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Biomedical subjects

G McCormack

Publications and source records attributed to G McCormack.

At least 19 recordsLinked to original sources
PubMed2000

The cause of neuronal degeneration in Alzheimer's disease.

Alzheimer's disease is associated with a specific pattern of pathological changes in the brain that result in neurodegeneration and the progressive development of dementia. Pathological hallmarks common to the disease include beta-amyloid plaques, dystrophic neurites associated with plaques and neurofibrillary tangles within nerve cell bodies. The exact relationship between these pathological features has been elusive, although it is clear that beta-amyloid plaques precede neurofibrillary tangles in neocortical areas. Examination of the brains of individuals in the preclinical stage of the disease have shown that the earliest form of neuronal pathology associated with beta-amyloid plaques resembles the cellular changes that follow structural injury to axons. Thus, the development of beta-amyloid plaques in the brain may cause physical damage to axons, and the abnormally prolonged stimulation of the neuronal response to this kind of injury ultimately results in the profound cytoskeletal alterations that underlie neurofibrillary pathology and neurodegeneration. Therapeutically, inhibition of the neuronal reaction to physical trauma may be a useful neuroprotective strategy in the earliest stages of Alzheimer's disease.

Alzheimer Disease↗
PubMed2000

Metallothionein is expressed in adipocytes of brown fat and is induced by catecholamines and zinc.

Metallothionein (MT) is thought to have an antioxidant function and is strongly expressed during activation of thermogenesis and increased oxidative stress in brown adipose tissue (BAT). Localization and regulation of MT expression in BAT was therefore investigated in rats and mice. Immunohistochemical analysis of BAT from rats exposed to 4 degrees C for 24 h showed that MT and uncoupling protein 1 (UCP1) were coexpressed in differentiated adipocytes, and both cytoplasmic and nuclear localization of MT was observed. Cold induction of MT-1 expression in BAT was also observed in mice. Administration of norepinephrine to rats and isoproterenol to mice stimulated MT and UCP1 expression in BAT, implying a sympathetically mediated pathway for MT induction. In mice, zinc, and particularly dexamethasone, induced MT-2 expression in BAT and liver. Surprisingly, zinc also induced UCP1 in BAT, suggesting that elevated zinc may induce thermogenesis. We conclude that expression of MT in mature brown adipocytes upon beta-adrenoceptor activation is consistent with a role in protecting against physiological oxidative stress or in facilitating the mobilization or utilization of energy reserves.

Adaptation, Physiological↗
PubMed1999

A practical guide to the management of oesophageal varices.

Bleeding oesophageal varices are a frequent and sometimes fatal complication of portal hypertension. Prompt resuscitation and arrest of haemorrhage are the immediate short term priorities. Vasoactive therapy to reduce portal pressure is administered on presentation. Early endoscopy is necessary to make a definitive diagnosis and initiate appropriate therapy; usually emergency sclerotherapy or banding. After the acute bleeding episode, follow-up therapy is instituted either to obliterate the varices by sclerotherapy or banding, or to chronically lower portal pressure and hence reduce the risk of bleeding pharmacologically; a combination of both strategies may be also used. Active surveillance of those at risk of developing varices is advocated. Long term beta-blocker therapy has been demonstrated to be effective in both the primary prevention of variceal haemorrhage and the prevention of rebleeding in those who have already bled. Despite a multitude of therapeutic regimes and ongoing clinical trials, mortality from this condition remains disappointingly high.

Esophageal and Gastric Varices↗
PubMed1998

Postpartum coma.

Explore the source record for details and available documents.

Adult↗
PubMed1996

The source of disparity vergence innervation determines prism adaptation.

