PubMed Health⌕ Search

Biomedical subjects

G A Robinson

Publications and source records attributed to G A Robinson.

At least 19 recordsLinked to original sources
PubMed1995

Axotomy-induced regulation of c-Jun expression in regenerating rat retinal ganglion cells.

Antibodies to c-Jun, JunD, JunB, c-Fos, FosB and Krox-24 proteins were used to examine the expression of these transcription factors in identified adult rat retinal ganglion cells with regenerating axons in a peripheral nerve graft. First, expression in ganglion cells 1 month after graft placement was compared to expression in these neurons 5 to 6 months after grafting. Whereas strong c-Jun expression was seen in most ganglion cells one month after grafting, most 5- to 6-month ganglion cells showed only basal expression. The maintained nucleolar expression of FosB in both ganglion cell groups was the only other transcription factor seen. Second, transcription factor expression was examined in these short- and long-term regenerating neurons after a second axotomy caused by graft transection and compared to the effects of a single axotomy on expression in non-regenerating ganglion cells. Only c-Jun was re-expressed in the regenerating ganglion cells after re-axotomy.

Animals↗
PubMed1994

A direct, general approach based on isobolograms for assessing the joint action of drugs in pre-clinical experiments.

Pharmacologists and other biologists frequently use methods based on the interpretation of isobolograms to quantify the extent of synergy or antagonism between drugs used in combination in pre-clinical studies. Most methods have been unsatisfactory from a statistical viewpoint, many because they have relied solely on visual evaluation, others because the methods have not taken into account the variability of the measurements. We describe a direct approach for quantifying the joint potency of two drugs, a central feature being the use of simple isobole models that lead directly to response surface models for the expected experimental outcomes. The approach is general in the sense that one can use it for discrete or continuous responses, different underlying probability distributions, linear or non-linear dose-response functions of the drugs used singly, and a variety of experimental designs. Our approach extends the suggestions made by Hewlett for measuring the joint potency of drugs, and is similar in spirit to the approaches proposed by Greco et al. and Weinstein et al. We describe the analysis of data from an in vitro experiment conducted to evaluate the efficacy of the antiviral drugs AZT and ddI used in combination.

Didanosine↗
PubMed1994

Gene structure and amino acid sequences of alcohol dehydrogenases of Bacillus stearothermophilus.

Partial amino acid sequences of the two alcohol dehydrogenases of Bacillus stearothermophilus and the oligonucleotide sequence of a cloned fragment containing the gene for ADH 2334 were determined and compared with the known, derived ADH 1503 amino acid sequence. The two proteins are identical at 244 of 349 positions. ADH 2334 is encoded in a transcription unit containing an aldehyde dehydrogenase.

Alcohol Dehydrogenase↗
PubMed1994

Immediate early gene expression in axotomized and regenerating retinal ganglion cells of the adult rat.

To determine if axotomy-induced immediate early gene (IEG) expression accompanies regenerative efforts in central nervous system (CNS) neurons, immunohistochemistry using antibodies to c-Jun, JunD, JunB, c-Fos, FosB and Krox-24 proteins was used to examine gene expression in identified adult rat retinal ganglion cells (RGCs) under two conditions: (1) after axotomy alone, and (2) 1 month after replacement of the optic nerve with an autologous peripheral nerve graft to allow axonal regrowth. Strong RGC c-Jun expression was induced 1 day, but not 3 h, after axotomy in most RGCs and was maintained in surviving cells throughout the 3-week study period. Axotomy also induced a limited number of RGCs to express Krox-24, but only transiently. c-Fos expression was also seen in a limited number of control RGCs, however, it was not induced by axotomy. Nucleolar FosB immunoreactivity in axotomized RGCs persisted 1 day after axotomy, but was subsequently lost. One month after axotomy and peripheral nerve graft placement, identified RGCs with regrown axons showed only nuclear c-Jun and nucleolar FosB expression. These findings support a role for IEG expression in the regeneration process of CNS neurons.

Animals↗
PubMed1994

Behavior of motor units in human biceps brachii during a submaximal fatiguing contraction.

