The regulation of''early'' enzymes during the development and dedifferentiation of Dictyostelium discoideum

The specific activities of the enzymes alpha-mannosidase and N-acetylglucosaminidase increase immediately after the initiation of the development of bacterially grown cell cultures of Dictyostelium discoideum. The regulation of these two enzymes was found to be dissociable in the developmental timer mutant, FM-1, which aggregates 4.5 h earlier than wild-type cells due to the absence of the first rate-limiting component of the preaggregative period. The increase in alpha-mannosidase activity occurs in the absence of the first rate-limiting component, but the increase in N-acetylglucosaminidase activity does not. These results indicate the following: (1) the increase in the specific activity of alpha-mannosidase is not related to the timing of subsequent developmental stages; (2) the increase in the specific activity of N-acetylglucosaminidase is not necessary for the subsequent developmental program; and (3) either the increase in the specific activity of N-acetylglucosaminidase is dependent upon progress through the first rate-limiting component, or the increase in this enzyme activity and the first rate-limiting component are both dependent upon an early event for which FM-1 is defective. In addition to early development, we monitored the two enzyme activities during dedifferentiation. The results demonstrate that there is no difference between dedifferentiating wild-type cells and dedifferentiation-defective mutant HI-4 cells. Changes in enzyme specific activity accompanying dedifferentiation are dependent upon the composition of the dedifferentiation-inducing media and are consistent with the levels of these enzymes observed in cells growing in the different nutrient media.     

Altered central monoamine response tod-amphetamine in rats chronically exposed to inorganic lead

Investigations of the mechanisms involved in the neurotoxicity resulting from chronic inorganic lead (Pb) exposure have centered on CNS biogenic amine function on the basis of behavioral and neurochemical findings. The following study examined the time course of the response of dopamine (DA) and 5-hydroxytryptamine (5-HT) neurons to d-amphetamine (AMPH) in rats chronically exposed to Pb from birth in order to further examine neurochemical mechanisms implicated by previous work. Offspring were exposed to 0.2% Pb acetate via the lactating dam and then weaned to the same drinking solution. At 120–140 days animals were injected with 1.0 mg/kg s.c. of the drug or with saline and sacrificed after various intervals. DA content in nucleus accumbens and corpus striatum in Pb-exposed animals was significantly higher than corresponding levels in controls at 20 minutes post-drug and remained significantly higher than baseline values at 80 minutes after the drug when DA concentrations in controls had returned to normal. These data suggest enhanced AMPH-induced DA synthesis in exposed rats. 5-Hydroxyindoleacetic acid (5-HIAA) content was significantly increased in three brain regions in exposed rats given AMPH compared to values in saline-injected exposed animals, indicating a compensation in these areas for the decreases in 5-HIAA values produced by Pb exposure alone. The results of this study reinforce the hypothesis that DA and 5-HT neurons are sensitive to relatively low levels of Pb exposure.     

The ultrastructure and formation of the calcareous ossicles in the body wall of the sea cucumber Leptosynapta clarki (Echinodermata,Holothuroida)

Summary The calcareous ossicles of the burrowing sea cucumber Leptosynapta clarki have been examined by scanning and transmission electron microscopy. The ossicles occur in the dermis of the body wall and comprise three main types: 1) curved rods; 2) miliary granules; and 3) anchorshaped structures that are paired with oval plates. Rods average about 80 m in length, and miliary granules are typically 20–30 m long. Both of these ossicles appear to form a protective skeleton in regions where the water vascular system and accompanying nerves are located. Anchors and plates are scattered throughout the interambulacra of the body at densities ranging from 2–8/mm². Each anchor measures about 145 m long and is attached to the plate underlying it by a flexible ligament that is composed of collagen fibrils. Tetracycline labeling studies indicate that anchors and plates take several months to reach full size. All developing ossicles appear to be surrounded by a syncytial network of sclerocytes that characteristically possess numerous mitochondria and a conspicuous external lamina. Fully formed anchors lie directly beneath the epidermis and do not protrude through the outermost layer of the body wall. During burrowing, the curved flukes of the anchorshaped ossicles may provide added traction as the buccal tentacles dig through the sediment.List of abbreviations a anchor - ar ambulacral region - cm circular muscle layer of body wall - cs cytoplasmic sheath - d dermis - ep epidermis - f fluke - ild inner layer of dermis - k keel - me myoepithelium - mg miliary granule - n nerve - old outer layer of dermis - os ossicle - pl plate - s sclerocyte - sh shank - st stock     

A syndromic approach to common parasitic diseases

Standard textbooks discuss parasitic disease according to specific organisms. In contrast, patients with parasitic infections present to physicians with a variety of clinical manifestations that may involve any of several organ systems and that often mimic nonparasitic diseases. A syndromic approach to the clinical situation may help the physician in considering the most important parasitic agents. Many parasitic infections can be acquired in temperate climates. While often considered tropical or exotic, other parasitic diseases are now seen more frequently in developed countries because of immigration and increased world travel. In this review the clinical syndromes associated with common parasitic diseases in North America are discussed, with an emphasis on risk factors and diagnosis of specific infections.     