A physiological model of prism adaptation argues that adaptation magnitude and rate are functions of the magnitude of reflex vergence innervation. It has also been shown that there is reduced prism adaptation magnitude for a given disparity stimulus where only peripheral sensory fusion is present (the 'eccentricity effect'). This study attempted to determine whether the eccentricity effect is attributable to reduced reflex vergence innervation in peripheral fusion. Experiments were run in a Maxwellian view haploscope. Convergence and divergence adaptation to 6 delta disparity stimuli were quantified for seven binocularly normal subjects using subjective heterophoria measurements. Vergence response during central or peripheral fusion was quantified objectively by infrared oculography. Six of seven subjects revealed an eccentricity effect. However, in three of seven subjects the eccentricity effect was not predictable from the manifest vergence response. The results suggest that the source of reflex vergence innervation affects prism adaptation. A model is proposed whereby different sources of reflex disparity vergence innervation stimulate prism adaptation by way of separate neurological pathways of differing responsiveness.

Adaptation, Ocular↗
PubMed1992

Infant VEP and preferential looking acuity measured with phase alternating gratings.

Previously, infants' grating acuity was found to be temporally tuned, but adults' grating acuity was not. In infants, acuity was higher for gratings phase alternating at 7.5 and 14 reversals/sec than for stationary gratings and gratings alternating at 2.5 or 23 reversals/sec. Also, when preferential looking (PL) and visually evoked potential (VEP) acuity were estimated with phase alternating gratings (14 reversals/sec), the acuity difference between the two techniques was smaller than that obtained when phase alternating gratings were used to estimate VEP acuity and stationary gratings were used to estimate PL acuity. In the present study, it was determined if PL grating acuity was tuned in older children and if the smaller difference between VEP and PL acuity found when infants were tested with phase alternating gratings was independent of temporal rate. Grating acuity in infants older than 2 yr was found to be not tuned, and the smaller difference between VEP and PL grating acuity in infants when both were measured with phase-alternating gratings was not rate dependent. VEP acuity and PL acuity for phase alternating gratings developed at different rates, converging to nearly equivalent levels by 12 mo of age.

Aging↗
PubMed1992

Non-fatal deliberate self-poisoning in Dublin's north inner city--an overview.

It is almost three decades since a survey of attempted suicide in Dublin City Hospitals was published. In 1962, 159 cases in the City of Dublin and Borough of Dun Laoghaire were studied and reported. Over a six month period (November 1989-April 1990) 147 cases of deliberate self-poisoning were admitted to the Mater Hospital, Dublin, of which 100 case notes were appropriate for examination. In 1973, a six month survey of attempted suicide was carried out at the Mater Hospital, Dublin where 38 patients were admitted following non-fatal deliberate self-poisoning. In our study, the female to male ratio was 2:1, 50% of cases took more than one drug type,, benzodiazepines being the most commonly ingested compound. Alarmingly over a quarter (28%) of females under 25 had overdosed on paracetamol either alone or in conjunction with other compounds. Alcohol was consumed in 46% of all cases. 40% of cases involved a past history of deliberate self-poisoning and 60% had a past history of psychiatric intervention. Our survey outlines current trends in deliberate self-poisoning in Dublin's North Inner City. We have compared our 1990 survey to the similar survey conducted by our unit seventeen years ago. Several characteristics remain unaltered. The number of overdoses has almost trebled. We have noted a sharp rise in unemployment, alcohol abuse and psychiatric history among female overdoses. We have noted the disturbing introduction of paracetamol overdose particularly among young females (25%). Finally we have documented the introduction of overdosing amongst the homeless population which did not exist in the 1973 survey, but which accounts for 12% of our survey.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗
PubMed1992

Differences in tests of aniseikonia.

The New Aniseikonia Test (NAT), a hand-held direct-comparison test using red/green anaglyphs, has several potential advantages as a screener. We compared the validity of the NAT to that of the Space Eikonometer in three experiments: (1) aniseikonia was induced by calibrated size lenses in a double-blind study of 15 normal subjects; (2) habitual aniseikonia was measured with both instruments in four patients; and (3) eight of the normal subjects were retested with a computer-video simulation of the NAT. The NAT underestimated induced aniseikonia by a factor of 3 in the normal subjects and underestimated habitual aniseikonia in four patients. The Space Eikonometer correctly measured the magnitude of induced aniseikonia in the normal subjects. The simulation test did not show underestimation in the eight normal subjects. We could not attribute the NAT's underestimation of aniseikonia to the red/green anaglyph method, printing error, psychophysical method, or the direct-comparison test format. We speculate that the NAT induces a different sensory fusion response to aniseikonia than do the other tests, and that this altered sensory fusion response diminishes measured aniseikonia. We conclude that the NAT is not a valid measure of aniseikonia.

