Biomedical subjects

T M Mayhew

Publications and source records attributed to T M Mayhew.

At least 55 records · Page 3Linked to original sources

PubMed1997

Photoreceptor number and outer segment disk membrane surface area in the retina of the rat: stereological data for whole organ and average photoreceptor cell.

A random sampling scheme is employed to obtain stereological estimates of disk membrane surface area in the entire retina and in the average photoreceptor cell. The scheme involves the use of vertical sections with combined light and electron microscopy at several magnification levels. Left and right retinas from six albino animals were analysed. There were no significant lateral differences. On average, the retina had a volume of 16 mm3, thickness of 200 microns and surface area of 80 mm2 (representing about 56% of the external surface of the eyeball). Photoreceptor disk membranes within outer segments amplified total retinal surface by almost 1000-fold (final surface 770 cm2 per retina). The retina contained 3 x 10(7) photoreceptors (packing density 374,000 mm-2) with an average disk membrane surface area of 2600 microns2. Mean nuclear volume in photoreceptor cells was 59 microns3 and the coefficient of variation for the distribution of nuclear volumes was 57%. The data are consistent with an average of 700 disks per photoreceptor cell, a membrane area of 4 microns2 per disk and a convergence ratio of approximately 260 photoreceptors per optic nerve fibre. The basic scheme could be modified for other species and for direct cell counts conducted on rods and cones separately.

Animals↗

PubMed1997

Recent applications of the new stereology have thrown fresh light on how the human placenta grows and develops its form.

The availability of design-based stereological methods has made it possible to readdress certain key and contentious issues in placental growth and morphogenesis. Three particular questions are: (i) does the population of cytotrophoblast cells decline during gestation?, (ii) is placental growth biphasic or monophasic? and (iii) what are the consequences for intervillous porosity of the elaboration of terminal villi? These questions cannot be answered definitively without recourse to the new stereology. Applying the disector to estimate nuclear number and star volume to assess pore size, recent studies have helped to resolve these issues. Their findings are reviewed. Nuclei were counted in the trophoblastic epithelium, stroma and vascular endothelium of placental villi. It was found that growth is monophasic and proliferative. All types of nuclei increased in number throughout gestation and this included cytotrophoblast. Trophoblast grows by the continuous recruitment of new proliferative units of uniform mean volume. The so-called 'loss' of cytotrophoblast cells is a misinterpretation of what is seen on microscopical sections and is attributable to disproportionate growth in villous surface area. Cells simply become more widely dispersed. Elaboration of finer terminal branches on villous trees leads to a decline in the star volumes of villi and intervillous pores. Some of the functional implications of these findings are discussed.

Chorionic Villi↗

PubMed1997

Response of substance P-immunoreactive nerve fibres in the anterior pituitary to plasma oestrogen levels in the rat.

The mammalian anterior pituitary has recently been shown to be innervated by substantial amounts of peptidergic nerve fibres. It has also been found that adrenalectomy increases the amount of calcitonin gene-related peptide-like immunoreactive nerve fibres in the anterior pituitary of the rat, and that stimulation of the nerve fibres in vitro can enhance release of ACTH. In the present study, the density of substance P-like immunoreactive nerve fibres in the anterior pituitary of the rat were examined in relation to variations in plasma oestrogen status. The amount of substance P-like immunoreactive nerve fibres increased significantly (P < 0.001) after ovariectomy, and decreased significantly (P < 0.01) under oestrogen replacement, in a dose-dependent manner. The results suggest the possibility of the direct neural involvement of oestrogen secretion in anterior pituitary regulation, which further substantiates the hypothesis of neural-humoral dual regulation of the mammalian anterior pituitary.

Animals↗

PubMed1997

Stereological estimates of nuclear number in human ventricular cardiomyocytes before and after birth obtained using physical disectors.