An interspecies comparison of normal levels of glycosylated hemoglobin and glycosylated albumin

Aminophenylboronic acid affinity chromatography was used to measure glycosylated hemoglobin and glycosylated albumin levels in a variety of species. The highest glycosylated hemoglobin levels were found in man, the lowest in the chicken and the pig. The highest glycosylated albumin levels were found in avian species, the lowest in the mouse and the rat. A simple kinetic model was used to analyze the rates of formation of glycosylated hemoglobin and albumin in the various species. Rates of glycosylated albumin formation were very similar across the species while rates of glycosylated hemoglobin formation were quite different, presumably reflecting wide differences in erythrocyte permeability to glucose among the species.     

Phytochrome control of its own accumulation and leaf expansion in tentoxin- and norflurazon-treated mung bean seedlings

Primary leaves of 4-day-old, dark-grown mung bean [ Vigna radiata (L.) Wilczek cv. Berken] seedlings were exposed to 24 h of white light (200 μmol m⁻² s⁻¹) which was terminated by a 15 min, phytochrome-saturating red or far-red light exposure. Phytochrome content (in vivo and in vitro) and leaf area were monitored during the subsequent dark period. Red light treatments resulted in lower phytochrome content and greater leaf expansion than did far-red treatments. Phytochrome accumulation and leaf expansion were less in norflurazon- (no carotenoids and very low Chl) than in tentoxin- (very low Chl) treated leaves. After 3 days of darkness, leaf expansion was about 25% greater and phytochrome content was about 50% less in red- than in far-red-treated leaves of all treatments. These effects generally took longer to develop in norflurazon- than in tentoxin-treated tissues. Norflurazon-treated tissues exposed to long white light periods apparently do not as accurately reflect phytochrome-controlled photomorphogenic events of green tissues as do tentoxin-treated tissues of mung bean seedlings.     

Light control of extractable nitrate reductase activity in higher plants

Light regulation of extractable nitrate reductase (NR) activity of higher plants is complicated by: 1) involvement of several photoreceptors, 2) differences in the relative importance of the several photoreceptors among species and among developmental stages of the same species, 3) two types of effects – alteration of activity of existing NR and influences on de novo synthesis of NR, and 4) differing forms of NR within the same species. The interrelationships of all of these factors are not clear. It may be that each system will have to be understood separately before a general model can be developed. Immunochemical quantification of NR from systems exposed to varied light regimes may enhance our understanding of this area. Currently few general conclusions can be made; however, we think that the following statements are true or are usually true: (1) Phytochrome influences extractable NR activity by the low irradiance response and high irradiance response in etiolated tissues. (2) In de-etiolated tissues phytochrome can influence NR activity decay at the end of a light period by the low irradiance response. (3) The phytochrome equilibrium or the absolute level of P_fr influences extractable NR activity in green tissues under white light. (4) Blue light influences extractable NR activity through phytochrome and another, unknown, blue light-absorbing pigment. Flavins may be involved in vitro in reactivation of inactivated NR. (5) Photosynthesis does not directly influence the induction of the forms of NR that require substrate and light for induction. (6) In some tissues there appears to be a close link between nitrite-reducing and nitrate-reducing capabilities. (7) Much circumstantial evidence from kinetic and protein-synthesis-inhibitor studies and the only available immunochemical data indicate that light induces de novo synthesis of NR, resulting in increased extractable activity.     

Benzodiazepine Receptor Binding in Cerebellar Cortex: Observations in Olivopontocerebellar Atrophy

Benzodiazepine receptor binding was measured in cerebellar cortex of 15 patients with dominantly inherited olivopontocerebellar atrophy (OPCA). The majority of these patients had a moderate to marked Purkinje cell loss, as judged by the lowered levels of dentate nucleus gamma-aminobutyric acid (GABA), a marker of Purkinje cells. Despite the reduction in Purkinje cell number cerebellar cortical benzodiazepine receptor density was either normal or slightly elevated in the OPCA patients. These results are in contrast to the findings in a mutant strain of mice deficient in Purkinje cells in which the concentration of benzodiazepine receptors in cerebellum is greatly reduced. Our data indicate that in the human, cerebellar cortical benzodiazepine receptors are either not significantly associated with Purkinje cells or that in OPCA Purkinje cell loss triggers a de novo synthesis of extra benzodiazepine binding sites. It is concluded that, in contrast with the rodent, in the human benzodiazepine receptor binding may not serve as a marker for cerebellar Purkinje cells.