摘要:

AbstractConsiderable evidence indicates that the pituitary‐gonadal axis is active in the fetus, but little is known about the relative times in development when the brain begins to secrete gonadotropin‐releasing hormone (GnRH) and the hypophysis begins to secrete gonadotropin. The objective was to correlate the time of appearance of GnRH in the median eminence and organum vasculosum of the lamina terminalis (OVLT) with differentiation of LH‐gonadotropes in the hypophysis of the fetal mouse by means of immunocytochemistry. Mice were studied at 15, 16, 17 and 19 days of gestation with the peroxidase‐antiperoxidase (PAP) method of Sternberger. GnRH was first detected at 17 days of gestation in presumptive axons and axon terminals located adjacent to the superficial portal capillaries near the surface of the median eminence and close to the capillaries of the OVLT. LH‐gonadotropes also were found initially at 17 days of gestation. They were prominent in the ventral half of the pars distalis. Most of these cells were ovoid or slightly angular, and almost all abutted one of the numerous sinusoidal capillaries present at this age in development. The number and staining intensity of both LH‐gonadotropes and GnRH foci increased by 19 days. The close temporal relationship between the developmental appearance of GnRH and its target cell, the gonadotrope, provides further evidence that the potential for neuroendocrine control of gonadotropin secretion exists in the fetal mouse as early as 17 days o

ISSN:0002-9106    

DOI:10.1002/aja.1001540102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractThe nexus of the anterior byssus retractor muscle (ABRM) ofMytilushas been observed with freeze‐fracture techniques. Pits appear in the EF face and particles in the PF face, designating it as an A‐type nexus. Under control conditions (lanthanum‐free) the center‐to‐center spacing of pits and particles ranged from 14.0 nm to 15.5 nm. When lanthanum chloride (5 mM) was used in incubation media before fixation and glycerination, marked changes in the nexal membrane were observed. These changes involved close packing and long‐range ordering of pits in the EF face, as shown by optical diffraction. In the presence of lanthanum the center‐to‐center spacing of the pits was 11.7 nm, while the particles remained at a spacing of 15.0 nm. From this we conclude that specific agents can alter the array of pits and particles in a nexus

ISSN:0002-9106    

DOI:10.1002/aja.1001540103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractThe development of cell types and regional differences in the rat epididymis was studied in specimens of the initial, middle and terminal segments prepared at intervals between birth and postnatal day 94. The development of the epididymis was divided into three phases: (1) an undifferentiated period; (2) a period of differentiation, and (3) a phase of expansion. During the undifferentiated period, from birth to day 15, the epithelial cells had a uniform appearance. Halo cells, which are believed to be migratory leukocytes, appeared on day 14. The period of differentiation extended from day 16 to day 44. Slender, densely staining cells, termed narrow cells, appeared in the epithelium of all three segments on day 16, constituting the first evidence of differentiation of cell types in the epididymal epithelium per se. In addition to their shape and apical nuclei, the narrow cells were distinguished from other epithelial cells by the presence of cup‐shaped apical vacuoles and mitochondria with tubular cristae. Principal cells and basal cells were identified on day 28, which also marked the first distinction of differences in epithelial height among the different segments. Narrow cells persisted into the adult in the initial segment. In the middle and terminal segments, however, narrow cells disappeared by day 35, when light cells made their appearance. The major event of the period of expansion, from day 45 to 3 months, was the appearance of sperm in the lumen between days 45 and 52. A model for differentiation of cell types in the epididymis is proposed and it is suggested that narrow cells are precursors to light cells in the middle and terminal segments. The development of ultrastructural features of adult cell types preceded the appearance of sperm in the lume

ISSN:0002-9106    

DOI:10.1002/aja.1001540104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractThe opisthonephric kidney of larval anadromous sea lamprey,Petromyzon marinusL., undergoes a programmed regression during metamorphosis. Degeneration is initiated in the anterior end of each kidney and progresses posteriorly until the kidneys are reduced to short, pigmented strands by the end of metamorphosis.The first sign of degeneration in both the epithelium of the renal corpuscles and the tubules is a folding of the basal lamina. Autolysis then occurs throughout the entire epithelium of the nephron with the gradual accumulation of larger and greater numbers of acid phosphatase‐containing autophagic vacuoles, cytosomes, and myelin figures. Cytoplasmic debris and electron‐dense material accumulates in the tubular lumina and in the urinary space. Although no definitive evidence is provided for the method of removal of the tubular epithelium, macrophages play a large part in the phagocytosis of the components of the renal corpuscle. Mesangial cells appear to engulf debris from the capillaries while a second type of macrophage is involved in the destruction of podocytes and parietal epithelial cells. The method of programmed degeneration of the renal corpuscle closely resembles descriptions of the mammalian renal corpuscle in diseased conditions. The sole surviving element of the degeneration of the entire nephron epithelium is a pleated basal lamina.The regressing larval opisthonephros has potential as an alternative system for studying a normal developmental pattern such as tissue regress

ISSN:0002-9106    

DOI:10.1002/aja.1001540105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractThe sacculi of five species of catfishes were studied by transmission and scanning electron microscopy. In four species, the sagitta exhibited a multifluted anterior part and a tapered posterior part; inCorydoras aeneus, however, the fluted part was absent, and a vertical component extended dorsally to terminate near the opening of the transverse canal. In all species, the otoliths had a laminar structure. An otolithic membrane was present, and hair cell bundles projected into cavities on the macular surface of the membrane. Attachments of the otolithic membrane to the neuroepithelium included short extensions of the membrane to the tallest components of the hair cell bundles of the peripheral cells and more delicate connections to the kinocilium and taller stereocilia of central cells; in addition, attachments to the microvilli of supporting cells were present. In both hair cells and supporting cells single microtubules and bundles of microtubules were present; the bundles had an orderly arrangement and were associated with cytoplasmic densities surrounding the desmosomes. The hair cells were innervated by both afferent and efferent nerve endings. Studies of the polarization of the hair cells in all species (exceptC. aeneus) showed that there was a single longitudinal axis that divided dorsally polarized cells from those oriented ventrally. InDoras spinosissimusandBunocephalus bicolor, an additional line of polarization was evident in a small area in the anterior part of the macula; therefore, in these forms there was a double bipolar orientation.

ISSN:0002-9106    

DOI:10.1002/aja.1001540106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractUltrastructural features of the tubular nephron of the garter snake, with special reference to modifications for conservation of water, were studied using transmission electron microscopy, freeze‐fracture and tracer experiments. Although a nephric loop (loop of Henle) is lacking, the tubules appear to be structurally well adapted for efficient ion and water reabsorption. The most prominent features are well developed microvilli in the proximal tubule and elaborate lateral folds, particularly in the distal tubule and collecting ducts. The latter structures are highly interdigitated, creating complex intercellular channels, perhaps facilitating transepithelial fluid transport. Only the proximal tubule actively absorbs and degrades protein tracers from the lumen. The cells of the collecting duct secrete mucus which may precipitate and bind urate salts in the lumen. This may be significant in the excretion of these salts, a process which combines maximal removal of salts and nitrogenous wastes with minimal loss of wate

ISSN:0002-9106    

DOI:10.1002/aja.1001540107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001540101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY