Experimentelle Untersuchungen über die Beziehung zwischen Schilddrüse und Hypophyse während der Larvalentwicklung und Metamorphose von Xenopus laevis Daudin

Zusammenfassung Die Normalentwicklung von Schilddrüse und Hypophyse während der Larvalentwicklung und Metamorphose von Xenopns laevis Daudin und die Veränderungen des Hypophysenvorderlappens (HVL) und der Schilddrüse auf Behandlung mit Dinitrophenol, Natriumthiocyanat, Methylthiouracil, Kaliumperchlorat und Thyroxin im Überschuß wurden untersucht.Die Selbstdifferenzierungsfähigkeit der Schilddrüse und die Wirkung exogenen Thyroxins auf die Schilddrüse wurde an hypophysektomierten Tieren herausgestellt.Schilddrüse und -Zellen des Hypophysenvorderlappens werden mit Beginn des Hinterbeinwachstums funktionsfähig. Zur gleichen Zeit wird das Körpergewebe gegenüber Schilddrüsenhormon empfindlich. Das HVL-Schilddrüsen-Regulationssystem wird ebenfalls zudiesem Zeitpunkt reaktionsbereit.Die Schilddrüse ist bis zu einem gewissen Grad selbstdifferenzierungsfähig; sie wird auch dann morphologisch ausdifferenziert — wenn auch verzögert und nicht in vollem Umfang —, wenn genügend exogenes Thyroxin vorhanden ist, um die Entwicklung weiterzuführen, und beim Fehlen der Hypophyse.Die Sekret-Produktion und -Speicherung in den -Zellen des HVL erfolgt auch dann, wenn genügend exogenes Thyroxin die TSH-Produktion überflüssig macht.Dinitrophenol dämpft die Aktivität der Schilddrüse, ohne daß die -Zellen des HVL hypertrophieren. Eine Hemmung des Rückkopplungsmechanismus ist wahrscheinlich.Natriumthiocyanat, Methylthiouracil und Kaliumperchlorat bewirken Kropfbildung und eine starke Hypertrophie der -Zellen des HVL. Dabei entsprechen die durch diese drei Substanzen verursachten Veränderungen der -Zellen nicht dem jeweiligen Aktivitätsgrad der Schilddrüse. So ist z. B. nach Thiocyanat-Behandlung die Schilddrüsenhemmung am stärksten, die Kernvergrößerung der -Zellen aber am geringsten. Natriumthiocyanat, Methylthiouracil und Kaliumperchlorat hemmen demnach nicht nur die Hormonproduktion der Schilddrüse unterschiedlich, sie greifen außerdem noch störend in das Regulationssystem ein: entweder durch Veränderung des Schilddrüsenhormons selbst oder des Rückkopplungsmechanismus.

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Summary The normal development of the thyroid gland and the pituitary during larval development and metamorphosis of the clawed toad Xenopus laevis Daudin and the changes of the anterior pituitary and the thyroid after treatment with dinitrophenol, thiocyanate, thiouracil, perchlorate and exceeding thyroxine were investigated.The capacity of self-differentiation and the effect of exogenous thyroxine on the thyroid were pointed out in hypophysectomized animals.Thyroid and TSH-producing cells (-cells) of the anterior pituitary start functioning at the beginning of the hindlimb-growth. At the same time the body tissue gets sensitive to thyroid-hormone and the anterior pituitary-thyroid-regulating system shows first signs of reactivity.The thyroid is able to selfdifferentiate up to a certain degree. The gland morphologically differentiates — though retarded and not to the full extent —, even if either sufficient exogenous thyroxine is available to proceed the development or the pituitary is lacking.The -cells of the anterior pituitary synthesize and store hormone, even if sufficient exogenous thyroxine makes the TSH-production unnecessary.Dinitrophenol restrains the activity of the thyroid without causing hypertrophy of the -cells of the anterior pituitary. An inhibition of the feed-back mechanism seems to be possible.Thiocyanate, thiouracil and perchlorate cause goitre and a strong hypertrophy of the -cells of the anterior pituitary. Considering the effects of these three substances, the changes of the -cells, caused by the lack of thyroid hormone, do not correspond with the respective activity of the thyroid. The inhibition of the thyroid is strongest after treatment with thiocyanate, but in this case the increase of the nuclear diameter of the -cells is smallest. Therefore thiocyanate, thiouracil and perchlorate do not only inhibit the hormone production of the thyroid. They also interfere with the regulation system in a different manner: they either modify the thyroid hormone itself or interfere with the feed-back mechanism.

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Dissertation der Naturwissenschaftlichen Fakultät der J. W. Goethe-Universität in Frankfurt a. M.Meinem Lehrer, Herrn Prof. Dr.H. Giersberg, danke ich für die Anregung dieser Arbeit, Herrn Prof. Dr. M. Lindauer für die weitere Überlassung des Arbeitsplatzes. Besonderen Dank schulde ich den Herren Prof. Dr. W. Hanke und Dr. F.-W. Pehlemann für jederzeit hilfreichen Rat.     

Effect of Long-Lasting Diabetes Mellitus on Rat and Human Brain Monoamines

Experimental alloxan- or streptozotocin-produced diabetes in rats was accompanied by an increase in the levels of norepinephrine, dopamine, and serotonin, whereas the contents of metabolites, i.e., 5-hydroxyindoleacetic acid and homovanillic acid, in the whole brain gradually decreased with the duration of diabetes. Among the striatum, thalamus, and hypothalamus of alloxan diabetic rats, monoamine alterations were observed only in the hypothalamus; after 1 week an increase of norepinephrine content and after 13 weeks an increase of norepinephrine and dopamine contents were found. Tissues of 11 brain regions of 10 diabetic and 12 control patients post mortem were investigated for monoamine concentrations. Patients were all male, of similar age and interval between death and autopsy. Diabetic patients had an increase in the content of serotonin in the medial and lateral hypothalamus. The content of dopamine increased in the medial hypothalamus, putamen, and medial and lateral pallidus. In diabetic patients, the content of norepinephrine increased in the lateral pallidus and decreased in the nucleus accumbens and claustrum. Thus, it seems that diabetes mellitus in rats, as well as in humans is associated with regionally specific changes in brain monoamines.     

