American Journal of Anatomy

doi: 10.1002/aja.1001840401pmid: N/A

O'Rahilly, Ronan; Müller, Fabiola

doi: 10.1002/aja.1001840402pmid: 2756902

The length of each neuropore was measured in 23 human embryos of stages 10–12 (about 22–26 days), and the closure of the lips of the rostral neuropore was studied in 24 embryos of stage 11 (about 24 days), with particular reference to the terminal lip. Graphic reconstructions were prepared from two particularly suitable examples, and mitotic figures were plotted for one of these. The lengths of the rostral and caudal neuropores are basically similar, but the rostral opening closes 1 day earlier and more abruptly (within a few hours) than the caudal (which takes a day). Closure of the rostral neuropore in the human embryo is bidirectional, proceeding simultaneously from (1) midbrain and diencephalon 2 and (2) the telencephalic region adjacent to the chiasmatic plate. Species differences are emphasized. Closure at the terminal lip of the neuropore is by fusion of right and left neural folds, as occurs elsewhere during primary neurulation. The rostral end of the neural plate in the median plane is, in the human embryo, at the rostral limit of the chiasmatic plate. Histological differences, however, exist between closure at the terminal lip and that at the dorsal lip: the surface epithelium plays a more significant role at the terminal lip, and the seam is more visible and presumably stronger. In future anencephaly it has been found that fusion at the terminal lip may occur, although that at the dorsal lip is deficient.

Maluf, N. S. R.

doi: 10.1002/aja.1001840403pmid: 2756903

The manatee kidney is com posed of several closely apposed lobes. These are formed by cortical folds (plicae corticales) that completely isolate the medullae, except where the medullae of adjacent lobes are partially fused. The cortex is continuous; its folds usually are separated, but only partially, by interlobar septa ex tending from the renal capsule. The cortex makes up ∼57% of renal mass in adults and 68% in the calf. There are about 3 million glomeruli per kidney. The average is somewhat less than that expected of an adult eutherian of equal mass. The glomeruli, however, are large; they form 7.38%±1.33 of cortical mass, which is above that for at least ten unrelated adult eutherians. The number of glomeruli per gram of cortex is considerably greater in the calf than in the adult.

Sakakura, Yasunori; Fujiwara, Naoki; Nawa, Tokio

doi: 10.1002/aja.1001840404pmid: 2756904

Mandibular first molars in mice ranging in age from 18 days prenatal to 5 days postnatal were used for light and electron microscopic examinations of the enamel‐free area (EFA) during development of the occlusal cusp (mesiobuccal cusp). Notable morphological changes in the inner enamel epithelium and the cells of the stratum intermedium were observed. At prenatal age of 18 days, the inner enamel epithelium of the EFA (EFA epithelium) was composed of a layer of columnar cells and covered by the cells of the stratum intermedium. Two days after birth, the EFA epithelium was made up largely of preameloblasts, with mitochondria located in the proximal side of the cells toward the stratum intermedium. The cells of the stratum intermedium were irregularly shaped, with wide intercellular spaces between them. At a postnatal age of 3 days, most of the EFA epithelial cells resembled maturation‐stage ameloblasts, being short and columnar in shape and having nuclei located in their proximal side. Distal cell membranes were folded, and mitochondria were scattered throughout the cytoplasm. In 4‐day‐old mice, the EFA epithelium was found to be formed of short columnar or cuboidal cells with distinct intercellular spaces. The cells of the stratum intermedium could no longer be detected, and cells of the EFA epithelium could not be distinguished from those of the stellate reticulum. Odontoblasts of the EFA were arranged and polarized parallel to the basal lamina, and odontoblastic processes extended toward the cusp tip. The orientation of thin and thick collagen fibers within predentin and dentin was also parallel to the basal lamina. Even after dentin mineraliza tion, disrupted basal lamina and long, aperiodic, fine fibrils were found between the epithelium and the dentin. Following the disappearance of the basal lamina and fine fibrils, stippled material and crystals appeared on the dentin surface. The mineralized matrix, which x‐ray microanalytical energy peaks identified as containing calcium and phosphorus, was continuous with enamel in the distal slope of the cusp at the cusp tip. Thus, the inner enamel epithelium of the EFA differentiated into secretory cells capable of enamel‐like matrix formation. In conclusion, development of EFA in mouse molars seems to be a system suitable for use in studying both the involvement of extracellular matrix, including basal lamina constituents, in ameioblast differentiation, and the role of the cells of the stratum intermedium, together with the ameloblasts, in comprising a single functional unit responsible for enamel formation.

