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.

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.

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.

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.

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.

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.

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.

The ultrastructure of the peritoneal membrane in chronically dialysed rats with spontaneous peritonitis: preliminary observations.

In this paper we describe ultrastructure of the peritoneal membrane from single peritoneal biopsies collected from chronically dialysed rats with spontaneous peritonitis. The results were compared with those obtained in chronically dialysed animals without peritonitis. In rats with peritonitis, peritoneum was much thicker than in peritonitis-free animals.

Lympho-epithelial interactions in rat thymus during pregnancy.

Alterations in the thymic epithelial cell activity were analysed during pregnancy and lactation in Wistar rats by examining the presence and in situ distribution of lymphoepithelial complexes formed by thymic nurse cells (TNC). TNC were identified in paraffin sections by their expression of MHC class II antigens, CD54 molecule and a neuromarker, protein gene product 9.5 (PGP9.

Age-related changes in rat thymic epithelial cells.

We investigated age-related changes in immunocytochemical localisation of cytokeratin 16 (CK16) in thymuses of female Wistar rats at various stages of adult life (months 1, 3, 6, 12). Within the 1 st month of life, distribution of CK typical for individual subsets of thymic epithelial cells (TEC) was observed. The most numerous CK16+ TEC were observed in the outer region of medulla, in the outer cells of Hassall's corpuscles and in the superficial epithelial layer neighbouring the connective tissue of the capsule, septa and vessels of the thymus.

Stages of the rat thymic medulla development in foetal period.

Development of thymic medulla was examined on consecutive gestational days (GD) in Wistar rats. Medullary thymic epithelial cells (TEC) were identified by immunocytochemical localisation of neuron-specific enolase (NSE). Organisation of thymic medullary architecture was determined by interaction of thymocytes with NSE-positive TEC, that led to formation of lymphoepithelial complexes (GD 19), in which the cells exhibited proliferative activity or traits of apoptosis.

Morphologic aspects of chronic peritoneal dialysis in a rat model.

Objective: We previously put forward an experimental model for evaluating peritoneal function in chronically dialyzed rats. In the present paper, we show the morphologic alterations detected by electron microscopy in the peritonea of chronically dialyzed rats.

Materials And Methods: The study was done in male Wistar rats.

The ultrastructure of the peritoneal membrane in chronically dialysed rats.

The model to estimate peritoneal function in chronically dialysed rats was previously presented by us. The aim of the paper is to report the findings obtained in electron microscopy of peritoneal biopsies from Wistar rats dialysed for 1 month with high glucose dialysis solution. In control animals, thin mesothelial cells were covered with microvilli.

Histogenesis of the rat thymic medulla during first stages of development.

We investigated first stages of thymic medulla organisation in foetuses of Wistar strain rats. between 13th and 17th days of foetal life (GD). Medullary cells were identified by immunocytochemical localisation of neuron-specific enolase (NSE) as well as by traits of ultrastructure.

Kinetics of thymic stroma development in the foetal period.

The kinetics of thymic epithelial cell development was examined in Wistar strain rats between 13th and 21st days of foetal life. The studies were based on immunocytochemical localisation of cytokeratin 16 (CK 16), Ki67 and on ultrastructural observations of thymus development. Expression of CK16 in individual groups was evaluated using the Micro Image v.

Studies on the involvement of endogenous neuropeptides in the control of thymocyte proliferation in the rat.

The possible involvement of endogenous vasoactive intestinal peptide (VIP), cholecystokinin (CCK) and neurotensin (NT) in the control of thymocyte proliferation has been investigated in vivo in the immature rat. For this task, we have studied the effects of the administration of selective antagonists of the receptors of the three neuropeptides on the mitotic index (% of metaphase-arrested cells after vincristin injection) of thymocytes. Both CCK- and TN-receptor antagonists were ineffective.

Subtypes of thymic epithelial cells defined by neuroendocrine markers.

The study attempted to define characteristics of thymic epithelial cells within rat thymus based on the expression of neuroendocrine markers. Using an immunohistochemical approach, the following markers were localised: protein gene product 9.5 (PGP 9.

Cholecystokinin, acting through the A receptor subtype, stimulates the proliferative activity of adrenocortical cells and thymocytes in the rat.

Cholecystokinin (CCK) is a multifunctional regulatory peptide, which acts through two main subtypes of receptors, named CCK-A and CCK-B. Evidence indicates that CCK modulates cell proliferation in various tissues in a paracrine manner, and proofs are available of the presence of CCK in both adrenal glands and thymus. Hence, we have investigated the possible mitogenic action of this peptide on these two tissues, by evaluating the /1000 of metaphase-arrested cells after vincristin injection (mitotic index).

Endothelin-1 enhances thymocyte proliferation in monolaterally adrenalectomized rats with contralateral adrenocortical regeneration.

Endothelins (ETs) are a family of vasoactive peptides widely distributed in the body systems, where they exert pleiotropic biological effects, acting through two main subtypes of receptors, named ETA and ETB. Evidence indicates that ET-1 plays a permissive role in the development of neural crest-derived structures, among which are the epithelial cells of the thymus. These cells are known to control proliferation and differentiation of thymocytes, a process requiring adequate levels of glucocorticoids.

Endothelin-1, acting via the A receptor subtype, stimulates thymocyte proliferation in the rat.

Endothelins (ETs) are a family of vasoactive peptides widely distributed in the body systems, where they carry out major autocrine/paracrine regulatory functions, acting through two main subtypes of receptors (ETA and ETB). Evidence suggests that ETs play a permissive role in the development of neural crest-derived craniofacial structures, among which the thymus. Therefore, we have investigated whether ETs regulate thymocyte proliferation in the adult rat ET-1 (which binds both ETA and ETB receptors) increased the mitotic index (% of metaphase-arrested cells) in the thymus cortex, while ET-3 (which preferentially binds ETB) and the selective ETB-receptor agonists BQ-3020 and IRL-1620 did not.

Thymic nurse cells: their functional ultrastructure.

Thymic nurse cells are defined in vitro as multicellular complexes of epithelial cells and thymocytes. Although these structures have been implicated in the intrathymic differentiation of thymocytes, little is known about the biology of this cell complex and about the occurrence of the cells in the thymus in situ. Therefore, to clarify the matter, in this review we have presented characteristics of epithelial cells capable of forming complexes with thymocytes, in light of the literature data and the experience of the authors.

Three dimensional analysis of thymic medulla.

In consecutive serial paraffin sections centers of gravity were defined for individual cross-sections of thymic medulla of the rat. Coordinates of the centers provided grounds for a three-dimensional reconstruction of thymic medulla using for the purpose computer techniques. In all cases the medulla exhibited continuity throughout the organ and showed dendritic character with up to IVth order branching.

Distribution of dividing thymocytes in rat thymic cortex during daily cycle.

In the present study, frequency of thymocyte divisions was analyzed in the rat thymic cortex, as related to (1) distance from thymic capsule and (2) the daily cycle. Frequency of thymocyte divisions was estimated in successive 10 micron(s) thick layers of the cortex. An evident daily cycle was detected in the thymic cortex with increase in the number of cell divisions around 8 pm.

Analysis of thymocytes contacts with other thymic cells.

The study aimed et defining morphological relationships between thymic stroma cells and thymocytes. The studies were conducted on 16-days old Wistar strain rats. The material was routinely processed for ultrastructural examination.