Design-based stereology is employed to estimate total numbers of myocyte nuclei and mean myocyte volume per nucleus in ventricles of fetal and early postnatal human hearts. Organs were collected postmortem from subjects varying in age from 16 gestational wk to 40 postnatal wk. Numbers of myocyte nuclei per unit volume of ventricle were estimated using physical disectors (parallel pairs of sections). Absolute numbers were calculated by multiplying nuclear packing densities by ventricular volumes estimated from ventricular mass and tissue density. Volumes per nucleus were obtained via estimates of the combined volumes of all myocytes (or of the myocardium as a whole) and the numbers of myocyte nuclei. The findings showed that numbers of myocyte nuclei increase linearly from 16 wk towards term. They were also consistent with the notion that hyperplasia ceases abruptly at birth or soon afterwards. The net rate of production of myocyte nuclei was about 38 x 10(7)/wk (2.3 million nuclei/h). The total volume of myocytes continued to expand in the same way from 16 wk to at least 35 wk of gestation. Published studies on the incidence of binucleate myocytes during early postnatal growth of the ventricles of rats suggest that the volume of a myocyte doubles prior to nuclear division. Prenatal growth in the human heart is consistent with this mechanism. Myocardial hypertrophy after birth must occur by cellular hypertrophy without karyokinesis.

Cell Nucleus↗

PubMed1997

A stereological comparison of villous and microvillous surfaces in small intestines of frugivorous and entomophagous bats: species, inter-individual and craniocaudal differences.

The extents of functional surfaces (villi, microvilli) have been estimated at different longitudinal sites, and in the entire small intestine, for three species of bats belonging to two feeding groups: insect- and fruit-eaters. In all species, surface areas and other structural quantities tended to be greatest at more cranial sites and to decline caudally. The entomophagous bat (Miniopterus inflatus) had a mean body mass (coefficient of variation) of 8.9 g (5%) and a mean intestinal length of 20 cm (6%). The surface area of the basic intestinal tube (primary mucosa) was 9.1 cm2 (10%) but this was amplified to 48 cm2 (13%) by villi and to 0.13 m2 (20%) by microvilli. The total number of microvilli per intestine was 4 x 10(11) (20%). The average microvillus had a diameter of 8 nm (10%), a length of 1.1 microns (22%) and a membrane surface area of 0.32 micron 2 (31%). In two species of fruit bats (Epomophorus wahlbergi and Lisonycteris angolensis), body masses were greater and intestines longer, the values being 76.0 g (18%) and 76.9 g (4%), and 73 cm (16%) and 72 cm (7%), respectively. Surface areas were also greater, amounting to 76 cm2 (26%) and 45 cm2 (8%) for the primary mucosa, 547 cm2 (29%) and 314 cm2 (16%) for villi and 2.7 m2 (23%) and 1.5 m2 (18%) for microvilli. An increase in the number of microvilli, 33 x 10(11) (19%) and 15 x 10(11) (24%) per intestine, contributed to the more extensive surface area but there were concomitant changes in the dimensions of microvilli. Mean diameters were 94 nm (8%) and 111 nm (4%), and mean lengths were 2.8 microns (12%) and 2.9 microns (10%), respectively. Thus, an increase in the surface area of the average microvillus to 0.83 micron 2 (12%) and 1.02 microns 2 (11%) also contributed to the greater total surface area of microvilli. The lifestyle-related differences in total microvillous surface areas persisted when structural quantities were normalised for the differences in body masses. The values for total microvillous surface area were 148 cm2g-1 (20%) in the entomophagous bat, 355 cm2g-1 (20%) in E. wahlbergi and 192 cm2g-1 (17%) in L. angolensis. This was true despite the fact that the insecteater possessed a greater length of intestine per unit of body mass: 22 mm g-1 (8%) versus 9-10 mm g-1 (9-10%) for the fruit-eaters.

Animals↗

PubMed1996

How to count synapses unbiasedly and efficiently at the ultrastructural level: proposal for a standard sampling and counting protocol.

