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Biomedical subjects

G Mitchell

Publications and source records attributed to G Mitchell.

At least 19 recordsLinked to original sources
PubMed1992

Normal conduction in pathways traversing an asymptomatic multiple sclerosis plaque.

A 31-year-old woman developed right facial myokymia as the initial manifestation of multiple sclerosis (MS). An MRI scan revealed a focal signal abnormality confined to the left dorsolateral pontomedullary region. Brain-stem auditory evoked potentials (BAEPs), somatosensory evoked potentials (SEPs), and blink reflex (BR) failed to show a conduction abnormality through the left brain-stem lesion. Instead, BAEP and BR indicated a conduction defect in the right pons and EMG showed myokymic discharges in right facial muscles. Our findings provide rare documentation of normal conduction through a presumably asymptomatic MS plaque. The abnormal MRI signal likely represents tissue edema, rather than demyelination. This case demonstrates that physical findings in MS patients may correlate better with electrophysiological abnormalities than with MRI abnormalities.

Adult↗
PubMed1992

Effects of dehydration and rehydration on the intravascular space in horses.

1. The resistance of sub-tropical horses, and desert-dwelling horses to 72 hr dehydration/24 hr rehydration was investigated via changes in red cell parameters and plasma protein concentration. 2. Red cell count, haemoglobin and haematocrit increased up to 48 hr dehydration. Between 48 and 72 hr dehydration these parameters decreased, implying a fluid shift onto the intravascular space from the interstitium/hindgut. Most parameters had regained baseline values by 24 hr rehydration. 3. Mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration and total plasma protein were not significantly different between breeds at, or between most stages of hydration. 4. Protection of plasma volume during dehydration/rehydration was aided by maintaining intravascular protein (especially albumin) levels. Red cells were transiently dehydrated and overhydrated but resisted osmolysis.

Animals↗
PubMed1979

Evidence for an indirect cholinergic regulation of blood flow in the hypothalamus of conscious rabbits.

1 The effects of methacholine, atropine and adrenoceptor blockade on hypothalamic blood flow (HBF) were measured in conscious rabbits. 2 A dose of 1 microgram methacholine increased HBF while smaller and larger doses had no significant effect. 3 The vasodilatation induced by methacholine was blocked by atropine and by chemical sympathectomy of the hypothalamus with 6-hydroxydopamine. 4 The vasodilatation was reversed by propranolol but was not affected by phenoxybenzamine. 5 These results suggest that the vasodilator action of muscarinic receptor agonists on hypothalamic resistance vessels depends upon the integrity of a noradrenergic system, and is mediated via beta-adrenoceptors.

Animals↗
PubMed1978

Strain differences in the immune response of mice to homologous sperm-specific lactate dehydrogenase (LDH-C4).

The sperm-specific isozyme of murine lactate dehydrogenase (LDH-C4) was injected into female mice of various strains. Two regulatory phenotypes characterize the resultant immunity to LDH-C4: one is manifested by high, intermediate or low levels of response, the other by the immediate or delayed maturation of peak titer. The response of several strains can be classified as high (SWR, SJL, BABL/c, C3H/He) and intermediate to low (A, CBA, DBA/2, DBA/1, C57BL/6) according to the level of antibody production and cell mediated immunity. BALB/c, SJL and SWR strains are immediate responders while DBA/2 and C3H/He mice are clearly delayed responders. Maturation and magnitude of response do not appear to be related. Both the antibody and cell mediated responses are T-dependent, but are not obviously associated with Ig allotype or H-2 regulation.

Animals↗
PubMed1978

X-ray fluorescence analysis of lead in teeth of urban children in situ: correlation between the tooth lead level and the concentration of blood lead and free erythroporphyrins.

The tooth lead level of 30 lead-exposed children was measured in situ using an X-ray fluorescence technique. The tooth lead concentration divided by the child's age correlated with the free erythroporphyrin (FEP) (r = 0.51) and the blood lead levels (r = 0.31). The mean tooth lead concentrations of 10 Class IV children (FEP greater than or equal to 190 micrograms/100 ml; blood lead 30-80 micrograms/ml) was 14.5 +/- 5.5 ppm/year. Reexamination of the histories of children who had been classified as Class II or III, but who had tooth lead concentrations within 1 SD of the Class IV level, indicated that many of these children could also be considered to be Class IV children. When the x-ray fluorescence technique was used to screen an urban population of 300 children, the tooth lead values indicated that 72% of the children had been exposed to low levels of environmental lead. Six percent of the children were found to have tooth lead concentrations in excess of 9 ppm/year and within 1 SD of the mean value exhibited by Class IV children. These children were considered to have a high body lead burden. The percentage of children having an elevated tooth lead level is similar to the number previously reported using exfoliated deciduous teeth.

Child↗
PubMed1978

Vasodilator mechanism of the intracerebral (non-sympathetic) adrenergic pathway.

Stimulation of the intracerebral noradrenergic pathway causes a vasodilatation in the hypothalamus. We have investigated whether this vasodilatation is caused by a direct vascular innervation or whether it is secondary to an activation of hypothalamic neurons. Non-specific neuronal activation using glutamate increased the mean hypothalamic blood flow. Depression of neuronal activity using barbiturate reduced hypothalamic blood flow and blocked the glutamate and the intracerebral noradrenergic pathway-induced vasodilatation. These results suggest that stimulation of the intracerebral noradrenergic pathway increases hypothalamic neuronal activity which indirectly causes a vasodilatation.

