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Biomedical subjects

J D Allison

Publications and source records attributed to J D Allison.

At least 37 records · Page 2Linked to original sources
PubMed1990

Bovine endometritis: comparative efficacy of alfaprostol and intrauterine therapies, and other factors influencing clinical success.

A comparative study of the treatment of 306 severe, moderate, or mild cases of bovine endometritis was carried out over two calving seasons. The cases were treated with alfaprostol, or an intrauterine antibacterial preparation, or with a combination of both therapies. There was no significant difference between the efficacies of these treatments, and a single injection of alfaprostol was effective in 74 per cent of the cases treated. The effectiveness of the treatments was related to the degree of self-cure of the endometritis after parturition, the luteal activity at the time of treatment, and farm management factors affecting the health and condition of the calving cows.

Animals↗
PubMed1989

Acoustic modulation of neural activity in the hypothalamus of the leopard frog.

Horseradish applications in the ventral hypothalamus of the northern leopard frog, Rana pipiens, demonstrated inputs from three auditory nuclei, the anterior and central thalamic nuclei and the secondary isthmal nucleus, in a pattern identical to that seen in Rana catesbeiana. Single-unit recordings from the area receiving these inputs revealed neurons with high spontaneous firing rates. In approximately half of the isolated neurons, the firing rate could be increased or, less often, decreased, by more than 20% by the presentation of a repetitive noise burst or conspecific mating call. Treatment with human chorionic gonadotropin prior to recording resulted in no significant differences in the number or response properties of the acoustically sensitive hypothalamic cells. These results suggest that acoustic signals such as those used for intraspecific communication can modulate neural activity in a part of the basal forebrain involved in endocrine regulation.

Animals↗
PubMed1989

Frequency and variation of the posterior pituitary bright signal on MR images.

Sagittal T1-weighted series with 3-mm sections have routinely been used for all cranial MR studies at our institution. It was apparent from examining these studies that the rate of occurrence of a normal posterior pituitary bright signal was lower than has been previously reported, particularly in older patients. This prompted both a retrospective and a prospective review and analysis of the posterior lobe bright signal in three patient categories. The overall frequency of posterior pituitary bright signal and the influence of sex and age were evaluated in one category. An age-related statistically significant decline in the frequency of posterior pituitary bright signal was found, with a decline rate of approximately 1% per year. An evaluation of the occurrence of anatomic variation in the location of posterior lobe bright signal was made in a second group of 1500 patients. Abberrant location of the posterior lobe was found to be uncommon and was seen most frequently in patients with a sellar fossula. Temporal variation in the presence or absence and size of the posterior lobe bright signal was evaluated in a third group of 36 patients who had at least two MR examinations available for review. Follow-up MR study showed an obvious posterior lobe bright signal in 8% of these patients for whom no bright signal was apparent at the time of initial examination. Loss of the posterior lobe bright signal was apparent in another 25% of patients. A significant change in size of the bright signal was apparent in 19% of patients within this category. Our results indicate that variation in the bright signal of the posterior pituitary lobe should be expected as a normal physiological occurrence.

Adolescent↗
PubMed1987

The rCBF response to Diamox in normal subjects and cerebrovascular disease patients.

Age-related norms for the regional cerebral blood flow (rCBF) response to Diamox (acetazolamide) were based on studies of 55 normal subjects at rest and on studies of 33 of these 55 normal subjects following an intravenous injection of Diamox (22 mg/kg). After the Diamox injection, rCBF increased at all locations measured in all subjects. On average, rCBF increased 1.7 times. The following were found for rCBF in both resting and Diamox-treated subjects: 1) rCBF decreased significantly with increasing age; 2) slope and intercept for the regression of rCBF on age were largest for frontal detectors, intermediate for parietal detectors, and smallest for occipital detectors; 3) rCBF hyperfrontality was most noticeable in younger subjects; 4) in subjects of any age, 95% confidence intervals for rCBF were relatively large (expected value +/- 30%) and lower 95% confidence intervals for Diamox rCBF tended to overlap the upper 95% confidence intervals for resting rCBF; and 5) side-to-side percentage difference in rCBF did not have a significant regression on age and tended to be less than 10% to 20%. Diamox did not have an important effect on blood pressure, pulse rate, or respiratory rate. The normative data for the rCBF response to Diamox was used in evaluating 20 patients with cerebrovascular disease. Forty percent of these patients, all of whom exhibited angiographic evidence of potentially hemodynamically significant lesions, had normal rCBF at rest and after Diamox injection. Twenty percent had normal resting flows with abnormal Diamox-activated flows. Asymmetry in rCBF was the most sensitive indicator of a potential abnormality in cerebral perfusion. Thirty percent of the abnormal studies showed only significant asymmetry. It is suggested that rCBF studies at rest and after Diamox treatment, with age-related norms, may be useful in the management of patients with cerebrovascular disease.

