The effect of back-transplants of the embryonic gut wall on growth of the neural tube

Experiments in which the developing gut of avian embryos was back-transplanted to permit the bowel to interact with the developing neural tube were undertaken. Segments of intestine from 4-day quail embryos were implanted between the somites and neural tubes of chick embryos of 7 to 24 somites. The spinal cord responded to the presence of the bowel by enlarging unilaterally on the side of the graft. This effect encompassed both gray and white matter and was accompanied by the extension of neuritic projections from the spinal cord into the enteric grafts. The growth-promoting effect of enteric transplants was manifest at all levels of the neural tube where the grafts were made and led to enlargement of the brain as well as the spinal cord; however, truncal neural crest derivatives in the region of the grafts, such as developing sympathetic and spinal ganglia, were unaffected. Neither sham operations nor grafts of ciliary ganglion, lung, pancreas, mesonephros, or rudiment of the eye mimicked the action of the gut. The effect of the bowel was manifest as early as 24 hr following back-transplantation and was found to be due to an increase in the number of cells in the neuroepithelium. The cell responsible for the ability of the gut wall to enhance neuroepithelial proliferation was not identified, but the effect lacked species specificity and could be elicited in the absence of endoderm or neural crest derivatives in the explant. We propose that the musculoconnective tissue of the gut produces a short-range diffusible factor that induces mitogenic activity in the neuroepithelial cells of the neural tube, but not in the crest cells that form sympathetic or sensory ganglia. Since the gut is not normally in apposition to the neural tube, we suggest that the physiological targets of this factor are the specialized crest cells that colonize the bowel and give rise to the enteric nervous system.     

A Concerted Molecular Design Method by Temperature-Guided Monte Carlo Search / Potential Applications for ab initio Ligand Design

This work demonstrates the conceptual feasibility of a method for systematic and concerted design of a molecular structure with a favorable interaction toward a prescribed target. Since a semi-empirical QM hamiltonian is used to calculate energies, the method described here allows the continual atomic change and reassessment of molecular structure with respect to its own internal energy and its target interaction energy. Modelling the ligand molecular structure on an atomistic basis, in contrast to a fragment basis, permits the construction of higher energy transitional structures which bridge between viable ligand structures. This allows a most thorough way to accomplish meticulous configurational sampling. The use of two examples, the creation of an ammonia molecule to interact with a formic acid target, and a formic acid molecule to form a dimer with a target, more clearly illustrates the features of a temperature guided Monte Carlo simulation which was developed to allow thorough configurational sampling. This is accomplished by appropriately varying the temperature of the MC simulation. A series of random starting configurations underwent this systematic MC sampling procedure to locate various structural and interaction energy minima. The results of these simulations demonstrate thorough configurational sampling and convergence.     

Autoradiographic evidence for two classes of mu opioid binding sites in rat brain using [I]FK33824

Previous studies demonstrated that pretreatment of brain membranes with the irreversible mu antagonist, beta-funaltrexamine (beta-FNA), partially eliminated mu binding sites [25,35], consistent with the existence of two mu binding sites distinguished by beta-FNA. This paper tests the hypothesis that the FNA-sensitive and FNA-insensitive mu binding sites have different anatomical distributions in rat brain. Prior to autoradiographic visualization of mu binding sites, [³H]oxymorphone, [³H]D-ala²-MePhe⁴, Gly-ol⁵-enkephalin (DAGO), and [¹²⁵I]D-ala²-Me-Phe⁴-met(o)-ol]enkephalin (FK33824) were shown to selectively label mu binding sites using slide mounted sections of molded minced rat brain. As found using membranes, beta-FNA eliminated only a portion of mu binding sites. Autoradiographic visualization of mu binding sites using the mu-selective ligand [¹²⁵I]FK33824 in control and FNA-treated sections of rat brain demonstrated that the proportion of mu binding sites sensitive to beta-FNA varied across regions of the brain, particularly the dorsal thalamus, ventrobasal complex and the hypothalamus, providing anatomical data supporting the existence of two classes of mu binding sites in rat brain.     