Animals↗
PubMed1977

Measurement of lead content of children's teeth in situ by x-ray fluorescence.

The central nervous system of young children is particularly sensitive to neurological damage due to excessive lead exposure. The lead stored in a tooth is permanent and related to the quantity of ingested lead. The lead is assayed by measuring the characterisitc radiation from lead in a tooth in situ irradiated with gamma rays from a cobalt-57 source. The sensitivity of the method is adequate to measure lead levels commonly associated with environmental background. The X-ray exposure to the tooth necessary for this determination is approximately one tenth of that required for a routine dental examination.

Child↗
PubMed1977

Sucrose-negative variants of Candida tropicalis.

Four cultures of a Candida sp. that lacked alpha-glucosidase activity were isolated from clinical specimens. Physiological, morphological, and serological characterizations of the yeasts and deoxyribonucleic acid reassociation studies supported their classification as a variant of C. tropicalis.

Antigens, Fungal↗
PubMed1976

Antenatal diagnosis of neural tube defects.

One hundred women with pregnancies at risk for the recurrence of neural tube defects have entered our monitoring programme of echography and alphafetoprotein estimation (AFP) on amniotic fluid and maternal serum during the second trimester. The results of these pregnancies, the application of the programme, sources of error, and the reliability of alphafetoprotein levels are discussed. Conclusions regarding the value of the tests and routine antenatal screening are made.

Adult↗
PubMed1976

Effects of sleep of restricted sleep. A cat case study.

One male cat was adapted to different schedules of restricted sleep. The cat was allowed to go to sleep during a certain number of hours per day. During the rest of the 24 h period, wakefulness was enforced by means of a treadmill. The following schedules of restricted sleep were run: 12 h sleep--12 h treadmill (12S--12T), 8S--16T, 4S--20T. The cat was also adapted to a 36 h day: 12S--24T. The sleep was investigated after at least 2 weeks on each schedule and compared to ad lib. sleep (24S--0T). As available sleep time bacame shorter, the composition of the sleep changed. LSWS (in % of available sleep time) decreased, while DSWS % and REM sleep % increased. The length of the DSWS and REM sleep episodes increased with decreasing sleep time, as did sleep cycle length.

Animals↗
PubMed1976

Evidence for a dual innervation affecting local blood flow in the hypothalamus of the conscious rabbit.

We have attempted to evaluate the role of adrenergic nerves which arise from the superior cervical ganglia or which are intracerebral throughout their course, in the control of local cerebral blood flow (CBF). Hypothalamic blood flow (HBF) was measured in the conscious rabbit by the 133Xe-clearance technique. Stimulation of the upper brainstem, using 5-Hz, 3-V, 1-msec, square wave pulses, increased by HBF by a mean of 7.6 ml/100 g per min (P less than 0.005). This effect was abolished by the intrahypothalamic injection of the beta-adrenoreceptor blocker, propranolol, and by chemical sympathectomy of the hypothalamus or of the upper brainstem with 6-hydroxydopamine, but was not altered by bilateral cervical ganglionectomy. Intrahypothalamic injection of 0.1 mug of tyramine caused a mean decrease in HBF of 15.6 ml/100 g per min (P less than 0.001). This effect of intrahypothalamic injection of tyramine was abolished by bilateral cervical sympathectomy but not by chemical sympathectomy of the upper brainstem. These results support the idea that local CBF, at least in the hypothalamus, is mediated by two distinct pathways. The first consists of the sympathetic nerves which arise in the cervical ganglia, and which activate intrahypothalamic alpha-receptors to cause constriction. The second is an entirely intracerebral noradrenergic pathway which stimulates beta-receptors to cause vasodilation.

Animals↗
PubMed1975

Physiological and DNA characterization of Candida maltosa, a hydrocarbon-utilizing yeast.

Selected yeast classified as Candida sake van Uden et Buckley were examined for their physiological, morphological and immunological properties and their DNA relatedness. Candida maltosa Komagata, Nakase et Katsuya is herein recognized as a species separate from C. sake, Candida maltosa was distinguished from C. sake and from C. tropicalis by insignificant DNA reassociation. In addition, C. maltosa was distinguished from C. sake by its higher maximal growth temperature and lower guanine plus cytosine content of its DNA and from C. tropicalis by its failure to utilize soluble starch for growth and its resistance to cycloheximide. The species C. cloacae and C. subtropicalis are placed in synonymy with C. maltosa.

Alkanes↗
PubMed1975

Initial heterosexual behavior of adolescent Rhesus monkeys (Macaca mulatta).

This report described the first heterosexual encounters of twelve 3-year-old rhesus monkeys, six of each sex. The subjects were all laboratory-born and were reared in wire cages for the first 8 months of life, accompanied only by their mothers. After these animals were weaned, each was placed in a cage with another animal of the same age and sex. The pairs formed in this way remained intact until the animals were 2 years old. When heterosexual dyads were formed, some of the subjects attached and bit the animal with which they had been paired, while the members of other pairs established almost immediate rapport as evidenced by mutual grooming and adequate sexual behavior. The initial sexual interactions of most pairs were uncoordinated, but all eventually demonstrated qualitatively species-typical patterns of sexual behavior. Despite their immaturity, two of these pairs succeeded in producing offspring, both of which were healthy.

Aggression↗