Brain insulin system dysfunction in streptozotocin intracerebroventricularly treated rats generates hyperphosphorylated tau protein

The intracerebroventricular (icv) application of streptozotocin (STZ) in low dosage was used in 3-month-old rats to explore brain insulin system dysfunction. Three months following STZ icv treatment, the expression of insulin-1 and -2 mRNA was significantly reduced to 11% in hippocampus and to 28% in frontoparietal cerebral cortex, respectively. Insulin receptor (IR) mRNA expression decreased significantly in frontoparietal cerebral cortex and hippocampus (16% and 33% of control). At the protein/activity level, different abnormalities of protein tyrosine kinase activity (increase in hippocampus), total IR beta-subunit (decrease in hypothalamus) and phosphorylated IR tyrosine residues (increase) became apparent. The STZ-induced disturbance in learning and memory capacities was not abolished by icv application of glucose transport inhibitors known to prevent STZ-induced diabetes mellitus. The discrepancy between reduced IR gene expression and increase in both phosphorylated IR tyrosine residues/protein tyrosine kinase activity may indicate imbalance between phosphorylation/dephosphorylation of the IR beta-subunit causing its dysfunction. These abnormalities may point to a complex brain insulin system dysfunction after STZ icv application, which may lead to an increase in hyperphosphorylated tau-protein concentration. Brain insulin system dysfunction is discussed as possible pathological core in the generation of hyperphosphorylated tau protein as a morphological marker of sporadic Alzheimer's disease.     

Leopard tortoises in southern Africa have greater genetic diversity in the north than in the south (Testudinidae)

In contrast to mammals, little is known about the phylogeographic structuring of widely distributed African reptile species. With the present study, we contribute data for the leopard tortoise (Stigmochelys pardalis). It ranges from the Horn of Africa southward to South Africa and westwards to southern Angola. However, its natural occurrence is disputed for some southern regions. To clarify the situation, we used mtDNA sequences and 14 microsatellite loci from 204 individuals mainly from southern Africa. Our results retrieved five mitochondrial clades; one in the south and two in the north‐west and north‐east of southern Africa, respectively, plus two distributed further north. Using microsatellites, the southern clade matched with a well‐defined southern nuclear cluster, whilst the two northern clades from southern Africa corresponded to another nuclear cluster with three subclusters. One subcluster had a western and central distribution, another occurred mostly in the north‐east, and the third in a small eastern region (Maputaland), which forms part of a biodiversity hotspot. Genetic diversity was low in the south and high in the north of our study region, particularly in the north‐east. Our results refuted that translocations influenced the genetic structure of leopard tortoises substantially. We propose that Pleistocene climatic fluctuations caused leopard tortoises to retract to distinct refugia in southern and northern regions and ascribe the high genetic diversity in the north of southern Africa to genetic structuring caused by the survival in three refuges and subsequent admixture, whereas tortoises in the south seem to have survived in only one continuous coastal refuge.     

Poly(ADP-ribose) polymerase-1: association with nuclear lamins in rodent liver cells

The distribution of poly(ADP-ribose) polymerase-1 (PARP-1) over different nuclear compartments was studied by nuclear fractionation procedures and Western analysis revealing a prominent role of the nuclear matrix. This structure is operationally defined by the solubility properties of the A- and B-type lamins under defined experimental conditions. We consistently observed that most of the nuclear matrix-associated PARP-1 partitioned, in an active form, with the insoluble, lamin-enriched protein fractions that were prepared by a variety of established biochemical procedures. These PARP-1-protein interactions resisted salt extraction, disulfide reduction, RNase and DNase digestion. An inherent ability of PARP-1 to reassemble with the lamins became evident after a cycle of solubilization/dialysis using either urea or Triton X-100 and disulfide reduction, indicating that these interactions were dominated by hydrophobic forces. Together with in vivo crosslinking and co-immunoprecipitation experiments our results show that the lamins are prominent PARP-1-binding partners which could contribute to the functional sequestration of the enzyme on the nuclear matrix.     

Identification and Characterization of a Peptide That Specifically Binds the Human, Broadly Neutralizing Anti-Human Immunodeficiency Virus Type 1 Antibody b12

Human monoclonal antibody (MAb) b12 recognizes a conformational epitope that overlaps the CD-4-binding site of the human immunodeficiency virus type 1 (HIV-1) envelope. MAb b12 neutralizes a broad range of HIV-1 primary isolates and protects against primary virus challenge in animal models. We report here the discovery and characterization of B2.1, a peptide that binds specifically to MAb b12. B2.1 was selected from a phage-displayed peptide library by using immunoglobulin G1 b12 as the selecting agent. The peptide is a homodimer whose activity depends on an intact disulfide bridge joining its polypeptide chains. Competition studies with gp120 indicate that B2.1 occupies the b12 antigen-binding site. The affinity of b12 for B2.1 depends on the form in which the peptide is presented; b12 binds best to the homodimer as a recombinant polypeptide fused to the phage coat. Originally, b12 was isolated from a phage-displayed Fab library constructed from the bone marrow of an HIV-1-infected donor. The B2.1 peptide is highly specific for b12 since it selected only phage bearing b12 Fab from this large and diverse antibody library.