentiated by peptidase inhibitors, raising the possibility that endogenously released SP may act quite locally in the rabbit retina. The relative potencies of SP and the related peptides substance K and eledoisin on different cells suggest that more than one tachykinin receptor subtype is present in the rabbit retina. The responses of ganglion cells to SP desensitized with repeated or prolonged applications. Comparison of a cell's light responses before and after the receptors were desensitized revealed no qualitative changes in receptive field characteristics, but quantitative changes in excitability were apparent. SP antagonist analogs, although not potent, specifically blocked the effects of SP on some ganglion cells. The effects of these antagonists on light responses reinforced the inferences from desensitization paradigms regarding the role of endogenous SP.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1990

The physiology of somatostatin in the rabbit retina.

The neuropeptide somatostatin (SS) has been localized to neurons of the rabbit retina by immunochemical and biochemical methods (Sagar et al., 1982, 1986; Marshak and Yamada 1984). We examined the effects of bath-applied SS on neurons of the rabbit retina, using intra- and extracellular electrophysiological techniques in an in vitro retina eyecup preparation. All commonly encountered ganglion cell receptive field types were affected by SS, and the effects were of 3 kinds: The first was a general excitation, occurring with a threshold concentration of about 100 nM; the onset of the excitation was too slow (seconds) for SS to participate in any rapid light-evoked responses. The second SS effect was an increase in the "signal-to-noise ratio," defined here as the ratio of light-evoked to spontaneous spiking, which resulted from a decrease in spontaneous activity and, usually, a concomitant increase in light-evoked spiking. The third effect was a shift in center-surround balance towards a more dominant center. The signal-to-noise and center-surround effects were evident at concentrations as low as 0.5 nM; both were slow onset (tens of seconds) and long lasting (tens of minutes). SS acted at multiple levels within the retinal circuitry to produce the observed changes in ganglion cell output. These effects included direct actions on ganglion and amacrine cells, and a decrease in the efficiency with which horizontal cells could drive the retinal network. At least part of these SS actions on third-order neurons resulted from a decrease in conductance to ions with an equilibrium potential more positive than dark membrane potential. The degradation-resistant SS agonist SMS201-995 had effects qualitatively and quantitatively similar to those of SS, suggesting that SS may be degraded slowly enough to act at a distance from its sites of release. While no adequate SS antagonist is available, the greater sensitivity to exogenous SS, in retinas depleted of their SS content (with cysteamine), suggests a role for endogenous SS. The potency of SS also reinforces this view. The results of this study suggest that SS may be a neuromodulator in the rabbit retina, producing long-lasting changes in the "signal-to-noise" discharge pattern and center-surround balance of ganglion cells.

Action Potentials↗
PubMed1989

A theoretical and experimental study of the effects of non-uniform membrane resistance on the shape of single-cell charging curves.

The isolated Muller glial cell of the neotenous tiger salamander retina is used as an experimental model for studying the effects of non-uniform membrane conductance on the shape of charging curves in response to step current inputs. A simple cable model of the Muller cell is formulated and used to interpret the experimental data. The Muller cell model is completely described by three parameters: (a) electrotonic length L; (b) the membrane time constant tau m; and (c) the percentage of the total membrane conductance accounted for by the endfoot S. Model analysis indicates that increasing S produces monotonic decreases in the rise time of charging curves. This effect is greatest when L is small. In such cases charging curve rise time can be substantially faster than that of a semi-infinite cable. When S greater than 0, the first time constant obtained by fitting the late exponential tail of the charging curve is not the membrane time constant (as is the case when S = 0), but is instead an equalizing time constant equal to the membrane time constant times a scale factor in the range of 0 to 1. This scaling factor becomes quite small as S approaches 100%. We describe a convergent numerical procedure for generating unique estimates of all three model parameters from charging curves. Application of the algorithm to experimentally measured Muller cell charging curves confirms Newman's finding that a large fraction of membrane conductance in these cells is accounted for by the endfoot (greater than 90%). The model prediction that charging curve rise time may be substantially faster than that of the semi-infinite cable when S greater than 0 is also confirmed. The error that results from misinterpreting the first equalizing time constant tau l as the membrane time constant tau m can have a significant effect on estimates of specific membrane resistance and capacitance. The algorithm described in this paper provides a means for obtaining direct estimates of the membrane time constant and will make possible more accurate estimates of specific membrane resistance and capacitance in Muller glial cells. The fact that the estimation procedure is based on a simple electrophysiological measurement suggests that it may be useful for studying asymmetry of membrane conductance in glial and neural elements of the intact nervous system.