After almost 40 years, there is still no consensus on criteria for identifying different types of synapse seen in electron microscopical thin sections or on methods for counting them unbiasedly in 3D. This review proposes a procedure which meets these aims and could be adopted as a standard best-practice sampling and counting convention. It deals exclusively with unbiased stereological methods for counting particles in 3D space because these are efficient and applicable to arbitrary particles regardless of their size, shape and orientation. Methods based on individual sections are excluded because arbitrary particles cannot be counted unbiasedly with such sections. Model-based methods (e.g. treating synaptic membrane densities as circular disks) are excluded because they are not unbiased in general and now have limited (mainly historical) interest only. For unbiased counting, the absolute minimum requirement is a pair of parallel sections (dissector). The following protocol is recommended for future studies on synapse number: (1) use para(membrane) densities as synaptic counting units, (2) do not qualify definition of the counting unit by reference to a minimum number of synaptic vesicle profiles, (3) sample and count synapses unbiasedly using the dissector, and (4) in preference convert number per volume into absolute number or, in this is not possible, estimate a synapse-to-neuron ratio.

Animals↗

PubMed1996

Patterns of villous and intervillous space growth in human placentas from normal and abnormal pregnancies.

OBJECTIVES: To apply a new stereological approach (relating an exponent of villous surface to volume) to test for patterns of change in placental villi and intervillous space from normal and abnormal pregnancies. STUDY DESIGN: Placentas from normal gestation and pregnancies associated with hypoxic stress (high altitude, diabetes, cigarette smoking) were sampled randomly, fixed in formalin and embedded in paraffin wax for stereological analysis. Volumes (villi, intervillous space) were estimated by point counting and surface areas (villi) by intersection counting. A dimensionless coefficient (S3/2/V) was then calculated to test for isomorphic changes. Comparisons within groups were drawn using analysis of variance. RESULTS: Changes in villi were isomorphic at high altitude and in placentas from women who smoked during pregnancy. The same pattern is seen in placentas associated with preeclampsia. Changes during gestation and diabetes are anisomorphic, i.e. villous surface area alters disproportionately to volume. A similar pattern is seen in maternal anaemia. Alterations in the intervillous space were isomorphic in diabetes and smoking but anisomorphic during gestation, at high altitude and in maternal anaemia and pre-eclampsia. CONCLUSIONS: The approach has advantages over alternatives (star volume and topological analysis). Structural changes influence placental transport and haemodynamics but there are subtle differences between groups which may depend on the nature of the hypoxic stress and the adaptations made by individual tissue compartments.

Altitude↗

PubMed1996

Assessment of wall structure and composition of varicose veins with reference to collagen, elastin and smooth muscle content.

OBJECTIVES: To compare collagen, elastin and smooth muscle contents of varicose and control long saphenous veins. DESIGN: Collagen, elastin and muscle were estimated stereologically using random sampling and histological staining. MATERIALS: Varicose vein samples were collected from nine patients (mean age 52 years, range 34-64 years) undergoing vein stripping, sample sites being saphenofemoral junction and knee. Control samples were taken from five patients (mean age 58 years, range 38-76 years) presenting for femoral-popliteal bypass at equivalent levels. METHODS: Veins were fixed, sectioned transversely, and stained with Picric Acid Sirius Red. Analysis of samples was performed using point and intersection counting on vertically projected images. RESULTS: Using two way analysis of variance tests, varicose saphenous veins had significantly larger wall areas (p < 0.01) and higher amounts of collagen (p < 0.01). Collagen content and wall area were significantly larger proximally compared to distally in both control and varicose veins (p < 0.05) with a higher content of smooth muscle and elastin in varicose veins proximally compared to distally (p < 0.05). There was no difference in wall thickness or elastin content between the two groups. CONCLUSIONS: This suggests that varicose veins are a dynamic response to venous hypertension and are not thin walled structures as previously thought.

Adult↗

PubMed1996

If you assume, you can make an ass out of u and me': a decade of the disector for stereological counting of particles in 3D space.

The year 1984 was a watershed in stereology. It saw the introduction of highly efficient and unbiased design-based methods for counting the number of arbitrary objects in 3-dimensional (3D) space using 2D sectional images. The only requirement is that the objects be unambiguously identifiable on parallel sections or successive focal planes. The move away from the ¿assumption-based' and ¿model-based' methods applied previously has been a major scientific advance. It has led to the resolution of several problems in different biomedical areas. The basic principle which makes possible 3D counting from sections is the disector. Here, we review the disector principle and consider its impact on the counting and sizing of biological particles. From now on, there can be no excuse for applying the biased counting methods of yesteryear. Their continued use, despite the availability of unbiased alternatives, should be seen as paying homage to History rather than advancing Science.

