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Biomedical subjects

M A Walker

Publications and source records attributed to M A Walker.

At least 55 records · Page 3Linked to original sources
PubMed1997

Illusion decrement as a function of duration of inspection and figure type.

Illusion decrement for the Müller-Lyer and Horizontal-Vertical illusions was examined. The experiment consisted of an initial adjustment of an illusion followed by 20 test trials, each with an intervening 60-sec. intertrial interval during which a comparator line and a standard line set to equality were visually inspected for 0, 20, 40, or 60 sec. After each intertrial interval the length of the comparator line was reset by the experimenter to either 0 or 90 cm, and subjects then adjusted its length to perceived equality with the standard line (42 cm). Illusion decrement was inversely related to the duration of inspection for each illusion, with significant reductions in magnitude of illusion observed for all groups. These results support prior demonstrations that perceptual learning mechanisms are operative during brief periods of visual inspection, especially when these periods are followed by the opportunity to make repeated adjustments.

Adult↗
PubMed1996

Case-control study of risk factors for the development of laminitis in the contralateral limb in Equidae with unilateral lameness.

OBJECTIVE: To identify risk factors associated with development of laminitis of the supporting limb in Equidae with unilateral laminitis and to determine the radiographic appearance of this type of laminitis. DESIGN: Retrospective analysis of medical records. ANIMALS: 20 Equidae with unilateral lameness that developed laminitis of the contralateral limb. PROCEDURE: Case animals were compared with matched and unmatched populations of control animals that did not develop contralateral limb laminitis. Lateromedial radiographic projections of affected feet were evaluated for evidence of laminitis. RESULTS: Body weight of case animals was not significantly different from that of control animals, but number of days that control animals were lame prior to recovery was significantly less than number of days that case animals were lame prior to the onset of laminitis. Lateromedial radiographic projections of the foot of the support limb were available for 16 of the 20 case animals. For all 16, thickness of the soft tissue dorsal to the distal phalanx was > 29% of the palmar cortical length of the distal phalanx, but only 1 had evidence of rotation of the distal phalanx. The proportion of case animals that were euthanatized was significantly greater than the proportion of control animals that were euthanatized. CLINICAL IMPLICATIONS: Duration of lameness, but not body weight, was a risk factor for development of laminitis in the contralateral limb in Equidae with unilateral lameness, and animals that developed this complication were more likely to be euthanatized than were animals that did not.

Animals↗
PubMed1996

Magnetic resonance imaging of the brain for diagnosis of neurocysticercosis in a dog.

Neurocysticercosis was diagnosed in a 2-year-old spayed Whippet by use of magnetic resonance imaging. The dog was evaluated because of a 3-month history of slowly progressive balance and directional abnormalities, which were indicative of brain stem disease. Magnetic resonance imaging of the brain and CSF analysis were chosen as the best diagnostic modalities for determination of the primary disease. Results of CSF analysis were within reference ranges. Examination of T1-weighted, contrast-enhanced, 3-mm-thick axial, sagittal, and coronal views of the brain revealed multiple cyst-like lesions. The cysts had high-signal-intensity, ring-like peripheral margins and were located in the subdural portion of the left occipital lobe and the dorsal midline and right dorsolateral aspect of the brain stem. A tentative diagnosis of neurocysticercosis was made on the basis of similar findings in human beings with this disease. Treatment with albendazole and prednisone was initiated, and clinical signs resolved during the following weeks. Repeat magnetic resonance imaging confirmed resolution of the disease.

Animals↗
PubMed1993

Relationship between clustering of post-ovulatory and hierarchical follicles and their order of ovulation in the mature domestic hen (Gallus gallus domesticus).

Hierarchical (> 8 mm) and post-ovulatory follicles from the ovaries of laying hens at 45 and 86 weeks of age were assigned to clusters defined by the coalescence of their follicular stalks. They were also classified by size to give the succession in which ovulation had occurred, or would occur for the hierarchical follicles. The association between the order of ovulation and the observed clusters was compared with randomness and with dependence on the cluster in which the immediately preceding ovulation occurred. The order of ovulation was associated randomly with clusters, and was independent of the cluster containing the preceding ovulation. Many perceived clusters of successive follicles and post-ovulatory follicles may be compatible with a random order of ovulation. These findings do not support theories of stimulation or inhibition of adjacent follicles, leading to eventual ovulation, by a dominant follicle.

Aging↗
PubMed1993

Repetitive injectable anesthesia in a 27-year-old horse.