Acetazolamide↗
PubMed1984

Improvements in the technique of spinal subarachnoid recirculatory perfusion.

With 14C-labeled dextran as the tracer, studies of the original configuration of spinal recirculatory perfusion and the original model for data analysis demonstrated that this approach does not yield acceptable accuracy in determining cerebrospinal fluid (CSF) formation (Fcsf) and absorption (Acsf) rates. A significant component of this error was due to the fact that the method of data analysis used originally is not based on a realistic mathematical model of the system. A more realistic mathematical model resulted in two simultaneous differential equations that did not have simple analytical solutions and, therefore, could not be used easily for data analysis. By computer simulation, a comparison of the more realistic model with the original model demonstrated that, under ideal conditions, there was a 10% error inherent in the original data analysis method. In the experimental setting, the magnitude of this inherent error is probably 20%. There were three other major problems with the original system: (a) one could not tell when enough data had been collected to ensure convergence of the data analysis algorithm; (b) calibration of the syringe pump in the external circuit was not accurate for short infusion periods; and (c) the presence of the syringe in the external circuit unnecessarily lengthened the period of nonhomogeneous mixing. A new system configuration and new data analysis methods have been developed. In the new system, the syringe is removed from the external circuit and intracranial pressure is controlled by infusion from a separate reservoir where the pressure head is maintained at any desired level by feedback control. Spectrophotometry is used to measure tracer concentration in the external circuit. Data collection and analysis are fully automated under computer control so that, during an experimental run, the investigators are updated at 1- to 2-second intervals as to the convergence of the data analysis routine. Data analysis methods for the new system are superior to previous methods because the models are realistic and no extrapolation is required. In addition, all of the data during the initial period of nonhomogeneous mixing are used to calculate Fcsf and Acsf. With the new system and a simple phantom of the CSF system, the mean error in finding Acsf was 1.7 +/- 1.2% for 27 determinations covering a wide range of absorption rates. Fcsf could be determined to within 0.001 ml/minute. In up to six sequential pressure plateaus, the magnitude of error did not increase with each subsequent run.(ABSTRACT TRUNCATED AT 400 WORDS)

Absorption↗
PubMed1983

Electromyographic study of muscular overflow during precision handgrip.

This study was designed to describe the "overflow" of muscular activity to muscles beyond the essential prime mover and synergists during a precision handgrip exercise. Five subjects performed a 10-minute isometric handgrip exercise consisting of one-second contractions alternated with one-second rests. Four different force levels were assigned: 5, 15, 25, and 40 percent of each subject's maximum handgrip force. All subjects demonstrated overflow activity at the 5-percent level, and three of the five subjects showed more overflow at the 5-percent level than at 15 percent. The greatest amount of overflow was shown at the 40-percent level. No striking interindividual or intraindividual consistency in recruitment order of overflow muscles was apparent. Two distinguishable types of overflow were observed: continuous overflow was the characteristic type at the lower force levels, whereas an interrupted pattern of overflow synchronized to the handgrip contraction was typical of the higher force levels. The possible effects of overflow on precision motor skills are discussed.

Adult↗
PubMed1983

Computer analysis of processor status.

The authors describe the use of a desk-top computer to analyze processor status. Quality control data (sensitometry, densitometry, thermometry, etc.) are collected conventionally. Analysis of the data is subsequently performed using specially designed software. This computer analysis results in a small savings in time and in greatly improved management and presentation of quality control data.

Diagnosis, Computer-Assisted↗
PubMed1980

A special procedures screen.

