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T M Mayhew

Publications and source records attributed to T M Mayhew.

At least 91 records · Page 5Linked to original sources
PubMed1991

Parathyroid hormone-(1-34) peptide activates cyclic adenosine 3',5'-monophosphate in the human placenta.

Dually perfused human term placental lobules were exposed to forskolin, bovine parathyroid hormone (bPTH(1-34)) and human parathyroid hormone related-peptides, hPTHrP(1-34), hPTHrP(67-86)NH2 or PTHrP(107-138) for 15 min in the presence of 3-iso-butyl-1-methyl-xanthine (IBMX); control lobules were exposed to IBMX alone. Homogenates of these tissues were then assayed for cyclic adenosine 3',5'-monophosphate (cyclic AMP) and results normalized per mg of protein. Exposure to forskolin or bPTH(1-34) on both sides, and exposure to bPTH(1-34) at a concentration of 30 nM on the maternal side of the placenta or 120 nM on the fetal side of the placenta, significantly enhanced tissue cyclic AMP production compared with tissue exposed to IBMX alone. Exposure to hPTHrP(1-34), hPTHrP(67-86)NH2 and hPTHrP(107-138) at a concentration of 30 nM on both sides of the placenta had no significant effect upon tissue cyclic AMP production.

Cyclic AMP↗
PubMed1991

Avian lower intestine adapts to dietary salt (NaCl) depletion by increasing transepithelial sodium transport and microvillous membrane surface area.

A tissue sampling scheme for tandem assessments of whole-organ physiology and ultrastructure was applied to the lower intestine (coprodaeum) of White Plymouth Rock hens on low- and high-NaCl diets. The objective was to correlate net amiloride-sensitive Na transport determined using the Ussing chamber with the plasma membrane surface areas due to microvilli at the epithelial cell apex. Hens kept on the low-NaCl diet for 3-4 weeks displayed a substantial increase in short-circuit current and in total microvillous membrane surface area. The latter rose from a group mean +/- S.E.M. of about 90 +/- 9.7 cm2 to one of 200 +/- 38 cm2 per organ. An increase in epithelial cell membrane contributed to, but did not fully explain, the increase in microvillous area. No differences in mean cell height or mean cell volume were found but the average cell in the low-NaCl birds was better developed in possessing a greater surface area of microvilli. On the high-NaCl diet, the epithelium was 33 +/- 2.7 microns tall and contained about 270 +/- 15 million cells. Each cell had a volume, on average, of 540 +/- 59 microns 3 and a microvillous surface of 32 +/- 2.6 microns 2. After NaCl depletion, there were 420 +/- 75 million cells and the average microvillous surface was 49 +/- 5.3 microns 2 per cell. The morphological adaptations alone do not explain the increased net Na transport found on the low-NaCl diet. Of cardinal importance is greater density of open Na channels in apical cell membranes.

Adaptation, Physiological↗
PubMed1991

Magnetic resonance imaging (MRI) and model-free estimates of brain volume determined using the Cavalieri principle.

A complete set of parallel (coronal) slices through a fixed human forebrain was generated by magnetic resonance imaging (MRI) and the Cavalieri principle, combined with point counting, was used to estimate brain volume. Alternative sampling schemes for estimating volume were then assessed by taking systematic and simple random selections of slices. Later, the brain was weighed and its fixed volume determined by fluid displacement. For the complete set of n = 28 MRI slices, the volume (1025 ml) was estimated with a coefficient of error (CE) of less than 1%. Decreasing the number of slices by systematic sampling increased the CE but this was still only 5% when just 5-6 slices were analysed. Estimated volumes varied from 947 ml to 1098 ml. Simple random sampling was less efficient (estimated volumes for 5-6 slices were 644-1187 ml). The forebrain actually weighed 1090 g and displaced 1060 ml of fluid. A set of 14 other brains was physically sliced in order to assess sampling errors in the context of observed brain-to-brain variation. It was found that 5-6 slices per brain is enough to yield efficient estimates of mean brain volume. The findings demonstrate the practicability of using MRI to estimate brain volumes unbiasedly and efficiently. The methods have great potential for noninvasive, longitudinal studies on in vivo brains and other organs.

