摘要:

AbstractCommon carp (Cyprinus carpio) initially weighing about 100 g were fed a low‐magnesium diet for 17 weeks. The fish survived this treatment and had a healthy appearance. However, the fish became hypomagnesemic and their growth rate decreased. The bone sodium concentration increased and the magnesium concentration decreased. It thus appears that in carp, under dietary magnesium deficiency, magnesium is mobilized from internal stores and that magnesium in the bone mineral is replaced by sodium. Low‐magnesium fed carp further showed a decreased branchial Na+/K+‐ATPase specific as well as total activity. Unexpectedly, the opercular chloride cell density increased. We tentatively conclude that more and new chloride cells with a lower Na+/K+‐ATPase content develop during this treatment. We further conclude that adult carp require dietary magnesium for the maintenance of their magnesium balance as well as for the proper functioning of branchial ionoregulatory mechanisms. Low‐magnesium fed carp do not acclimate but appear to tolerate a dietary magnesium deficiency. © 1992 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402640302

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

年代:1992

数据来源: WILEY

摘要:

AbstractBehavioral observations demonstrate that bilateral deafferentation of the hypoglossal nerves in the marine toad (Bufo marinus) prevents mouth opening during feeding. In the present study, we used high‐speed videography, electromyography (EMG), deafferentation, muscle stimulation, and extracellular recordings from the trigeminal nerve to investigate the mechanism by which sensory feedback from the tongue controls the jaw muscles of toads. Our results show that sensory feedback from the tongue enters the brain through the hypoglossal nerve during normal feeding. This feedback appears to inhibit both tonic and phasic activity of the jaw levators. Hypoglossal feedback apparently functions to coordinate tongue protraction and mouth opening during feeding. Among anurans, the primitive condition is the absence of a highly protrusible tongue and the absence of a hypoglossal sensory feedback system. The hypoglossal feedback system evolved in parallel with the acquisition of a highly protrusible tongue in toads and their relatives. © 1992 Wiley‐Liss,

ISSN:0022-104X    

DOI:10.1002/jez.1402640303

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis study determined whether uterine tissue of alligators produce prostaglandins F2α(PGF) and E2(PGE) and examined the relationship between secretion of prostaglandins and reproductive stage. Uterine tissue from alligators (n = 8) was incubated in the presence of arachidonic acid (AA), banamine (B), arginine vasotocin (AVT), AA + AVT or incubation medium alone. Aliquots of the culture medium were collected at 0, 30, 60, and 90 min and at 24 h of culture. Secretion of PGF was not detected from uterine tissue collected from gravid alligators, whereas non‐gravid and post‐oviposition alligators secreted appreciable amounts of PGF. The addition of AA to uterine tissue from non‐gravid alligators increased secretion of PGF (P<0.05), whereas AVT had no effect. Addition of AA or AVT decreased secretion of PGF and PGE by uterine tissue from post‐oviposition alligators (P<0.05). Secretion of PGF and PGE by uterine tissue was greater from post‐oviposition than from non‐gravid and gravid alligators. Secretion of PGE from uterine tissue of non‐gravid alligators was not altered by AA or AVT. However, secretion of PGE from uterine tissue from gravid alligators increased in the presence of AVT and decreased when incubated with AA + AVT. Arachidonic acid alone did not significantly alter secretion of PGE in this group. This study demonstrated that uteri of alligators secrete PGF and PGE and production is related to reproductive status. © 1992

ISSN:0022-104X    

DOI:10.1002/jez.1402640304

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn toadsXenopus laevisliving at 11° (winter), the microtubular density of 4‐μm myelinated axons of lumbosacral nerves was assessed with the electron microscope. In controls, the density was 11.2 microtubules/μm2. In nerves incubated at 0°, microtubules decreased following a simple exponential curve with a half time of 4.7 min (k = 0.149 min−1); residual microtubules were 4.5%. After rewarming, the full complement of microtubules reappeared within 60 min. In steady state, the microtubular density exhibited a linear relationship with temperature (range: 0–22°;slope 0.94 microtubules/μm2per degree; r, 0.96). After heating the nerve by 11° above the physiological temperature, microtubules increased by 83%, whereby the pool of unpolymerized tubulin was at least 2.7 mg/ml of axoplasm. A seasonal variation of the microtubular density was observed which accorded with the environmental temperature. The macroscopic kinetics of microtubule disassembly in the axoplasm is similar to that reported for purified tubulin but that of assembly is slower. Microtubules of peripheral axons ofXenopusare cold‐labile and vary during the annual cycle. © 1992

