Arnold Tamarin

Myoepithelium of the rat submaxillary gland.

Myoepithelium in the rat submaxillary gland is associated exclusively with acini and intercalated ducts. Acinar myoepithelial cells (MEC) arborize in a stellate pattern and constitute 12% of the acinar volume. Intercalated duct MEC are longitudinally arranged over the ductal epithelium and constitute 40% of the duct wall volume. Myoepithelium makes up 9% of the total intralobular parenchyma. MEC lie within the periparenchymal basement membrane and are “attached” to acinar or ductal epithelium by a small number of desmosomes. MEC plasma membranes have relatively smooth contours, and no substantial interfolding with the membranes of neighboring cells occurs. Mitochondria, ergastoplasm, and other organelles are sparse and mainly are concentrated within circumscribed juxtanuclear zones. Minute vesicles and surface caveoli occur on the stromal side of the cell but are essentially absent from the parenchymal side. Streams of parallel filaments traverse a large portion of the cytoplasm. Because of close packing they form dense zones in many areas. These filaments have a mean diameter of 64 A (SE ±3). Nerves do not contact these MEC, but unmyelinated axons skirt within 0.1 μ of their plasma membranes. It is concluded that rat submaxillary gland MEC are similar to visceral smooth muscle cells and could efficiently serve as an adjunctive mechanism in the egestive phase of secretion.

Submaxillary gland recovery from obstruction. I. Overall changes and electron microscopic alterations of granular duct cells

Rat submaxillary glands were ligated for 31 days and then the ligatures were removed. Groups of animals were killed after 31 days of ligation and 7, 15, 30, 60, 120, and 180 days after the ligatures were removed. Overall gland recovery was studied by light microscopy in 1.5 μ sections, while the fine-structure details of recovery in the exocrine cells of the granular duct were studied by electron microscopy. There is a pronounced morphologic similarity of glands ligated for 31 days to immature glands of neonatal rats. However, evidence of parenchymal cell death or mitotic activity is extremely rare and therefore gland recovery is the result of cell recovery, not the result of de novo cell differentiation. Evidence of secretory activity appears in acinar cells before it does in granular ducts. Prior to 30 days after unligation granular duct cells contain no secretion granules, almost no RER, and very small Golgi areas. After 30 days, small dense granules appear in the apical cytoplasm, and there is a slight increase of RER. At 120 days, a small number of these cells appear mature, i.e., they are full of large secretion granules and contain well formed RER and Golgi patterns. By 180 days the gland appears essentially normal but there are still fewer mature granular duct cells than in the control.

Submaxillary gland recovery from obstruction. II. Electron microscopic alterations of acinar cells.

The recovery of secretory activity by acinar cells was studied in rat submaxillary glands after the removal of ligatures following 31 days of obstruction. Evidence of cell death or mitotic activity is extremely rare, indicating that the observed changes occur in the original cell population and that recovery is not dependent on de novo cell differentiation. The ultrastructural character of secretion granules changes from very dense, sometimes crystalloid, forms early in recovery, to lighter heterogeneous granules, to granules with distinct ropelike aggregations of secretory material, and finally to the characteristic mature granules containing a sparse uniform distribution of filaments. The filamentous secretory product of later time periods is demonstrated in Golgi saccules, in granules, and in luminal spaces. The filaments are about 80 A wide. RER and Golgi cisternae undergo complementary alterations: they are sparse in early periods when few granules are present and increase as granules increase and become more mature. In an early phase of recovery, the lumina of acini are filled with dense material which has membranelike characteristics.

An ultrastructural study of the byssal thread forming system in Mytilus.

This study demonstrates the submicroscopic morphology of the three cell types involved with the formation of byssus threads in Mytilus californianus . (1) Collagen gland cells have unique ellipsoid secretion granules with parallel internal periodic filaments. (2) Phenol gland cells contain dense homogenous spherical secretion granules. (3) Enzyme gland cells have heterogeneous secretion granules. The Golgi areas and condensing vacuoles of the three cell types also differ from one another. All three cell types have long cell processes through which the granules are conducted to their sites of egestion. These processes have complex multiple infolded plasma membranes, microtubules, and terminal elongated microvilli.