A mobile screen of plate glass for use in special procedures is described. The screen offers protection for the head and neck of physicians, allows for full visibility, is easily maneuvered, and attenuates at least 86% of incident photons.

Humans↗
PubMed1978

Isometric torque of the finger extensors at the metacarpophalangeal joints.

A pilot study was undertaken to evaluate the isometric torque produced at the metacarpophalangeal joint during finger extension. Fifteen women with normal right hands, aged 21 to 29 years, participated. Each subject was tested for maximal force of isometric extension at the metacarpophalangeal joint angles of 0, 30, and 60 degrees on each of the four fingers. Torque was computed by multiplying the recorded tension and measured length of the proximal phalanx (lever arm). The mean torque for the long finger was significantly greater than the average torque for each of the other three fingers. The mean torque at the joint angle of 60 degrees was significantly greater than at 0 degrees but not at 30 degrees. Reasons for the findings are discussed.

Adult↗
PubMedDate not supplied

The influence of input from the lower cortical layers on the orientation tuning of upper layer V1 cells in a primate.

The receptive fields of cells in the primary visual cortex (area 17 or V1) show clear orientation selectivity, unlike those of the lateral geniculate nucleus (LGN) cells which provide their visual input. The intrinsic circuitry of V1 cells is believed to be partly responsible for this selectivity. We investigated the influence of ascending projections from neurons in the lower layers (5 and 6) of V1 on the orientation selectivity of single neurons in the upper layers (2,3, and 4) by reversibly inactivating ("blocking") lower layer neural activity with iontophoretic application of gamma-aminobutyric acid (GABA) while recording from upper layer cells in the prosimian primate, Galago crassicaudatus. During lower layer blocking, the majority (20/28 = 71.4%) of upper layer neurons exhibited a change in the orientation of their preferred stimulus, a reduction in their orientation tuning, and/or an increase in their response amplitude. Twelve (42.9%) neurons exhibited shifts in their preferred orientation averaging 11 (+/- 4) deg. These neurons were located on average, 272 (+/- 120) microns tangential from the vertical axis of the pipette center. Eleven neurons (39.2%) exhibited an average reduced orientation tuning of 52.5%. Their average location was 230 +/- (115) microns away from the vertical axis of the pipette. Five (17.9%) neurons with average location 145 (+/- 75) microns from the vertical axis exhibited both effects. Two (7.1%) neurons that exhibited significant increases in response amplitude to stimulus angles within 10 deg of the peak excitatory stimulus without changes in orientation selectivity or tuning were located less than 100 microns from the vertical axis. The effects on the orientation tuning of cells were restricted in all cases to within +/- 30 deg of the preferred stimulus orientation. This suggests that layer blocking affects cells with preferred stimulus orientations similar to those of the recorded neurons. Only cells located within 500 microns tangential to the vertical axis of the injection site exhibited these effects. These results suggest that cells within layers 5 and 6 provide organized, orientation-tuned inhibition that sharpens the orientation tuning of cells in the upper cortical layers within the same, or closely neighboring, cell columns.

Animals↗
PubMedDate not supplied

GABAB-receptor-mediated inhibition reduces the orientation selectivity of the sustained response of striate cortical neurons in cats.

Blocking GABAA-receptor-mediated inhibition reduces the selectivity of striate cortical neurons for the orientation of a light bar primarily by reducing the selectivity of their onset transient (initial 200 ms) response. Blocking GABAB-receptor-mediated inhibition with phaclofen, however, is not reported to reduce the orientation selectivity of these neurons when it is measured with a light bar. We hypothesized that blocking GABAB-receptor-mediated inhibition would instead affect the orientation selectivity of cortical neurons by reducing the selectivity of their sustained response to a prolonged stimulus. To test this hypothesis, we stimulated 21 striate cortical neurons with drifting sine-wave gratings and measured their orientation selectivity before, during, and after iontophoretic injection of 2-hydroxy-saclofen (2-OH-S), a selective GABAB-receptor antagonist. 2-OH-S reduced the orientation selectivity of six of eight simple cells by an average of 28.8 (+/- 13.2) % and reduced the orientation selectivity of eight of 13 complex cells by an average of 32.3 (+/- 27.4) %. As predicted, 2-OH-S reduced the orientation selectivity of the neurons' sustained response, but did not reduce the orientation selectivity of their onset transient response. 2-OH-S also increased the length of spike "bursts" (two or more spikes with interspike intervals < or = 8 ms) and eliminated the orientation selectivity of these bursts for six cells. These results are the first demonstration of a functional role for GABAB receptors in visual cortex and support the hypothesis that two GABA-mediated inhibitory mechanisms, one fast and the other slow, operate within the striate cortex to shape the response properties of individual neurons.

