The effects of acute pesticide exposure on neuroblastoma cells chronically exposed to diazinon

Speculation about potential neurotoxicity due to chronic exposure to low doses of organophosphate (OP) pesticides is not yet supported by experimental evidence. The objective of this work was to use a cell culture model of chronic OP exposure to determine if such exposure can alter the sensitivity of nerve cells to subsequent acute exposure to OPs or other compounds. NB2a neuroblastoma cells were grown in the presence of 25 microM diazinon for 8 weeks. The OP was then withdrawn and the cells were induced to differentiate in the presence of various other pesticides or herbicides, including OPs and OP-containing formulations. The resulting outgrowth of neurite-like structures was measured by light microscopy and quantitative image analysis and the IC(50) for each OP or formulation was calculated. The IC(50) values in diazinon-pre-exposed cells were compared with the equivalent values in cells not pre-exposed to diazinon. The IC(50) for inhibition of neurite outgrowth by acute application of diazinon, pyrethrum, glyphosate or a commercial formulation of glyphosate was decreased by between 20 and 90% after pre-treatment with diazinon. In contrast, the IC(50) for pirimiphos methyl was unaffected and those for phosmet or chlorpyrifos were increased by between 1.5- and 3-fold. Treatment of cells with chlorpyrifos or with a second glyphosate-containing formulation led to the formation of abnormal neurite-like structures in diazinon-pre-exposed cells. The data support the view that chronic exposure to an OP may reduce the threshold for toxicity of some, but by no means all, environmental agents.

Quantitative unbiased estimates of endometrial gland surface area and volume in cycling cows and heifers

Entire reproductive tracts were removed from seven normal healthy heifers and qualitative unbiased estimates made of endometrial gland volume density and glandular surface density. After examining approximately 55 microscopic fields of endometrium from each tract, a mean glandular surface density value of 10.2 mm(2)/mm(3) (CE 3.1%) was obtained. The stereological method was then employed in optimising the design of the main study. The endometrial height was measured for 17 healthy cycling heifers and 19 similar cows. Subsequently, unbiased estimates were made of intercaruncular endometrial gland volume per unit surface for all cattle were investigated; differences between heifers and cows generally, and the possible effect of the follicular and luteal phases of the oestrous cycle were compared. The mean surface area of glands per unit area of endometrium at the intercaruncular site in heifers and cows was approximately 18 mm(2)/mm(2) in the follicular phase and 26 mm(2)/mm(2) in the luteal phase, figures similar to the gland area found in women. The intercaruncular gland volume increased significantly, by about 30% during the luteal phase of the bovine oestrous cycle in heifers, from 0.01 to 0.13 per mm(3). The differences in endometrial anatomy between site of sampling and either follicular or luteal phases of the oestrous cycle were always more significant in heifers than cows. The endometrial thickness in cows was always greater than for heifers, irrespective of the site of sampling. It was concluded that the intercaruncular endometrium of cattle was far more active physiologically than recognised previously.

Dietary lectins can stimulate pancreatic growth in the rat

Lectins are proteins or glycoproteins of nonimmune origin, which bind specifically to carbohydrate structures. They are widespread in the human diet, and many are resistant to digestion. High doses of lectins have been shown to stimulate intestinal and pancreatic growth. The aim of the present study was to investigate the long-term actions of low doses of lectins on the rat intestine and pancreas. A long-term carcinogenesis study was performed using low levels (40 micro g/rat/day) of peanut (PNA) or mushroom lectin (ABA) which bind to O-linked (mucin-type) oligosaccharides in the gut. While this was primarily designed as a colon carcinogenesis study, the pancreas was also investigated. No significant changes in colon carcinogenesis were seen, however, the colons were slightly heavier in the lectin treated groups. The weight of the pancreas was significantly greater (by 18 and 23%) in both lectin treated groups (P < 0.03/0.001). The weights of the acini and septal tissue were also increased by 39-46% in PNA and ABA fed animals, respectively (P < 0.002); there was no significant change in the endocrine pancreas. In conclusion, long-term feeding of low doses of lectin can influence pancreatic growth, and this trophic action may have potential adverse implications for the development of pancreatic cancer in humans.