Animals↗

PubMed1996

The gyrification of mammalian cerebral cortex: quantitative evidence of anisomorphic surface expansion during phylogenetic and ontogenetic development.

Describing the shapes of 3D objects has proved to be as problematical in biology as in other areas. In an attempt to tackle this problem, established stereological methods (the Cavalieri principle and vertical sectioning) have been used to estimate a 3D shape-dependent quantity which can detect anisomorphic changes and is related to the degree of cortical convolution or gyrification. This isomophy factor is employed to assess phylogenetic and ontogenetic changes in the mammalian cerebral cortex. Gross anatomical differences between cerebral hemispheres of adult domestic mammals (horses, oxen, pigs, goats, dogs, cats and rabbits) were tested by paying attention to species, laterality and sex differences. Human fetal brains were also studied. Mean body weights of domestic mammals varied from 4 kg to 460 kg and brain weights from 10 g to 636 g. Fetuses weighed 39-610 g (crown-rump lengths 85-185 mm) and brain volumes were 4-56 cm3. Isomorphy factors were derived from estimates of hemisphere volumes and cortical surface areas. Hemisphere shape varied between species but no lateral or sex differences were detected. It is concluded that these mammalian brains are, in terms of their gross anatomy, symmetric and not sexually dimorphic. Fetal brains became more convoluted during uterine development. The isomorphy factor offers a convenient measure of gyrification which demonstrates that brains become more convoluted as they enlarge.

Animals↗

PubMed1996

Stereological and allometric studies on mammalian cerebral cortex with implications for medical brain imaging.

Design-based stereological methods (the Cavalieri principle and vertical sectioning) have been used to estimate the volumes, surface areas and thicknesses of the cerebral cortex. Cortices of individual hemispheres were analysed in a selection of 31 adult domestic mammals (horses, oxen, pigs, goats, dogs, cats and rabbits). There were 13 females and 18 males. After correcting for fixation shrinkage effects, results were tested for species, laterality and sex differences using linear regression and analysis of variance. Mean body weights of domestic mammals varied from 4 kg to 460 kg and brain volumes from 11 cm3 to 603 cm3. Hemisphere dimensions varied between species but, except for volume (which exhibited a species x sex interaction effect), no other differences were detected. It is concluded that these mammalian brains are, in terms of their gross anatomy, symmetric and not sexually dimorphic. Apparent cortical thickness (measured directly on slices) proved to be a satisfactory estimate of true thickness (estimated by dividing cortical volume by the mean of outer and inner cortical surfaces). This has implications for medical slice images on which mean cortical thickness can be estimated only from apparent local thicknesses.

Analysis of Variance↗

PubMed1996

Adaptive remodelling of intestinal epithelium assessed using stereology: correlation of single cell and whole organ data with nutrient transport.

Adaptation in the intestinal epithelium depends on cell number and the properties of individual cells but these responses operate within different time frames. Changes in number take days to accomplish but those in behaviour may occur within hours. This article reviews the value of stereology for characterising structural features of the average enterocyte and the entire organ (mammalian small intestine or avian lower intestine) during adaptation. Stereological data are correlated with the physiology and molecular biology of glucose and Na+ transport. In small intestine, account is taken of vertical (crypt-villus) and longitudinal (craniocaudal) gradients and of adaptations to chemically-induced diabetes and diet. Results show that longer-term adaptation depends critically on epithelial renewal. In diabetic small intestine, changes in glucose transport are accompanied by changes in the number, but not morphology, of villous enterocytes. In avian, lower intestine, increased Na+ transport requires changes in cell number and the extent of their apical, but not basolateral membrane surfaces. These changes allow opportunities to incorporate more (or more active) transport sites in apical and basolateral membrane domains of individual cells and of whole organs.