Association of 1 hydroxypyrene glucuronide in human urine with cigarette smoking and broiled or roasted meat consumption

Humans are exposed to polycyclic aromatic hydrocarbons PAHs from various occupational, dietary, environmental and medicinal sources. We measured 1 hydroxypyrene glucuronide 1 OHP gluc concentration in urines from male non smokers n = 50, smokers of blond tobacco n = 31, smokers of black tobacco n = 16, and pipe smokers n = 3 . Immunoaffinity chromatography was used as a preparative step and synchronous fluorescence spectroscopy as the quantitation method. The concentration of 1 OHP gluc in urine from smokers mean SE: 1.04 0.13 pmol ml-1 urine was significantly higher than in urine from non smokers 0.55 0.05 pmol ml-1 urine by the Wilcoxon rank sum test non smokers versus all smokers, p = 0.001; vs black tobacco smokers, p = 0.001; vs blond tobacco smokers, p = 0.007 . Urinary 1 OHP gluc concentration among subjects who had consumed roasted, grilled or broiled meat within the past 24 h was elevated compared with those who had not p = 0.025 . Multiple linear regression showed significant associations of urinary 1 OHP gluc with number of cigarettes smoked p = 0.002 and consumption of roasted, grilled or broiled meat p = 0.028 . Systemic CYP1A2 activity estimated by caffeine metabolism was significantly correlated with urinary 1 OHP gluc concentration. However, this association was probably due to cigarette smoking, since adjusting for cigarette smoking by multiple linear regression made the association between urinary 1 OHP gluc and CYP1A2 phenotype non significant. These results further support the use of urinary 1 OHP gluc as a biomarker of recent pyrene exposure through inhalation or diet.     

Protein targeting to the yeast vacuole

Mutational and gene fusion studies have identified localization signals that target proteins to the yeast lysosome-like vacuole. Genetic analyses have also identified groups of genes (VPS and PEP) whose products are required for recognition of these signals, and sorting and transport of proteins to the vacuole. One of the components involved in protein sorting has been shown to be the vacuolar H+-ATPase, presumably via its role in vacuolar acidification.     

Transpancreatic transport of digestive enzyme

When porcine α-amylase or bovine chymotrypsinogen A was added to the medium bathing the rabbit pancreas in short-term organ culture, the secretion of these enzymes collected via the duct system increased greatly. To determine if it was indeed the amylase added to the bath that was recovered in secretion, endogenous enzyme stores were prelabeled during a 4 h incubation with [³H]- leucine and the specific radioactivity of amylase in secretion followed. The addition of unlabeled exogenous amylase to the bathing medium reduced the specific radioactivity of secreted amylase of about 90% suggesting that the response was due to the transpancreatic transport of the added enzyme. This inhibition was maintained over time, and was a result, not only of the increased secretion of unlabeled enzyme, but also of a 72% steady-state inhibition in the secretion of endogenous (labeled) amylase. This latter observation indicates that the exogenous enzyme crosses the acinar cell and mixes with endogenous cellular stores. A cellular route is also suggested by the observation that the addition of amylase to the bath increased the amylase concentration in ductal fluid relative to that in the bath by about 20 times; it did not reduce it as would be expected if paracellular shunts were involved. In addition, a cellular pathway is suggested by the observation that a 2 h prior incubation in bovine chymotrypsinogen resulted in a greatly augmented chymotrpsinogen response to a maximal cholinergic stimulus. In all, the data support the prediction of the equilibrium theory of digestive enzyme secretion that enzyme secretion should be responsive to mass action, and the prediction of the enteropancreatic circulation hypothesis that a capacity exists for a substantial transpancreatic flux of digestive enzyme.     

Clonal analysis of the glycosylation of immunoglobulin G secreted by murine hybridomas

A panel of 10 hybridomas was assembled to assess the influence of various genetic and biological factors upon glycosylation of secreted monoclonal IgG. After exhaustive Pronase digestion of IgG, glycopeptides were characterized chromatographically by apparent size, charge, and concanavalin A (Con A)-Sepharose and Lens culinaris (LcH)-agarose affinity. Six glycosylation phenotypes were found to be common among all clones studied. Despite this phenotypic heterogeneity in glycosylation of IgG, considerable similarity exists between different clones. In particular, virtually all IgG glycopeptides bear a core fucose residue. Second, the majority of the glycosylation repertoire is comprised of two phenotypes, characterized by glycopeptides which differ in affinity for Con A-Sepharose. Of these, the predominantly expressed phenotype is the same for all clones. The carbohydrate structure derived from this phenotype, elucidated by 500-MHz 1H NMR spectroscopy, is (Formula: see text). Significant variability between different hybridomas exists in the relative expression of the two major phenotypes. Other differences between clones may reflect the expression of an additional site which is glycosylated differently. However, there is no apparent correlation of phenotype with either the hybridoma's parentage or the serologically defined polypeptide structure of the IgG which it secretes. In addition to clonal variability, other sources of variability in phenotypic expression were identified. A generational variability is apparent upon continuous culturing of the same hybridoma. Also, differences in culture medium pH or proliferative state of the cells may have a modest influence upon the glycosylation phenotype.