In vitro development ofXenopus skin glands producing 5-hydroxytryptamine and caerulein

The granular glands of amphibian skin synthesize and store a large amount of bioactive amines and peptides which are structurally similar to mammalian brain-gut peptides. To investigate the development of peptide- and amine-producing cells in the granular glands, pieces of dorsal skin taken at various stages fromXenopus laevis tadpoles were cultured, and the contents of caerulein and 5-hydroxytryptamine (5-HT) were measured. When pieces of skin from tadpoles at stages 57 to 60 (Nieuwkoop and Faber stages) were cultured in a medium containing 10% fetal calf serum (FCS medium) or one containing FCS treated with charcoal (chFCS medium), the caerulein and 5-HT levels were increased for the six days of the incubation period. The caerulein content was lower in the chFCS medium than in the FCS medium. Addition of thyroxine to the chFCS medium had no significant effect on the caerulein content. These results show that the caerulein-and 5-HT-producing cells of the granular glands can develop in a culture system with FCS- or chFCS-containing media, and suggest that FCS contains substances which are absorbed by charcoal and stimulate development of the amine- and peptideproducing cells of the glands. In a preliminary search for correlation between caerulein and 5-HT synthesis, addition of 5-hydroxytryptophan (5-HTP), a precursor to 5-HT, to the FCS medium increased 5-HT content and, conversely, caused significant decrease in caerulein content, suggesting that accumulation of caerulein in the granular glands is influenced by the amount of 5-HT synthesis. These studies indicate that this culture system is a useful model for investigating the development of peptide- and amine-producing cells.     

Can purchasing power parity help forecast the dollar?

This paper examines the information on future exchange rate movements provided by the doctrine of purchasing power parity (PPP). Previous research has studied this issue by analyzing the time-series properties of period-by-period levels of, or changes in, exchange rates. In contrast, the present study focuses on the durations of periods in which exchange rates deviate from their PPP levels. If PPP provides information about future exchange rate movements, these durations should exhibit positive duration dependence. That is, the probability of returning to PPP levels should increase as the period of deviation increases. Parametric hazard functions estimated using data from eighteen countries provide no evidence of positive duration dependence. These results are robust to alternative definitions of PPP and to alternative functional specifications. While exchange rates take prolonged swings away from their PPP levels and then eventually return, these movements apparently constitute Monte Carlo cycles in which, at any point in time, the probability of moving back toward PPP is the same as the probability of moving farther away. Thus, PPP provides no useful information on future exchange rate changes, a result consistent with market efficiency.     

A mixture likelihood approach for generalized linear models

A mixture model approach is developed that simultaneously estimates the posterior membership probabilities of observations to a number of unobservable groups or latent classes, and the parameters of a generalized linear model which relates the observations, distributed according to some member of the exponential family, to a set of specified covariates within each Class. We demonstrate how this approach handles many of the existing latent class regression procedures as special cases, as well as a host of other parametric specifications in the exponential family heretofore not mentioned in the latent class literature. As such we generalize the McCullagh and Nelder approach to a latent class framework. The parameters are estimated using maximum likelihood, and an EM algorithm for estimation is provided. A Monte Carlo study of the performance of the algorithm for several distributions is provided, and the model is illustrated in two empirical applications.     

贵州植物园珍稀濒危蕨类植物

本文介绍引种自贵州各地及我国华中、华东和华东的贵州植物园内的珍稀濒危蕨类植物。除列表表示来源、现状等情况外，还对桫椤Ａｌｓｐｈｉｌａ ｓｐｉｎｕｌｏｓａ （Ｈｏｏｋ）Ｔｒｙｏｎ，扇蕨Ｎｅｏｃｈｅｉｒｏｐｔｅｒｉｓ ｐｌａｍａｔｏｐｅｄａｔａ （Ｂａｋ．）Ｃｈｓｉｓｔ，宽叶水韭Ｉｓｏｅｔｅｓ ｊａｐｏｎｉｃａ Ａ．Ｂｒ．，中华水韭Ｉ．ｓｉｎｅｎｓｉｓ Ｐａｌｍｅｒ和截基盾蕨Ｎｅｏｌｅｐｉｓｏｒｕｓ     

消失场荧光测量的理论和应用研究

消失场荧光技术已被广泛应用在工业、生物和医学等领域的研究工作中．本文给出各种分层结构中消失场分布的严密电磁理论．在生物和医学上，利用受激荧光强度正比于局部电场能量的规律，可根据测得的相对荧光强度算出细胞和基板的间距．文中还给出一些消失场荧光测量的应用．     