Brain↗
PubMed1991

Scaling placental oxygen diffusion to birthweight: studies on placentae from low- and high-altitude pregnancies.

Stereological analysis of tissue sections has been used to estimate partial and total conductances of the human placental oxygen diffusion pathway. Analyses were undertaken for neonates and term placentae from populations living at low (400 m) and high (3600 m) altitude in Bolivia. Relationships between conductances and birthweight (and between trophoblast volume and birthweight) were explored by linear regression analysis and allometry. At both altitudes, the three partial conductances on the maternal side of the oxygen pathway scaled to birthweight in a similar fashion. This similarity did not extend to conductances on the fetal side. Beyond a limiting weight of roughly 3 kg, the highland fetus was disadvantaged in terms of its placental oxygen diffusive conductances and trophoblast volume. The findings support the notion that the structural adaptations seen at high altitude are more successful on the maternal rather than the fetal side of the placenta.

Adaptation, Physiological↗
PubMed1990

Striated brush border of intestinal absorptive epithelial cells: stereological studies on microvillous morphology in different adaptive states.

Different regions of small bowel were examined in five groups of rats in three separate experiments. The effects on mucosal morphology of position along the bowel, induced hypoproliferation (due to fasting), and induced hyperproliferation (due to streptozotocin diabetes) were investigated. Intestines fixed by in situ perfusion with buffered glutaraldehyde were sampled by strictly randomised procedures. Pieces of tissue from segments of roughly equal length were processed for electron microscopy and embedded in resin. Complete transverse sections were cut for light microscopy and estimates of villous surface areas were obtained by stereological methods devised for the purpose. Ultrathin sections from random sectors of the same tissue blocks were sampled systematically to obtain micrographs of the villous surface. These were analysed for quantitative information about microvilli (length, diameter, surface area, and number). Structural quantities from individual segments were pooled to provide values for the entire small bowel. Significant regional differences in villous and microvillous dimensions were found in all groups. The numbers of microvilli per bowel were remarkably constant in all control groups. Other variables were estimated reproducibly in rats of the same sex, strain, and average body weight. Effective absorptive surfaces did not show a linear gradient but tended to peak in middle segments. Neither fasting nor induced diabetes altered the mean length, diameter, or packing density of microvilli. However, surfaces due to villi and microvilli altered commensurately during fasting and induced diabetes. Therefore cell number seems to be the key quantity for determining villous and microvillous surface areas. The findings are discussed in the context of kinetic, biochemical, and physiological changes found in different adaptive states.

Adaptation, Physiological↗
PubMed1990

A sampling scheme intended for tandem measurements of sodium transport and microvillous surface area in the coprodaeal epithelium of hens on high- and low-salt diets.

A tissue sampling protocol for combined morphometric and physiological studies on the mucosa of the avian coprodaeum is presented. The morphometric goal is to estimate the surface area due to microvilli at the epithelial cell apex and the proposed scheme is illustrated using material from three White Plymouth Rock hens. The scheme is designed to satisfy sampling requirements for the unbiased estimation of surface areas by vertical sectioning coupled with cycloid test lines and it incorporates a number of useful internal checks. It relies on multi-level sampling with four levels of stereological estimation. At Level I, macroscopic estimates of coprodaeal volume are obtained. Light microscopy is employed at Level II to calculate epithelial volume density. Levels III and IV require low and high power electron microscopy to estimate the surface density of the epithelial apical border and the amplification factor due to microvilli. Worked examples of the calculation steps are provided.

Animals↗
PubMed1990

Fractionator studies on Purkinje cells in the human cerebellum: numbers in right and left halves of male and female brains.

Direct estimates of the numbers of Purkinje cell nucleoli in 22 aged human cerebella of known weight were obtained from paraffin-embedded sections using the fractionator. The nucleoli were counted in single sections. The estimates are unbiased by fixation, section thickness or sampling errors and are free from any assumptions about shape, size or spatial orientation. Left and right sides of the cerebellum were analysed in ten subjects whilst sex differences were examined in eleven subjects. No significant lateral differences in fixed weight or nucleolar number were observed. The group means (coefficients of variation) per side were 45 g (18%) and 7.8 millions (26%) respectively. The average complement of nucleoli in 22 cerebella amounted to 15.6 millions (22%). Estimated numbers did not show any significant correlation with cerebellar weights and, in a subsample of these brains (five male and six female), apparent sex differences were not significant.

