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Biomedical subjects

J Becerra

Publications and source records attributed to J Becerra.

At least 37 records · Page 2Linked to original sources
PubMed1996

Demineralized bone matrix mediates differentiation of bone marrow stromal cells in vitro: effect of age of cell donor.

Bone maintenance requires a continuous source of osteoblasts throughout life. Its remodeling and regeneration during fracture repair is ensured by osteoprogenitor stem cells which are part of the stroma of the bone marrow (BM). Many investigators have reported that in cultured BM stromal cells there is a cell population that will differentiate along an osteogenic lineage if stimulated by the addition of osteogenic inducers, such as dexamethasone (dex), beta-glycerophosphate (beta-GP), transforming growth factor beta-1 (TGF-beta 1) and bone morphogenetic protein-2 (BMP-2). Here we report the effects of demineralized bone matrix (DBM) on the osteogenic differentiation of BM stromal cells in vitro, using morphological criteria, alkaline phosphatase (AP) activity, and calcium accumulation. DBM and DBM-conditioned medium (DBMcm) enhanced bone formation in the presence of dex and beta-GP, whereas DBM particles caused changes in the cell phenotype. Temporal expression of total and skeletal AP by BM stromal cells from 4-week-old rats showed a biphasic pattern enhanced by DBM and suggesting the presence of two cell populations. In one population, AP synthesis reaches a maximum during the first week in culture, following which cells either die or loose their ability to synthesize AP. A second, less abundant population begins to proliferate and synthesize AP during the second and third weeks. The synthesis of AP, which often decreases by the third week, can be maintained at high levels only if DBM is added to the cultures. BM stromal cells isolated from 24- and 48-week-old rats showed a decrease or loss of this biphasic AP expression pattern compared with cells isolated from 4-week-old rats. The addition of DBM to cultures derived from 24- and 48-week-old rats stimulated mostly the second cell population to synthesize AP, suggesting that DBM contains a factor(s) that acts on a specific bone marrow cell population by increasing the proliferation of active cells or inducing the differentiation of dormant cells.

Aging↗
PubMed1996

Regeneration of fin rays in teleosts: a histochemical, radioautographic, and ultrastructural study.

Regeneration followed partial amputation of the tail fin in three representative species of teleosts. A systematic study, using histochemical methods, radioautography and transmission electron microscopy, disclosed the essentials of the natural history of regeneration of the fin soft-rays. At about 24 hours, epidermal cells had completely covered the cut edge. By the second day an apical epidermal cap was established. Beneath this cap a blastema was formed by about three days after amputation. A collagenous lepidotrichial matrix had begun to develop by 4 days after excision. Actinotrichia were first detected in the regenerates at 5 days. During these processes, the basal lamina of the epidermis played an important morphogenetic role. The cells responsible for the regenerate underwent regressive changes after form and function had been restored.

Animals↗
PubMed1995

[Mercury in the hair of pregnant and lactating Chilean mothers].

Mercury-containing industrial waste has been released into the coastal waters of the Eighth Region of Chile for around two decades. This study, carried out from 1991 to 1993, sought to measure mercury concentrations in the hair of pregnant and lactating women from villages near the coast and in the interior of the region in order to examine the relationship between the concentration of mercury and seafood consumption. The survey questionnaire used in 1991 to determine seafood consumption did not ask about the frequency of consumption of fish, shellfish, and algae but only whether the women who were pregnant or breast-feeding consumed a minimum of one fish-based meal per week. The questionnaire used in 1992 and 1993 asked about the daily and weekly consumption of seafood in general (fish, shellfish, and algae). Spectrophotometry was used to determine the total mercury concentration in samples of 100 mg of hair from 153 pregnant and lactating women in 11 fishing villages of the Eighth Region where seafood is regularly consumed. None of the women had occupational exposure to mercury. Total mercury concentration was also determined in hair samples from a control group composed of 26 pregnant and lactating women from Pinto and El Carmen, villages in the interior of the same region where seafood was rarely eaten. The arithmetic mean of the total mercury concentration in hair was 1.81 mg/kg of body weight for the study group (standard deviation [SD] 1.52) and 0.42 mg/kg for the control group (SD 0.15)--a statistically significant difference (P < 0.01). Pairwise comparisons also revealed statistically significant differences (P < 0.05) between the mean for the interior group and the means for the women in the nine villages closest to the sources of the pollution, but not between the mean for the interior group and those for women in the two villages at the extreme north and south of the study zone, who lived farthest from the contaminated waters. The total mercury concentration in hair was significantly higher in women who indicated that they ate fish seven or more times per week; in those who said they ate fish, shellfish, or algae five or more times per week; and in those who had lived 20 or more years in their village. No statistically significant differences were found when the results were analyzed by age.