A 27-year-old horse was anesthetized 3 times a week for 4 weeks, to facilitate cobalt therapy of a squamous cell carcinoma in the left paranasal sinus. Limitations of facilities required transport of the anesthetized horse to and from the cobalt therapy room, therefore, injectable anesthesia was used. Initially, the horse was preanesthetized with xylazine (at 1.1 mg/kg IV) and butorphanol (0.04 mg/kg IV). After 3 anesthetic episodes, the xylazine dose was reduced to 0.4 mg/kg IV and the butorphanol was deleted from the regimen. Tiletamine-zolazepam (1.1 mg/kg IV) was used for induction and maintenance of anesthesia (although on 2 occasions a bolus of ketamine was used to maintain immobility). The length of the procedure varied from 10-45 minutes, and the recovery times to sternal and standing varied from 23-76 and 55-105 minutes respectively. Although numerous complications might be expected given the age of this horse and the physiologic and metabolic demands of repetitive injectable anesthetics, none were observed.

Anesthesia, Intravenous↗
PubMed1992

Changes in ovarian function of female turkeys photostimulated at 18, 24 or 30 weeks of age and fed ad libitum or restricted until point of lay.

1. Females from a medium body weight strain of turkeys were fed ad libitum or restricted to 0.6 of ad libitum-fed body weight at sexual maturity and were photostimulated at 18, 24 or 30 weeks of age. Ovarian follicular structure was assessed in 8 birds from both rearing treatments at photostimulation, after photostimulation for 6 or 12 weeks and at 55 weeks of age. 2. The patterns of small white follicles and of larger yellow follicles were similar in restricted and in ad libitum-fed turkeys for birds in lay at the same age, regardless of the time elapsed since photostimulation. 3. Among birds in lay the number of normal yellow follicles and the proportion of multiple yellow follicles declined with age. A relatively low proportion of restricted birds photostimulated at 18 and 24 weeks were in lay after 12 weeks of photostimulation. 4. For birds in lay the number of white follicles 1.4 to less than 1.8 mm in diameter increased and the number greater than 1.8 mm declined with age. There was a corresponding increase in the rates of atresia in follicles 1.8 to less than 5.0 mm in diameter.

Age Factors↗
PubMed1991

Urinary hormonal concentrations and spinal bone densities of premenopausal vegetarian and nonvegetarian women.

We evaluated the relationships among nutrition, hormone concentrations, and bone density of the spine in 27 vegetarian and 37 nonvegetarian premenopausal women. The two groups were indistinguishable with respect to age, height, weight, menarche, years of formal education, and medical histories. The frequency of menstrual irregularity was significantly higher in the vegetarian group. The bone densities of the vegetarians and the nonvegetarians were not significantly different. Caffeine intake in both groups had a positive effect on urinary calcium excretion, but no association was observed between bone density and caffeine intake. Total fat, monosaturated fat, and oleic acid intake were positively associated with luteinizing hormone concentrations of the vegetarians only. Overall, the differences in dietary practices of these premenopausal vegetarian and nonvegetarian women did not appear to have major effects on bone biology or reproductive history.

Adult↗
PubMed1991

Effects of chilling on the biochemical and functional properties of thylakoid membranes.

The mechanism of chilling resistance was investigated in 4-week-old plants of the chilling-sensitive cultivated tomato, Lycopersicon esculentum Mill. cv H722, and rooted cuttings of its chilling-resistant wild relative, L. hirsutum Humb. and Bonpl., which were chilled for 3 days at 2 degrees C with a 14-hour photoperiod and light intensity of 250 micromoles per square meter per second. This chilling stress reduced the chlorophyll fluorescence ratio, stomatal conductance, and dry matter accumulation more in the sensitive L. esculentum than in the resistant L. hirsutum. Photosynthetic CO(2) uptake at the end of the chilling treatment was reduced more in the resistant L. hirsutum than in L. esculentum, but recovered at a faster rate when the plants were returned to 25 degrees C. The reduction of the spin trap, Tiron, by isolated thylakoids at 750 micromoles per square meter per second light intensity was taken as a relative indication of the tendency for the thylakoids to produce activated oxygen. Thylakoids isolated from the resistant L. hirsutum with or without chilling treatment were essentially similar, whereas those from chilled leaves of L. esculentum reduced more Tiron than the nonchilled controls. Whole chain photosynthetic electron transport was measured on thylakoids isolated from chilled and control leaves of the two species at a range of assay temperatures from 5 to 25 degrees C. In both species, electron transport of the thylakoids from chilled leaves was lower than the controls when measured at 25 degrees C, and electron transport declined as the assay temperature was reduced. However, the temperature sensitivity of thylakoids from chilled L. esculentum was altered such that at all temperatures below 20 degrees C, the rate of electron transport exceeded the control values. In contrast, the thylakoids from chilled L. hirsutum maintained their temperature sensitivity, and the electron transport rates were proportionately reduced at all temperatures. This sublethal chilling stress caused no significant changes in thylakoid galactolipid, phospholipid, or protein levels in either species. Nonchilled thylakoid membranes from L. hirsutum had fourfold higher levels of the fatty acid 16:1, than those from L. esculentum. Chilling caused retailoring of the acyl chains in L. hirsutum but not in L. esculentum. The chilling resistance of L. hirsutum may be related to an ability to reduce the potential for free radical production by close regulation of electron transport within the chloroplast.

