首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   27篇
  完全免费   3篇
  2022年   1篇
  2020年   1篇
  2019年   2篇
  2014年   4篇
  2013年   1篇
  2012年   1篇
  2011年   1篇
  2010年   1篇
  2009年   5篇
  2008年   4篇
  2007年   1篇
  2006年   1篇
  2002年   1篇
  2001年   2篇
  2000年   1篇
  1998年   1篇
  1995年   1篇
  1990年   1篇
排序方式: 共有30条查询结果,搜索用时 93 毫秒
1.
The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), is a potent inhibitor of gap junctional intercellular communication (GJIC). This inhibition requires activation of protein kinase C (PKC), but the events downstream of this kinase are not known. Since PKC can activate extracellular signal regulated kinases (ERKs) and these also downregulate GJIC, we hypothesized that the inhibition of GJIC by TPA involved ERKs. TPA treatment (10 ng/ml for 30 min) of WB-F344 rat liver epithelial cells strongly activated p42 and p44 ERK-1 and -2, blocked gap junction-mediated fluorescent dye-coupling, and induced connexin43 hyperphosphorylation and gap junction internalization. These effects were completely prevented by inhibitors of PKC (bis-indolylmaleimide I; 2 microM) and ERK activation (U-0126; 10 microM). These data suggest that ERKs are activated by PKC in response to TPA treatment and are downstream mediators of the gap junction effects of the phorbol ester.  相似文献
2.
3.
The evolution of signals has mainly been considered in the contextof an emitter-receiver dyadic interaction. However, communicationusually occurs in the presence of individuals (an audience)that are not directly involved in the communication interaction,and it is more realistic to assume that signal evolution occursin a network. Several types of information could be available to an audience, and, therefore, the presence of an audiencecould have effects on the behavior of the communicating animalsand on signal evolution. We investigated whether the presenceof an audience of conspecifics affected intrasexual aggressivecommunication in male fighting fish. We found that if the audiencewas a female, males increased the intensity of conspicuous displays that can be used in communication with both males andfemales and decreased highly aggressive displays that are solelydirected to males. If the audience was a male of similar size,there was no significant change in the way in which males displayed.These results suggest that the presence of an audience couldbe one reason that many long-range and conspicuous signals are often shaped to transmit information to both males and females  相似文献
4.
1.  During courtship behavior, males of the fiddler crab, Uca pugilator, drum on the ground with their large chela. The types of waves this produces and some of their properties were investigated using a laser Doppler vibrometer and accelerometers under field and laboratory conditions.
2.  Rhythmical impact onto the substratum by Uca produces 3 types of surface waves: Rayleigh waves and Love waves which contain most of the energy, and the weaker surface P-waves.
3.  The group velocity of Love-waves is 50–60 m/s in wet sand. Rayleigh waves travel at 70–80 m/s in wet sand and obout 40 m/s in dry sand. The propagation velocity of surface P-waves is 150–160 m/s in compact wet sand and about 140 m/s in wet sand perforated by crab burrows. The group velocity of Rayleigh and Love waves is not influenced by the presence of crab burrows.
4.  Fast Fourier transform (FFT) spectra of single beats reveal that the energy maxima of Rayleigh and Love waves lie in the frequency range of 340–370 Hz, i.e., at much higher frequencies than the beat rate of the fiddler crabs, which is usually below 40/s. The optimal frequency is independent of the distance from the signalling male.
5.  In the optimal frequency range, the specific damping coefficient 10 for Rayleigh waves is very low and amounts to 0.13–0.16 dB/cm in wet sand and 0.23–0.49 dB/cm in dry sand. Substrate vibrations of higher frequencies are more strongly damped.
6.  Considering the size of a fiddler crab, the physical properties of the Rayleigh and Love waves in the optimal frequency range provide a suitable signal for localizing mechanisms which rely on time or phase differences but not on intensity or spectral differences of propagating substrate vibrations.
In partial fulfillment of the requirements for the Dr. rer. nat. degree, University of Konstanz.  相似文献
5.
