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Biomedical subjects

D Kennedy

Publications and source records attributed to D Kennedy.

At least 217 records · Page 12Linked to original sources
PubMed1966

The distribution of pre- and postsynaptic inhibition at crustacean neuromuscular junctions.

The relative contribution of pre- and postsynaptic mechanisms to peripheral inhibition has been analyzed in the abdominal slow flexor muscles of crayfish and lobsters. The conductance of the muscle fiber membrane may be increased to five or more times its resting value by repetitive stimulation of the peripheral inhibitory axon, and this effect accounts for all of the attenuation exerted by the inhibitor against excitatory junctional potentials. No "critical interval" has been found at which an inhibitory nerve impulse produces anomalously large reduction of a following depolarizing junctional potential; electrotonic depolarizations and junctional potentials are identically affected under all phase conditions. The presynaptic inhibitory mechanism is, therefore, absent in this system. In the dactyl opener muscle, on the contrary, most of the attenuation of excitatory junctional potentials is achieved presynaptically, though equally large postjunctional conductance changes are also seen (Dudel and Kuffler, 1961). The difference is correlated with a difference in the reflex operation of the two muscles. Reflex inhibition in the abdominal slow flexors is primarily central, whereas in the dactyl opener, inhibition is brought about by an increase in inhibitory nerve discharge frequency without central suppression of the single excitatory axon. The function of peripheral inhibition in the abdominal flexors is presumably to terminate residual depolarization by reducing the long time-constant of the muscle fibers.

Animals↗
PubMedDate not supplied

Pregnancy outcome following gestational exposure to organic solvents: a prospective controlled study.

CONTEXT: Numerous women of childbearing age are exposed occupationally to organic solvents. Previous retrospective studies have reported conflicting results regarding teratogenic risk. OBJECTIVE: To evaluate pregnancy and fetal outcome following maternal occupational exposure to organic solvents. DESIGN: A prospective, observational, controlled study. SETTING: An antenatal counseling service in Toronto, Ontario. PATIENTS: One hundred twenty-five pregnant-women who were exposed occupationally to organic solvents and seen during the first trimester between 1987 and 1996. Each pregnant woman who was exposed to organic solvents was matched to a pregnant woman who was exposed to a nonteratogenic agent on age (+/-4 years), gravidity (+/-1), and smoking and drinking status. MAIN OUTCOME MEASURE: Occurrence of major congenital malformations. RESULTS: Significantly more major malformations occurred among fetuses of women exposed to organic solvents than controls (13 vs 1; relative risk, 13.0; 95% confidence interval, 1.8-99.5). Twelve malformations occurred among the 75 women who had symptoms temporally associated with their exposure, while none occurred among 43 asymptomatic exposed women (P<.001). (One malformation occurred in a woman for whom such information was missing.) More of these exposed women had previous miscarriage while working with organic solvents than controls (54/117 [46.2%] vs 24/125 [19.2%]; P<.001). However, exposed women who had a previous miscarriage had rates of major malformation that were similar to exposed women who had no previous miscarriage. CONCLUSIONS: Occupational exposure to organic solvents during pregnancy is associated with an increased risk of major fetal malformations. This risk appears to be increased among women who report symptoms associated with organic solvent exposure. Women's exposure to organic solvents should be minimized during pregnancy. Symptomatic exposure appears to predict higher fetal risk for malformations.

Abortion, Spontaneous↗
PubMedDate not supplied

A rapid and sensitive method for measuring the conditional emotional response. II: On-the-baseline excitatory conditioning and extinction.

The present study outlines a rapid and sensitive on-the-baseline conditional emotional response (CER) procedure. Using rats as the experimental subject, the method detects delay conditioning, incubation, extinction and spontaneous recovery. In addition, the method detects conditional responding using electric shock ranging from 0.23 to 0.50 mA as the unconditional stimulus. Because of its speed and sensitivity, the method shelters the subject from unnecessary long-term deprivation and pain.

Animals↗
PubMedDate not supplied

Moderate alcohol consumption during pregnancy and the incidence of fetal malformations: a meta-analysis.