Adolescent↗
PubMed1994

Perinotochordal connective sheet of gilthead sea bream larvae (Sparus aurata, L.) affected by axial malformations: an histochemical and immunocytochemical study.

BACKGROUND: Spinal malformations in adult teleosts occur under natural conditions and, more frequently, in culture exploitations. Skeletal deformities are linked with dysfunctions in collagen metabolism. We studied axial deviations appearing in early larval stages of cultured sea bream (Sparus aurata, L.). METHODS: To evaluate connective tissue components of normal and lordotic fish we used histochemistry (alcian blue, picrosirius-polarization, clorhydric orcein, fuchsin resorcin), immunohistochemistry (anti-collagen I, II, III, and IV), and specific enzymatic digestions. The results were evaluated by semiquantitative methods. RESULTS: Lordosis appeared before a vertebral column was developed, thus affecting the only skeletal structure present in the animal body, the notochord. At this stage the animal depends on the vitelline sac and an inflated swim-bladder is missing. The region of the curvature showed strong alterations in the arrangement of the muscle bundles and irregularities in notochord and perinotochordal collagen sheet. Histochemical and immunocytochemical analysis of the perinotochordal sheet revealed the presence of type II collagen, non-sulfated glycosaminoglycans, and elastic fibers in normal and lordotic specimens. Low collagen-proteoglycan interactions occurred in lordotic animals. CONCLUSIONS: Lordosis in Sparus aurata originated during embryonic development and was characterized by disorganized connective tissue and muscle bundles. No major differences in connective tissue constituents were seen with respect to normal specimens.

Animals↗
PubMed1994

Skeletal deformities of the gilthead sea bream (Sparus aurata, L.): study of the subcommissural organ (SCO) and Reissner's fiber (RF).

A high incidence of lordotic curvatures has been detected in commercial cultures of Sparus aurata. We have studied juvenile and adult lordotic specimens to elucidate whether the subcommissural organ and its secretion, the Reissner's fiber, play any role in the development of this syndrome. Animals were X-radiographed and then the brain and spinal cord dissected out and processed for light microscopy. Adult lordotic fishes had a well developed swim-bladder whereas juvenile did not. The central canal of the spinal cord showed dramatic alterations, and an altered Reissner's fiber was always present. Our histochemical results suggested a hyperactivity of the subcommissural organ in lordotic fishes.

Aging↗
PubMed1994

Determination of total mercury in scalp hair of pregnant and nursing women resident in fishing villages in the Eighth Region of Chile.

Total mercury (Hg-T) content in scalp hair of 59 pregnant and nursing women-with normal to high fish and seafood consumption-resident in fishing villages distributed throughout the coastal zone of the Eighth Region of Chile, and of 7 pregnant and nursing women-with negligible or no fish and seafood consumption-resident in a town located inland (Pinto) in the same region, was determined. Hair samples were collected, washed and stored according to IAEA recommendations, and were wet-digested in sealed Pyrex ampoules prior to the determination of Hg-T by gold amalgamation cold-vapour atomic absorption spectrometry. The absolute detection limit was estimated as 0.13 +/- 0.01 ng Hg-T (3 x sigma B1). Accuracy and precision were assessed with the aid of various biological and environmental certified and standard reference materials including human hair, and were satisfactory for ppm and sub-ppm Hg-T. Instrumental neutron activation analysis was used as a reference method for external quality control. The Hg-T content in hair of the study group (2.06 +/- 1.45(8) mg/Kg) was significantly higher than that of the control group (0.43 +/- 0.18(4) mg/kg) (p = 0.0001). These results were characterized according to geographical location, fish and seafood consumption, age and residence period in the fishing village.

Adolescent↗
PubMed1992

Interactions of the lepidotrichial matrix components during tail fin regeneration in teleosts.

