American Journal of Anatomy

doi: 10.1002/aja.1001550401pmid: N/A

Lacy, Eric R.; Schmidt‐Nielsen, Bodil

doi: 10.1002/aja.1001550402pmid: 484509

The renal pelvis of the hamster has been studied by light microscopy (epoxy resin sections), transmission electron microscopy, and morphometric analysis of electron micrographs. Three morphologically distinct epithelia line the pelvis, and each covers a different zone of the kidney. A thin epithelium covering the outer medulla (OM) consists of two cell types: (1) granular cells are most numerous and have apically positioned granules which stain intensely with toluidine blue, are membrane‐bound, and contain a fine particulate matter that stains light grey to black in electron micrographs. (2) Basal cells do not have granules, are confined to the basal lamina region, and do not reach the mucosal epithelial surface. The inner medulla (IM) is covered by a pelvic epithelium morphologically similar to collecting duct epithelium of IM. Some cells in this portion of the pelvic epithelium (IM) stain intensely dark with toluidine blue, osmium tetroxide, lead, and uranyl acetate. Transitional epithelium, which separates cortex (C) from pelvic urine, has an asymmetric luminal plasma membrane and discoid vesicles, each of which is similar to those previously observed in mammalian ureter and urinary bladder epithelia. Based on morphological comparisons with other epithelia, the IM and OM pelvic epithelia would appear permeable to solutes and/or water, while the transitional epithelium covering the C appears relatively impermeable. It would also appear that the exchange of solutes and water between pelvic urine and OM would involve capillaries, primarily, since morphometric analysis showed that both fenestrated and continuous capillaries of the OM were extremely abundant ( > 60% of OM pelvic surface area) just under the thin pelvic epithelium.

Kaufman, Matthew

doi: 10.1002/aja.1001550403pmid: 484510

The overall pattern of cephalic neurulation and the concomitant early development of the optic vesicles in mouse embryos were examined by scanning electron microscopy. Paraffin‐sectioned specimens were also examined.

Schoenwolf, Gary C.

doi: 10.1002/aja.1001550404pmid: 484511

Neuropore closure was studied in chick embryos by light and electron microscopy. Surface ectoderm reflects over the crests of the neural folds at all craniocaudal levels, merging with the neural ectoderm lining the neural groove. Apices of surface ectodermal cells have an essentially identical morphology prior to approximation of folds, both within the presumptive fusion sites and more laterally. Cells of these areas have slightly convex profiles exhibiting few cellular protrusions. Each neural fold contains a superficial half, composed of neural ectoderm covered by surface ectoderm, and a deep half consisting entirely of neural ectoderm. Initial contact between folds usually occurs near the junction between these halves in cranial regions, but is restricted primarily to surface ectoderm at caudal levels. Subsequent fusion of folds at all levels involves both ectodermal layers. Cellular protrusions and small, morphologically unspecialized intercellular junctions often interconnect cells of apposed folds in areas undergoing fusion. The anterior neuropore closes at stages 10–11, but fusion of folds in this region is not completed until stages 13–14. Fusion occurs dorsoventrally in this area and is more advanced internally than externally. Numerous pleomorphic inclusions and a few apparently necrotic cells are present in areas bordering the anterior neuropore. The posterior neuropore closes at stages 12–13 and fusion is completed in this region during stages 13–14. The caudal end of the posterior neuropore closes dorsal to the developing tail bud. Several morphological features of this closure may at least partially account for the high susceptibility to myeloschisis localized specifically at caudal spinal cord levels.

Felten, David L.; Crutcher, Keith A.

doi: 10.1002/aja.1001550405pmid: 114041

A fluorescence histochemical and electron microscopic study of the monoaminergic cell groups in the squirrel monkey and Rhesus monkey brains has revealed the direct apposition of blood vessels to perikarya and dendrites of monoaminergic neurons. Capillaries and small arterioles or venules, ranging from 8–50 μm in diameter, showed perikarya and dendrites abutting the basement membrane without evidence of glial interposition. This neuronal‐vascular relationship was present in 20% to 30% of the small vessels in the serotonergic nuclei raphe dorsalis and centralis superior and in the nor‐adrenergic locus coeruleus. Such contacts were clearly present but observed less frequently in the dopaminergic substantia nigra pars compacta and in the serotonergic nuclei raphe obscurus, pallidus, magnus, and pontis. We postulate that monoamine‐containing neurons apposed to blood vessels in certain regions of the brain may be influenced directly by hormones or other substances in blood.

Maier, Alfred

doi: 10.1002/aja.1001550406pmid: 158306

The occurrence and distribution of muscle spindles was studied in histochemically and conventionally stained serial cross sections of 6‐week‐old and adult rat masticatory and suprahyoid muscles. Spindles were present in moderate to large numbers in jaw closers, but they were absent in jaw openers and two of four muscles of an accessory suprahyoid group. In jaw closers, 67% or more of the total spindle population was concentrated relatively distant from the temporomandibular joint, in muscle portions which contained large numbers of extrafusal fibers reacting strongly for oxidative enzymes. Because of their location, spindles in these portions should be stretched more and, subsequently, should respond with a greater afferent discharge at any given muscle length than spindles situated nearer to the joint. Spindles in jaw closers, especially the medial pterygoid and deep masseter, often occurred in clusters and complex forms near the terminal branching of intramuscular nerve trunks. No such concentrations were seen in the two muscles of the accessory suprahyoid group that had spindles. The association in jaw closers of spindles with extrafusal fibers high in oxidative enzyme activity is consistent with the view that spindles are the sensory component of a reflex system that recruits these fibers for finely‐graded contractions in response to small internal length‐changes of the muscle (Botterman et al., 1978); however, in jaw openers and two muscles of the accessory suprahyoid group, the absence of spindles, coupled with the presence of large populations of extrafusal fibers high in oxidative enzyme activity, is not easily reconciled with this concept.

Hoff, Martin B.; Chang, William W. L.

doi: 10.1002/aja.1001550407pmid: 573548

The regulatory role of estrogen on cell population kinetics in the descending colon was studied in intact female and ovariectomized mice. In the colonic crypts from intact mice, the crypt size (the number of epithelial cells per crypt column) and the proliferative activity of epithelial cells fluctuated slightly during the estrous cycle. Peak cellularity per crypt column was exhibited during estrus and early diestrus, whereas peaks in labeling index were seen during estrus and late metestrus. While the population size of mucous cells showed a minimal variation, the number of proliferative vacuolated cells per crypt column varied inversely with that of differentiated columnar cells during estrous cycle. The vacuolated cells were increased in number in the preovulatory phase and the columnar cells in the postovulatory phase.