Maternal periconceptional exposure to drinking water disinfection by-products and neural tube defects in offspring.

BACKGROUND: Associations between maternal periconceptional exposure to disinfection by-products (DBPs) in drinking water and neural tube defects (NTDs) in offspring are inconclusive, limited in part by exposure misclassification. METHODS: Maternal interview reports of drinking water sources and consumption from the National Birth Defects Prevention Study were linked with DBP concentrations in public water system monitoring data for case children with an NTD and control children delivered during 2000-2005. DBPs analyzed were total trihalomethanes, the five most common haloacetic acids combined, and individual species. Associations were estimated for all NTDs combined and selected subtypes (spina bifida, anencephaly) with maternal periconceptional exposure to DBPs in public water systems and with average daily periconceptional ingestion of DBPs accounting for individual-level consumption and filtration information. Mixed effects logistic regression models with maternal race/ethnicity and educational attainment at delivery as fixed effects and study site as a random intercept were applied. RESULTS: Overall, 111 case and 649 control children were eligible for analyses. Adjusted odds ratios for maternal exposure to DBPs in public water systems ranged from 0.8-1.5 for all NTDs combined, 0.6-2.0 for spina bifida, and 0.7-1.9 for anencephaly; respective ranges for average daily maternal ingestion of DBPs were 0.7-1.1, 0.5-1.5, and 0.6-1.8. Several positive estimates (≥1.2) were observed, but all confidence intervals included the null. CONCLUSIONS: Using community- and individual-level data from a large, US, population-based, case-control study, we observed statistically nonsignificant associations between maternal periconceptional exposure to total and individual DBP species in drinking water and NTDs and subtypes.

Diffusion patterns on domains representing developing Xenopus retina.

The retinotectal map of mature Xenopus frogs has linear metrics. The regions of the Xenopus retina were modeled during embryonic and early larval development with a set of standard geometrical shapes. A disk was used to model the entire early retina, rings of various thickness were used to model the ciliary margin (the growth zone of the larval retina), and portions of a sphere were used to model the entire late embryonic and larval retina. Gradients produced by several reaction-diffusion pattern-generating configurations were considered: Gierer-Meinhardt and Kauffman-type activator-inhibitor systems; an ideal Turing-like two morphogen system; a point source with diffuse sinks; and variously placed point source-point sink combinations. A few special arrangements produced linear metrics: a point source-point sink system produced linear angular metrics on a thin ring; and ideal Turing system produced linear cartesian metrics on a thin ring; and carefully configured multiple sources and sinks produced linear metrics on a disk. These cases could lead to linear map metrics, but are biologically implausible. Thus linear map metrics are probably not a direct consequence of linear positional values, and more generally, most embryonic tissues probably use non-linear gradients of positional information. Formation of linear map metrics may be functionally important for Xenopus frogs, accounting in part for the evolutionary preservation of mechanisms for interactions among neighboring retinal fibers.

Three-dimensional computer-assisted analysis of graded contusion lesions in the spinal cord of the rat.

Histological analysis of spinal cord injury in experimental animals has focused primarily on the microanatomy of damaged tissue. The current study presents an analysis of the three-dimensional structure of lesion sites in the spinal cord of rats contused with an injury device which produces consistent lesions. Three levels of injury were produced by systematically varying the cord displacement and the duration of the displacement during impact. The resulting groups of subjects exhibited mild, moderate, and severe neurological deficits. Comparisons of equivalent mild impacts made at thoracic versus lumbar spinal cord levels were also made. The results indicate that the overall shape of the lesions is generally biconical, with extensions in the base of the dorsal funiculus, irrespective of the degree of damage or the spinal level of the injury. Lower displacement injuries yielded shorter lesions rostrocaudally with less spread into the white matter. Similar impacts in the lumbar versus thoracic spinal cord produced shorter, more truncated lesion sites at lumbar levels with less involvement of the white matter than in the thoracic lesions. Three-dimensional analyses can can provide additional information about the lesion beyond that available from conventional histopathological measures. Such information could be useful in assessing the results of posttraumatic manipulations which are directed at reducing tissue damage or tissue replacement via transplantation.

Neurons expressing thyrotropin-releasing hormone-like messenger ribonucleic acid are widely distributed in Xenopus laevis brain.

Neurons containing messenger ribonucleic acid encoding thyrotropin-releasing hormone (TRH) in the brain of Xenopus laevis were visualized using in situ hybridization histochemistry. TRH-like mRNA-containing cells were detected in each coronal section tested, from the rostral tip of the telencephalon to the brainstem. In the telencephalon, labeled cells were observed in the olfactory nucleus, nucleus accumbens, striatum, diagonal band, and amygdala. Many intensely labeled cells were found in the hypothalamus, especially the preoptic nucleus and infundibular nuclei (dorsal and ventral). TRH-like mRNA-containing cells were also observed in the thalamus, optic tectum, and brain stem. These results suggest that the TRH neuronal system of X. laevis is organized in a manner similar to that of mammals, in that it is widely distributed throughout forebrain. However, Northern blot analysis of RNA extracted from Xenopus brain indicated that additional mRNAs possessing a TRH-like sequence may be present, suggesting that the regulation of TRH gene expression in Xenopus is different from that of the rat.

Synthesis and analgesic activity of pemedolac (cis-1-ethyl-1,3,4,9-tetrahydro-4-(phenylmethyl)pyrano[3,4-b]ind ole-1- acetic acid).

The synthesis of cis-1-ethyl-1,3,4,9-tetrahydro-4-(phenylmethyl)pyrano[3,4-b]indole -1-acetic acid, pemedolac (USAN), is described. This compound has been found to be a potent analgesic agent in primary screening. Pemedolac has been resolved and the active (+)-enantiomer assigned a 1S,4R absolute configuration on the basis of a crystallographic analysis of its (S)-(-)-borneol ester.