Animals↗
PubMed1989

Functional role of spines in the retinal horizontal cell network.

Compartmental models derived from serial electron-microscopic reconstructions of horizontal cell processes entering cone pedicles and rod spherules are used to show that these processes have the morphological and electrical characteristics of dendritic spines. Properties of these spines are incorporated into a distributed model of the horizontal cell network. Expressions relating the magnitude of conductance changes applied at the spine heads to hyperpolarization of cells within the network are derived. Model analyses show that spine properties play a critical role in determining network responses. Specifically, increasing spine stem resistance increases the network input resistance and space constant, hyperpolarizes the resting potential, decreases response to full-field light stimuli, and increases response to small light spots. Increasing spine-stem resistance also decouples potential at the spine head from potential at the cell body. This result suggests that the location of feedback neurotransmitter release sites (e.g., at the spine heads versus the cell body) may have a profound influence on properties of horizontal cell inhibition of cone response. Because of these important functional consequences, structurally realistic models of the horizontal cell network must incorporate spine properties.

Animals↗
PubMed1989

Reversible zidovudine-induced pure red-cell aplasia.

The treatment of patients with AIDS and AIDS-related complex (ARC) with zidovudine is limited by major haematological toxicity. In an open study of the use of zidovudine, 10 out of a total of 81 patients developed a severe anaemia within the first 3 months of treatment. In five of these 10 patients the mean cell volume did not increase but remained within the normal range. Bone marrow examination of three of these five showed a pure red-cell aplasia. In all five patients the anaemia resolved on discontinuation of the drug and in three that were re-challenged, the anaemia recurred. Zidovudine-induced anaemia has usually been reported as macrocytic and megaloblastic, but in our experience erythroid aplasia appears to be a major cause of anaemia occurring within the first 3 months of treatment. The earliest sign is anaemia with a stable or only a slight increase in the mean cell volume (MCV).

Acquired Immunodeficiency Syndrome↗
PubMed1989

Diagnosis of pulmonary disease in human immunodeficiency virus infection: role of transbronchial biopsy and bronchoalveolar lavage.

The value of transbronchial biopsy and bronchoalveolar lavage was assessed in the diagnosis of pulmonary disease in patients infected with the human immunodeficiency virus (HIV). Seventy four transbronchial biopsy and 66 bronchoalveolar lavage specimens (60 paired specimens) from 80 examinations in 64 patients were reviewed. Pneumocystis carinii was the most common pathogen isolated (43 patients). Bronchoalveolar lavage was superior to transbronchial biopsy for the diagnosis of this pathogen, the sensitivities being 90% and 56%. Cytomegalovirus was identified three times by lavage and once by transbronchial biopsy. Neither method detected Kaposi's sarcoma in the one patient shown to have it by open lung biopsy. The complication rate in a concurrent study of bronchoscopy with transbronchial biopsy in 74 consecutive HIV positive patients was 22%. This study does not support the use of transbronchial biopsy in these patients.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Empirical treatment without bronchoscopy for Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome.

An empirical approach to treating Pneumocystis carinii pneumonia was adopted in a prospective study of 73 men with antibodies to human immunodeficiency virus 1 (HIV-1) presenting with respiratory problems. At presentation 49 patients (group 1) were thought to have a history, findings at clinical examination, chest radiograph, and arterial blood gas tensions typical of pneumocystis pneumonia, and empirical treatment was begun immediately. Twenty four patients (group 2) were thought to have features not typical of pneumocystis pneumonia. All patients were subsequently referred for bronchoscopy to determine the diagnosis. In group 1 four patients were excluded from the analysis because bronchoscopy was not possible. Of the remaining 45, 42 had pneumocystis pneumonia, which was diagnosed at bronchoscopy in 40, and on the basis of the clinical response to co-trimoxazole in two who had negative results from investigations. Of the three patients without pneumocystis pneumonia, one patient with lymphoid interstitial pneumonitis and Branhamella catarrhalis infection would have failed to respond to empirical treatment. The other two had multiple bacterial pathogens at bronchoscopy; one already had Kaposi's sarcoma and the other would have been misdiagnosed as having AIDS. In group 2 a specific diagnosis was made at bronchoscopy in 21 cases, including pneumocystis pneumonia in seven (all had atypical chest radiographs). In three cases no diagnosis was made and spontaneous recovery occurred. Adopting an empirical approach to treatment for typical pneumocystis pneumonia (group 1) led to the correct treatment in 43 of 45 cases (95%) and would have saved 44 of the 45 of bronchoscopies in this group. Adopting an empirical approach would have caused one patient to be misdiagnosed as having AIDS. Overall, 44 out of 69 bronchoscopies (64%) would have been saved; the specificity for the diagnosis of pneumocystis pneumonia was 85% and the sensitivity was 85%. Adopting an "empirical" treatment policy for typical pneumocystis pneumonia will cause a large reduction in the number of "high risk" bronchoscopies performed.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Nebulised pentamidine as treatment for Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome.

