Search PubMed⌕ Search

Biomedical subjects

T M Mayhew

Publications and source records attributed to T M Mayhew.

At least 73 records · Page 4Linked to original sources
PubMed1994

Rate of discharge and morphology of sweat glands in the perineal, lumbodorsal and scrotal skin of cattle.

The rates of evaporation of moisture from the skin in the lumbodorsal, perineal and scrotal regions of cattle were measured in thermoneutral and high environmental temperatures. The rates of evaporation from the perineal and scrotal regions of heifers and bulls were significantly (P < 0.001) greater than those from the lumbodorsal areas. The lumbodorsal rate of evaporation increased significantly (P < 0.001) when cows and bulls were transferred from a thermoneutral to a hot environment and the rate of evaporation from the scrotum of bulls showed a similar increase; the rate of evaporation from the perineum of cows increased to a smaller extent (P < 0.05) under the same conditions. The rate of evaporation from the perineum of cows reached a maximum on the day of oestrus but the stage of the oestrous cycle had no effect on the lumbodorsal rate of evaporation.

Animals↗
PubMed1994

Quantitative evidence for the spatial dispersal of trophoblast nuclei in human placental villi during gestation.

A common assertion in the literature is that Langhans cells in placental villi decline in number during gestation but this is a misinterpretation which may be caused by the greater growth of villous surface area compared with trophoblast volume. To test this possibility, human placentae were collected at 12-41 weeks of gestation for a cross-sectional study on the packing density of nuclei within villous trophoblast. Numbers of nuclei in the cyto- and syncytiotrophoblast were estimated using a design-based stereological device, the physical disector (parallel pairs of sections). Surface areas were estimated in order to assess the overall growth of villous arborizations. Packing densities of nuclei were calculated and expressed as numbers/1000 microns 2 of villous surface. Densities decreased during gestation and this can be explained by expansion of villous surface area and thinning of trophoblast. The biggest drop in packing density of cytotrophoblast nuclei (30 per cent) occurred between 17-21 and 22-26 weeks and this period coincided with the largest changes in villous surface area (62 per cent increase) and trophoblast thickness (30 per cent decrease). Results are consistent with the notion of an epithelial proliferative unit of constant volume and comprising about nine syncytiotrophoblast nuclei per Langhans cell.

Cell Nucleus↗
PubMed1994

Growth and maturation of villi in placentae from well-controlled diabetic women.

Placentae from controls and two groups of diabetic women (one White classes A, B, C and the other classes D, F/R) were collected at 37-42 weeks of gestation. Tissue sections were analysed using stereological methods in order to quantify the growth and maturational status of villi. Birth and placental weights were recorded and placentae sampled in a systematic manner. Fields of view on formalin-fixed, paraffin-embedded sections were analysed to obtain estimates of volumes, surface areas, lengths and diffusion (harmonic mean) distances. Comparisons were drawn using three-way analyses of variance with group, mode of delivery and sex of newborn as the principal effects. Mean weights were similar in controls and diabetic groups. Diabetic placentae had a more voluminous fetal capillary bed of greater length, diameter and surface area. In addition, the diffusion distances across fetal plasma (erythrocyte to endothelium) were shorter. Stromal diffusion distance and villous diameter were greater in vaginal deliveries. Interaction effects influenced also villous capillarization, capillary volume, capillary diameter, trophoblast thickness and stromal thickness. Our results emphasize the importance of adaptations on the fetal side of the diabetic placenta. They show that changes can affect the placentae of appropriate-for-age as well as large-for-age babies and provide no evidence that they increase with the severity and duration of diabetes.

Adult↗
PubMed1994

Stereological studies on red corpuscle size produce values different from those obtained using haematocrit- and model-based methods.

The routine methods for estimating erythrocyte size (volume and surface area) are not generally unbiased. Using geometric models introduces a bias determined by the ways in which real red blood corpuscles depart in size and shape from the simplistic ideal. Employing haematocrit and red corpuscle count to estimate mean corpuscular volume relies on an implicit assumption that erythrocytes fill three-dimensional space. However, a biconcave circular disc cannot be space-filling. The bias is positive and its magnitude depends on erythrocyte geometry and packing density within the centrifuge pellet. We have estimated the volumes, surface areas and shape factors of red blood corpuscles in normal adults (three males, three females) using transmission electron microscopy and stereology. We confirm the lack of sexual dimorphism and find that the mean corpuscular volume is 44 fl (between-subject coefficient of variation 5%), mean membrane surface area is 87 microns2 (6%) and the shape factor is 18.4 fl/fl (11%). The surface is 44% greater than that of a sphere of equal volume. The possible reasons for discrepancies with standard haematological values are discussed. On the basis of observed volumes, we predict that red blood corpuscles account for only 51% of the volume of the red column in standard haematocrit pellets.