Teleost fin rays are able to regenerate, when they are cut, restoring the whole structure in a few weeks. Following the formation and growth of an apical blastema, deposition of lepidotrichial matrix occurs. We have histo and immunochemically analyzed the maturation process of the lepidotrichial hemisegment, pointing out the interactions between their components and likewise the temporal and spatial distribution of some extracellular matrix components during regeneration. Lepidotrichial matrix is rich in sulfated glycosaminoglycans (GAGs), most of which are forming proteoglycans. Collagen is abundant and it strongly interacts with GAGs, as the tissue differentiates. The use of specific digestions with papain and collagenase suggests that some mannose rich glycoproteins may be also implicated in lepidotrichial maturation before mineralization. In each hemisegment a central band (CB) can be observed. In spite of the histochemical similarities between the CB and the subepidermical basement membrane, neither collagen IV nor laminin are present. This CB could be the result of a transient transdifferentiation of the outer lepidotrichial synthesizing cells.

Animals↗
PubMed1991

Tail fin regeneration in teleosts: cell-extracellular matrix interaction in blastemal differentiation.

The fins of teleosts are appendices capable of regenerating by an epimorphic process that completely restores in a few days the original shape and size. After a partial amputation, the process that follows consists of: wound healing, blastema formation and cell differentiation to form a particular cell population responsible for the building of the different tissue elements. The present work deals with the histochemical and ultrastructural characterisation of the extracellular matrix (ECM) components in different blastemal regions. In the subepidermal space of the tip of a regenerating ray, two zones can be identified: the blastema proper (BP) that occupies the more apical region and extends proximally along the centre of the regenerating ray, and the actinotrichial blastemic region (ABR), located laterally to the former, about some micrometres beneath the tip and tightly related with the palisade of the actinotrichia. Hyaluronate is the more prominent glycosaminoglycan (GAG) in BP whereas sulphated GAGs and collagen are scarce in distal portions but they can be identified proximally. In the ABR a network composed mainly of sulphated GAGs and in part of collagen is developed. This network connects the actinotrichia of each palisade and extends around them. The significance of the ECM components in the morphogenetic processes of the regenerating rays is discussed. In addition a model for the synthesis of lepidotrichia by lepidotrichium-forming cells, differentiated from blastemal cells, is given.

Animals↗
PubMed1989

Elastoidin turn-over during tail fin regeneration in teleosts. A morphometric and radioautographic study.

During teleostean fin regeneration the actinotrichia, rods of a collagen-like protein, the elastoidin, are immersed in the blastema, maintaining their apical position. In this epimorphic event the latter fact might be achieved by either a cellular carriage or a continuous turn-over of these hyperpolimerized fibrils. By means of a 3H-proline pulse and radioautographic chase experiment of the isolated actinotrichia we have found a turn-over of collagen within the structure. From these and additional morphometric results, we present in this work an operational hypothesis of how gradually differentiating blastemal cells and an appropriately shaped basal lamina, can control the number and distribution of actinotrichia which might be under the balanced control of their synthesis and degradation.

Animals↗
PubMed1988

Sterilization regret among Puerto Rican women.

This study examined sterilization regret among Puerto Rican women with contraceptive tubal sterilizations (TS) using retrospective data from a population-based survey of women aged 15 to 49 years. Twenty-one percent of the 846 respondents expressed some regret, with 11% stating definite dissatisfaction with the decision. Factors associated with regret were young age at TS, absence of daughters, someone else making the decision to be sterilized, medical indications for TS, sterilization failure, and living with a new marital partner. There were no significant effects associated with the timing of sterilization, whether interval or postpartum, or with the type of last delivery. Other factors not independently associated with regret included years since TS, parity, education, and age at follow-up.

Adolescent↗
PubMed1984

Morphological evidence for the presence of two cell types in the ependyma of the subcommissural organ of the snake, Natrix maura.

Two different types of ependymal cells were found in the subcommissural organ (SCO) of Natrix maura. Most secretory cells showed morphological features resembling the general structure and ultrastructure of cells in the SCO of other vertebrates. This report describes a second population of cells lining a portion of the dorsal groove of the SCO. These cells were not selectively stained by chromalum-hematoxylin and, under the electron microscope, they were characterized by scarce surface differentiations, sparse apical cytoplasm and short basal processes. Flat, parallel cisternae of the rough endoplasmic reticulum produced vesicles that appeared to be transported to the well-developed Golgi apparatus. Dense secretory granules about 200 nm in diameter were found in the Golgi region. Similar granules were seen in the vicinity of the apical plasma membrane; some of them opened toward the ventricle. All these characteristics clearly differentiate this cell group from the other secretory cells lining the SCO laterally and ventrally.

Animals↗