The activity of 50 single motor units was recorded in the biceps brachii muscle of human subjects while they performed submaximal isometric elbow flexion contractions that were sustained to induce fatigue. The purposes of this study were to examine the influence of fatigue on motor unit threshold force and to determine the relationship between the threshold force of recruitment and the initial interimpulse interval on the discharge rates of single motor units during a fatiguing contraction. The discharge rate of most motor units that were active from the beginning of the contraction declined during the fatiguing contraction, whereas the discharge rates of most newly recruited units were either constant or increased slightly. The absolute threshold forces of recruitment and derecruitment decreased, and the variability of interimpulse intervals increased after the fatigue task. The change in motor unit discharge rate during the fatigue task was related to the initial rate, but the direction of the change in discharge rate could not be predicted from the threshold force of recruitment or the variability in the interimpulse intervals. The discharge rate of most motor units declined despite an increase in the excitatory drive to the motoneuron pool during the fatigue task.

Action Potentials↗
PubMed1993

Adaptation of cat motoneurons to sustained and intermittent extracellular activation.

1. The main purpose of this study was to quantify the adaptation of spinal motoneurons to sustained and intermittent activation, using an extracellular route of stimulating current application to single test cells, in contrast to an intracellular route, as has been used previously. In addition, associations were tested between firing rate properties of the tested cells and other type (size)-related properties of these cells and their motor units. 2. Motoneurons supplying the medial gastrocnemius muscle of the deeply anaesthetized cat were stimulated for 240 s with microelectrodes which passed sustained extracellular current at 1.25 times the threshold for repetitive firing. Many cells were also tested following a rest period with intermittent 1 s current pulses (duration 600 ms) at the same relative stimulus strength. Cell discharge was assessed from the EMG of the motor unit innervated by the test neuron. The motoneurons and their motor units were assigned to four categories (i.e. types FF, FR, S and F; where F = FF + FR) based on conventional criteria. In all, twenty F (16 FF, 4 FR) and fourteen S cells were studied with sustained stimulation. Thirty of these cells (17 F, 13 S) and an additional two cells (1 F, 1 S) were studied with intermittent stimulation. 3. The mean threshold current required for sustained firing for a period of > or = 2 s was not significantly different for F and S cells. However, most of the other measured parameters of motoneuron firing differed significantly for these two cell groups. For example, at 1.25 times the threshold current for repetitive firing, the mean firing duration in response to 240 s of sustained activation was 123 +/- 88 s (+/- S.D.) for F cells vs. 233 +/- 19 s for S cells. These values were significantly longer than those from a comparable, previously reported study that employed intracellular stimulation. With intermittent stimulation, the firing durations of F and S cells were not significantly different from each other. 4. All cells exhibited a delay from the onset of current to the first spike, followed by a brief accelerating discharge that was followed by a slower drop in firing rate. Some cells (21 of 34 with sustained activation; 20 of 32 with intermittent) exhibited doublet discharges (interspike intervals < or = 10 ms) that were intermingled with the more predominant singlet discharges. Doublets were more common in the S cell type.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Immobilization-induced changes in motor unit force and fatigability in the cat.

The purpose of this study was to examine the effects of 3 weeks of immobilization on the mechanical properties of motor units in a cat hindlimb muscle. The muscle, tibialis posterior, was immobilized in a shortened position. Motor units were classified as type FF, F(int), FR, or S. Force, axonal conduction velocity, fatigability, and proportions of motor unit types were compared in control and immobilized muscles. All properties exhibited some change after immobilization, including slower axonal conduction velocities, greater twitch forces, slower twitch contraction times, and greater tetanic forces. In addition, most motor units were less fatigable after immobilization. The number of motor units that could not be included in one of the four classification categories increased significantly after immobilization; these units exhibited normal axon conductivity but failed to produce measurable force or associated EMG. Short-term immobilization induced a variety of physiological adaptations in neuromuscular processes that varied with motor unit type.

Action Potentials↗
PubMed1991

Optical immunosensing systems--meeting the market needs.