Erythrocyte Indices↗
PubMed1994

Crypt and villous epithelial cells in adult rat small intestine: numerical and volumetric variation along longitudinal and vertical axes.

Previous studies on the small intestines of certain adult rodents have suggested that the total number of crypt epithelial cells is equal to the number of villous epithelial cells. This possibility is examined on adult male Sprague-Dawley rats using design-based stereological methods. Small intestines were removed and divided into four segments of equal length. For each segment, numbers and mean volumes of epithelial cells in crypts and villi were estimated and then combined to give values for the entire intestine. Variations along the vertical (crypt-villus) axis and the intestinal long (pyloro-ileocaecal) axis were examined. Cell numbers in crypts and on villi varied from segment to segment. Villus:crypt cell ratios proximally were roughly double those found distally. The ratio for the entire intestine was, on average, 1.6 villous cells per crypt cell. These results demonstrate that numbers of crypt and villous cells need not be equivalent. Previous findings may reflect the fact that ratios fluctuate according to circumstances (e.g., with species, age, nutritional status, disease, etc) or may be due to technical differences in tissue sampling and morphometry. Cell volumes varied along the crypt-villus axis as well as between segments, confirming known gradients of maturation and activity. Finally, the size of the intestinal epithelial proliferon was calculated in terms of the average numbers of epithelial cells per villus and of crypt epithelial cells feeding on to it.

Animals↗
PubMed1994

Proliferative versus hypertrophic growth in tissue subcompartments of human placental villi during gestation.

A cross-sectional sample of human placentae was collected at 12-41 wk, and growth mechanisms within villous subcompartments (trophoblast epithelium, stroma and fetal capillary endothelium) were assessed using state-of-the-art design-based stereological methods. Physical disectors (adjacent pairs of sections) were used to count nuclei in syncytiotrophoblast and in cells of the cytotrophoblast, stroma and endothelium. The volumes of trophoblast and stroma and the surface areas and lengths of capillaries were employed to assess the overall growth of each compartment. Growth within compartments was monitored as total number of nuclei (a measure of nuclear proliferation) and compartment size per nucleus (a measure of hypertrophy). During gestation, all compartments grew dramatically. Numbers of nuclei increased exponentially and followed an uninhibited growth model. Volumetric growth of the placenta did not keep pace with the increase in total nuclear number (all types). Growth of trophoblast was exclusively hyperplastic and proceeded at an average net recruitment rate of 15 million nuclei per hour with a numerical predominance of syncytiotrophoblast nuclei of 9:1. There was no evidence of hypertrophy: trophoblast volume per nucleus averaged 1080 microns 3. Growth within stroma involved cell proliferation (17 million nuclei per hour) and the volume of stroma per nucleus declined at a rate of about 24 microns 3 per week. Capillary growth was hyperplastic (5 million endothelial squames per hour) and, possibly, hypertrophic (the mean area of a squame increased by about 18 microns 2 per week). Linear growth of vessels exceeded cellular recruitment and the density of squames along the capillaries decreased each week by about 5 per mm.(ABSTRACT TRUNCATED AT 250 WORDS)

Capillaries↗
PubMed1993

Oxygen diffusive conductance in placentae from control and diabetic women.

Random tissue sections of placentae from control and diabetic deliveries were analysed stereologically. The aim was to test whether or not adaptations in oxygen diffusive conductances occur to help compensate for fetal hypoxic stress in utero. Organs were from 34 control and 55 diabetic deliveries (39 from White's classes A, B, C and 16 from classes D, F/R) arranged in two major groups (ABC and DFR). Tissue samples were fixed in formalin and processed for wax histology. Stereological and physicochemical quantities were used to calculate the partial conductances of six tissue layers, viz. maternal erythrocytes and plasma, villous trophoblast, villous stroma, fetal plasma and fetal erythrocytes. From partial conductances and birthweights, total and specific conductances for each placenta were determined. No differences were detected between diabetic placentae in different classes (A, B, C, D, F/R). However, both the ABC and DFR groups of diabetic placentae had higher total diffusive conductances than control organs. The increase was in the order of 7-25% and persisted even when adjustments were made for apparent differences in birthweights. The principal contributors to these changes were the post-trophoblastic (fetally located) tissue layers. These findings suggest that the diabetic placenta adapts to facilitate the diffusion of oxygen across the placenta and, thereby, to assist the hypoxic fetus.