Journal Article↗
PubMed1991

Recurrent strangulated obturator hernia.

A case of recurrent strangulated obturator hernia is presented. The difficulty in diagnosing obturator hernia and the high mortality associated with strangulation are highlighted from a literature review. A high index of suspicion in older patients presenting with intestinal obstruction without an obvious cause, possibly combined with CT scanning of the pelvic region, may lead to earlier diagnosis and operation and a more favourable outcome in such cases.

Aged↗
PubMed1989

Control of the development of the ovarian follicular hierarchy in broiler breeder pullets by food restriction during rearing.

1. The increase in the numbers of yellow and of white ovarian follicles was studied from 10 weeks of age to sexual maturity in broiler breeder pullets fed ad libitum and on a restricted intake. The growth of follicles greater than 1 mm diameter commenced at 14 to 16 weeks of age in ad libitum birds and at 22 to 24 weeks in those which were restricted. 2. In a second experiment, groups of birds restricted from 4 d of age were transferred to ad libitum feeding at 2-week intervals and examined at first egg. The numbers of yellow follicles at first egg were not affected by restriction to 14 weeks of age but, thereafter, declined linearly with time on restriction. 3. In the second experiment there were no comparable responses in the numbers of white follicles or in the rates of atresia. 4. Food restriction to 22 weeks of age produced about half the response in numbers of yellow follicles as restriction continued to point of lay (27 to 32 weeks of age). In practical situations, the results suggest that food intake should be restricted up to the onset of lay and then increased in relation to the rise in egg production. 5. Atresia was greatest in white follicles 3.15 to 6.30 mm diameter and was less outside this range.

Animals↗
PubMed1989

Adoptive transfer of tsk skin fibrosis to +/+ recipients by tsk bone marrow and spleen cells.

The tight skin mouse (Tsk/+) is an autosomal dominant example of inherited fibrosis whose pathogenesis is unclear. Autoimmune phenomena have been described previously. This study demonstrates the adoptive transfer of skin fibrosis to lethally irradiated syngeneic +/+ recipients by the transplantation of both bone marrow and spleen cells. The recipient skin fibrosis was not associated with mast cell proliferation or degranulation as it is in the tsk/+ mouse, representing for the first time a dissociation between mast cells and fibrosis and introducing the potential for direct T cell-fibroblast interactions.

Animals↗
PubMed1989

Early renal ultrasonographic findings in dogs with experimentally induced ethylene glycol nephrosis.

Renal ultrasonographic changes were evaluated in 5 dogs administered 10 ml of commercial antifreeze (95% ethylene glycol)/kg of body weight, PO, and in 2 dogs given placebos. Studies were made prior to and after ingestion on an hourly basis over a period of 8 to 10 hours. All dogs were anesthetized immediately after toxin or placebo ingestion for the duration of the study. Renal cortical echogenicity was evaluated in comparison with that of the adjacent liver and spleen. Echogenicity of the renal medulla and definition of the corticomedullary junction were assessed. Within 4 hours after ethylene glycol administration, renal cortical echogenicity of all intoxicated dogs increased from normal to surpass that of liver and approach or equal that of the spleen. Medullary echogenicity in all intoxicated dogs progressively increased over the course of the study, with changes recognized within 5 hours after ethylene glycol administration. An ultrasonographic pattern consisting of nearly equal, marked increase in cortical and medullary echogenicity and relatively hypoechoic corticomedullary junction and central medullary regions was recognized concurrent with the development of anuria in 3 of the 5 intoxicated dogs. Mild, transient increases in cortical and medullary echogenicity were observed in anesthetized control dogs. However, no statistical difference (P less than 0.05) was detected between baseline, peak, and terminal echogenicity values in these dogs. Blood and urine samples were collected hourly from intoxicated dogs to coincide with ultrasonographic studies. Most clinicopathologic values derived from these samples were not statistically different (P less than 0.05) from those reported in a study that used a similar intoxication protocol in nonanesthetized dogs.

Animals↗