Efficient embedding technique for preparing small specimens for stereological volume estimation: zebrafish larvae

Stereological sampling regimes, in particular volume and number estimation, often require systematic uniformly random sections throughout a specimen. A method has been developed to increase the efficiency of preparing fish larvae for sectioning prior to histological or stereological analysis. Embedding a group of larvae in a resin block using this technique greatly reduces the quantity of sections produced and allows easy assessment of sample groups. Saving time in this way therefore makes stereology a more viable research tool.

Interactions between pesticides and components of pesticide formulations in an in vitro neurotoxicity test

Organophosphate (OP) pesticides are often used in combination with one another and with the components of formulations. Evidence already exists for interactions in the neurotoxic effects of OPs through interference with metabolism, but there is also potential for interactions related directly to cell damage. The purpose of this work was to investigate this possibility for OPs and the components of one of their common formulations in vitro. NB2a neuroblastoma cells were induced to differentiate in the presence of the OPs diazinon and chlorpyrifos, in combination with a commercial formulation (identified as Commercial Formulation 1) of the compounds and, independently, the components of that formulation. The compounds were tested in pairs in various proportions and the resulting inhibition of neurite outgrowth was measured by light microscopy and quantitative image analysis. Interactions were determined in terms of enhanced or reduced effects of the paired compounds in comparison with the expected additive effects estimated from the effects of each compound on its own. Synergism was detected between combinations of: 10 microM chlorpyrifos and 500 nM pyrethrum; chlorpyrifos and one of the solvents (regular spirit) found in Commercial Formulation 1. All other combinations of OPs and products were additive in their neurotoxicity. The data suggest that exposure to multiple OP-containing pesticide formulations may lead to synergistic neurotoxicity by a direct mechanism at the cellular level.

St Vincent's Declaration 10 years on: outcomes of diabetic pregnancies

AIMS

To monitor pregnancies in women with pregestational Type 1 diabetes for pregnancy loss, congenital malformations and fetal growth parameters, in a geographically defined area in the north west of England.

METHODS

Population cohort study of 547 pregnancies in women with Type 1 diabetes from maternity clinics in 10 centres over a 5-year period (1995-1999 inclusive). Main outcome measures were numbers and rates of miscarriages, stillbirths, neonatal and post-neonatal deaths; prevalence of congenital malformations; birth weight in relation to gestational age.

RESULTS

Among 547 pregnancies, there were six (1.1%) pairs of liveborn twins, 439 (80.3%) liveborn singletons; 72 (13.2%) spontaneous abortions, 14 (2.6%) stillbirths and 16 (2.9%) terminations. Four of the terminations were performed because of congenital malformations. Both the stillbirth rate (30.1/1000 total births (95% confidence interval (CI) 16.6-50.0)), and prevalence of congenital malformations (84.3/1000 live births (95% CI 60.3-113.8)) were significantly higher than the local population (P < 0.001). When corrected for gestational age, mean birth weight in the sample was 1.3 sd greater than that of infants of non-diabetic mothers (P = 0.12). Infants with congenital malformations weighed less than those without.

CONCLUSION

In an unselected population, the infants of women with pregestational Type 1 diabetes mellitus have 6.4 times the reported risk of a congenital malformation and 5.1 times the reported risk of perinatal mortality than infants in the general population. Further improvements in the management of diabetes and pregnancy in these women are needed if the St Vincent's Declaration target is to be met.

Estimation of mean nuclear volume of neocortical neurons in sudden infant death syndrome cases using the nucleator estimator technique

At present, no information is available with regards to either neocortical neuronal mean nuclear volume or maturation (functional or morphological) in abnormal paediatric brains. Using the nucleator estimator technique, the mean neocortical nuclear volume was estimated in sudden infant death syndrome (SIDS) cases [10 normal birth weight (NBW) and 10 low birth weight (LBW) cases classified by birth weight for gestational age] and compared to 10 NBW control cases. Both the control and SIDS LBW cases showed an increase in mean nuclear volume with age; the SIDS NBW cases showed no increase. At 8 months, the SIDS NBW cases showed a reduced mean nuclear volume (p = 0.02) when compared to controls. The SIDS LBW cases showed no statistically significant difference (p = 0.10) when compared with controls. A deficiency in mean neuronal nuclear volume may represent a deficiency in neuronal function.