To determine whether there is an association between moderate alcohol consumption in the first trimester of pregnancy and increased risk of fetal malformations, we conducted a literature search using Medline (1966-present), PsycLit (1974-1995), and EMBASE (1988-1995). The following inclusion criteria were used to select the studies to be evaluated: 1) pregnant women; 2) moderate alcohol consumption (> 2 drinks/week to 2 drinks/day); 3) case-control or cohort studies; 4) presence of an abstainer group (0 to 2 drinks/wk); 5) outcome measures include major or minor malformations; 6) papers published in the English language. The exclusion criteria were: 1) studies in which moderate alcohol consumption could not be confirmed; 2) case reports, and editorials. The Methods section of each study was examined independently by two blinded investigators with a third investigator settling any disagreement. The number of malformations in the abstainer and moderate alcohol consuming groups in two by two tables. Out of 24 studies which met the inclusion criteria, only seven had extractable data. The included studies evaluated 130,810 pregnancy outcomes, with 24,007 in the moderate alcohol group and 106,803 in the control group. An overall Mantel-Haenszel odds ratio showed that the relative risk for fetal malformations was 1.01 with 95% confidence limits of 0.94 to 1.08 and a chi-square for homogeneity of 8.26 (p = 0.220). Quality of the studies did not correlate with their showing negative or positive association. Moderate alcohol consumption during the first trimester of pregnancy is not associated with increased risk of fetal malformations.

Abnormalities, Drug-Induced↗
PubMedDate not supplied

The selective impairment of the perception of first-order motion by unilateral cortical brain damage.

First-order (Fourier) motion consists of stable spatiotemporal luminance variations. Second-order (non-Fourier) motion consists instead of spatiotemporal modulation of contrast, flicker, or spatial frequency. In spite of extensive psychophysical and computational analysis of the nature and relationship of these two types of motion, it remains unclear whether they are detected by the same mechanism or whether separate mechanisms are involved. Here we report the selective impairment of first-order motion, on a range of local and global motion tasks, in the contralateral visual hemifield of a patient with unilateral brain damage centered on putative visual areas V2 and V3 in the medial part of the occipital lobe. His perception of second-order motion was unimpaired. As his disorder is the obverse of that reported after damage in the vicinity of human visual area MT (V5), the results support models of motion processing in which first- and second-order motion are, at least in part, computed separately at the extrastriate cortical level.

Aged↗
PubMedDate not supplied

Attention-deficit hyperactivity disorder: magnetic resonance imaging morphometric analysis of the corpus callosum.

OBJECTIVE: The following study seeks to document possible differences in corpus callosal area and shape between children with attention-deficit hyperactivity disorder (ADHD) and controls. METHODS: Fifteen carefully diagnosed right-handed male subjects with ADHD with overactivity symptomatology were compared to 15 right-handed male control subjects. The corpus callosum was divided into seven areas on the midsagittal slice of a magnetic resonance image with shape analysis also conducted. RESULTS: An exploratory shape analysis showed no significant differences in shape between the groups. No group differences were found in the area, length, or anterior regions of the corpus callosum. The ADHD subjects were found to have significantly smaller posterior corpus callosum regions than the control group, with the splenium accounting for most of the variance between the groups. CONCLUSIONS: The splenial area of the corpus callosum is smaller in children with ADHD than in a sample of normally developing children. These smaller areas may relate to commonly seen sustained attention deficits which in turn negatively impact on the development of more advanced levels of attention such as self-regulation. Further study of the regions surrounding the splenial area is suggested to determine whether they are correlated in size to the smaller corpus callosum.

Adolescent↗
PubMedDate not supplied

Lichen striatus.

Lichen striatus is a self-limiting inflammatory condition of unknown etiology in which the lesions follow the lines of Blaschko. We report a series of 61 cases of this condition in children, describing the clinical features, age distribution, and season of onset. The preponderance of cases in the preschool-age group and onset in the spring and summer months support the hypothesis of an environmental agent, possibly an infection, in the etiology of the condition.

Age Distribution↗