Adult↗
PubMed1993

Validation of acoustic rhinometry by using the Cavalieri principle to estimate nasal cavity volume in cadavers.

The ability of acoustic rhinometry to provide valid estimates of nasal cavity volume has been tested using cadaveric heads. Values obtained for the cavities in five intact heads were compared with unbiased estimates of the volumes of the same specimens. An unbiased estimate is one which does not depart in a systematic manner from the true value. Here, unbiased estimates were made by applying the Cavalieri principle to uniform random samples of 4-7 macroscopic slices per specimen. Using acoustic rhinometry, the mean volume (left and right sides combined) amounted to 31.3 ml with a co-efficient of variation of 77%. On the same specimens, the Cavalieri estimate of mean volume (both cavities plus the adjacent nasopharynx) was 31.1 ml (66%). There was a significant and positive correlation between the two data sets (correlation co-efficient 0.97). Repeated acoustic measurements on the same cavities gave a measuring error of about 4%. We conclude that acoustic rhinometry can provide valid and efficient estimates of the volume of the nasal cavity plus nasopharynx.

Acoustics↗
PubMed1993

Purkinje cell complements in mammalian cerebella and the biases incurred by counting nucleoli.

An unbiased stereological counting device (the fractionator) was used to count Purkinje neurons in mammalian cerebella of known weights in order to define the relationship between weight and number. Nucleoli were chosen as the counting unit and numbers were estimated from uniform random samples of wax-embedded tissue sections. For the cerebella of rat, rabbit, cat, dog, goat, sheep, pig, ox, horse and human, there was a significant linear relationship between log number and log weight. The allometric relationship took the form N = 748,500 x W0.627. The relative bias associated with using nucleoli as counting units was assessed separately on disector pairs of sections and amounted to roughly -5% but varied between species. When the brains of females and males were analysed separately (cat, goat, pig, ox, horse, human), there were no significant differences between the regression lines. These results are consistent with earlier findings. They imply that Purkinje neuron packing densities decrease as brain size increases. Moreover, our preliminary findings appear to indicate that, for any given cerebellar weight, females and males have similar numbers of neurons.

Animals↗
PubMed1993

The effects of mode of delivery and sex of newborn on placental morphology in control and diabetic pregnancies.

Placentae from control and diabetic subjects were analysed using stereological techniques in order to assess the effects of mode of delivery (vaginal versus caesarean) and sex of neonate on parenchymal morphology. Effects were assessed using indices of peripheral villous and fetal capillary growth, villous maturity, extent of maternal intervillous space and thickness of intervascular tissue layers. Placentae were from pregnancies (37-42 wk) which were either uncomplicated (control group) or complicated by diabetes mellitus (diabetic group, White class D) which was reasonably well controlled in terms of glucose and glycated haemoglobin levels. Neonatal and placental weights were recorded and placentae sampled in a systematic random fashion. Fields of view on formalin-fixed, paraffin-embedded sections were analysed to obtain estimates of volumes, surface areas, lengths and diffusion (harmonic mean) distances. Comparisons were drawn using 3-way analyses of variance with group, mode of delivery and sex as the principal effects. The mean length of gestation was 2 wk longer in controls (39 versus 37 wk). Despite this, mean birth weight was similar (3.5 kg) in control and diabetic groups. Moreover, diabetic placentae were 17% heavier and showed shorter fetal plasma distances (30%) and larger fetal capillaries (volume 45%, surface 39% and length 30% greater). Mode of delivery had significant main and interaction effects on stromal diffusion distance (25% greater in vaginal deliveries) and an interaction effect on fetal capillary volume. Sex had significant main effects on the maternal plasma distance (21% greater in males) and capillary volume (30% bigger in males) and an interaction effect on placental weight and mean capillary diameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Cesarean Section↗
PubMed1992

Structural and enzymatic studies on the plasma membrane domains and sodium pump enzymes of absorptive epithelial cells in the avian lower intestine.