Optical immunosensors and sensing systems are biosensors which produce a quantitative measure of the amount of antibody, antigen or hapten present in a complex sample such as serum or whole blood. The market needs for such devices and their associated instrumentation are reviewed. A brief history of the development of optical immunosensors is presented and the performance of the most well-developed optical immunosensors for meeting these market needs is reviewed. One device, the fluorescent capillary fill device (FCFD) is reviewed in detail with respect to it fulfilling the market needs for an optical immunosensor. Areas for the future development of such sensing systems are also discussed.

Biosensing Techniques↗
PubMed1991

An assay for human chorionic gonadotrophin using the capillary fill immunosensor.

Recently there has been much research effort directed towards the development of immunosensors. Optical technologies are currently proving very attractive for the construction of such sensors. The fluorescence capillary fill device (FCFD) has been designed to fulfil these needs. The development of an assay for human chorionic gonadotrophin (hCG) in the FCFD for a variety of body fluids (whole blood, serum, urine and saliva) demonstrates the versatility and assay performance of the device.

Biosensing Techniques↗
PubMed1991

Sensitivity enhancement of optical immunosensors by the use of a surface plasmon resonance fluoroimmunoassay.

Optical immunosensors employing evanescent wave techniques have the potential to address the requirements of the 'alternative site' market; however, this potential has yet to be realised. The development of 'direct' sensors, such as those using surface plasmon resonance (SPR), has been hampered by problems of non-specific binding and poor sensitivity to small molecules. 'Indirect' sensors (for example, those employing a fluorescently labelled reagent) overcome many of the problems of direct sensors but require more sophisticated instrumentation because of the low light levels detected. In an attempt to combine the best features of the two techniques, an indirect SPR fluoroimmunoassay (SPRF) technique has been investigated. The surface field intensity enhancement produced by SPR is used to boost the emission from a fluorescently labelled immunoassay complex at a metal surface. The potential of the method is demonstrated by assaying for human Chorionic Gonadotrophin (hCG) in serum. Enhanced sensitivity over conventional total internal reflection fluorescence (TIRF) and SPR techniques was achieved.

Biosensing Techniques↗
PubMed1990

Detection of rubella antibody using an optical immunosensor.

Since the first biosensor was reported in 1962 different sensors have been developed in different areas; their attraction being that they hold out the possibility of a rapid test which can specifically detect the analyte, without the necessity for additional reagents. Immunosensors make use of antibodies and can be extremely specific if the appropriate monoclonal antibodies are used. We report on the development of an optical immunosensor used for the detection of rubella antibody in serum, plasma and whole blood. The assay time is less than 10 min and requires no accurate measurement of the sample or any additional reagents. The sensitivity is in the region of 30 IU/ml; with a correlation of 94% with conventional assays.

Antibodies, Monoclonal↗
PubMed1990

Accumulation and distribution of ions of group-IIIA elements in the tissues and eggs of the Japanese quail.

Solutions of salts of the five Group-IIIA elements were given, intravenously, to mature Japanese quail. By 18 h, the accumulation maxima in the major tissues were: leg bones, 20% for Ga+3 (67Ga label) in estradiol-treated males; liver, 51% for Al+3 (26Al label) in control males; kidneys, 32% for In+3 (114mIn label) in estradiol-treated males; and growing oocytes plus ova, 37% for In. Accumulations of Tl+1 (202Tl label) were 6 times those for Ga or In in the brain and muscles, and .1 times in plasma. The cumulative maxima in egg components over 8 (B; Tl) or 10 (Al; Ga; In) days were B, 23% in albumen; Al, 38%, Ga 27%, In, 43% in yolks; Tl, 12% in shells. The accumulation of thallium in the eggshells markedly exceeded (P less than .001) the deposits of the other IIIA elements in shells, Al being the next highest at .54%.

Aluminum↗
PubMed1989

Linearity of the accumulation of various dosages of uranium in the major organs of mature male Japanese quail. Effect of various doses of estradiol-17 beta.