Dziadek, Marie; Mitrangas, Katherine

doi: 10.1002/aja.1001840405pmid: 2526998

We have studied susceptibility of basement membranes in a variety of tissues to solubility in guanidine hydrochloride and to proteolytic degradation by trypsin and thermolysin. Unfixed sections from embryonic and adult mouse tissues and the EHS tumor were subjected to sol vent buffers or digested with enzymes. The retention or disappearance of the basement‐membrane components nidogen, laminin, collagen IV, and heparan sulfate proteoglycan was subsequently assayed by immunofluorescence. Our data show ed that in all tissues nidogen was the most readily solubilized component and the most susceptible to proteolytic degradation. With few exceptions, nidogen in embryonic tissues was more susceptible to degradation than that in adult tissues, and this correlated well with the susceptibility of the other basement‐membrane components to be degraded. We conclude that basement membranes differ quite markedly in their solubility and their susceptibility to proteolytic degradation and that these properties reflect differences in their molecular structure.

Pisam, M.; Prunet, P.; Rambourg, A.

doi: 10.1002/aja.1001840406pmid: 2756905

Two types of mitochondria‐rich cells were identified in the gill epithelium of the freshwater‐adapted rainbow trout, Salmo gairdneri, after selective impregnation of their tubular system with reduced osmium. A first type consisted of large cells with a poorly developed and loosely anastomosed tubular system; thus, that resembled the chloride cells commonly encountered in the gill epithelium of freshwater‐adapted euryhaline fishes. A second type comprised smaller cells with an extensively developed and tightly anastomosed tubular system. These never reached the basal lamina of the gill epithelium and were adjacent to chloride cells, to which they were linked by shallow apical junctions (100‐200 nm); thus, they resembled accessory cells, which are currently found in the gill epithelium of sea‐water‐adapted fishes but are usually lacking in freshwater living fishes. Transfer of the freshwater‐adapted trout into seawater induced the proliferation of the tubular system in the chloride cells and the formation of lateral plasma membrane interdigitations between accessory cells and the apical portion of the chloride cells. The length of the apical junction sealing off this ex tended intercellular space was reduced to 20‐50 nm. The tubular system of the accessory cells was not modified. The extension of the tubular system in the chloride cells of the seawater‐adapted fishes indicated that, as in most euryhaline fishes, these cells have a role in the adaptation of the rainbow trout to seawater. In contrast, the function of the presumptive accessory cells in fresh water trout remains to be established.

Gilloteaux, Jacques; Pomerants, Boris; Kelly, Thomas R.

doi: 10.1002/aja.1001840407pmid: 2474241

The zinc iodide‐osmium tetroxide (ZIO) fixative‐staining method was used along with topographical ultrastructure to investigate cholecystectomized human gallbladders under light and electron microscopic techniques. This method delineated neuronal structures which may be involved in controlling the functions of the gallbladder epithelium. Three epithelial cell types were described in the surface epithelium: (1) Co lumnar clear cells; (2) dark, tuft osmiophilic cells; and (3) basal clear cells with electron‐dense granules and showing intense ZIOphilic staining properties. While mucous granules were delineated in the first two cell types, the columnar epithelial clear cells are of uncertain function(s) and content but are probably absorptive cells. The small basal clear cells displaying intense ZIOphilia are associated with intraepithelial nerve endings. These nerve structures may have a sensory and/or motor function(s); they were detected throughout the gallbladder epithelial lining and mucosa.

Michaels, Leslie; Soucek, Sava

doi: 10.1002/aja.1001840408pmid: 2756906

The development of the stratified squamous epithelium of the tympanic membrane and external canal was studied in 167 embryonic, fetal, and postnatal human ears. It originates as a tube derived from the epithelium of the fundus of the primary external canal (zone 1). The tube is composed of a thin, flat epithelium on the medial side (zone 2), continuous with a thicker one (zone 3) on the lateral side; zone 3 thereafter merges with the external epithelium of the primary external canal (zone 4). Proliferative activity, as indicated by a thickened epithelium, with rete ridges in later fetal life, is present mainly in zones 1 and 3.