Animal Nutritional Physiological Phenomena↗

PubMed1995

The small intestine in experimental diabetes: cellular adaptation in crypts and villi at different longitudinal sites.

Intestinal adaptation at the cellular level was examined in groups of streptozotocin-diabetic and age-matched control rats. Small intestines were removed and divided into four segments of roughly equal length. For each segment, epithelial volume, villous and microvillous surface areas and the mean volumes of epithelial cells in crypts and villi were estimated. From these data, we were able to estimate total numbers of epithelial cells in crypts and villi, assess adaptation at the level of the average cell and explore variation along the crypt-villus axis, between segments and between groups. Whilst the villus:crypt cell ratio did not change, diabetic animals contained about 80% more epithelial cells than control rats. The morphophenotype of villous epithelial cells (represented by nuclear volume, cell height, area and volume, and number and surface area of microvilli) was basically the same as that in controls. By contrast, crypt cells and their nuclei were 40-50% bigger in diabetic rats. Significant differences between segments were confined to the numbers and sizes of crypt cells and their nuclei. We conclude that experimental diabetes leads to both proliferative and hypertrophic responses within crypts. Crypt cells become fatter but not taller. Crypt hyperplasia is accompanied by an equiproportionate increase in villous epithelial cells, but these are of essentially normal morphophenotype.

Adaptation, Physiological↗

PubMed1995

Number and ultrastructure of epithelial cells in crypts and villi along the streptozotocin-diabetic small intestine: a quantitative study on the effects of insulin and aldose reductase inhibition.

This study has quantified the effects of insulin treatment with and without aldose reductase inhibitor (ponalrestat) on intestinal epithelial cell morphology in streptozotocin-diabetic rats. Epithelial volumes, villous and microvillous surface areas and mean volumes of cells (and their nuclei) in crypts and villi were estimated in each of four segments and in the entire intestine. We derived total numbers of cells, quantified the ultrastructural features of average cells and explored variation along the intestine and between experimental groups. In crypts, insulin and ponalrestat had significant effects on cell number (reduced towards normal values) and size (volume and apex area increased beyond normal values). There were interaction effects between insulin and ponalrestat for cell volume and apex area (insulin producing more exaggerated effects when given without ponalrestat). On villi, insulin and ponalrestat returned cell numbers towards normal values but neither treatment normalised cell size or the number and area of microvilli per cell. Indeed, ponalrestat increased microvillous number and area beyond values found in untreated diabetic animals. Again, there were interaction effects between insulin and ponalrestat. Patterns of segmental variation seen in crypts of normal rats (values tending to be higher in proximal or mid-intestinal regions) were not preserved, and only some of the segmental differences seen on villi (higher values at proximal or mid-intestinal sites) were maintained during therapy. Apart from reducing the abnormally high numbers of cells in untreated diabetic rats, these results show that insulin and ponalrestat treatment fail to restitute epithelial cell morphology in the small intestines of experimental diabetic rats.

Animals↗

PubMed1995

Human placental cytochrome P450 and quinone reductase enzyme induction in relation to maternal smoking.

Components of cigarette smoke such as cadmium and polycyclic aromatic hydrocarbons have been shown to induce quinone reductase (QR) activity in placental explants. This study examines the relationship of maternal smoking habit and maternal plasma cotinine concentration with the activities in vitro of both QR and the cytochrome P450 (CYP1A) marker ethoxyresorufin O-deethylase (EROD) in placental tissue. Maternal plasma samples were taken at Week 34 of gestation, and placental tissues were obtained at term. Plasma cotinine concentrations were determined by high-performance liquid chromatography. Trophoblast cytosolic QR and microsomal EROD activities were measured by resazurin reduction and ethoxyresorufin O-dealkylation respectively. QR activity was inhibited 70% by a mixture of dicoumarol (1 microM) and rutin (20 microM). Plasma cotinine concentrations correlated significantly (P < 0.001) with both declared smoking rate (r = 0.67, N = 37) and placental EROD activity (r = 0.63, N = 36), but not with QR activity, whether measured as total QR activity or specifically as either DT-diaphorase or carbonyl reductase. It is concluded that smoking up to 40 cigarettes per day induces EROD but does not affect QR activity in the placenta at term.