Adult↗
PubMed1991

Retinal eccentricity of fusion detail affects vergence adaptation.

Adaptation of tonic vergence ("vergence adaptation" or "prism adaptation") may be produced by sustained accommodative, disparity, or proximal vergence innervation. Phoria measures were used in the present study as indices of tonic vergence adaptation to convergence and divergence stimuli in five subjects. Amblyoscope targets stimulated fusion either over the central or peripheral retina while holding accommodative and proximal stimuli constant. The magnitude and rate of tonic vergence adaptation were greater under the central fusion condition than under the peripheral fusion condition, even though the vergence stimuli were matched between central and peripheral fusion conditions. These results show that tonic vergence adaptation is influenced by the retinal eccentricity of target fusional patterns. However, additional work is required to identify the mechanism(s) underlying this eccentricity effect.

Adaptation, Ocular↗
PubMed1990

Normal retinotopic mapping in human strabismus with anomalous retinal correspondence.

Burian proposed that a functional retinotopic remapping of the deviated eye on striate visual cortex may be the physiologic basis for the perceptual phenomenon of anomalous retinal correspondence (ARC) in human strabismus. This investigation searched for this type of retinotopic remapping in five esotropes and one exotrope with ARC by means of visual evoked potential (VEP) topographic mapping. Uniocular stimulation of the foveas (corresponding points) during binocular vision in a normal subject yielded identical VEP scalp topographies from each eye. Stimulation of anomalously corresponding points produced different VEP scalp topographies from each eye in the six strabismic subjects. Uniocular stimulation of the anatomic foveas of each eye (noncorresponding points) in a strabismic subject during binocular vision produced identical VEP scalp topographies. These results suggest that there is no significant functional binocular realignment of retinotopic mapping in the visual cortex of human strabismics with ARC.

Brain Mapping↗
PubMed1988

Infant grating acuity is temporally tuned.

Studies of infant visual development have shown that acuity estimated with pattern visually evoked potential (VEP) techniques is higher than acuity estimated with preferential looking (PL) techniques. A major difference is that VEP stimuli are temporally modulated while PL stimuli are typically stationary. We measured PL acuity in 2-10-month-old infants for stationary gratings and for gratings phase alternating at 2.5, 7.5, 14 and 23 reversals/sec using a computer generated staircase method. The acuity functions were temporally tuned at 7.5 or 14 rev/sec for infants 3 months and older. Acuity for 7.5 and 14 rev/sec gratings was 0.5 to 1.0 octave higher than for stationary, 2.5 and 23 rev/sec gratings. When adults' grating acuity was measured foveally and 5 deg eccentrically, tuning occurred only for the eccentric targets, suggesting that the retinal area used by the infants to detect gratings acts like the adult perifovea. In a second experiment, VEP and PL acuity were both measured from the same infants using 14 reversals/sec gratings. The VEP/PL acuity difference was less for phase alternating gratings than for stationary gratings. The magnitude of the difference was age dependent, decreasing from 2 octaves at 2 months to 0.5 octave at 12 months. Even though the use of phase alternating gratings results in improved PL acuity, temporal modulation does not completely account for the difference between VEP and PL acuity.

Adult↗
PubMed1986

Blink vergence in an antimetropic patient.

A patient with uncorrected antimetropia was found to attain motor fusion through blinking. Although this patient was also able to attain motor fusion through saccadic vergence and slow fusional vergence, he usually relied on blink vergence. In this patient, blink vergence was an efficient alternative to slow fusional vergence.

