Characteristics of age-related changes in rat thymus: morphometric analysis and epithelial cell network in various thymic compartments.

Structural alterations in thymuses of female rats during the first 2 years of life were evaluated by morphometric analysis and, then, correlated with organization of epithelial cells in various thymic compartments, examined for their cytokeratin immunoreactivity. With an advancing age, the thymuses demonstrated morphological modifications related to maturation and senescence, the dynamics of which varied between particular thymic compartments, and involved subpopulations of thymic epithelial cells. In the entire period of life the most dynamic changes were found in the cortex while the medulla was demonstrated to be a rather "stable" region. Morphometric studies revealed a negative correlation between the volume of thymic cortex and medulla and age of rats and a linear, positive relationship between the volume of connective tissue compartment and age. Changes in organization of epithelial network in the medulla preceded those observed in the cortex. Decreased proliferative activity of subset of medullary cells, which probably represented a self-renewable population, was accompanied by alterations in the immunocytochemically characterized (cytokeratines) differentiation process. At the same period of life, hypertrophy and hyperplasia of superficial epithelial cells seems to functionally replace medullary cells. This process begins around 3rd month of life and expands on all thymic compartments. The first changes in the cortex appeared around 8th month and were connected with reduced cytokeratin immunoreactivity. The involution observed in older animals was preceded by age-related alterations in epithelial network pattern which, in the course of stable morphometric parameters (between 5th and 12th month), showed character of a structural and functional adaptation.

Homing of hemopoietic precursor cells to the fetal rat thymus: intercellular contact-controlled cell migration and development of the thymic microenvironment.

Colonization of rat thymic anlage by the first wave of hemopoietic precursor cells (HPc) was investigated by means of transmission electron microscopy and immunocytochemistry. HPc began migration into the thymic anlage between 13 and 13.5 gestation days (GD), terminated colonization at about GD 16, and migrated sequentially through the two compartments of the thymic anlage under the control of typical populations of stromal cells. First, HPc migrated through the external compartment of the perithymic mesenchyme, tightly interconnected with fibroblasts. The type of junctions between the cells indicated that the fibroblasts played a role in the control of HPc trafficking and in their entrance to the epithelial compartment. The second stage of colonization was initiated by the entrance of HPc to the epithelial compartment and their interaction with thymic epithelial cells (TECs). Based on morphological criteria, two populations of HPc were distinguished that colonized the anlage at various stages of its development. The predominant population with ultrastructural traits common to thymocytes "homed" into the epithelial type primordium. A small number of HPc, identified by protein S-100 expression and by Birbeck's granules as precursors of dendritic cells, colonized lymphoepithelial anlage in which subsets of cortical and medullary TECs could be distinguished. Thymocyte migration and their reciprocal interactions with cortical TECs differed from the trafficking of dendritic cells toward the medulla. The results demonstrated the influence of maturing thymocytes on the development of cortical epithelial cells and the dynamic organization of the medullary microenvironment with direct involvement of dendritic cells.

Pneumadin in the ventral prostate of rats during postnatal development: a radioimmunological and immunocytochemical study.

We have recently demonstrated that the ventral prostate of adult rats contains high levels of pneumadin (PNM), a decapeptide originally isolated from mammalian lung, and that testosterone is needed for the maintenance of a normal level of the peptide in the prostate. Hence, we have investigated, by radioimmunoassay (RIA) and light ultrastructural immunocytochemistry (ICC), PNM concentration and localization in the rat ventral prostate during postnatal development. RIA showed that PNM content increased steadily from day 20 to day 90 of postnatal life, parallel to the increase in the prostate weight. In contrast, PNM concentration remained rather stable, although it showed a marked rise at day 40 when rat testes are known to reach their full maturation. ICC demonstrated that PNM immunoreactivity was mainly located in the apical pole of epithelial cells of rat ventral prostate, especially in the subcellular organelles involved in protein secretion, i.e. rough endoplasmic reticulum cisternae, vacuoles and granules. Taken together our study suggests the involvement of PNM in the functional control of rat prostate during postnatal maturation, although its exact role remains to be elucidated.

Evidence for less irritation to the peritoneal membrane in rats dialyzed with solutions low in glucose degradation products.

BACKGROUND: Acidic pH and the presence of glucose degradation products (GDP) are believed to compromise the biocompatibility of peritoneal dialysis fluids (PDF). The present study examines the effects of long-term exposure to GDP and low pH by comparing conventional PDF and a new, neutral pH, low GDP solution. METHODS: All experiments were performed using a chronic infusion model of dialysis in nonuremic rats. The animals were treated for 6 weeks with 2 daily injections of 4.25% glucose-containing PDF. The following PDF were tested: CAPD3 (single-chamber bag, low pH, high GDP), CAPD3 pH 7.4 (single-chamber bag, neutral pH, high GDP), CAPD3-Balance (double-chamber bag, neutral pH, low GDP). All test solutions were obtained from Fresenius Medical Care, Bad Homburg, Germany. RESULTS: After 6 weeks of exposure, peritoneal permeability to water, urea, creatinine, glucose, and sodium, assessed by peritoneal equilibration test, was similar in all groups. However, compared to other PDF, dialysis with CAPD3-Balance was associated with reduced concentrations of protein and hyaluronan in the dialysate, decreased peritoneal eosinophilia, and reduced dialysate levels of chemokines CCL2/MCP-1 and CCL5/RANTES. Morphologic changes in the peritoneal membrane of CAPD3-Balance-treated animals were much less pronounced and included reduced vascular density, preservation of the mesothelial monolayer and intercellular junction, and no reduplication of the submesothelial basement membrane. CONCLUSIONS: A new generation of PDF with physiologic pH and low GDP level produce less irritation to the peritoneal membrane and better preserve its structural integrity. This effect seems to be related predominantly to minimized GDP concentrations.