Cotinine↗

PubMed1995

Stereological methods for estimating the functional surfaces of the chiropteran small intestine.

A tissue sampling protocol has been devised for studying the functional surfaces of chiropteran small intestine and drawing comparisons within and between species. The goal was to obtain minimally biased stereological estimates of villous and microvillous surface areas and the numbers of microvilli. The approach is illustrated using the intestines of 3 bats (from frugivorous and entomophagous groups) and is based on the use of vertical sections and cycloid test arcs. A sampling scheme with 3 levels was employed. At level 1 (macroscopy), primary mucosal area was estimated from intestinal length and perimeter. Amplification factors due to villi were estimated at level 2 (light microscopy, LM) whilst microvillous amplifications were estimated at level 3 (transmission electron microscopy, TEM). The absolute surfaces, lengths and diameters of microvilli were used to calculate packing densities and absolute numbers. Estimated villous surface areas of the entire small intestine were 44.4 cm2 (Miniopterus inflatus, entomophagous), 410 cm2 (Epomophorus wahlbergi, frugivorous) and 237 cm2 (Lisonycteris angolensis, frugivorous). Corresponding microvillous surface areas were 0.11, 1.69 and 1.01 m2 whilst the numbers of microvilli per intestine were 4.5, 23.4 and 8.8 x 10(11). When normalised for body weights, microvillous surfaces were 122, 246 and 133 cm2/g respectively. The functional surfaces of the fruit bat appear to be more extensive than those of the entomophagous bat.

Anatomy, Regional↗

PubMed1995

Star volumes of villi and intervillous pores in placentae from low and high altitude pregnancies.

Histological sections of placentae from pregnancies completed at low altitude (400 m) and high altitude (3600 m) in Bolivia were analysed using a stereological estimator of the star volumes of villous 'domains' and intervillous 'pores'. The purpose was to test whether or not differences in the overall volumes of these compartments are accompanied by changes in their geometrical relationships. Whilst total placental volume did not vary with altitude, the total volume of villi declined by about 25% and total intervillous volume increased by 40% at high altitude. The star volume of villi also decreased by 25% (from 1.5 x 10(6) microns 3 at low altitude to 1.1 x 10(6) microns 3 at high altitude) whilst the star volume of intervillous pores increased 4-fold (from 87 x 10(6) microns 3 to 461 x 10(6) microns 3). These figures imply that villous domains decrease in size but may be constant in number. The most likely explanation is that villous trees at high altitude are scaled-down versions of their low-altitude counterparts. By contrast, although the intervillous pores enlarge they may decrease in number in the highland organ. This may reflect a change in the number of maternal cotyledons or in the spatial arrangement of villous trees.

Altitude↗

PubMed1995

A stereological method for estimating the total number of ventricular myocyte nuclei in fetal and postnatal hearts.

An experimental protocol is presented for obtaining efficient estimates of the total numbers of myocyte nuclei in the ventricles of human hearts from archival collections. Hearts were collected postmortem from fetuses at 31-42 weeks of gestation and infants at 7 days-9 months postnatal age. Ventricles from normal and abnormal subjects were examined. Numbers of myocyte nuclei per unit volume of myocardium were estimated separately for left and right ventricles using a design-based stereological device, the physical disector (parallel pairs of sections). Absolute numbers were calculated by multiplying nuclear packing densities by myocardial volume. The latter was estimated from ventricular mass and the percentage of ventricle occupied by myocardium. The findings, albeit preliminary, suggest that (1) myocyte number may rise during the last trimester of gestation, (2) postnatal ventricular growth is probably hypertrophic and/or interstitial rather than hyperplastic and (3) whilst absolute numbers are greater in the left ventricle, the pattern of growth is similar in both ventricles. Nuclear numbers found in 2 abnormal hearts (1 from a case of sudden infant death) tended to be lower than normal.

Cell Count↗