ISSN:0022-104X    

DOI:10.1002/jez.1402640305

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

年代:1992

数据来源: WILEY

摘要:

AbstractGlutamine metabolism was investigated in the little skate (Raja erinacea), spiny dogfish (Squalus acanthias), and hagfish (Myxine glutinosa). Amino acid analysis revealed that dogfish plasma glutamine concentration was 11.6 nmol/ml, whereas 48‐fold higher levels, 0.56 μmol/gm, were found in the red muscle. Mitochondria were isolated from the red muscle of the skate and dogfish. The isolation procedure yielded well‐coupled mitochondria, which oxidize glutamine and β‐hydroxybutyrate more rapidly than any other substrate tested. Palmitoyl carnitine was not oxidized, confirming previous studies that elasmobranch red muscle has a negligible capacity for fatty acid oxidation. Glutaminase and glutamine synthetase were measured in the muscle of the hagfish, dogfish, as well as several tissues of the skate. The brain and red muscle have the highest activities of glutaminase, and the activity in dogfish muscle is the highest reported for any muscle. Glutamine synthetase activity is highest in the brain, liver, and kidney, whereas the activity of this enzyme is low or not detectable in elasmobranch and hagfish muscle. The high glutaminase/glutamine synthetase ratio in the muscle indicates that the metabolic organization of elasmobranch and agnathan muscle is geared toward glutamine catabolism. The present study shows that, in addition to β‐hydroxybutyrate, glutamine is an important fuel for elasmobranch red muscle. © 1992 Wile

ISSN:0022-104X    

DOI:10.1002/jez.1402640306

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn the regenerating newt tail, epimorphic regeneration—which recapitulates morphologically normal embryonic development—proceeds along a rostrocaudal differentiation gradient. Innervation of the new myomeres results from the spinal roots of segments rostral to the amputation plane and from ventral roots emerging from the lateroventral region of the regenerating spinal cord, in which motor neurons are differentiating. Electron microscopy and an indirect immunofluorescence study with anti‐glial fibrillary acid protein (GFAP) confirm that the ventrolateral part of the regenerated ependymal tube gives rise to cells of the ventral root sheath and the spinal ganglia. Anti‐GFAP and anti‐neurofilament antibodies showed that ependymoglial cells and Schwann cells may play a role in neuronal pathfinding by helping guide and stabilize pioneering axons as they extend toward the myomeres. The carbohydrate epitope NC‐1 is expressed in the spinal cord, in sheath cells of the spinal ganglia and in the non‐myelin‐forming Schwann cells of the peripheral nervous system. L1, a Ca+ +independent neural cell adhesion molecule, was detected in the axonal compartments of the regenerating spinal cord, on immature and/or non‐myelin‐forming Schwann cells within the peripheral nervous system (PNS), and on nerve fibers within the regenerate. These immunohistochemical observations collectively support the hypothesis that Schwann cells already present in the blastema could be involved in organizing neural pathways. ©

ISSN:0022-104X    

DOI:10.1002/jez.1402640307

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn the black‐headed bunting,Emberiza melanocephala, thyroidectomy suppressed the amplitude of light‐induced testicular growth and accelerated the onset of photorefractoriness. Extirpation of the thyroid glands during progressive phase inhibited further testicular growth and led to immediate testicular regression when performed during peak phase of a photostimulated cycle. The inhibitory influence of thyroidectomy on light‐induced testicular growth was fully reversed by daily im injection of L‐T4at a dose level of 2 μg/bird/day. Neither thyroidectomy nor L‐T4had any effect on the regressing testes of thyroidectomized buntings. Body weight which was about 26 g increased to about 37 g within 15 days of photostimulation by 20L/4D. Removal of thyroid glands suppressed light‐induced increase in body weight and resulted in premature decline. The inhibitory influence of thyroidectomy on body weight depended upon lipid reserves at the time of operation, an effect which could be reversed by daily im treatments of L‐T4at dose level 2 μg/bird/day. It is suggested that in the black‐headed buntings thyroid hormones are required for sustaining light‐induced increase in the testes and body weight and may not necessarily be involved in the development of photorefractory states—gonadal and metabolic.