The coprodaeum of the domestic hen maintained on a low-NaCl diet adapts by enhanced sodium transport. This study examines the adaptive response at the single cell and whole organ levels. Surface areas of apical (microvillous) and basolateral plasma membranes of columnar absorptive epithelial cells were estimated by use of ultrastructural stereology. The activities of succinic dehydrogenase (a mitochondrial enzyme) and ouabain-sensitive, potassium-dependent paranitrophenyl phosphatase (a sodium pump enzyme) were determined in tissue homogenates. Sodium, potassium-ATPase (pump enzyme) activity in cell membranes was localized by ultrastructural cytochemistry. Apical and basolateral membranes responded differently. In high-NaCl hens, the membrane signature of the average cell was 32 microns 2 (apical), 932 microns 2 (lateral) and 17 microns 2 (basal). Cells from low-NaCl hens had more apical membrane (49 microns 2 per cell) but essentially the same area of basolateral membrane. However, total surfaces per organ were greater for all membranes. Sodium pump enzymes were localized in basolateral membranes. Enzyme activities per unit mitochondrial volume and per unit basolateral membrane surface were higher in low-NaCl birds. These findings are discussed in the context of known mechanisms of transcellular sodium transport via apical ion channels and basolateral pumps.

4-Nitrophenylphosphatase↗
PubMed1992

A review of recent advances in stereology for quantifying neural structure.

The science of stereology has undergone a revolution over the past decade with the introduction of design-based (assumption- or model-free) methods which are highly efficient and generally unbiased. No other morphometric approach currently offers these twin benefits. Stereology is ideal for extrapolating 3-D structural quantities (real volumes, surface areas, lengths and numbers) from simple counts made on 2-D slice images. The images may take various forms (e.g. physical or optical sections, MRI slices, CT scans) but they must be sampled so as to be random in orientation and/or position if valid estimates are to be made. All the recent developments in stereology are applicable to problems in neuromorphometry. This review provides an account of major developments and the state of the art, emphasizes the importance of properly randomized sampling and identifies some applications to neural structure at different levels of organization. These include the counting and sizing of synapses, neurites, cells and whole brains.

Animals↗
PubMed1992

Responses of enterocyte microvilli in experimental diabetes to insulin and an aldose reductase inhibitor (ponalrestat).

The small intestine of 12-week-old streptozotocin-diabetic rats was examined by light and transmission electron microscopy in order to study the effects of alternative treatments on microvillous morphology. Four groups were examined: untreated diabetic rats, insulin-treated diabetics and rats treated with an aldose reductase inhibitor (ponalrestat) given with and without insulin. Numbers and dimensions of microvilli at the apex of columnar absorptive epithelial cells (enterocytes) were estimated using stereological principles. Values were obtained for the organ as a whole as well as for different sites along its length. In the untreated diabetic intestine, the mean (standard error of mean) number of microvilli was 4.5 (0.8) x 10(12) with a total surface area of 1.9 (0.50) m2. On average, the microvilli were 1.1 (0.08) microns long, 104 (3.8) nm in diameter and packed on the villous surface at a density of 3400 (50) per 100 microns 2. Their length at least varied with intestinal location. Significant effects of insulin therapy were detected. In contrast, the study failed to find any significant effect of aldose reductase inhibition on any variable except microvillous packing density.

Aldehyde Reductase↗
PubMed1992

Quantitative analysis of factors contributing to expansion of microvillous surface area in the coprodaeum of hens transferred to a low NaCl diet.

A stereological study of the lower intestine (coprodaeum) of the domestic hen was undertaken using combined light and electron microscopy. Numbers of columnar absorptive epithelial cells and the dimensions and numbers of microvilli were estimated. The aim was to identify the main factors contributing to an increase in microvillous surface area following transfer of hens from a high to a low NaCl diet on which they were kept for at least 3 wk. The principal contributor to observed changes between organs was cell number. Birds adapted to the low NaCl diet had 57% more cells than high NaCl controls. The average cell had a larger microvillous surface (55%) and this could be explained by the presence of longer (34%) and more densely packed (38%) microvilli. The total number of microvilli per coprodaeum doubled (from 35 x 10(9) on the high NaCl to 71 x 10(9) on the low NaCl diet). The increase in cell number accounted for 67% of the change in surface area and 78% of the change in number of microvilli per organ. These findings emphasise that, when assessing the form and function of a whole organ, it is important to monitor cell populations as well as single cells. This is especially true when studying renewing and expanding (rather than static) populations.

