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J Schechter

Publications and source records attributed to J Schechter.

At least 37 records · Page 2Linked to original sources
PubMed1992

Neural tissue within anterior pituitary tumors generated by oncogene expression in transgenic mice.

Pituitary tumorigenesis occurs in a transgenic line of mice, alpha-T7, which carries a hybrid transgene composed of the 5' flanking region of the human glycoprotein hormone alpha-subunit gene (1.8 kb) linked to the coding region of the SV40 T-antigen gene (alpha-Tag). Tumor foci were identified within the anterior pituitary of both male and female transgenic mice. In addition to a parenchyma with hypertrophied endocrine cells, mostly of the gonadotrope lineage, we here report the unexpected presence of neural tissue within the anterior pituitary, either as foci as large as 1.0 mm in diameter or greater, or in delicate bundles ramifying amongst the granulated parenchymal cells. Areas richest in neural tissue frequently were associated with tumor tissue composed of giant cells of three varieties, all with electron-lucent cytoplasm and similar organellar distribution including small secretory granules (80-160 nm diameter). In type I cells, the secretory granules were aligned at the plasma membrane; in type II cells, the secretory granules were distributed throughout the cytoplasm; type III cells formed colloid-filled follicles and their secretory granules rarely exceeded 100 nm diameter. These giant cells frequently had bizarre pleomorphic nuclei intensely immunopositive for T-antigen and cytoplasm which was lightly immunopositive for alpha-subunit, and immunopositive either for the LH-beta or TSH-beta subunits. Neural tissue contacted the normal granulated parenchymal cells directly, i.e., without a basal lamina or any connective tissue intervening, but only rarely formed synaptoid junctions with these granulated cells. Synaptoid junctions containing round, smooth vesicles, as well as dense core vesicles, were numerous between the neural processes themselves and between the neural tissue and the giant cells of the tumor tissue. These data suggest that in alpha-T7 transgenic mice the giant cells represent highly transformed gonadotropes or thyrotropes, and that a neurotrophic factor may be expressed by these transformed pituitary parenchymal cells.

Animals↗
PubMed1991

Pars distalis vasculature: Discovery Shuttle STS-29 rats compared to ground-based antiorthostatic rats.

The anterior pituitary glands of male, adult Long Evans rats carried 5 days in the Space Shuttle Discovery (STS-29) have been compared with two groups of ground-based controls. All of the animals were part of a study (SE82-08) into the effects of gravity versus a microgravity environment on fracture healing. All had sustained a right, mid-shaft fibular osteotomy. The duration of the study was 10 days, and animals in all groups were weight bearing for the 5 days prior to shuttle lift off. The three experimental groups consisted of four rats each: flight (F) and two ground-based control groups, weight bearing (WB) and suspended (S). The suspension group was in a Holton/Sweeney head-down suspension apparatus (antiorthostatic) for the final 5 days of the study. The anterior pituitary glands of F and WB rats were essentially identical. The vasculature and parenchymal cells appeared unaffected in both instances. However, the anterior pituitary glands of S rats were dramatically altered. The vasculature was widely expanded with proteinaceous deposition covering the lumenal endothelial surfaces, and entrapping numerous platelets and aggregates of red blood cells. Parenchymal cells were highly vacuolated, occasionally with membranous vacuoles, but most often revealing large, clear cytoplasmic zones unlined by any membranes. Whereas profiles of exocytosis were numerous in F rats, and present in WB rats, they were essentially absent in S rats. These results indicate that weightlessness over a 5-day flight period does not influence the structural integrity of the anterior pituitary gland and may in fact promote secretory granule release. However, the head-down tilt model, frequently used to study fracture repair under conditions that mimic weightlessness, has a profound impact on the vasculature of the anterior pituitary gland which then affects the structural and functional characteristics of the parenchymal cells.

Animals↗
PubMed1991

Changes in basic fibroblast growth factor coincident with estradiol-induced hyperplasia of the anterior pituitaries of Fischer 344 and Sprague-Dawley rats.

Adult female Fischer 344 (F344) and Sprague-Dawley (SD) rats were treated with estradiol via Silastic implants for 10 and 20 days. This treatment period in F344 rats is sufficient to produce dramatic hyperplasia of anterior pituitary lactotropes, activation of folliculo-stellate cells (FS) as phagocytes, and reorganization of the blood supply, i.e. hemorrhagic lakes and arteriogenesis from vessels in the adjacent meninges. Estradiol-treated SD rats do not demonstrate a comparable response. We now report intense focal concentrations of cells immunopositive for basic fibroblast growth factor (FGF) in estradiol-treated F344 rats predominantly near the posterolateral edge of the anterior pituitary, a zone rich in gonadotropes and lactotropes. Immunostaining for FGF, by both light and electron microscopy, revealed that the immunopositive cells were gonadotropes, and that the immunoprecipitate was cytosolic and was most abundant in the cytosol facing the capillaries. Immunostaining for extracellular matrix-associated FGF also revealed foci of positivity at the postero-lateral edge. Estradiol-treated SD rats did not reveal comparable localization for FGF. Morphological analysis and immunolocalization of S-100 protein, a marker for FS cells, revealed that the periphery of the anterior pituitary of estradiol-treated F344 rats included numerous disrupted gonadotropes and, furthermore, was largely devoid of FS cells. This zone was more intact in control F344 rats, but lacked FS cells. The peripheral parenchyma of control and estradiol-treated SD rats was intact compared to that of F344 rats and consistently included FS cells. These results suggest that disruptions of gonadotropes at the pituitary periphery may release FGF, which could then stimulate angiogenesis from blood vessels within the adjacent meninges. The resultant systemic blood supply would stimulate lactotrope hypertrophy and hyperplasia. Since FS cells are known phagocytes within the anterior pituitary, their absence from the periphery of F344 rats may intensify or prolong the effect of the peripherally released FGF.

Animals↗
PubMed1990

Persistent Schistosoma mansoni infection in Yemeni immigrants to Israel.

Following sporadic reports on persistent Schistosoma mansoni (S.m) infections in Israelis of Yemeni origin, we systematically surveyed a group of 129 individuals who immigrated to Israel 38 years ago. Physical examination was uneventful in all members of the study group. A single stool examination revealed S.m eggs in 15 of 129 subjects (12%). Specific anti-S.m. IgE was detected in the sera of 48 individuals (37%). Among the 15 egg-positives, 14 had specific IgE (sensitivity 93.3%), but only 80 of the 114 egg-negatives were also negative for specific IgE (specificity 70%). This specific IgE positivity among egg-negatives in the study group (34/114) and its complete absence from two control groups, one of them comprising Yemenites born in Israel, suggest either an S.m infection with low egg output stemming from a low worm burden or low fecundity of senescent worms, or occult infections. Since the S.m infections could not have been contracted in Israel, our findings point to inordinately persistent infections in the members of our study group, and incidentally also to the diagnostic usefulness of specific IgE testing in such cases.

Adult↗