The egg capsule of the muricid gastropod Urosalpinx cinerea: an integrated study of the wall by ordinary light, polarized light, and electron microscopy

The wall of the vase-shaped egg capsule of the snail Urosalpinx cinerea represents a specialized exocrine product. It has a species-specific shape and a precise architectural organization. It consists of four laminae, three of which are anisotropic but with different patterns in the transverse as compared to the longitudinal plane. The third lamina is completely isotropic. Ultrastructurally, the birefringent matrix reveals a precise periodicity of alternating light (290 A) and dark (240 A) zones, each subdivided into five sub-zone striae. The third lamina and the basal core consists of dispersed filaments (50 A wide) which, in some places aggregate into characteristic periodic fibers.

Early Development of Oral, Olfactory and Adenohypophyseal Structures of Agnathans and Its Evolutionary Implications

Ideas concerning the earliest evolution of the vertebrate head must be based on paleontological evidence as well as on adult and embryonic morphology of present day agnathans. Unfortunately, paleontological evidence for evolution of certain soft structures of the head is not really available, so that embryonic development of such structures is often the basis for speculation in this field (e.g. Stensio, 1968). Here, we would like to address one phase of this problem; the formation of the agnathan adenohypophysis and some contiguous structures from the nasopharyngeal canal, and the presumed homology of the nasopharyngeal canal with the adenohypophyseal anlage, or Rathke’s pouch, of higher vertebrates.

An ultrastructural study of byssus stem formation in Mytilus californianus

In Mytilus californianus, root lamellae of the byssus stem are formed by two morphologically distinct exocrine cell types. Type 1 cells contain large ellipsoid granules which are ultrastructurally identical to those of the collagen gland associated with byssus thread formation: these granules are secreted only at the base of the stem generator. Type 2 cells contain small cylindroid granules which are secreted only from the lateral surfaces of generator septa. The resultant matrix is biphasic because the two secretions are incompletely mixed. Lamellar sheets of matrix are propelled outward by the action of cilia and are molded into a cylinder at the neck region of the stem. However, the stem retains a lamellar pattern.

A longitudinal study of parotid secretory kinematics by cinemicrography and computer analysis.

SummaryThe kinematic responses of parotid gland acini to isoproterenol were studied in vitro by timelapse cinemicrography. It was shown that once secretion begins, granule depletion accelerates to a maximum rate in 8–10 min, continues at a steady rate for 5–8 min and then slows, depletion becoming essentially complete 25–30 min after stimulation.The continuum of morphologic change manifested by the acinar lumen during secretion was quantified by computer analysis of sequential cine-frames representing a time resolution of 0.1 min. Interpretation of seventh-order and eleventh-order polynominal nonlinear least squares trend curves shows that the lumen enlarges from an initial cross-sectional area of ≈23μm2 to a maximum of ≈96μm2 at 14.9 min. The shape of these curves suggests that after an initial partial enlargement the lumen shrinks (or remains steady) before climbing to the maximum. The basic pattern resembles distortion curves characteristic of two-phase viscoelastic compliance systems. It is also shown that luminal plasma membranes undergo a very active ebb and flow during the egestive phase of secretion.

Morphometrics of living specimens. A methodology for the quantitative three‐dimensional study of growing microscopic embryos

A methodology is described which permits quantitative three‐dimensional studies of growing microscopic (and substantially transparent) animals to be made. The methodology has been applied in a limited way to the study of blastula formation in sand dollar embryos. A preliminary analysis has been made of the errors likely to arise (see Appendix).

THE EFFECT OF INANITION ON THE SUBMANDIBULAR SALIVARY GLANDS AND EXOCRINE PANCREAS OF THE RAT

The object of this study was to determine the relative reactivity of three different exocrine organs of the rat to the effects of total starvation. The three organs are the major sublingual gland (SL), the submaxillary gland (SM), and the exocrine pancreas (P). The sublingual gland is mainly a mucus-producing organ; the pancreas is a digestive enzyme-producing organ showing no mucinous moiety; the submaxillary gland has characteristics of both, for it can be shown that mucinous as well as enzymatic components are produced.