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51.
Planktivory in Pagothenia borchgrevinki (Pisces: Nototheniidae) in McMurdo sound,Antarctica 总被引:2,自引:2,他引:0
Summary Specimens of the Antarctic fish P. borchgrevinki were collected from just beneath the sea-ice in McMurdo Sound over the period 8 November to 6 December, 1985. The stomach contents of 200 fish were analysed and compared with the co-occurrence of the prey species in the plankton. Numerically, the dominant prey was a thecosomatid pteropod Limacina helicina (83%), followed by a hyperiid amphipod Hyperiella dilatata (5%). Other prey species in decreasing order of occurrence were Euphausia crystallorophias, Euchaeta antarctica, other copepods, a decapod crustacean larva, chaetognaths, the amphipods Orchomene plebs and Epimiriella macronyx, and unidentified juvenile fish. The order of frequency of occurrence of these prey in the guts of all the fish was H. dilatata (in 73% of the fish), L. helicina (71%), calanoid copepods (55%), chaetognaths (51%), E. crystallorophias (42%), decapod crustacean larva (32%), O. plebs (27%), juvenile fish (20%), and E. macronyx (14%). In volumetric terms, the dominant diet contributors were O. plebs (38%), L. helicina (17%) and chaetognaths (15%). All prey except O. plebs and E. macronyx were taken in concurrent plankton samples. Although planktivory of Pagothenia borchgrevinki is confirmed, it is not certain whether feeding is confined to the immediate sub-ice environment. 相似文献
52.
D. Jane Bower 《Chromosoma》1987,95(1):76-80
At least one-third of mouse trophoblast cells undergo endoreduplication during the first half of gestation. It has been suggested that the endoreduplicated chromosomes may be polytenised. Here it is shown, using in situ hybridisation to the -1 antitrypsin genes, which map at a unique site, that while there is a tendency for duplicated chromosomes to cluster, this does not involve the complete fusion of replicated chromatids found in fully polytene chromosomes, and in a substantial proportion of homologues the sites on the chromosome arms corresponding to these genes are widely separated. The centromeres do not fuse into a single chromocentre but the possibility is not ruled out that individual chromosomes may be polytenised in the centromeric region. Evidence is also presented showing that endoreduplication in trophoblast nuclei is not accompanied by the formation of new prekinetochore structures, in contrast to the situation in polyploid mouse liver and C127 cells. 相似文献
53.
54.
Dr. Brian H. Peters 《Cell and tissue research》1987,249(2):341-350
Summary An electron-microscopical study of locust thoracic ganglia reveals that synapses in the neuropily are morphologically heterogeneous. In addition to the conventional dyadic type described frequently in the literature, there is a second type with a complex arrangement of presynaptic dense material and a non-dyadic postsynaptic configuration. Serial-section analysis of these synapses suggests that the presynaptic structures include irregular or curved bars, and small projections.Although the proportion of non-dyadic synapses in the neuropile as a whole is small, a substantial number have been found on the branches of an identified flight motor neurone, labelled intracellularly with metal ions in conjunction with silver intensification. Samples from the arborization of this neurone give some indications of the distribution of non-dyadic synapses on it.The results are discussed in the context of distribution of synapses on other identified locust neurones, and the functional morphology of synapses in other phyla. 相似文献
55.
GABA-mediated synaptic inhibition of projection neurons in the antennal lobes of the sphinx moth,Manduca sexta 总被引:3,自引:0,他引:3
Brian Waldrop Thomas A. Christensen John G. Hildebrand 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1987,161(1):23-32
Responses of neurons in the antennal lobe (AL) of the moth Manduca sexta to stimulation of the ipsilateral antenna by odors consist of excitatory and inhibitory synaptic potentials. Stimulation of primary afferent fibers by electrical shock of the antennal nerve causes a characteristic IPSP-EPSP synaptic response in AL projection neurons. The IPSP in projection neurons reverses below the resting potential, is sensitive to changes in external and internal chloride concentration, and thus is apparently mediated by an increase in chloride conductance. The IPSP is reversibly blocked by 100 microM picrotoxin or bicuculline. Many AL neurons respond to application of GABA with a strong hyperpolarization and an inhibition of spontaneous spiking activity. GABA responses are associated with an increase in neuronal input conductance and a reversal potential below the resting potential. Application of GABA blocks inhibitory synaptic inputs and reduces or blocks excitatory inputs. EPSPs can be protected from depression by application of GABA. Muscimol, a GABA analog that mimics GABA responses at GABAA receptors but not at GABAB receptors in the vertebrate CNS, inhibits many AL neurons in the moth. 相似文献
56.
Scott Brian Lew James Clandinin M. T. Cinader B. 《Cellular and molecular neurobiology》1989,9(1):105-113
1. SJL/J mice were maintained on semipurified diets which differed in the ratio of polyunsaturated/saturated fatty acid content (P/S). Exposure was from conception and was maintained for periods ranging from 6 to 34 weeks. 2. Neural cell cultures were prepared from dorsal root ganglia (DRG). After 6 and 20 days of culture, neuronal electric membrane properties were determined quantitatively by intracellular recording. 3. A number of significant differences were observed for the two dietary conditions. DRG from mice on the low-P/s diet had an increase in the rate of fall of both phases of repolarization which, in conjunction with the reduced action potential overshoot, led to a reduced action potential duration. This shift to shorter-duration action potentials was accompanied by a shift to more monophasic falling phases. The low-P/S neurons also exhibited a decreased afterhyperpolarization, decreased specific membrane resistance, and decreased membrane electrical time constant compared to high-P/S neurons. 4. It was concluded that the P/S ratio in the diet can have a significant effect on the electric properties of neurons. The high-P/S neurons tended to have action potentials with biphasic repolarizations and longer durations. In contrast, the low-P/S neurons tended to have action potentials with monophasic repolarizations and shorter durations. Moreover, the known ionic dependence of these two types of action potentials suggested that the low-P/S diet resulted in action potentials with a more exclusive Na dependence, while the high-P/S diet resulted in action potentials with both Na and Ca dependence. 相似文献
57.
58.
Brian M. Boom 《Brittonia》1989,41(2):129-130
Pagamea aracaënsis Boom, endemic to Serra Aracá, Brazil is described and illustrated, and its relationship toP. anisophylla Standley & Steyerm, is discussed. 相似文献
59.
Ronald J. Hauptman Brian A. Perry David G. Capco 《Development, growth & differentiation》1989,31(2):157-164
Proteins of the detergent-resistant cytoskeleton fraction and the detergent-soluble fraction from Xenopus oocytes and embryos are examined using a procedure which allows rapid and uniform extraction of tissues and large, single cells. SDS-polyacrylamide gels reveal only a few prominent cytoskeletal proteins in the early embryo, however qualitatively different proteins begin to appear after gastrulation. Incorporation of [35 S]-methionine into newly synthesized proteins indicates that there is synthesis and assembly of proteins into the cytoskeleton, but the amount remains low until after gastrulation. The use of nucleic acid probes for alpha-tubulin and actin mRNA indicates that about 80% of these mRNAs in the oocyte and meiotically mature egg are bound to the detergent-resistant cytoskeleton. 相似文献
60.