Action Potentials↗
PubMedDate not supplied

Contrast adaptation in striate cortical neurons of the nocturnal primate bush baby (Galago crassicaudatus).

It has been argued that in order for the visual system to detect edges accurately under a range of conditions, the visual system needs to adapt to the local contrast level to preserve sensitivity (Blakemore & Campbell, 1969). Cells in the primary visual cortex of cats adapt to stimuli with low to moderate contrast. Curiously, macaque monkey neurons in primary visual cortex (V1) do not show evidence for similar adaptation. To address the question of whether this differential sensitivity in contrast adaptation might be due to phylogenetic variation between cats and primates or to specializations for visual niche (e.g. nocturnal vs. diurnal), contrast adaptation to temporally and spatially optimized gratings was examined in 30 V1 cells of three nocturnal primate bush babies (Galago crassicaudatus). A second objective was to examine the relationship between the degree of contrast adaptation and cell classification or cell location relative to cortical layers or compartments [i.e. cytochrome-oxidase (CO) blobs and interblobs]. All cells were classified (simple vs. complex) and anatomically localized relative to cortical layers and cytochrome-oxidase (CO) blob and interblob compartments. Two independent measures of contrast adaptation were used. In the first test, contrast was sequentially increased from 3-56% and then decreased. The contrast required to maintain a half-maximum response amplitude in the 30 cells tested increased an average of 0.24 (+/- 0.12) log units during the sequential decrements in contrast. For the second test, four sets of five interleaved contrasts within +/- 1 octave of a central adapting contrast (10%, 14%, 20%, and 28%, respectively) were presented. The cells produced a mean adaptation index of 0.57 (+/- 0.47) which is very similar to that exhibited by cat cortical neurons (0.54 +/- 0.41). Interestingly, cells in interblobs showed a trend toward greater adaptation than did blob cells. Moreover, cells in the supragranular layers exhibited greater adaptation than cells in the infragranular layers. No significant differences in adaptation were found to correlate with other cell classification indices. Taken together, our results suggest that contrast adaptation may be more important for maintaining sensitivity in nocturnal species (primates or cats) than in diurnal species (macaque monkeys), and that in the nocturnal bush baby, cells in cortical layers and compartments may be differentially specialized for contrast adaptation.

Adaptation, Ocular↗
PubMedDate not supplied

Differential contributions of magnocellular and parvocellular pathways to the contrast response of neurons in bush baby primary visual cortex (V1).

How neurons in the primary visual cortex (V1) of primates process parallel inputs from the magnocellular (M) and parvocellular (P) layers of the lateral geniculate nucleus (LGN) is not completely understood. To investigate whether signals from the two pathways are integrated in the cortex, we recorded contrast-response functions (CRFs) from 20 bush baby V1 neurons before, during, and after pharmacologically inactivating neural activity in either the contralateral LGN M or P layers. Inactivating the M layer reduced the responses of V1 neurons (n = 10) to all stimulus contrasts and significantly elevated (t = 8.15, P < 0.01) their average contrast threshold from 8.04 (+/- 4.1)% contrast to 22.46 (+/- 6.28)% contrast. M layer inactivation also significantly reduced (t = 4.06, P < 0.01) the average peak response amplitude. Inactivating the P layer did not elevate the average contrast threshold of V1 neurons (n = 10), but significantly reduced (t = 4.34, P < 0.01) their average peak response amplitude. These data demonstrate that input from the M pathway can account for the responses of V1 neurons to low stimulus contrasts and also contributes to responses to high stimulus contrasts. The P pathway appears to influence mainly the responses of V1 neurons to high stimulus contrasts. None of the cells in our sample, which included cells in all output layers of V1, appeared to receive input from only one pathway. These findings support the view that many V1 neurons integrate information about stimulus contrast carried by the LGN M and P pathways.