Stereological estimation of eye volume using the Pappus method

The estimation of object volume from rotationally randomised sections relies on an ancient geometrical principle due to the Alexandrian mathematician Pappus. In this paper we describe two studies that make estimates of eye volume using a stereological version of the Pappus principle. The first study uses a design-based version of the Pappus theorem to make estimates of eye volume in Sprague-Dawley rats and the second uses a model-based implementation for estimating eye volume in juvenile Dover sole. In the sole study we compare the estimates of volume with estimates made using the Cavalieri method and show that the Pappus method gives identical volume estimates with a markedly lower coefficient of variation (2.5%) than the Cavalieri method (13.5%).

Lung development: number of terminal bronchiolar duct endings and gas exchange surface area in victims of sudden infant death syndrome

Previous research has demonstrated impaired renal development, particularly with respect to glomerular number, in victims of sudden infant death syndrome (SIDS). The present study used stereological principles to estimate the volume of the upper lobe of the right lung, total number of terminal bronchiolar duct endings (TBDE), and gas exchange surface area of this lobe within a group of human infants. The infants were classified according to cause of death (SIDS or non-SIDS), and further subdivided according to birth-weight: normal birth-weight (NBW) or low birth-weight (LBW). The results demonstrated that TBDE density was significantly reduced in SIDS compared to non-SIDS (P = 0.014), but only reduced from non-SIDS NBW values in the SIDS NBW group (P = 0.044). Total TBDE number was significantly reduced in SIDS from non-SIDS (P = 0.001), and was significantly reduced from non-SIDS NBW values in SIDS NBW (P = 0.023). Mean gas exchange surface area per TBDE was significantly increased in SIDS compared to non-SIDS cases (P = 0.049). The results of the present study indicate developmental delay of the lung in SIDS NBW infants who had previously not been considered growth retarded based on their normal body parameters.

Renal developmental delay expressed by reduced glomerular number and its association with growth retardation in victims of sudden infant death syndrome and in "normal" infants

In victims of sudden infant death syndrome (SIDS), renal development has been reported to be significantly impaired. In the present study, we used stereological techniques to estimate volume of kidney cortex and total number of glomeruli in a group of human infants. Infants were classified according to cause of death-SIDS or non-SIDS. Cases were further subdivided according to birth weight-normal birth weight (NBW) or low birth weight (LBW) (we were unable to identify any non-SIDS LBW infants for our study). No significant differences were found between NBW and LBW infants (irrespective of cause of death) for cortical volume, glomerular density, or total glomerular number (p > 0.140). Kidney cortical volume, glomerular density, and total glomerular number were not significantly different between SIDS and non-SIDS infants (p > 0.510). Glomerular number was only significantly less in SIDS infants of LBW (p = 0. 032) than in controls according to the Wilcoxon rank sum test; using the Kruskal-Wallis for one-way analysis, no significant difference was found (p > 0.010). These results contrast with those from previous studies, as a reduction in glomerular number was not noted in SIDS NBW infants, and the mean value for the control (non-SIDS NBW) group was significantly reduced (p < 0.01) from those of previous studies. This indicates that glomerular number reduction is seen in SIDS NBW and non-SIDS NBW cases and is therefore directly associated with growth retardation rather than with SIDS.

Terminal bronchiolar duct ending number does not increase post-natally in normal infants

Organ development may be assessed by estimating the total number of functional units within an organ over time; the potential functional capacity of that organ may be represented by the total number of functional units present in the fully developed, mature organ. Relative development of the lung at birth is essential to provide sufficient oxygenation of body tissues and so maintain ex utero life. Estimation of the number of one type of functional unit of the lung - terminal bronchiolar duct endings - provides important information regarding development of the lung. This investigation used stereological techniques, specifically Cavalieri's Principle and the "physical disector", to estimate total number of terminal bronchiolar duct endings in the upper lobe of the right lung of a group of 14 control infants between 0 and 66 weeks post-natal age. Results demonstrate that total terminal bronchiolar duct ending number does not increase significantly over the first 24 weeks of post-natal life in normal infants (P=0.997). The unbiased, design-based techniques used in this paper confirm previous model-based research that indicates that terminal bronchiolar duct ending development is completed before birth.

