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Biomedical subjects

M Lawrence

Publications and source records attributed to M Lawrence.

At least 91 records · Page 5Linked to original sources
PubMed1986

Biochemical genetics of TL antigens.

TL antigens are class I glycoproteins which are expressed on thymocytes and which are coded by the Tla region of the major histocompatibility complex of the mouse. Biochemical analysis of TL molecules from different strains of mice revealed structural variation determined by the Tla region which is detectable by peptide mapping, isoelectric focusing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two-dimensional gels, and by differential reactivity of allelic forms of TL molecules with a panel of anti-TL reagents. The quantity of TL expressed on thymocytes is also influenced by the Tla region; three quantitative phenotypes were identified: high (Tlaa, Tlad, Tlae), intermediate (Tlac, Tlaf), and low (Tlab). (Relative amounts: 1000: 100: 1.) Some thymic leukemias arising in (Tlab, Tlac) mice with genetically determined reduced levels of thymic TL were found to express TL molecules which were structurally indistinguishable from TL isolated from thymocytes but were present in larger amounts. This suggests that TL structural genes are intrinsically capable of full expression in all mice but that the Tla region of mice expressing an intermediate or low quantity of TL is marked by some feature which causes the thymocyte to express less than the full amount of TL possible.

Age Factors↗
PubMed1986

A computer generated patient carried health check card.

A computerized record system has been programmed so a patient's important medical information can be printed out and given to the patient in the form of a ;health check card'. One aim was to enable patients to take more responsibility for their own preventive care. Following the issue of cards to 331 patients in 126 families, there was an increase in the uptake of cervical cytology screening, blood pressure recordings and tetanus immunization. Replies to a questionnaire enclosed with the card were received from 161 patients (in 86 of the families): most found the cards acceptable and believed they would be useful.

Adolescent↗
PubMed1986

Maternal nutrition and breast feeding.

In this short review we will first summarize current theories relating to maternal nutritional needs during human lactation, then deal with dietary situations where theory and experimental findings differ. In fact such a divergence occurs most of the time, both in affluent countries and especially in the Third World. We will then consider the various hypotheses which are currently being tested in an attempt to rationalize this complex but crucially important enigma. These hypotheses suggest that the mother can 'adapt' both physiologically and behaviourally in order to protect the adequate nutrition of her baby. Finally we will discuss the health significance of what happens when the mother's ability to accommodate the nutritional stresses of pregnancy and lactation fails. Although we have been asked to deal just with lactation, from time to time it will also become necessary to consider events occurring during pregnancy in order to place the nutritional stresses of lactation within a rational biological perspective. Whilst in the medical world, parturition tends to be a watershed event which divides one clinical specialty from another, in nutritional terms its main significance is merely that the mother switches feeding her baby from one part of her anatomy to another. In so far as her nutritional requirements are concerned pregnancy and lactation are part of the same continuum.

Adaptation, Physiological↗
PubMed1985

A quantification of child care and infant-caregiver interaction in a West-African village.

We have investigated infant-caregiver interactions in an isolated African subsistence farming community where women perform arduous agricultural tasks in addition to their normal domestic duties which include child care. 49 babies aged 3-18 months were studied on one or two occasions. Detailed observations were made of the level of care and of positive and negative stimulation offered to the child. Children were left in the charge of young nursemaids for up to 40% of the day while the mothers tended the crops. Despite this the total amount of positive and negative stimulation and care were similar whether or not the mother was engaged in fieldwork on the day of study. Grandmothers and fathers were both relatively unimportant caregivers. Total positive stimulation did not increase with age; on the contrary, young babies (3-9 months of age) were offered more positive stimulation and less negative stimulation than older ones (12-18 months). A positive correlation was found between total positive stimulation and developmental quotient (assessed by the Griffiths test). Similar amounts of care were given at all ages and there was no difference in the treatment of the two sexes.

Age Factors↗
PubMed1985

The energy cost of common daily activities in African women: increased expenditure in pregnancy?

We have performed, by open-circuit indirect calorimetry, a total of 1546 measurements of energy expenditure on 142 nonpregnant, pregnant, or lactating Gambian village women. Of the 47 common daily activities measured, only 7 would be classified as moderate according to internationally accepted standards, the remainder being light (ie requiring less than 3.5 kcal/min). This was unexpected since many of the tasks, judged subjectively, appeared quite demanding. Furthermore there was no increase towards the end of pregnancy in the energy cost of a range of activities requiring 1-5 kcal/min and involving a variety of body movements, despite the substantial weight gains observed. Only for walking was there the expected increase in energy expenditure. Although in the past it has been assumed that the heavier pregnant women would require additional energy for activity, no special allowance for this is included in current dietary recommendations. The present results indicate that, for women from the developing world, no allowance is necessary. The finding that most activities were light is also of relevance to total energy requirements in this community.