Whole eyes reconstituted from embryonic half anlagen: alterations in donor-derived territories in Xenopus pigment chimerae.

Grafts from pigmented donor embryonic eye rudiments into albino hosts were used to chart i) fates of local cell groups in three positions in whole eye rudiments, and ii) alterations in graft-derived territories when the posterior half of the rudiment was ablated. Small pigmented patches of graft-derived tissue were conspicuous in albino embryos and tadpoles, enabling us to directly monitor their location and size in the eyes of living animals. The three (right eye) positions marked by pigmented grafts were dorsal (12 o'clock), anterior (3 o'clock), and anteroventral (5 o'clock). Control transplants reared without secondary ablation produced black sector territories in pigment retinal epithelium and iris at corresponding 12 o'clock or 2 o'clock or 4 o'clock positions on the larval eyeball. In the experimental series posterior half-anlagen were ablated. The remaining anterior half-anlagen, each containing a pigmented graft, reconstituted spherical larval eyeballs of reduced size. During healing, donor-derived pigmented sector territories remained coherent, but were altered in position and size compared to controls. Dorsal cells (from 12 o'clock grafts) appeared to move rapidly along the newly formed cut edge into the wound and went on to form expanded black sectors in posterior eye regions. More gradually, sector territories of anterior cells (3 o'clock grafts) and anteroventral cells (5 o'clock grafts) shifted toward dorsal in a counterclockwise direction. Thus all three types of graft derived pigment territories were altered in eye anlage fragments as they healed to form half-size spherical eyes.

Immunocytochemical studies of vasotocin, mesotocin, and neurophysins in the Xenopus hypothalamo-neurohypophysial system.

Mesotocinergic and vasotocinergic neurons, which constitute the principal neurons in the hypothalamo-neurohypophysial system in Xenopus, were studied by immunocytochemical techniques. Antibodies that could unequivocally distinguish mesotocin, vasotocin, and their respective neurophysins were used in these studies. A monoclonal antibody directed at rat oxytocin-associated neurophysin (PS-36) detected an antigen that was colocalized with vasotocin, whereas a monoclonal antibody to rat vasopressin-associated neurophysin (PS-45) crossreacted with an antigen in mesotocinergic cells. As vasotocin is regarded as an evolutionary precursor of vasopressin, and as mesotocin is usually associated with oxytocin, we were surprised to see this apparent eptitope switch in the associated neurophysins. One interpretation of this epitope switch is that the final exons encoding for the carboxy-terminals of the mammalian neurophysins, which contain the PS-45 and PS-36 antibody epitopes, are in reversed positions in Xenopus. Approximately 4,000 mesotocinergic and vasotocinergic neurons and their fibers were topographically mapped in the Xenopus hypothalamus. The two types of neurons were intermingled and scattered throughout a large contiguous region including but not limited to the preoptic recess. Small, medium size, and large cells contained these antigens. Immunoreactive fibers were seen in the preoptic area, the neurohypophysial tract, the median eminence, and the neural lobe of the pituitary. The neurophysin-specific monoclonal antibodies have several advantages as phenotypic markers in development; i.e., high titer, low background, and affinity for the prohormone forms as well as for the fully processed neurophysin polypeptides. Their antigens are related gene products whose expression is central to the identity of the two cell types and whose expression is differentially controlled in development. This characterization of their adult distribution provides a basis for future studies of the development of peptidergic phenotype in the central nervous system of Xenopus.

Demonstration of a polarizing signal that reverses future retinotectal patterns across Nuclepore filter barriers, in Xenopus embryonic eye.

We have studied the interactions which occur in surgically disarranged eye rudiments by recombining a left anterior half-eye graft from a donor Xenopus embryo with a right host posterior half eye, across a variety of physical barriers, at embryonic stages 31 or 32. The anterior half-eye graft and barrier were removed 18 h later at stage 38, and the host posterior half-eye was allowed to reconstitute a whole eye whose visuotectal projection could be mapped electrophysiologically after metamorphosis. Anteroposteriorly reversed maps and double-anterior twinned maps that are characteristic of anterior half-eyes, were found in 50-65% of cases in each of the experimental series using no barrier (N = 16), or using Nuclepore filter barriers (N = 47), including 5 of 8 cases when a filter of 0.015 micrometer pore diameter was used. The latter cases are especially interesting, because the filter pores were much smaller than the minimum size known to permit cell-cell contact through the pores. No animals showed AP-reversed retinotectal maps or double-anterior twinned maps when the graft and host half-eyes were separated by a tantalum or plastic barrier (N = 21). Only a single case of AP-reversed mapping was found in 115 control animals including simple posterior half-eye preparations at stage 32 or 38 (N = 13), sham fusions (30 min) across Nuclepore filters (N = 35), or chronic application of a filter (or plastic or tantalum) barrier from stages 32-38 (N = 55) without a left anterior half-eye graft. We conclude that signals from an anterior half-eye can act to repolarize a posterior half-eye in the absence of cell transfer and under conditions which permit little or no direct cell-cell contact.

Arousal of sexual and aggressive contact by exposure to stressors in albino rats.

Since certain forms of aggressive and sexual activity are associated with elevated adrenal steroid activity, the hypothesis explored here was whether subjection to a stressful environment which is known to elevate adrenal output would arouse both sexual and aggressive behavior. Accordingly, 24 male Sprague-Dawley rats were subjected to either physical restraint and heat or a nonstress control environment for 13 days. Following this treatment Ss were tested for sexual and aggressive behavior. As predicted, the stressed Ss showed increased levels of ano-genital sniffing of an estrus female, as well as increased intermale aggressiveness.