Unbiased and efficient estimation of the total number of terminal bronchiolar duct endings in lung: a modified physical disector

A novel modification of the physical disector is described which was used to estimate the total number of terminal bronchiolar duct endings (TBDEs) in human infant lung. TBDEs are closed three-dimensional space curves of complex shape that are inherently difficult to count from histological sections. However, careful consideration of the microanatomy of the terminal duct endings provides us with the opportunity to define a very simple and unbiased counting rule. To apply the rule in practice we also need to determine a suitable disector height. Owing to the complex shape of the TBDE we had no prior knowledge of what disector height would be suitable for counting the TBDE structures. Exhaustive serial sectioning of complete TBDE structures was carried out and showed that any disector height under 90 microm would give unbiased counts. A further empirical study was then undertaken to determine the most efficient disector height. This was found to be 50 micro. The total number of TBDEs in the upper lobe of the right lung of six human infants aged between 13 and 25 weeks was also estimated. The estimates of numerical density obtained with our modification of the physical disector were multiplied by estimates of lung lobe volume obtained using Cavalieri's Principle. The total number of TBDEs in the lobes ranged from 15 323 to 57 768, with a mean of 40 306. The average coefficient of error of the number estimates was 19%, which was deemed precise enough given the biological coefficient of variation between TBDE number of 36%.

Stereological estimation of covariance using linear dipole probes

Classical stereology is capable of quantifying the total amount or 'density' of a geometrical feature from sampled information, but gives no information about the local spatial arrangement of the feature. However, stereological methods also exist for quantifying the 'local' spatial architecture of a 3D microstructure from sampled information. These methods are capable of quantifying, in a statistical manner, the spatial interaction in a structure over a range of distances. One of the key quantities used in a second-order analysis of a volumetric feature is the set covariance. Previous applications of covariance analysis have been 'model-based' and relied upon computerized image analysis. In this paper we describe a new 'design-based' manual method, known as linear dipole probes, that is suitable for estimating covariance from microscopic images. The approach is illustrated in practice on vertically sectioned lung tissue. We find that only relatively sparse sampling per animal is required to obtain estimates of covariance that have low inter-animal variability.

Localisation of connective tissue and inhibition of autofluorescence in the human optic nerve and nerve head using a modified picrosirius red technique and confocal microscopy

The use of picrosirius red to localise connective tissue in thin tissue sections viewed by bright-field microscopy is well documented. Its use on thin tissue sections imaged by fluorescence confocal microscopy has also been reported. Here we describe modifications to published procedures that allow picrosirius red staining of thick 60-microm sections and their subsequent analysis by confocal microscopy. The use of phosphomolybdic acid pre-treatment was found to be essential for confocal analysis; in addition to preventing non-specific staining, it also quenched tissue autofluorescence. By incubating sections free-floating, pre-treating them with phosphomolybdic acid for 30 min and imaging them using an argon ion laser we were able to use confocal microscopy to image the entire depth of 60-microm human optic nerve and nerve head sections stained with picrosirius red. The application of this modified picrosirius red and confocal microscopy technique should be useful for analysing the three-dimensional structure of the optic nerve and other tissues with a similarly complex arrangement of connective tissue.

The effect of benomyl on neurite outgrowth in mouse NB2A and human SH-SY5Y neuroblastoma cells in vitro

The commercial fungicide methyl 1-[(butylamino) carbonyl]-1H-benzimidazol-2-ylcarbamate (benomyl) is teratogenic in rats. Its mode of action is believed to be related to its ability to inhibit the polymerization of brain tubulin. In this study its effects were studied in cultured neuronal cells during differentiation and neurite outgrowth. Mouse NB2a and human SH-SY5Y neuroblastoma cells were induced to differentiate by addition of dibutyryl cyclic AMP and at the same time were exposed to various concentrations of benomyl. Benomyl significantly inhibited neurite outgrowth in both cell lines at concentrations of 10(-8) M and above with IC50 values of 5.9 x 10(-7) M and 1.0 x 10(-6) M in the NB2a and SH-SY5Y cells respectively. The results show that benomyl inhibits neuronal cell differentiation at concentrations likely to be achieved during the development of fetal abnormalities in rats in vivo.