Nebulised pentamidine was used to treat 30 patients with Pneumocystis carinii pneumonia. Fourteen patients (group 1) received pentamidine isethionate 4 mg/kg (six patients) or 8 mg/kg (eight patients) via a standard jet nebuliser (Acorn, system 22) with a flow rate of 8 l/min. The aerosol droplets had a mass median aerodynamic diameter of 2.6 microns (geometric standard deviation (GSD) 2.9) and 46% of droplets were less than 3.9 microns. A further 16 patients (group 2) received 8 mg/kg pentamidine via a jet nebuliser with baffles to limit droplet size to below 4 microns (Respirgard II). This generated aerosol droplets with a mass median aerodynamic diameter of 0.8 micron (GSD 1.5) and 98% were less than 3.9 microns. Only three of the 14 patients in group 1 responded clinically to treatment, one after the lower dose of pentamidine. Treatment was discontinued in 10 patients and one patient died at bronchoscopy from haemorrhage. Thirteen of the 16 patients in group 2 responded. Side effects occurred infrequently; two patients from group 1 had a cough, six patients (four from group 2) had contact bleeding at bronchoscopy, and two further patients had haemoptysis. The differing response rate may be due to differences in the mean droplet size of the aerosols produced by the nebulisers. Nebulised pentamidine (8 mg/kg) when delivered by Respirgard II nebuliser appears to be as effective as conventional treatment for Pneumocystis carinii pneumonia of mild to moderate severity.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Measurement of passive membrane parameters with whole-cell recording from neurons in the intact amphibian retina.

1. Whole-cell recordings have been obtained from intact, photoactive retinal neurons using patch-clamp electrodes in the amphibian superfused retina eyecup preparation. 2. After removal of the vitreous humor from the surface of the retina, using a collagenase with low tryptic activity, high-resistance seals (1-10 G omega) could be formed between the patch pipette and the cell membrane by applying mild suction to the pipette. Additional suction broke the membrane patch and provided continuity between the low-resistance pipette and the interior of the neuron. 3. Measurements of input resistance and time constant were obtained from bipolar, amacrine, and ganglion cells. Assuming the membrane capacitance was 1 microF/cm2, time constant data were used to derive the specific membrane resistance. The average specific membrane resistance for the inner retinal neurons in our sample was 68,000 omega.cm2. 4. Analysis of the charging curve induced by a brief current pulse applied to the soma was used to analyze the average electrotonic length of dendrites. The charging curves of some ganglion cells were well represented by a single exponential, suggesting that they were essentially isopotential. 5. The voltage decay along an equivalent cylinder model of a ganglion cell was calculated, using the experimentally obtained values of membrane resistance to compute decay of steady-state voltages along the dendritic tree. The calculations indicate that with the high membrane resistance values implied by this study, the electrotonic length of dendritic cables were short, and there may be relatively little attenuation of the synaptic potentials irrespective of their location along the dendritic tree.

Ambystoma↗
PubMed1989

Kainate receptor-mediated synaptic currents in mudpuppy inner retinal neurons reduced by D-O-phosphoserine.

1. The effects of D-O-phosphoserine (DOS) were examined on proximal neurons in the superfused mudpuppy retinal-eyecup preparation by measuring their synaptically evoked whole-cell currents with the use of patch-clamp electrodes. 2. DOS reduced the light-evoked excitatory postsynaptic potentials (EPSPs) of amacrine and ganglion cells. This suppression was present even though the center responses of both ON- and OFF-bipolar cells were unaffected by DOS. 3. When recordings were done under voltage-clamp conditions. DOS diminished the magnitude of light-evoked synaptic currents associated with a reduction in synaptic conductance. 4. To determine which acidic amino acid receptor mediated the network-selective action of DOS, various glutamate agonists were tested against this excitatory amino acid receptor (EAAR) antagonist. DOS blocked the depolarizing effects of kainate (KA), but not those of N-methyl-D-aspartate (NMDA) or quisqualate (QQ). Thus DOS was a selective KA antagonist, and KA receptors appear to be the dominant EAAR subtype that mediates synaptic inputs into the inner retina of the mudpuppy.

