Robert Earle Waterman

Formation and perforation of closing plates in the chick embryo

The morphology of the closing plates between adjacent pharyngeal arches was examined in chick embryos between stages 11 and 21 (HamburgerHamilton). Each closing plate is formed by apposition between the basal surfaces of portions of the pharyngeal pouch endoderm and the ectoderm of the overlying pharyngeal cleft. Initial contact between ectoderm and endoderm occurs at several small points which are separated by regions containing mesenchymal cells and extracellular material. Contact between the opposed epithelia is made by extension of cellular processes through the intervening basal laminae and extracellular space. Endodermal and ectodermal cells then interdigitate to create a cellular layer which rapidly thins. The interposed extracellular material is sequestered into small pools as cellular interdigitation proceeds. Perforations form through certain regions of closing plates 1–3 and persist during the stages studied. Small slit‐like depressions appear between cells of the closing plate just prior to perforation. The initial perforations enlarge until they are separated only by thin cellular strands. These strands presumably rupture, leaving small cellular accumulations which persist for a short time marking the junction between ectoderm and endoderm along the walls of adjacent pharyngeal arches. Clear evidence of cell degeneration is rare. These results suggest that cellular reorganization, rather than cell death, is a major mechanism of initial perforation.

Early effects of thyrotropin on the surface morphology of thyroid cells in culture

The surfaces of ovine thyroid cells in monolayer culture respond characteristically to the addition of thyrotropin (TSH) to the medium. Pseudopodia and microvilli appear within minutes of TSH addition and the cell surface assumes a rough texture. The response is maximal between 15 and 30 min after stimulation. This action of TSH is mimicked by N6, O2-dibutyryl adenosine 3′,5′-cyclic monophosphate and by prostaglandin E1 and to a lesser degree by cyclic AMP. TSH action is not mimicked by cyclic GMP, dibutyryl cyclic GMP, or by the protein hormones: human chorionic gonadotropin, ACTH, insulin, or prolactin. Surface activity, including bleb formation which is maximal at Day 2, has subsided by the fourth day after TSH addition and the surface appears smooth and flat, thus resembling nonstimulated cultures. The response to thyrotropin is greatly diminished in the presence of Li+, cycloheximide, actinomycin D, vinblastine, and cytochalasin B. The cell surface response of thyroid cells in culture is consistent with the acute responses of the intact gland to TSH such as endocytosis and colloid droplet formation.

Xanthogranulomatous abscess of a mullerian duct remnant. A rare lesion of the rectum and anus

A rare example of xanthogranulomatous inflammatory mass and abscess of a Mullerian duct remnant involving the anorectal area is reported. A barium enema showed a bilobed precoccygeal mass of moderate size involving the posterior aspect of the distal rectum. Computed tomography (CT) showed two nonfatty, round masses, one of which contained a small central cystic area. The other mass had a homogeneous appearance and was believed to be in the wall of the rectum. The pathologic specimen showed organizing abscesses and a chronic xanthogranulomatous inflammation in tissue compatible with urogenital tissue, presumably a Mullerian duct remnant. This is the first documented report of anorectal xanthogranulomatous abscess in a Mullerian duct remnant with radiologic findings and histopathologic correlation. Though rare, this lesion should be considered in the differential diagnosis of extrinsic and intramural rectal masses seen on barium enema and CT examinations.