Morphological aspects of opossum (Didelphis aurita) pancreas during intramarsupial development

Abstract: This study reported the relevant morphological features found in the pancreas of the Brazilian opossum Didelphis aurita, a marsupial mammal, during its intramarsupial development. Newborns and young opossums removed from the pouch were divided into groups according to their average body length. The animals with few hours of intramarsupial life had visibly immature pancreas, due to the presence of early arrangement of endocrine and exocrine components. There was an only very large pancreatic duct, and blood vessels full of nucleated erythrocytes. In the individuals who were in the second third of intramarsupial development, the exocrine components were arranged in developing acini and endocrine cells were found arranged in early islets. The presence of connective tissue and the division of the organ into lobes became more evident at this stage. In the last third of the external gestation, we found better structured acini with relatively small lumens. The islets were well-organized, and the presence of connective tissue around them was the most evident. Morphometric analyses showed considerable variations in the proportion of pancreatic structural components between the stages of intramarsupial development, indicating that marsupial pancreas undergoes morphological modifications and grows during the period of external gestation. Keywords: Embryo; Marsupials; Digestive system; Organogenesis.

Zinc sulfate chronic exposure effects on large intestine of adult Wistar rats: a histological evaluation

Abstract: The present study aimed to investigate possible morphological changes in the large intestine of adult Wistar rats submitted to chronic exposure to zinc sulfate at different doses. The animals were divided into three groups: control, treated with 5mg and treated with 20mg of zinc sulfate. The experiment had 56 days of exposure period and after this period the animals were anesthetized and euthanized. After dissection, a fragment of the cranial portion of the ascending colon of each animal was removed, fixed in Karnovsky solution for 24 hours, dehydrated in a growing ethanolic series and included in glycolmethacrylate resin. In a manual microtome, slices of 3μm thickness were obtained and then, stained with blue toluidine, for tissue description and morphometric analysis. The samples were also also submitted to histochemical techniques: Periodic acid of Schiff (PAS) and Alcian Blue (pH 2.5), for marking neutral and acidic mucus producing cells, respectively. The morphological parameters analyzed were: crypt depth, intestinal epithelium height, and number of PAS-positive and Alcian Blue-positive goblet cells. A decrease of neutral mucin-producing cells number and an increase in the height of the intestinal epithelium were observed in the animals treated with 20 mg of zinc sulfate. These results indicate morphological changes in the large intestine due to chronic zinc exposure, indicating a stress condition. Keywords: Toxicity, Zinc, Intestine, Mammal, Morphology.

Postembryonic development of rectal pads in bees (Hymenoptera, Apidae)

The morphology and development of the digestive tract of insects has been extensively studied, but little attention has been given to the development of the rectal pads. These organs are responsible for absorption of water and salts. In insects where they occur, there are usually six ovoid rectal pads located in the medial-anterior portion of the rectum. The rectal pad has three types of cells: principal, basal, and junctional. The arrangement of these three cell types delimits an intrapapillary lumen. The aim of the current study is to describe the development of the rectal pads during postembryonic development of Melipona quadrifasciata anthidioides and Melipona scutellaris. Specimens were analyzed at the following developmental stages: white-, pink-, brown-, and black-eyed pupae, and adult workers. The development of the rectal pad begins as a thickening of the epithelium in white-eyed pupae at 54 hr. At this stage, there is neither a basal cell layer nor intrapapillary lumen. The basal layers begin to form in the pink-eyed pupa and are completely formed at the end of the development of the brown-eyed pupa. In the brown-eyed pupal stage, the intrapapillary lumen is formed and the junctional cells are positioned and completely differentiated. Necrotic and apoptotic cell death were detected along with cell proliferation in the whole rectum during pupal development, suggesting that the development of the rectal pads involves cell proliferation, death, and differentiation. The rectal pads originate only from the ectoderm. Anat Rec, 2009. © 2009 Wiley-Liss, Inc

FMRFamide-like midgut endocrine cells during the metamorphosis in Melipona quadrifasciata anthidioides (Hymenoptera, Apidae)