Aged↗
PubMed1990

Comparative morphometry of the mammalian brain: estimates of cerebral volumes and cortical surface areas obtained from macroscopic slices.

Stereological methods for obtaining unbiased estimates of brain volumes and surface areas are illustrated on fixed brains (cerebrum only) from mammals varying in body weight between 2 kg (cat) and 550 kg (ox). Brain sampling was designed so that Cavalieri estimates of volumes (derived via point counting) could be combined with vertical sectioning estimates of surface areas (via intersection counting). Total volumes, cortical volumes and cortical surface areas were calculated. Each cerebral hemisphere was cut into 3 slabs. Each slab was cut further into macroscopic, parallel vertical slices having a uniform random start position. The term vertical as used here signifies orthogonal to the medial aspect of the hemisphere. The direction of vertical slices also had a random start but was varied systematically across the slabs. Test lattices bearing test points and cycloid test lines were superimposed on vertical slices. Fixed volumes and surfaces were corrected for shrinkage effects. A worked example of the calculation sequence is provided. The experimental design was flexible. Brains of different sizes could be analysed by simply altering the distance between slices and the size of the test lattice. Analyses took 30-45 minutes per hemisphere. Whilst volumes and surfaces increased with body weight, specific values declined. Thus, specific surfaces for the cortex fell from 25 cm2/kg (cat) to 2 cm2/kg or less (pig and ox).

Animals↗
PubMed1989

On the number of Purkinje cells in the human cerebellum: unbiased estimates obtained by using the "fractionator".

Stereological estimates of the numbers of Purkinje cell nucleoli in human cerebellar cortex have been obtained from systematic random samples of tissue by using the fractionator. The estimates are unbiased by fixation, section thickness, or sampling errors and are independent of any assumptions about cell shape, size, or spatial orientation. Twelve brains from aged subjects of both sexes were examined. The average complement of nucleoli in four female brains (age range 71-93 years) amounted to 14.8 millions (with an observed coefficient of variation between subjects of 29%). For three male brains (76-91 years), the corresponding estimates were 15.7 millions (10%). No significant sex differences were found for these small samples. Five brains of unknown sex and age yielded values of 15.8 millions (18%). For the twelve brains examined, the total number of Purkinje cell nucleoli per cerebellum was found to be 15.4 millions (19%). Estimated numbers showed a significant positive correlation with cerebellar weights. The number of nucleoli in an individual cerebellum was obtained with high precision in as short a time as 4 hours.

Aged↗
PubMed1989

Small intestinal morphology in experimental diabetic rats: a stereological study on the effects of an aldose reductase inhibitor (ponalrestat) given with or without conventional insulin therapy.

The gross and microscopical dimensions of small intestines from 12-week old streptozotocin-diabetic rats receiving no therapeutic intervention were compared with those from animals receiving insulin alone or in conjunction with the aldose reductase inhibitor, ponalrestat. Four regions along each intestine were analysed stereologically. Insulin had significant beneficial effects on body weight as well as on intestinal length, width, surface area and volume. In contrast, ponalrestat did not improve body weight deficits and was associated with crypt hypertrophy and a reduced villous surface/crypt volume ratio. There were interaction effects between insulin and ponalrestat for intestinal length and primary mucosal surface area. All groups displayed significant regional differences in surface area of primary mucosa and volume of muscularis externa. Only untreated diabetic rats failed to reveal regional variation in the surface area and volume of villi. Ratios of villous surface area/crypt volume varied from region-to-region in insulin-treated diabetic rats but not in other groups. The study fails to reveal any beneficial effect of aldose reductase inhibition on the changes in intestinal morphology seen in experimental diabetes.

Analysis of Variance↗
PubMed1989

Microangiopathy in human diabetic neuropathy: relationship between capillary abnormalities and the severity of neuropathy.