Animals↗
PubMed1988

Mudpuppy retinal ganglion cell morphology revealed by an HRP impregnation technique which provides Golgi-like staining.

A new technique of retrograde labeling of ganglion cells with horseradish peroxidase (HRP) has been developed, based on orbital injections of HRP combined with a detergent (lysolecithin). When injections are followed by an appropriate survival time, dense staining of a small number of widely scattered cells results in Golgi-like filling of each neuron. This technique, as well as a variation which causes mass staining of ganglion cell somas, has been used to analyze the morphology of mudpuppy retinal ganglion cells. Morphological analysis has relied on computer reconstruction techniques for display, analysis of dendritic sublamination pattern, and morphometric analysis of the dendrites and soma. Based on morphological criteria, the mudpuppy retina contains a rich variety of ganglion cell types which vary according to soma placement, dendritic field size, polar vs. non-polar dendritic fields, dendritic branching pattern, and dendritic sublamination. The mudpuppy retina contains both conventional and displaced ganglion cells: the latter constitute about 15% of the total ganglion cell population. Both conventional and displaced ganglion cells show morphological diversity of dendritic sublamination branching pattern; cells from each group have a dendritic branching pattern confined to either distal or proximal divisions of the inner plexiform layer, whereas other cells have dendrites which branch in both sublaminae. Using morphological criteria, two subtypes of ganglion cells were identified, which have a distinctive branching pattern and dendritic tree size. The size and distribution of ganglion cell somas were analyzed from retinas in which mass staining of ganglion cells was present. The total number of ganglion cells was estimated at approximately 14,500 cells per retina. There was a tendency for soma size and density to decrease near the optic disk. The somas of displaced ganglion cells are smaller than their conventional counterparts, at the same retinal eccentricity. The somas of all HRP filled cells swell when compared to those of unstained fixed and freshly dissected retinas. The degree of swelling is proportional to the length of exposure to HRP. Cell swelling was evident for both retrograde labeling and intracellularly injected HRP. This artifact of HRP staining could influence the interpretation of studies in which quantitative differences in soma sizes are based on the use of HRP labeling.

Animals↗
PubMed1988

T4+ (helper phenotype) chronic lymphocytic leukemia: case report with liver failure and literature review.

T-cell lymphomas and leukemias are a heterogeneous group of neoplasms found in each anatomic compartment of the T system (marrow, thymus, and various peripheral tissues) and that have varying phenotypic expressions. Histopathologic features of the thymic and peripheral T neoplasms do not fit into a clearly defined pattern, and clinical expressions of T neoplasms are likewise variable. This report describes a 60-year-old man with "chronic" lymphocytic leukemia of T4+ (helper) phenotype. Rapid deterioration in liver function, presumably due to tumor infiltration, was unexpected and has not previously been reported. The unusual clinical and pathologic features are reviewed in the context of T-cell neoplasms, particularly T4+ processes.

Humans↗
PubMed1988

Meclofenamate blocks the pulmonary arterial vasopressor effects of leukotriene B4 in awake sheep.

This study examined the hemodynamic effects of leukotriene B4 (LTB4) in chronically instrumented awake sheep, and the role of cyclooxygenase products in the sheep's response to LTB4. LTB4 (25 micrograms) was given as a bolus into the pulmonary artery. Six sheep were studied with LTB4, both before and after pretreatment with meclofenamate (5 mg/kg load, 3 mg/kg/hr maintenance infusion). LTB4 alone caused a rapid rise in pulmonary arterial pressure from 15 +/- 1 to 42 +/- 11 cm H2O. LTB4 had no effect on pulmonary arterial pressure following pretreatment with meclofenamate. LTB4 alone caused an increase in serum thromboxane B2 (TxB2) from 130 +/- 35 to 320 +/- 17 pg/ml 3 minutes after dosing but did not increase TxB2 following pre-treatment with meclofenamate. LTB4 caused a slight decrease in mean systemic arterial pressure and a transient fall in circulating white blood cells, both of which were unaffected by meclofenamate pre-treatment. The vasoactive effects of LTB4 in the pulmonary circulation appear to be mediated indirectly through the production of cyclooxygenase metabolites of arachidonic acid.

Animals↗