The FMRFamide, gastrin and cholecystokinin (CCK) occurrence in endocrine cells of insects has been described by several authors, although their functions are still not well defined for this group of animals. In the present study, the occurrence of endocrine cells producing FMRFamide, gastrin 1 and CCK-8 in the midgut (ventriculus) of Melipona quadrifasciata anthidioides (Hymenoptera, Apidae), before, during and after the metamorphosis, were investigated by means of pre-embedding immunofluorescence techniques. FMRFamide reactivity was found in the endocrine cells as well as in the nervous fibers and neurons of the intestine of these bees. ‘Open’ and ‘closed’ types of FMRFamide-like cells were observed in last instar larvae. In the black eyed pupae the producing cells of FMRFamide seemed to be immature, and, in the workers, where the FMRFamide producing cells were more abundant, the production of this substance seemed to occur only in the open cells. Reactivity of the nervous fibers and neurons were observed, during the prepupae, white eyed pupae, and pink eyed pupae. The same did not occur with the midgut endocrine cells. There were no immunoreactivity observations for gastrin 1 and for CCK-8. The FMRFamide-like cells were present in the midgut of these insects during or close to the period that they were eating, which indicates that the FMRFamide may be involved in the control of the digestive process

Aedes aegypti midgut remodeling during metamorphosis

The Aedes aegypti midgut is restructured during metamorphosis; its epithelium is renewed by replacing the digestive and endocrine cells through stem or regenerative cell differentiation. Shortly after pupation (white pupae) begins, the larval digestive cells are histolized and show signs of degeneration, such as autophagic vacuoles and disintegrating microvilli. Simultaneously, differentiating cells derived from larval stem cells form an electron-dense layer that is visible 24 h after pupation begins. Forty-eight hours after pupation onset, the differentiating cells yield an electron-lucent cytoplasm rich in microvilli and organelles. Dividing stem cells were observed in the fourth instar larvae and during the first 24 h of pupation, which suggests that stem cells proliferate at the end of the larval period and during pupation. This study discusses various aspects of the changes during midgut remodeling for pupating A. aegypti

Digestive cells in the midgut of Triatoma vitticeps (Stal, 1859) in different starvation periods

Triatoma vitticeps (Stal, 1859) is a hematophagous Hemiptera that, although being considered wild, can be found in households, being a potential Chagas’ disease vector. This work describes the histology and ultrastructure of the midgut of T. vitticeps under different starvation periods. Fifteen adults of both sexes starved for 3, 7, 20 and 25 days were studied. In general, digestive cells had apical microvilli, basal plasma membrane infoldings and central nucleus. The perimicrovillar membrane was found in all insects examined. Digestive cells of anterior midgut had lipid droplets, glycogen granules, developed basal labyrinth associated with mitochondria suggesting their role in nutrient storage and in fluid and ion transport. The cells of median and posterior regions of the midgut were rich in rough endoplasmic reticulum, lysosomes, vesicles and granules with different electron-densities. Moreover, cells of the posterior portion of the midgut had hemozoyn granules and mitochondria in the apical cytoplasm close to microvilli, suggesting their role in blood digestion and active nutrient absorption. The midgut of T. vitticeps showed differences in digestive cells associated with the time after feeding, and the increase of vesicles amount in long starvation periods, which suggests enzyme storage, which is readily used after a blood meal

The regenerative cells during the metamorphosis in the midgut of bees

The midgut epithelium of bees is formed by the digestive cells, responsible for enzyme secretion and nutrient absorption and for small regenerative cells that are placed in nests scattered among the digestive cells. During metamorphosis, the larval midgut epithelium degenerates and a new adult midgut epithelium is built during larval differentiation of regenerative cells. The present work focuses on the midgut epithelial modifications during the post-embryonic development of the stingless bee Melipona quadrifasciata anthidioides worker and the occurrence of regenerative cell proliferation during midgut metamorphosis in order to test the hypothesis that adult midgut epithelium of worker bees results from regenerative cell proliferation during the pupal stage. Regenerative cell proliferation was detected during larval lifespan. Larval aging is followed by an increase in the number and the size of the nests of regenerative cells. Larval epithelium degeneration begins 2 days after the start of defecation process and in this period the nests of regenerative cells are in contact by means of cytoplasmic extension which have many septate desmosomes and gap junctions. The BrdU immunoreactive regenerative cells were found in the prepupae 12 h after BrdU injection, suggesting that regenerative cell population increase during this larval period. Regenerative cell proliferation results in the increase of the regenerative cell population and not in the formation of new digestive cells because the proliferation of regenerative cells would not be enough to reestablish the nests of regenerative cells and at the same time form new adult digestive cells. In this sense the hypothesis that digestive adult cells originate from regenerative cell proliferation during midgut metamorphosis in M. quadrifasciata anthidioides was rejected