Animals↗
PubMedDate not supplied

Nonlocal origin of response suppression from stimulation outside the classic receptive field in area 17 of the cat.

A stimulus located outside the classic receptive field (CRF) of a striate cortical neuron can markedly influence its behavior. To study this phenomenon, we recorded from two cortical sites, recorded and peripheral, with separate electrodes in cats anesthetized with Propofol and nitrous oxide. The receptive fields of each site were discrete (2-7.3 deg between centers). A control orientation tuning (OT) curve was measured for a single recorded cell with a drifting grating. The OT curve was then remeasured while stimulating simultaneously the cell's CRF as well as the peripheral site with a stimulus optimized for that location. For 22/60 cells, the peripheral stimulus suppressed the peak response and/or shifted the center of mass of the OT curve. For 19 of these 22 cells, we then reversibly blocked stimulus-driven activity at the peripheral site by iontophoretic application of GABA (0.5 M). For 6/19 cells, the response returned to control levels, implying that for these cells the inhibitory influence arose from the blocked site. The responses of nine cells remained reduced during inactivation of the peripheral site, suggesting that influence was generated outside the region of local block in area 17. This is consistent with earlier findings suggesting that modulatory influences can originate from higher cortical areas. Three cells had mixed results, suggesting multiple origins of influence. The response of each cell returned to suppressed levels after dissipation of the GABA and returned to baseline values when the peripheral stimulus was removed. These findings support a cortical model in which a cell's response is modulated by an inhibitory network originating from beyond the receptive field that supplants convergence of excitatory lateral geniculate neurons. The existence of cells that exhibit no change in peripherally inhibited responses during the GABA application suggests that peripheral influences may arise from outside area 17, presumably from other cortical areas (e.g. area 18).

Action Potentials↗
PubMedDate not supplied

Cadmium telluride matrix gamma camera.

An experimental gamma camera that has significant performance has been designed, constructed, and tested. The new camera has a matrix of cadmium telluride semiconductors as the detecting medium. The detectors are located within the collimating holes (rather than behind them). Coincident outputs from each row and column are used to digitally identify the individual detector in which the energy deposition occurred. Direct digital localization of detected events and the attenuation of scatter radiation between matrix elements by the collimator septa that separate detectors, contribute to reasonable resolution and imaging time. The superior radiation detection characteristics of cadmium telluride (in comparison to sodium iodide) could provide superior discrimination against scattered radiation that contributes only spurious information to the image. Detector reliability and uniformity limit the camera's performance; however, the availability of large numbers of small cadmium telluride detectors that have uniform radiation detection properties would make a clinical camera viable.

Cadmium↗
PubMedDate not supplied

Inhalation regional cerebral blood flow: the use of tidal CO2 data to find radionuclide activity associated with exhaled alveolar gas.

When calculating cerebral blood flow by the inhalation regional cerebral blood flow technique, radionuclide activity associated with exhaled alveolar gas is used to represent the arterial input function for each brain region. In this study, tidal CO2 data are used to identify respiratory gas samples that contain alveolar gas. Traditional methods identify alveolar gas samples by searching for maxima and minima in the raw air curve. The raw air curve is determined by sequentially counting radionuclide activity in respiratory gases sampled at the mouth. Traditional methods sometimes erroneously identify and use maxima or minima that do not represent alveolar gas. The use of CO2 data is advantageous since the range of CO2 during exhalation can identify those exhalations that approach the functional reserve capacity and hence represent alveolar gas. The arterial input function is represented by counting intervals from the raw air curve which coincide with exhalation of alveolar gas as identified by CO2 data. This approach for representing the arterial input function is fully automatic, accurate, and reproducible.

Brain↗
PubMedDate not supplied

Analysis of inhalation rCBF data.

Relative to other approaches that have been recommended, fitting all head data, solving for a time shift, and including an air passage artifact term in the model significantly improved the estimate of gray matter blood flow by the inhalation technique. A robust algorithm, which incorporates these features, has been developed. Formulas which facilitate implementation of this algorithm are reported. An artifact from large scalp arteries was not significant and does not need to be included in the model.

Administration, Inhalation↗