Adolescent↗
PubMed1984

Maintenance energy cost of pregnancy in rural Gambian women and influence of dietary status.

A major assumption in current dietary advice for pregnancy is that the amount of energy expended on tissue maintenance increases by 36 000 kcal over the whole gestation period. In a group of rural Gambian women engaged in subsistence farming, the increase was much smaller and depended on maternal dietary status. In women having the customarily low food intake the net extra cost of tissue maintenance was just 1000 kcal; even in those given a dietary supplement in amounts previously shown to increase birthweight it was only 13 000 kcal. This finding partly explains why mothers, particularly those in the Third World, can apparently accomodate pregnancy without substantially increasing their dietary energy intake. The findings are of importance in the formulation of realistic dietary health strategies for such communities.

Adult↗
PubMed1983

Cochlear inner hair cells: effects of transient asphyxia on intracellular potentials.

Intracellular potentials were recorded from inner hair cells in the guinea pig cochlea. Transient asphyxia was induced by interrupting respiration for brief periods. Asphyxia caused a hyperpolarization of the resting membrane potential (resting Em). The hyperpolarization averaged 2.9 mV for 30 s asphyxias and 5.7 mV for 45 s asphyxias. The membrane potential recovered quickly after normal ventilation was resumed. Asphyxia also induced a rapid and profound decrease of the d.c. receptor potential in response to moderate intensity tone bursts at the characteristic frequency of the inner hair cell. At maximal depression, the receptor potential was reduced about 60% for a 30 s asphyxia and 100% for a 45 s asphyxia. The receptor potential recovered slowly after normal ventilation was resumed. A similar percent reduction and time course of recovery were observed for the a.c. receptor potential. In recordings from the same animals, the round window compound action potential (CAP) was as severely depressed by asphyxia as the hair cell receptor potentials. The time course of recovery for the CAP was similar to the slow recovery of the d.c. receptor potential. In contrast, the round window cochlear microphonics (CM) and the endolymphatic potential (EP) were affected less by asphyxia and recovered quickly after ventilation was resumed. Frequency tuning curves (FTCs) for the d.c. receptor potential were measured during the period of maximal receptor potential depression. These FTCs showed decreased tip sensitivity and a decrease in sharpness of tuning, as measured by the Q10. These changes were fully reversible. Low frequency (tail) segments of the FTCs were much less affected by asphyxia. The inner hair cell FTC changes during asphyxia were compared with neural FTC changes reported by other investigators. The similarities lead us to the conclusion that the inner hair cell and the auditory neural response to sound are equally sensitive to asphyxia.

Animals↗
PubMed1983

The effect of the guinea pig maximization protocol on the irritant response to deodorized kerosene - the excited skin syndrome.

Deodorized kerosene in a concentration of 50 g/100 g in pet. did not cause cutaneous inflammation in 10 control guinea pigs. The proportion of 19 guinea pigs exhibiting inflammation following exposure to deodorized kerosene in the guinea pig maximization test increased, but the increase was not significant. The response in a group of 40 animals, half exposed to tetraethyleneglycol diacrylate and half to nonylphenol polyethoxylate-6, increased (z = 3.505, p = 0,004). The inflammatory response was related to concentration in both groups of animals which exhibited inflammatory responses to deodorized kerosene. The relevance of this alteration and irritant response to the interpretation of predictive tests in animals for sensitization, routine patch testing and repeated insult contact dermatitis is discussed.

Animals↗
PubMed1982

Acute perilymphatic perfusion of the guinea pig cochlea.

A method for the continuous perfusion of the perilymphatic space of the inner ear in the guinea pig is described. Artificial perilymph is supplied to the cochlea and drained away through a tubing system while flow rates from 10 microliters/min to 0.3 ml/min are established by gravity syphon pressure. Techniques are also presented which allow control over the temperature of the perfusate and over the level of dissolved oxygen in the perfusate. Alone with these variables, the pH of the artificial perilymph can be manipulated and various drugs can be added to the perfusate to test their effect on the inner ear. The function of the inner ear is monitored by continuous recording of the sound evoked bioelectric potentials, the cochlear microphonic and the compound action potential. The cochlear perfusion technique has many applications in the study of cochlear physiology and metabolism, and in testing the sensitivity of the inner ear to ototoxic drugs.