Adult↗
PubMed1983

Dynamics of cover test eye movements.

The dynamics of unilateral cover test eye movements, never before systematically investigated with an objective recording system, are shown to be more complex than textbook accounts of them. We administered the cover test to nine heterophoric subjects by means of electromechanical occluders. Eye movements were recorded using the infrared photoelectric technique. Saccadic and vergence movements of the fixating eye were observed in almost all records when the occluded eye was uncovered. These movements were found in esophores and exophores and in both large and small phoria cases. Such movements were previously described in other asymmetric vergence tasks and appear to obey Hering's law of equal innervation. Uncovering the dominant eye, in cases of clear dominancy, resulted in shorter latency and larger amplitude saccades than did uncovering the nondominant eye. These large saccades were frequently of unequal amplitude in each eye. Trained subjects appear to use dynamic overshoots to increase this saccadic inequality and thereby attain vergence during saccades. Movements after the application of a cover to one eye, while grossly similar to textbook descriptions of them, are found to contain small vergence drifts and refixation (correcting) saccades in the nonoccluded eye.

Adult↗
PubMed1983

Randomized phase II studies in advanced colorectal carcinoma: a North Central Cancer Treatment Group study.

5-FU, semustine (MeCCNU), triazinate (TZT), and razoxane (ICRF-159) have each shown activity against advanced colorectal cancer in studies by at least two investigative groups. Objective response rates, however, have been low, without evidence of increased patient survival. The hope of this study was that enhanced activity might result from giving these agents in two-drug combinations. There were 167 eligible and evaluable patients randomized among the programs: 5-FU at a dose of 500 mg/m2/day by iv push X 5 (F); 5-FU at a dose of 400 mg/m2/day iv X 5 plus TZT at a dose of 175 mg/m2/day iv X 3 (FT); 5-FU at a dose of 400 mg/m2/day plus ICRF-159 at a dose of 600 mg/m2/day orally X 3 (FI); MeCCNU at a dose of 150 mg/m2/day orally plus TZT at a dose of 200 mg/m2/day iv X 3 (MT); MeCCNU at a dose of 150 mg/m2 orally plus ICRF-159 at a dose of 500 mg/m2/day orally X 3 (MI); and ICRF-159 at a dose of 425 mg/m2/day orally X 3 plus TZT at a dose of 125 mg/m2/day iv X 3 (IT). Patients with limiting conditions (serum creatinine greater than 1.5 mg/dl or elevated bilirubin) were randomized among programs F, FI, and MI. Objective response rates by treatment arm were: F--13% (four of 31 patients); FT--13% (four of 31); FI--15% (four of 27); MT--11% (three of 28); MI--13% (four of 32); and IT--6% (one of 17). Response rates of combination arms were not significantly larger than those of 5-FU alone. With regard to survival, patients initially treated with 5-FU alone had the most favorable experience (median, 10.8 mos). Multivariate analysis showed the following factors to have a significant and independent influence on survival: Eastern Cooperative Oncology Group performance score, grade, site of indicator lesion, and the presence of 5-FU in the treatment regimen. Toxic effects most frequently seen were nausea, vomiting, thrombocytopenia, leukopenia, diarrhea, stomatitis, alopecia, and dermatitis. The incidence and severity of toxicity were roughly comparable among the six treatment arms.

Adult↗
PubMed1982

Measurement of interpupillary distance with chromostereopsis.

Chromostereopsis is a perceived depth difference between coplanar objects of different color and can be used for highly accurate measurement of interocular separation (PD). A survey of PD measurement with chromostereopsis and with the PD rule on 83 subjects shows that these methods on average result in the same PD, indicating that chromostereopsis is a valid technique for PD measurement. Repeated PD measures by these 83 individuals on the authors, using the PD rule and chromostereopsis, shows that the chromostereopsis result is far more repeatable than the PD rule. Suggestions are made for the use of the chromostereopsis technique in optometric practice.

Biometry↗