Biomedical subjects

J D Allison

Publications and source records attributed to J D Allison.

At least 19 recordsLinked to original sources

PubMed1996

Leukocyte trafficking in response to magnetic resonance imaging.

There were significant increases in total T cells and in T helper cells in blood samples collected immediately following magnetic resonance imaging (MRI) examinations of brains of male volunteers and patients. Percentages of total lymphocytes and suppressor/cytotoxic T cells decreased in these same samples. There were no significant changes in any leukocyte subpopulations in males undergoing lumbar MRI and females undergoing brain MRI. Thus, it is unlikely that stress from the procedure is the explanation for these changes. Our results show that MRI has specific effects on a brain system(s) that controls lymphocyte subpopulations.

Adult↗

PubMed1995

Magnetic resonance imaging compared to echocardiography to assess left ventricular mass in the hypertensive patient.

Echocardiography (ECHO) is useful to document changes in left ventricular mass (LVM) in groups of patients, but may be too variable for use in the individual patient. Magnetic resonance imaging (MRI) may be a more precise and reliable method to quantify the mass of the left ventricule. This study reports the accuracy, precision, and reliability of LVM estimates by MRI as compared to data obtained by ECHO in hypertensive patients. Accuracy referred to the comparison of LVM by MRI to anatomical LVM determined by autopsy. Precision was examined using 34 duplicate MRI images and by blindly reading 24 duplicate M-mode strips. Reliability was assessed by MRI in four subjects over 2 months, and by ECHO in 22 hypertensive patients over 2 weeks. Agreement between MRI and ECHO estimates of LVM was determined in the same 17 hypertensive patients using linear regression. MRI LVM estimates were within 17.5 g (95% CI) of the true LVM. The linear agreement between MRI and ECHO estimates of LVM could be described by the equation MRI = 0.61 x ECHO + 49.57 (r = 0.63, P < .01). The precision of LVM by MRI (11 g) was over twice that observed with ECHO (26 g). The reliability of MRI LVM estimates was more consistent (+/- 8 g) than that for ECHO (+/- 49 g). MRI appears to be a more precise and reliable method for measuring LVM, and would be more suitable than ECHO for the clinical evaluation of the individual patient.

Adult↗

PubMed1994

Inactivation of the infragranular striate cortex broadens orientation tuning of supragranular visual neurons in the cat.

Intracortical inhibition is believed to enhance the orientation tuning of striate cortical neurons, but the origin of this inhibition is unclear. To examine the possible influence of ascending inhibitory projections from the infragranular layers of striate cortex on the orientation selectivity of neurons in the supragranular layers, we measured the spatiotemporal response properties of 32 supragranular neurons in the cat before, during, and after neural activity in the infragranular layers beneath the recorded cells was inactivated by iontophoretic administration of GABA. During GABA iontophoresis, the orientation tuning bandwidth of 15 (46.9%) supragranular neurons broadened as a result of increases in response amplitude to stimuli oriented about +/- 20 degrees away from the preferred stimulus angle. The mean (+/- SD) baseline orientation tuning bandwidth (half width at half height) of these neurons was 13.08 +/- 2.3 degrees. Their mean tuning bandwidth during inactivation of the infragranular layers increased to 19.59 +/- 2.54 degrees, an increase of 49.7%. The mean percentage increase in orientation tuning bandwidth of the individual neurons was 47.4%. Four neurons exhibited symmetrical changes in their orientation tuning functions, while 11 neurons displayed asymmetrical changes. The change in form of the orientation tuning functions appeared to depend on the relative vertical alignment of the recorded neuron and the infragranular region of inactivation. Neurons located in close vertical register with the inactivated infragranular tissue exhibited symmetric changes in their orientation tuning functions. The neurons exhibiting asymmetric changes in their orientation tuning functions were located just outside the vertical register. Eight of these 11 neurons also demonstrated a mean shift of 6.67 +/- 5.77 degrees in their preferred stimulus orientation. The magnitude of change in the orientation tuning functions increased as the delivery of GABA was prolonged. Responses returned to normal approximately 30 min after the delivery of GABA was discontinued. We conclude that inhibitory projections from neurons within the infragranular layers of striate cortex in cats can enhance the orientation selectivity of supragranular striate cortical neurons.

Animals↗

PubMed1994

Efferents from the suprachiasmatic nucleus to basal forebrain nuclei in the green treefrog (Hyla cinerea).

Injections of horseradish peroxidase (HRP) into the eye, striatum, preoptic area, or ventral hypothalamus of the green treefrog (Hyla cinerea) demonstrated an indirect retinal pathway to each basal forebrain region via the suprachiasmatic nucleus (SCN). Intraocular injections resulted in HRP-filled fibers within the ventral portion of the SCN bilaterally. Apparent en passant and terminal swellings on these fibers were seen adjacent to SCN cells. Cells in both the ventral and dorsal portions of the SCN were retrogradely filled following each of the forebrain injections, but the relative distributions of filled cells were different. The striatum receives a bilateral projection mainly from cells in the ventral portion of the SCN. A small ipsilateral projection from this same SCN region reaches the ventral hypothalamus. The SCN projection to the preoptic area arises from a more uniform distribution of cells, with the majority located in the ipsilateral dorsal region of the nucleus. The striatum is believed to be involved in orientation responses, while the preoptic area and ventral hypothalamus regulate gonadal activity related to reproduction. Each of these areas receives auditory input carrying information about acoustic communication signals, social cues important for coordinating reproductive activity. Input from the SCN could provide these same basal forebrain centers with information about the photic environment, an important environmental cue regulating reproduction.

Animal Communication↗

PubMed1993

Differentiation of benign from malignant breast masses by time-intensity evaluation of contrast enhanced MRI.