Clinical, electrophysiological and ultrastructural morphometric observations were made in 5 diabetic non-neuropathic patients, 5 diabetic patients with mild neuropathy and 11 diabetic patients with severe neuropathy. Capillary abnormalities were assessed in simultaneous nerve, muscle and skin biopsies and compared with results from 6 age-matched, non-diabetic control subjects. Nerve capillaries demonstrated markedly greater pathology than skin and muscle capillaries. Endoneurial capillary density was significantly reduced in severely neuropathic diabetic patients (p less than 0.01) when compared with control subjects. Capillary basement membrane (p less than 0.002), endothelial cell (p less than 0.003) and total diffusion barrier (endothelial cell, pericyte, basement membrane) (p less than 0.001) thickness were significantly increased, and oxygen diffusing capacity was significantly reduced (p less than 0.001) in the nerves of patients with severe diabetic neuropathy when compared to control subjects. Endothelial cell profile number and luminal perimeter were significantly increased in asymptomatic (p less than 0.01), (p less than 0.05) and severely neuropathic (p less than 0.001), (p less than 0.05) diabetic patients respectively. However, endothelial cell outer perimeter, a measure of capillary size, showed no significant increase in diabetic patients when compared with control subjects. An association was observed between neurophysiological and neuropathological measures of neuropathic severity. There was no significant correlation between the duration of diabetes and HbA1 levels with capillary pathology or with neuropathic severity. Very few abnormalities of muscle and skin correlated with neuropathic severity. However, all measures of nerve capillary pathology correlated significantly with neurophysiological and neuropathological measures of neuropathic severity.

Adult↗
PubMed1989

Mechanisms of adaptation in rat small intestine: regional differences in quantitative morphology during normal growth and experimental hypertrophy.

The gross and microscopical dimensions of small intestines from three groups of rats were investigated by morphometric (mainly stereological) methods. The groups were chosen to represent relatively 'steady state' situations: normal growth (over a 12 week period) and intestinal hyperplasia due to streptozotocin-diabetes of 12 weeks duration. Four intestinal segments were sampled along each intestine. For normal groups, no interaction effects were found, suggesting that growth affected all regions of the small intestine in the same way. Older rats were heavier and their intestines were longer and narrower. In addition, villous surface area was more extensive and the villi differed in shape. Volumes of crypts, submucosa and muscularis externa were all reduced. Diabetic animals weighed less than age-matched controls and their intestines were wider but not significantly longer. All surface areas and volumes were increased substantially. However, hypertrophy of the muscularis externa was not detected by measuring muscularis thickness. Villi altered their shape. At least for villous height, the effects of diabetes were greater in terminal segments. These findings are discussed in the context of the reported effects of age and experimental hyperplasia (including diabetes) on intestinal architecture and behaviour.

Adaptation, Physiological↗
PubMed1989

The cerebrum and cerebellum of the fixed human brain: efficient and unbiased estimates of volumes and cortical surface areas.

Extremely old and relatively new stereological methods for the efficient and unbiased estimation of volumes and surface areas were applied to fixed human brains. Brains from twelve subjects (six males aged 76-81 years, six females aged 70-98 years) were hemisected. Cerebral hemispheres and cerebellar halves from both sides were sliced systematic randomly for Cavalieri estimates of volume and vertical sectioning estimates of cortical surface area. Weights and linear dimensions were also recorded. It took less than 30 minutes per cerebral hemisphere to estimate total volume and cortical surface area. Cerebellar halves were analysed even more quickly. No significant differences between brain sides and no interaction effects were found but sex differences were confirmed. For male cerebrum (both hemispheres combined), the average volume was 840 cm3 and cortical surface area was 1640 cm2. Two thirds of this surface was hidden within sulci and in the insula. Cortical volume was 320 cm2 with an arithmetic mean thickness of 2.2 mm. In females the cerebral hemisphere was smaller and the cortex was less extensive but just as voluminous. In males, the cerebellum occupied 70 cm3 with a cortical surface of 550 cm2 of which 86% was hidden in fissures. Values were not significantly different from those found in females.

Aged↗
PubMed1989

Stereological studies on rat spinal neurons during postnatal development: estimates of mean perikaryal and nuclear volumes free from assumptions about shape.