Thymic epithelial cells in age-dependent involution.

Aging involves morphological and functional alterations within the microenvironment of the thymus where heterogenous populations of thymic epithelial cells (TEC) play the main roles. The studies performed to date on thymic involution signalize a disturbed interaction between individual thymic compartments that disrupt thymocyte-TEC interactions and, as a sequele, disturb differentiation of both TEC and thymocytes. The process of aging affects the various subsets of TEC at different periods of life. Changes in different subsets of TEC are documented on the basis of their phenotypical characteristics, involving morphological analysis and immunocytochemistry. The character and kinetics of changes in TEC are typical for individual subsets and probably sex-dependent. In the course of life, the involutionary changes, expressed by disorganised thymic structure and function, are accompanied by changes in medullary TEC, manifested by alterations in the differentiation process of the cells. In parallel, at the same stage of individual life, the aging process induces increased proliferative and secretory activity of subseptal TEC, which seem to functionally replace medullary TEC. Structural and phenotypic modifications of TEC are locally controlled by complex sets of different factors and seem to represent a morphological adaptation of the gland to the process of aging. Microsc. Res. Tech. 62:488-500, 2003.

Morphologic changes in the liver of dialyzed rats--preliminary observations.

Peritoneal dialysis affects both the quantity and quality of connective tissue in the visceral peritoneum. In the present study, we report the alterations observed in the morphology of the superficial liver lobuli of dialyzed rats. The studies were performed in male Wistar rats weighing 250-350 g. Rats were exposed intraperitoneally to 0.9% NaCl, phosphate-buffered saline (PBS), or commercial dialysis solutions containing 3.86% glucose (Dianeal 3.86%: Baxter Healthcare SA, Castlebar, Ireland; CAPD3 and CAPD3-Balance: Fresenius Medical Care, Bad Homburg, Germany) twice daily for 4-6 weeks. At the end of the study, samples of the liver were taken and stained for light microscopy (hematoxylin and eosin, van Gieson). The results obtained in dialyzed rats were compared with those from the control, non dialyzed animals. In control animals, the surface of the hepatic parenchyma was smooth. In all dialyzed rats, irrespective of the solution used, folding of the surface of the liver parenchyma was found owing to penetration of connective tissue elements between the hepatocytes. In effect, folds of hepatocytes within the liver capsule became detached and isolated from the remaining cells of the lobules. The distinctive feature of that pathologic change was that its severity increased with the thickness of the peritoneum. The change was seen in rats exposed to any of the experimental solutions, and therefore appeared to be attributable to a non-specific reaction caused by exposure of the peritoneum to dialysis fluid and not to specific components of the fluid. The observed alterations in morphology seem to suggest disturbed function within the affected lobules. Further studies are necessary to confirm this hypothesis.

Effects of galanin on proliferation and apoptosis of immature rat thymocytes.

Evidence indicates that some regulatory peptides (endothelins, cholecystokinin and VIP) are involved in the control of thymus growth, and we have investigated whether galanin may be included in this group of peptides. In fact, galanin, a 29-amino acid peptide acting through three subtypes of G protein-coupled receptors (GalR1, GalR2 and GalR3), seems to play a role in the control of the immune system. Reverse transcription (RT)-polymerase chain reaction (PCR) allowed the detection of galanin, GalR1 and GalR3 mRNAs in the thymus cortex of immature (20-day-old) rats, while GalR2 expression was very weak or absent. Immature rats were given three subcutaneous injections (28, 16 and 4 h before sacrifice) of 2 nmol/100 g galanin and or the galanin-receptor antagonist (galanin-A) [D-Thr(6),D-Trp(8,9),15-ol]-galanin(1-15), and 0.1 mg/100 g vincristine 3 h before sacrifice. Thymuses were processed for light microscopy and the percentage of metaphase-arrested cells (mitotic index) was evaluated. Galanin-A increased the thymus mitotic index, while galanin was ineffective, thereby suggesting that endogenous galanin exerts a maximal tonic inhibitory effect on the proliferative activity of thymocytes in immature rats. Immature rat thymocytes were cultured in vitro for 12 h in the presence of 10(-6) M galanin and/or galanin-A. Hoechst 33342 and propidium iodide were added to the cultures, and the percentage of apoptotic and necrotic cells was determined under fluorescence microscope. Galanin increased apoptotic index, and the effect was prevented by galanin-A. Neither galanin nor galanin-A altered necrotic index. Collectively, our findings indicate that galanin, probably acting through GalR1 and GalR3, exerts antiproliferative and proapoptotic effects on immature rat thymocytes, which makes it likely that this peptide plays a role in the autocrine/paracrine functional regulation of immune system in the rat.