灰色理论在化学研究中用作建模与预测新的方法

研究了灰色理论作为一种有用的化学计量学多元建模与定量预测新方法的可行性，将其应用于某些不确定关系如电泳迁移率，色谱保留值和农药需求量等建模，定量预测结果良好。     

铬酸钒为基的PTC陶瓷的研究

本文使用ＳＥＭ、ＥＤＳ、ＥＡＳ、ＸＲＤ和电阻率测量技术，研究了工艺参数和加入（Ｃｏ，Ｆｅ２Ｏ３）对ＰＴＣ（Ｖ１－ｘ，Ｃｒｘ）２Ｏ３陶瓷的显微结构和电性能的影响。实验结果表明，为了制造优良性能、高可靠的热敏电阻器，必须精确控制陶瓷组份和工艺。引人象Ｃ。这样的添加物是重要的，它主要以金属形式分布在基体中，同时发现添加物对试样致密度和电性能的影响也是有益的。     

T gamma protein is expressed on murine fetal thymocytes as a disulphide-linked heterodimer

During the search for genes coding for the mouse alpha and beta subunits of the antigen-specific receptor of mouse T cells we encountered a third gene, subsequently designated gamma. This gene has many properties in common with the alpha and beta genes, somatic assembly from gene segments that resemble the gene segments for immunoglobulin variable (V), joining (J) and constant (C) regions; rearrangement and expression in T cells and not in B cells; low but distinct sequence homology to immunoglobulin V, J and C regions; other sequences that are reminiscent of the transmembrane and intracytoplasmic regions of integral membrane proteins; and a cysteine residue at the position expected for a disulphide bond linking two subunits of a dimeric membrane protein. Despite these similarities the gamma gene also shows some interesting unique features. These include a relatively limited repertoire of the germ-line gene segments, more pronounced expression at the RNA level in immature T cells such as fetal thymocytes and an apparent absence of in-frame RNA in some functional, alpha beta heterodimer-bearing T cells or cultured T clones and hybridomas. To understand the function of the putative gamma protein it is essential to define the cell population that expresses this protein. To this end we produced a fusion protein composed of Escherichia coli beta-galactosidase and the gamma-chain (hereafter referred to a beta-gal-gamma) using the phage expression vector lambda gt11 and raised rabbit antisera against the gamma determinants. Using the purified anti-gamma antibody we detected a polypeptide chain of relative molecular mass 35,000 (Mr 35K) on the surface of 16-day old fetal thymocytes. The gamma-chain is linked by a disulphide bridge to another component of 45K. No such heterodimer was detected on the surface of a cytotoxic T lymphocyte (CTL) clone 2C from which an in-phase gamma cDNA clone was originally isolated.     

cDNA cloning of bovine substance-K receptor through oocyte expression system

The neuropeptide receptors which are present in very small quantities in the cell and are embedded tightly in the plasma membrane have not been well characterized. Mammals contain three distinct tachykinin neuropeptides, substance P, substance K and neuromedin K, and it has been suggested that there are multiple tachykinin receptors. By electrophysiological measurement, we have previously shown that Xenopus oocytes injected with brain and stomach mRNAs faithfully express mammalian substance-P and substance-K receptors, respectively. Here we report the isolation of the cDNA clone for bovine substance-K receptor (SKR) by extending this method to develop a new cloning strategy. We constructed a stomach cDNA library with a cloning vector that allowed in vitro synthesis of mRNAs and then identified a particular cDNA clone by testing for receptor expression following injection of the mRNAs synthesized in vitro into the oocyte system. Because oocytes injected with exogenous mRNAs can express numerous receptors and channels, our new strategy will be applicable in the general molecular cloning of these proteins. The result provides the first indication that the neuropeptide receptor has sequence similarity with rhodopsin-type receptors (the G-protein-coupled receptor family) and thus possesses multiple membrane-spanning domains.     

Suppression of in vitro haematopoiesis following human immunodeficiency virus infection

Viral infections are frequently associated with haematological disorders. Abnormalities including leukopenia, anaemia and thrombocytopenia are commonly observed in patients with the acquired immune deficiency syndrome (AIDS) or the AIDS-related complex (ARC). The underlying cause of these haematological abnormalities is poorly understood. We report here that bone marrow progenitors isolated from AIDS or ARC patients are responsive to recombinant human granulocyte-macrophage colony stimulating factor (rGM-CSF) and recombinant erythropoietin. Antibodies present in the serum of patients infected with the human immunodeficiency virus (HIV), however, could suppress the growth of these progenitors, but not the growth of progenitors from HIV seronegative controls. A component of this immune-mediated suppression appears to be antibodies directed towards the envelope glycoprotein (gp120) of HIV.