1. Male Japanese quail were given 2.20 x 10(-4)-14.53 mg uranium/kg intravenously as uranyl ion (235U label). 2. The relationship between dosage and the 18-hr accumulation of U in leg bones, liver, kidneys and testes was linear. 3. Increases in U deposition with increased dosage were approximately 1:1, except for kidneys where 10-fold increases in dosage resulted in 25-fold increases in deposition. 4. Estradiol-17 beta increased U deposition in bones by 15-fold thereby providing some protection for the kidneys as now the ratio of dosage to accumulation was 1:1.

Animals↗
PubMed1989

Warfarin and cataract extraction.

Ten cataract extractions were performed on eight patients for whom warfarin was not discontinued prior to surgery. Three were complicated by hyphaema. No retrobulbar haemorrhages occurred in the four cases given a local anaesthetic. Cataract surgery can be performed successfully without discontinuing warfarin.

Aged↗
PubMed1989

Task and fatigue effects on low-threshold motor units in human hand muscle.

1. The activity of single motor units was recorded in the first dorsal interosseus muscle of human subjects while they performed an isometric ramp-and-hold maneuver. Motor-unit activity was characterized before and after fatigue by the use of a branched bipolar electrode that was positioned subcutaneously over the test muscle. Activity was characterized in terms of the forces of recruitment and derecruitment and the discharge pattern. The purpose was to determine, before and after fatigue, whether motor-unit activity was affected by the direction in which the force was exerted. 2. Regardless of the task during prefatigue trials, interimpulse intervals were 1) more variable during increases or decreases in force than when force was held constant at the target value (4-6% above the recruitment force), and 2) more clustered around an arbitrary central value than would be expected with a normal (Gaussian) distribution. Both effects were seen during the flexion and abduction tasks. The behavior of low-threshold motor units in first dorsal interosseus is thus largely unaffected by the direction of the force exerted by the index finger. The absence of a task (i.e., a direction of force) effect suggests that the resultant force vector about the metacarpophalangeal joint of the index finger is not coded in terms of discrete populations of motor units, but, rather, it is based on the net muscle activity about the joint. 3. Motor-unit behavior during and after fatigue showed that the relatively homogeneous behavior seen before fatigue could be severely disrupted. The fatiguing protocol involved the continuous repetition, to the endurance limit, of a 15-s ramp-and-hold maneuver in which the abduction target force was 50% of maximum and was held for 10-s epochs (ramps up and down were approximately 2 s each). Motor-unit threshold was assessed by the forces of recruitment and derecruitment associated with each cycle of the fatigue test. Changes in recruitment force during the protocol were either minimal or, when present, not systematic. In contrast, the derecruitment force of all units exhibited a marked and progressive increase over the course of the test. 4. After the fatigue test, when the initial threshold tasks were repeated, the behavior of most motor units changed. These changes included the derecruitment of previously active motor units, the recruitment of additional motor units, and an increased discharge variability of units that remained recruited. The variation in recruitment order seemed to be much greater than that reported previously for nonfatiguing conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

A stable, selective electrode for recording single motor-unit potentials in humans.

A new application of electrode technology has enabled recording of single motor-unit potentials in human first dorsal interosseus muscle with more versatility than has been traditionally associated with this paradigm. The design, manufacture, and application are detailed for an electrode which has been used to discriminate potentials during efforts up to maximal voluntary contraction. The electrode comprises a branched, bipolar configuration which is positioned subcutaneously over the belly of the muscle. This extramuscular location maximizes stability and, with appropriate orientation of the electrode relative to the architecture of the muscle, ensures adequate selectivity of single motor-unit potentials.

Action Potentials↗
PubMed1988

Distribution of nanomole quantities of 235U in young and adult Japanese quail and in the F1 generation. Comparison with 153Gd.

Enriched uranium, 93.16% for 235U, served as a tracer of uranium deposition in an avian species, the Japanese quail. A second label, 153Gd, provided for monitoring of procedures and for estimation of the 235U content of live eggs. Depositions of 235U were greater than for 153Gd in all tissues except the yolk sac and the liver. Skeletal levels for 235U were age- and sex-dependent. Feathers contained only 0.11% of the 235U tracer in contrast to 50% of the endogenous uranium. The results show that 235U provides for tracing uranium metabolism in small animals, since in quail the tracer increased the uranium burden of the body by only 1-8%.

Animals↗