Animals↗
PubMed1982

Influence of blood viscosity on cochlear action potentials and oxygenation.

Impairment of the cochlear blood supply of guinea pigs was induced in order to study the effects of hypoxia on the cochlear action potentials. The oxygenation of the cochlear structures was decreased by perfusing the ears with polycythemic hyperviscous blood. The validity of using this model of cochlear blood flow was based on the propensity of the blood to flow in a laminar way. Because of the streamlined flow pattern, the blood supplied by the two vertebral arteries does not mix within the common trunk of the basilar artery. The retrograde injection of polycythemic hyperviscous blood into one vertebral artery will affect the ear on the injected side only. The high viscosity of the polycythemic blood decreases the rate of flow of blood through the cochlear vessels; the high oxygen content of this blood, however, avoids hypoxia of the cochlea. Therefore, in order to make the slowdown in the blood flow evident, its oxygen content was reduced to a 'precritical level' before it was infused. Injecting normoviscous blood with a 'precritical level' of oxygen caused a mild reduction in the scala media pO2 of 15.2% for the whole group of twenty animals. The hyperviscous blood with the same level of oxygenation, however, reduced the pO2 in the scala media to 53.3% of normal. These findings explain the difference in the altered click-evoked action potentials in the two groups of animals.

Action Potentials↗
PubMed1982

Structure and function of the ear and auditory nervous system.

The transduction from sound vibrations to a nerve ending stimulus takes place in the organ of Corti. This process, resulting from fluid particle movement of a magnitude equivalent to the dimensions of the electron cloud around an atom, involves more than a simple deformation of the sensory cell. The fluid environment of these cells must be such that it provides sufficient oxygen and nutrients for the cells' survival and at the same time maintains a condition to enhance the biophysical process. The spiral capillaries beneath the tunnel of Corti furnish the metabolites for the Cortilymph surrounding the sensory cells. The capillaries of the stria vascularis provide this structure, an organ in its own right, so that it can maintain the high potassium concentration and positive potential of endolymph which are necessary for the transduction process. The stria vascularis itself and its blood supply and the sensory cells and their blood supply are all vulnerable to attack by various toxic agents, thus altering the homeostatic condition and resulting in a hearing loss.

Animals↗
PubMed1982

Recovery from prolonged sensorineural hearing loss.

Five cases of sensorineural hearing loss are presented in which partial or complete recovery of hearing occurred after periods of deafness lasting from three months to more than five years. Three of the cases were diagnosed as Meniere's disease, one as sudden deafness of probable viral origin, and one as idiopathic sudden deafness. A review of the literature reveals brief mention of only a few similar cases, although it is suspected that the phenomenon is not as rare as these isolated reports suggest. It is proposed on the basis of experimental work in animals that the reversible deafness in these patients may be due to temporary obstruction of capillaries in the stria vascularis, which produces strial hypoxia resulting in a reduction in the endolymphatic potential, with consequent hearing loss.

Adult↗
PubMed1981

Inner hair cell responses to the velocity of basilar membrane motion in the guinea pig.

Triangular wave acoustic stimulation at 200 Hz produced the expected square wave cochlear microphonic at the round window membrane and within the scala media. Intracellular recordings from inner hair cells (IHC) of the first cochlear turn showed a combination waveform having both spike impulse and square wave features. The IHC response suggests a sensitivity of these cells to both the displacement and to the velocity of basilar membrane motion.

Acoustic Stimulation↗
PubMed1981

Does loud sound influence the intracochlear oxygen tension?

The effect of loud sound on the perilymphatic oxygen tension was studied in anesthetized guinea pigs. Pure tone (4 kHz) and broad-band noise were given at 85-130 dB SPL for 3-8 min. No effects were seen either in the animals exposed to pure tone or in the animals exposed to 85 dB broad-band noise. In the animals exposed to noise at 130 dB SPL both increases and decreases of perilymphatic oxygen were measured but the changes were only of about 12% or less. The response to anoxia was normal. In animals with hypotension ( less than 8 kPa) the perilymphatic PO2 fluctuated with the blood pressure. When the sound was delivered directly into the opened bulla the measured PO2 dropped immediately but was found to be caused by the cooling effect of an air current produced by the noise. Flushing the opened bulla with nitrogen, air or oxygen caused the same temperature-induced drop of measured PO2. The results and the artifacts are discussed.

Animals↗