Using gadolinium-DTPA enhanced MRI we analyzed the enhancement characteristics of palpable breast masses in 23 patients--10 cancers and 13 benign lesions. The most specific finding for separating benign from malignant lesions was a ratio of maximum intensity change divided by the time interval during which this first occurred. Designated ranges of this ratio were specific for benign disease and sensitive for malignancy in this small patient group. Three of eight fibroadenomas exhibited enhancement patterns indistinguishable from cancer.

Adenofibroma↗

PubMed1993

Measurement of left ventricular mass in hypertrophic cardiomyopathy using MRI: comparison with echocardiography.

Left ventricular mass (LVM) is an important consideration in the management of cardiac hypertrophy associated with hypertrophic cardiomyopathy (HCM), systemic hypertension, and other diseases. A brief MRI cardiac imaging procedure used to monitor regression of LVM during treatment would be beneficial in management of these patients, since echocardiograms cannot be obtained in all patients and since the volume of a hypertrophic heart can straightforwardly be assessed from a series of tomographic slices. The present study was designed to evaluate a brief cardiac MRI procedure for measurement of LVM in HCM and compare it to echocardiography. MRI images acquired in a simulated transverse body plane were used to evaluate the mass of the left ventricle in 6 ex vivo human hearts obtained at autopsy. The estimates of LVM by MRI in the ex-vivo hearts were within 8% of the actual LVM. MRI images were acquired to evaluate LVM in 5 normal subjects and 12 patients diagnosed with HCM. Echocardiography was accomplished on 4 of the normal subjects and 10 of the patients having HCM. There were no significant differences in LVM by MRI and echocardiographic techniques in normal subjects. Transverse MRI images acquired on normal subjects demonstrated that estimates of LVM are reproducible when repeated over 3-w to 3-mo intervals. Images selected for analysis represented the heart in an early diastolic phase. MRI and echocardiographic techniques demonstrated significant differences in LVM in HCM patients. Estimates of LVM in normal subjects and patients diagnosed with HCM were normalized for body weight. The LVM estimates for HCM patients were very significantly different than normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Weight↗

PubMed1993

Sensory pathways linking social and environmental cues to endocrine control regions of amphibian forebrains.

The secretion of gonadotropin releasing hormone (GnRH), and hence sex steroids, is influenced by social signals produced by conspecifics and by environmental cues such as day length. The sensory systems processing these varied signals must therefore connect with the GnRH control centers in the preoptic area and hypothalamus. Forebrain pathways in frogs provide a model for how vertebrates accomplish this. Auditory information, which can transmit the features of the vocal communication signals used by frogs during reproductive social behavior, reaches both the preoptic area and ventral hypothalamus via thalamic and midbrain nuclei. An examination of these auditory pathways suggests that there are subtle differences in their anatomical, physiological, and histochemical characteristics. The suprachiasmatic nucleus, which is important for controlling circadian rhythms in vertebrates, also projects to both the preoptic area and ventral hypothalamus, providing information about environmental characteristics in parallel with the information about social signals. This pattern of connections suggests that the two major GnRH control centers in amphibian brains receive independent, parallel information about the social and environmental cues influencing reproduction.

Amphibians↗

PubMed1992

Acoustic modulation of neural activity in the preoptic area and ventral hypothalamus of the green treefrog (Hyla cinerea).

Responses of neurons in the preoptic area and ventral hypothalamus to conspecific mating calls or white noise bursts were examined in male green treefrogs (Hyla cinerea) during different seasons. In the winter, 34.3% of preoptic neurons and 46.7% of ventral hypothalamic cells demonstrated significant changes in activity level during presentation of a conspecific mating call. In contrast, only 13.3% of preoptic units and 16.7% of ventral hypothalamic cells responded to the white noise. The percentage of preoptic and hypothalamic units responding to the advertisement call did not differ significantly during the summer breeding season. Type I units exhibited a dramatic increase in activity during acoustic stimulation followed by a rapid return to baseline activity levels after stimulus offset. Type II cells showed a robust activity increase during stimulation, but maintained an intermediate activity level after stimulus offset. In the preoptic area, a third response type exhibited suppressed activity during acoustic stimulation. Although seasonal condition did not alter the percentage of acoustically responsive units within either nucleus, the proportion of Type I units in the ventral hypothalamus was greatest during the summer.

Acoustic Stimulation↗

PubMed1991

Thalamic and midbrain auditory projections to the preoptic area and ventral hypothalamus in the green treefrog (Hyla cinerea).

Iontophoretic injections of horseradish peroxidase (HRP) into either the preoptic area or ventral hypothalamus of the green treefrog, (Hyla cinerea), demonstrated inputs from thalamic and midbrain auditory nuclei. In a pattern similar to that seen in Rana catesbeiana and Rana pipiens, the central thalamic and secondary isthmal nuclei were found to provide heavy input to the ventral hypothalamus. Additionally, a lighter input from the anterior thalamic nucleus was seen. In contrast, the preoptic area receives a major input from the anterior thalamic and secondary isthmal nuclei, and possibly a sparse input from the central thalamic nucleus. These results suggest that in treefrogs multimodal and auditory information may reach the preoptic area and ventral hypothalamus, two regions involved in endocrine regulation and the control of reproductive behavior, via largely separate major pathways from the thalamus combined with a common midbrain input. Furthermore, the ventral hypothalamus receives heavy input from the preoptic area, lateral amygdala, suprachiasmatic nucleus, anterior entopeduncular nucleus, and a lighter input from the striatum. Nonauditory afferents to the preoptic area originate in the medial and lateral septal nuclei, medial pallium, and the dorsal-, lateral-, and ventral hypothalamus. The preoptic area and ventral hypothalamus are reciprocally connected.

Animals↗

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↗