ISSN:0022-104X    

DOI:10.1002/jez.1402640308

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

年代:1992

数据来源: WILEY

摘要:

AbstractAllogeneic recognition and sex differentiation inEphydatia muelleriwere studied with two types of chimeric sponges, mixed and unmixed. Using gemmules of nine original sponges (stocks) collected in a pond, chimeras were prepared in the laboratory. Subsequently, the chimeric sponges were transferred to and cultured in the pond of their origin. They were observed macroscopically and histologically. The unmixed chimeras consisted of halves of different stocks. All unmixed chimeras grew as a continuous sheet for more than 10 days. Then, some of them showed a demarcation line at the boundary of the paired partners. Histologically, the demarcation line of a grown chimera was detected as a gap, on either side of which a narrow zone of tissue was more or less disorganized, containing no sexual elements. The combinations of stocks showing a demarcation line in unmixed chimeras are calledincompatible, and those with no demarcation linecompatible. Five histocompatibility strains were distinguished among the nine stocks used. Some interstrain combinations were compatible. In the chimeric individuals, the putative male region contained spermatic cysts, and the putative female region contained oocytes and embryos. In compatible heterosexual chimeras, male and female sexual elements were sometimes more or less separated but often were intermingled in the boundary zone. Gender seems to be genetically determined. The mixed chimeras were produced from randomly mixed gemmules of different stocks. Mixed chimeras of heterosexual combinations gave the following results. Many chimeras of the incompatible combinations showed a few to several irregular demarcation lines and contained both male and female sexual elements. Some incompatible mixed chimeras, however, did not show a demarcation line and contained only male sexual elements. Some compatible mixed chimeras contained both male and female sexual elements, but the male area was usually larger than the female area. Moreover, some compatible mixed chimeras contained only male sexual elements. Thus, a dominance of the male over the female was revealed in the mixed chimeras. A replacement of female tissues by male tissues during a short period following gemmule hatching is assumed. This may be considered an example of somatic cell parasitism. © 1992 Wiley‐Liss, I

ISSN:0022-104X    

DOI:10.1002/jez.1402640309

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

年代:1992

数据来源: WILEY

摘要:

AbstractPrimary mesenchyme formation in sea urchin embryos occurs when a subset of epithelial cells of the blastula move from the epithelial layer into the blastocoel. The role of microfilaments in producing the cell shape changes that characterize this process, referred to asingression, was investigated in this study. f‐Actin was localized by confocal microscopy using labeled phalloidin. The distribution of f‐actin was observed before, during, and after ingression and was correlated with cellular movements. Prior to the onset of ingression, staining became intense in the apical region of putative primary mesenchyme and disappeared following the completion of mesenchyme formation. The apical end of these cells constricted coincidentally with the appearance of the intensified staining, indicating that f‐actin may be involved in this constriction. In addition, papaverine, a smooth muscle cell relaxant that interferes with microfilament‐based contraction, and that was shown in this study to inhibit cytokinesis, diminished apical constriction and delayed ingression. Despite this interference with apical constriction, the basal surface of ingressing cells protruded into the blastocoel. It is suggested that apical constriction, while not necessary for ingression, does contribute to the efficient production of mesenchyme and that protrusion of the basal surface results from changes that occur independent of apical constriction. © 1992 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402640310

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

年代:1992

数据来源: WILEY

摘要:

AbstractGenes carrying the homeobox were originally identified inDrosophila, in which they are now known to play key roles in establishing segmentation patterns and in determining segment identities. A number of genes with striking homology to theDrosophilahomeobox genes have now been found in the mouse genome, and mutational analysis is beginning to shed light on their function in mammalian development. To understand better the developmental significance of the murineHox‐2.2gene, we have generated gain of function mutants by using the chicken β‐actin promoter to drive ubiquitous expression in transgenic mice. The resultingHox‐2.2misexpression produces early postnatal lethality as well as craniofacial and axial skeletal perturbations that include open eyes at birth, cleft palate, micrognathia, microtia, skull bone deficiencies, and structural and positional alterations in the vertebral column. We repeatedly observe complete or partial absence of the supraoccipital bone and malformations of the exoccipital and the basioccipital bones. These results suggests a role for theHox‐2.2gene in specifying positional identity along the anterior‐posterior axis. © 1992 Wile

ISSN:0022-104X    

DOI:10.1002/jez.1402640311

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

年代:1992

数据来源: WILEY