Animals↗
PubMed1992

A fractionator study of the effects of undernutrition during early life on rat Purkinje cell numbers (with a caveat on the use of nucleoli as counting units).

The effects of varying periods of general protein-calorie undernutrition during early life on Purkinje cells in the cerebellum of the rat were examined. In Experiment 1, animals were undernourished from d 18 of gestation until either d 30 or d 60 of postnatal age, followed in some cases by a period of nutritional rehabilitation. In Experiment 2, rats were undernourished from conception until d 30 postnatally, followed by a period of rehabilitation until 60 d of age. The 'fractionator' method was employed to estimate the total number of cerebellar Purkinje cell nucleoli. If each cell has one nucleolus, this number is equal to the number of Purkinje cells. In Experiment 1, the estimated mean number of Purkinje cell nucleoli varied between 188,000 and 273,000 for the groups of animals studied. However, the interanimal variation was large and 2-way analysis of variance tests failed to reveal any statistically significant age, nutrition or interaction effects. In Experiment 2, rats killed immediately after the period of undernutrition possessed significantly fewer Purkinje cell nucleoli than age-matched controls. This did not represent a real decrease in cell number. Instead, the result could be explained by a change of Purkinje cell morphology in undernourished rats. The change included nucleolar regression. Nutritionally rehabilitated animals had similar numbers of nucleoli to control rats. It is concluded that the levels and periods of undernutrition used in these experiments did not affect significantly the total numbers of cerebellar Purkinje neurons.

Animals↗
PubMed1991

Accurate prediction of Purkinje cell number from cerebellar weight can be achieved with the fractionator.

Purkinje cell nucleoli are used as counting units in order to obtain unbiased (fractionator) estimates of the number, N, of Purkinje neurons in adult mammalian cerebella of known weight, W. Regression analysis is then employed to establish the nature of the relationship between logN and logW. The linear regression equation defines an allometric relation that is employed to predict number in cerebella of known weight from other mammals. Predicted numbers are tested against empirical estimates. For 19 cerebella ranging in weight from 0.2 g (rat) to 113 g (human), the allometric relation between Purkinje cell number and organ weight was determined. By using this relation, the mean complement in three rabbit cerebella (average weight, 0.87 g) is predicted to be 0.63 million. This figure is confirmed by fractionator estimates made on the same three brains. The cat cerebellum should contain about 1.5-2.0 million Purkinje cells. An estimate of 1.2-1.3 million cells is to be found in the literature. Including rabbit cerebella in a refined equation yields the following relation: N = 686000W(0.695). With this refined equation, further predictions are made about the numbers likely to be found in the cerebella of the dog, goat, pig, ox, and horse. The numbers predicted for these animals must await experimental verification, but they are entirely consistent with previous suggestions that neuronal packing densities decrease with increasing brain size.

Algorithms↗
PubMed1991

Inhibitor action on placental calcium transport.

Human term placental lobules were dually perfused with Krebs Ringer solution at 37 degrees C under open circuit conditions. Provided that perfusate Ca2+ concentrations were between 2.33 and 2.55 mM, there was a steady release of Ca2+ into the fetal circulation and uptake of Ca2+ from the maternal circulation. There was no significant calcium (Ca) protein binding in the perfusates. Addition of dinitrophenol altered the release of Ca2+ to an uptake on the fetal circuit and enhanced Ca2+ uptake on the maternal circuit. It also produced a release of potassium (K)+ and an uptake of Na+ on both sides of the placenta. Ouabain had no significant effect on Ca movements although it produced a marked release of K+ into the fetal perfusate. The effect of cooling on the fetal circuit was similar to that of dinitrophenol (DNP), although it did not produce significant changes in either Ca2+ or K+ movements on the maternal side of the lobule. Both DNP and cooling reduced the Ca concentration ratio between fetal and maternal outflows to unity. Replacement of Na+ by choline Ringer had only transient effect on the extraction of 45Ca from fetal perfusate. These observations indicate that a Ca2+/Na (sodium)+ exchanger does not make a major contribution to the transplacental movement of Ca2+ from mother to fetus and that this process is more probably associated with membrane-bound ATPases.

Adenosine Triphosphatases↗