A stereological method for estimating the mean volumes of particles independent of assumptions about their shapes is illustrated using neurons in the ventral horn of rat cervical spinal cord. Male rats of 20 and 120 days post partum age were killed by intracardiac perfusion with formaldehyde/glutaraldehyde solutions. Cervical enlargements were removed, trimmed and embedded in resin. Randomised sections of ventral horn were photographed in a systematic pattern and used to estimate the volume-weighted mean volumes of neuronal perikarya and their nuclei. Volumes were estimated from point-sampled intercepts using rulers to classify intercept lengths. Classifying motoneuron perikarya was extremely reproducible, group means (coefficients of variation) at 120 days post partum being 25,190 microns3 (23%) and 24,250 microns3 (25%) in two separate trials. Classifying all neurons at the same age gave values of 20,520 microns3 (22%) and 22,490 microns3 (28%) in two trials. The mean perikaryal volumes of motoneurons at 20 and 120 days of age were not significantly different but nuclear volumes increased from 1,580 microns3 (16%) at 20 days to 2,660 microns3 (28%) at 120 days. These results illustrate the value of the method for obtaining unbiased and efficient estimates of the sizes of irregular perikarya and their nuclei. The benefit is that sizes can be estimated without biases due to simplifying assumptions about perikaryal/nuclear shape or nucleolar location. The influence of section thickness (even of thick paraffin sections) on the estimates is also negligible.

Animals↗
PubMed1988

An efficient sampling scheme for estimating fibre number from nerve cross sections: the fractionator.

Biopsies were made on six rat tibial nerves and 'absolute' numbers of myelinated fibres determined by counting all fibres in all nerve trunks. Subsequently, two unbiased sampling schemes-systematic random quadrat (SRQ) and 'fractionator' sampling-were used to select fibres from the same nerves and to obtain estimates of their numbers. Both schemes captured roughly 200 out of the total of 3000 myelinated fibres found in these nerve trunks, all of which were sampled exhaustively, without replacement. Estimates of fibre number were derived by an established approach, the 'ratio technique' (using SRQ samples), and by a new principle, the fractionator (using fractionator samples). Counting all fibres in every nerve trunk took almost 6 hours. Both the ratio technique and the fractionator approaches provided efficient and unbiased estimates of fibre numbers. Six nerve trunks were analysed by SRQ sampling in 77 minutes, compared with 65 minutes by the fractionator. Apparent differences between the two approaches were of minor interest when set against the benefits of sampling per se. These findings are likely to be of practical concern to those wishing to examine nerves with great numbers of fibres and/or to examine large numbers of nerves.

Animals↗
PubMed1988

A geometric model for estimating villous surface area in rat small bowel is justified by unbiased estimates obtained using vertical sections.

Sampling schemes developed for use with a geometric model of rat small bowel are tested against a design-based scheme (vertical sectioning with cycloid test lines) which offers unbiased estimates of surface amplifications due to villi. The model-based methods comprise transverse and longitudinal sectioning coupled with putative correction factors. Comparisons are based on proximal, middle and distal segments of six small bowels. Transverse and longitudinal sections through the same segments of each animal were analysed by conventional intersection counting (using straight test lines). Appropriate intersection ratios were multiplied by their respective correction factors in order to calculate surface amplifications. Longitudinal sections were employed further as vertical sections and intersections were counted with cycloid arcs to obtain unbiased estimates of surface amplifications. Both model-based schemes (transverse and longitudinal) gave group mean values similar to those obtained by vertical sectioning. Therefore, the use of a geometric model in past studies on rat small bowel can now be justified on grounds of negligible bias.

Animals↗
PubMed1987

Effects of continuous subcutaneous insulin infusion on renal morphology in experimental diabetes. I. Blood glucose levels, body size, kidney weight and glomerulotubular morphometry.

Observations have been made over a period of 16 weeks on three groups of rats: controls, untreated streptozotocin-diabetics and diabetics treated with continuous subcutaneous insulin infusion. Good control of circadian and diurnal blood glucose levels was achieved in the insulin-treated diabetics. Body weights and tibial lengths were reduced in untreated diabetics and improved, but not normalized, by insulin therapy. Kidney weights were similar in all groups. Glomerular size and number, tubule volume, glomerular basement membrane volume and surface area were essentially the same in all groups. However, the untreated diabetics possessed tubules of larger diameter and shorter length than those in controls. Both variables were preserved at normal values by insulin infusion therapy. These results illustrate the value of early blood glucose control for preventing at least some of the structural alterations associated with experimental diabetic nephropathy.

Animals↗