Surface-weighted star volume: concept and estimation

The estimation of 'size' for an interconnected nonconvex phase is an ongoing problem in materials science and biomedicine. Examples of this type of phase include the pore space in a porous rock such as sandstone or the marrow space found in cancellous bone. A reasonable definition of size for this type of phase is provided by the mean volume-weighted star volume. This is defined as the average volume of the phase of interest seen unobscured from a typical point within the phase. One practical advantage of this definition of size is that it is easy to estimate stereologically. In this paper we extend the concept of star volume to consider the mean surface-weighted star volume. The mean surface-weighted star volume is the volume of a continuous phase seen unobscured from a typical point of the interface. We expect that this parameter could be useful in biological problems involving mass transfer across an interface. The stereological estimation of mean surface-weighted star volume is described and the method is illustrated on piglet lung tissue.

Quantitative microscopy in studies of intrauterine growth retardation

In the past, the detection of fetal damage has tended to be restricted to the naked eye identification of major malformations, with the period of organ maturation being relatively neglected. Increasingly, however, unbiased design-based stereology is being used in developmental toxicological studies. In the field of intrauterine growth retardation, such methods are capable of providing new insights into fetal vulnerability during critical periods in organogenesis, with consequences for both post-natal and adult disease.

Outcomes of pregnancy in insulin dependent diabetic women: results of a five year population cohort study

OBJECTIVE

To monitor pregnancies in women with pre-existent insulin dependent diabetes for pregnancy loss, congenital malformations, and fetal growth in a geographically defined area of north west England.

DESIGN

Population cohort study.

SETTING

10 maternity units in Cheshire, Lancashire, and Merseyside which had no regional guidelines for the management of pregnancy in diabetic women.

SUBJECTS

462 pregnancies in 355 women with insulin dependent diabetes from the 10 centres over five years (1990-4 inclusive).

MAIN OUTCOME MEASURES

Numbers and rates of miscarriages, stillbirths, and neonatal and postneonatal deaths; prevalence of congenital malformations; birth weight in relation to gestational age.

RESULTS

Among 462 pregnancies, 351 (76%) resulted in a liveborn infant, 78 (17%) aborted spontaneously, nine (2%) resulted in stillbirth, and 24 (5%) were terminated. Of the terminations, nine were for congenital malformation. The stillbirth rate was 25.0/1000 total births (95% confidence interval 8.9 to 41.1) compared with a population rate of 5.0/1000, and infant mortality was 19.9/1000 live births (5.3 to 34.6) compared with 6.8/1000. The prevalence of congenital malformations was 94.0/1000 live births (63.5 to 124.5) compared with 9.7/1000 in the general population. When corrected for gestational age, mean birth weight in the sample was 1.3 standard deviations greater than that of infants of non-diabetic mothers. Infants with congenital malformations weighed less than those without.

CONCLUSION

In an unselected population the infants of women with pre-existent insulin dependent diabetes mellitus have a 10-fold greater risk of a congenital malformation and a fivefold greater risk of being stillborn than infants in the general population. Further improvements in the management of pregnancy in diabetic women are needed if target of the St Vincent declaration of 1989 is to be met.

Growth characteristics of the human nasal septum

Using a specially designed algorithm for the measurement of the surface area of shapes with highly irregular contours, growth curves were developed for post-natal septal growth in humans using post-mortem specimens of a study population of 30 cases, distributed over the age range from birth to 62 years. From the results a rapid growth phase for the total septum is evident immediately after birth, lasting until the second year of life. Then, a gradual deceleration of growth is recognized with a plateau eventually being reached at the age of 36 years. Mathematical analysis of the growth curve shows that the curve for the total septum is the sum of two separate mathematical equations, representing the cartilaginous and bony contribution, respectively. It is demonstrated that the cartilaginous septum reaches adult dimensions (lateral surface area) at the age of two years. Subsequent growth of the septum is due to expansion of the perpendicular plate, i.e. the bony parts of the septum.