Robert E. Coalson

Localization of Carboxyl Groups in Gastric Mucosa as Possible Sites of Gastrin

SummaryHuman and pig gastrins contain a sequence of five consecutive glutamic acid residues. An attempt was made to localize gastrin using methods known or assumed to operate on a carboxyl mechanism. General methods for acidic groups were combined with selective blocking (methylation) and unblocking (saponification) methods to increase COOH specificity. Epithelial cells with weakly metachromatic granules could be identified in untreated sections stained with toluidine blue (pH 5). After prolonged methylation and saponification, the same and previously obscured cells were moderately to intensely metachromatic, this residual basophilia attributable to weak COOH groups. Specifically marked metachromatic cells were iron-positive after colloidal iron staining, but were delineated easily only after methylation-saponification. Metachromatic cells were also clearly demonstrated by the carboxyl method of Barrnett and Seligman and by silver impregnation (pH 5). The granular metachromatic cell demonstrated by these methods contains significant amounts of a weakly acidic component which the Barrnett-Seligman reaction indicates to be glutamic acid. Comparable staining results were obtained with gastrin producing Zollinger-Ellison islet cell adenomas. It is postulated that the COOH-rich substance is gastrin or gastrin precursor and that the metachromatic cell is responsible for its production.

Oral Cavity and Development of the Branchial Apparatus

The region of the future oral cavity is indicated by the position of the prochordal plate in bilaminar and trilaminar embryos during the second and third weeks of development. (The prochordal plate is a circumscribed area of columnar endodermal cells located in the cephalic part of the yolk sac roof; it is roughly coextensive with the endodermal layer of the oropharyngeal membrane. The prochordal plate is thought to play an important organizing role in initiating development of the forebrain and heart.) Before body fold development (head, tail, lateral) converts the flattened embryonic plate (trilaminar embryo) into the tubular configuration of the definitive organism, the prochordal plate (oropharyngeal membrane) is located in the same plane, and cranial to the notochord. Head fold formation is especially important in bringing the future oral cavity into its definitive anterior position while producing the floor of the foregut and at the same time establishing the definitive relationships of the developing heart, foregut and their associated coelomic structures.

Differentiation of the Branchial Apparatus

Skeletal Muscle Fibers: The skeletal muscle fibers originating from segmented (somites) and unsegmented (lateral plate) mesoderm are indistinguishable morphologically but they can be distinguished on the basis of their efferent (motor) innervation.