Continuous communication between cells is necessary for development of any multicellular organism and depends on the recognition of secreted signals. A wide range of molecules including proteins, peptides, amino acids, nucleic acids, steroids and polylketides are used as intercellular signals in plants and animals. They are also used for communication in the social ameba Dictyostelium discoideum when the solitary cells aggregate to form multicellular structures. Many of the signals are recognized by surface receptors that are seven-transmembrane proteins coupled to trimeric G proteins, which pass the signal on to components within the cytoplasm. Dictyostelium cells have to judge when sufficient cell density has been reached to warrant transition from growth to differentiation. They have to recognize when exogenous nutrients become limiting, and then synchronously initiate development. A few hours later they signal each other with pulses of cAMP that regulate gene expression as well as direct chemotactic aggregation. They then have to recognize kinship and only continue developing when they are surrounded by close kin. Thereafter, the cells diverge into two specialized cell types, prespore and prestalk cells, that continue to signal each other in complex ways to form well proportioned fruiting bodies. In this way they can proceed through the stages of a dependent sequence in an orderly manner without cells being left out or directed down the wrong path.  相似文献
6.
7.
The communication signals of electric fish can be dynamic, varying between the sexes on a circadian rhythm and in response to social and environmental cues. In the gymnotiform fish Brachyhypopomus gauderio waveform shape of the electric organ discharge (EOD) is regulated by steroid and peptide hormones. Furthermore, EOD amplitude and duration change on different timescales and in response to different social stimuli, suggesting that they are regulated by different mechanisms. Little is known about how androgen and peptide hormone systems interact to regulate signal waveform. We investigated the relationship between the androgens testosterone (T) and 11-ketotestosterone (11-KT), the melanocortin peptide hormone α-MSH, and their roles in regulating EOD waveform of male B. gauderio. Males were implanted with androgen (T, 11-KT, or blank), and injected with α-MSH before and at the peak of androgen effect. We compared the effects of androgen implants and social interactions by giving males a size-matched male stimulus with which they could interact electrically. Social stimuli and both androgens increased EOD duration, but only social stimuli and 11-KT elevated amplitude. However, no androgen enhanced EOD amplitude to the extent of a social stimulus, suggesting that a yet unidentified hormonal pathway regulates this signal parameter. Additionally, both androgens increased response of EOD duration to α-MSH, but only 11-KT increased response of EOD amplitude to α-MSH. Social stimuli had no effect on EOD response to α-MSH. The finding that EOD amplitude is preferentially regulated by 11-KT in B. gauderio may provide the basis for independent control of amplitude and duration.  相似文献
8.
Sexually-selected communication signals can be used by competing males to settle contests without incurring the costs of fighting. Steroid regulation of these signals can render them as reliable indicators of a male's physiological state. We investigated how plasticity in electrocommunication signals is driven by social competition for mates, mediated by steroid hormones, and subject to the effects of past social experience. We measured the electric waveform's amplitude and duration and steroid hormone levels of male gymnotiform electric fish (Brachyhypopomus gauderio) following week-long periods of social isolation, and low or high social competition. To quantify the effect of social history on the modulation of the electric signal, six groups of six males experienced all three social conditions but in different order. We found that males differentially modulate their electric signals depending on the order they experienced these conditions. Thus, past social interactions affect both present and future social electric signals. Cortisol levels and the amplitude of the electric signal appeared to track the intensity of competition, while androgen levels and the duration of the electric signal only responded to the presence (low and high competition) or absence (isolation) of a social environment (low and high androgens respectively). In addition, cortisol levels were related to the body size of the males at high social competition. Taken together, these findings suggest that the capacity of males to modulate their signals in response to social competition is regulated by steroids.  相似文献
9.
Airborne communication can affect systemic induced resistance to herbivory on neighboring branches and individual plants. Sagebrush is the best known example of this phenomenon although the mechanisms of this communication system remain unidentified. We do not know the timing of emission or the chemical nature of the active cue. We investigated the timing of this phenomenon by using plastic bags to prevent propagation of volatile compounds and experimentally manipulated the timing of removal of these bags. We found that blocking the volatiles prevented systemic induced resistance. Experimentally allowing clipped branches to release cues for up to 3 days after clipping caused a reduction in damage in neighboring branches on the clipped plants. This indicates that active cues are released from the time we clipped for the next 3 days or that cues released immediately remained active over this time period. As we continue to evaluate potential chemicals as active cues in plant communication, this prolonged effectiveness may provide an important screen against which to evaluate any putative signals. Handling editor: Robert Glinwood  相似文献
10.
Serotonin (5-HT) is an indirect modulator of the electric organ discharge (EOD) in the weakly electric gymnotiform fish, Brachyhypopomus pinnicaudatus. Injections of 5-HT enhance EOD waveform "masculinity", increasing both waveform amplitude and the duration of the second phase. This study investigated the pharmacological identity of 5-HT receptors that regulate the electric waveform and their effects on EOD amplitude and duration. We present evidence that two sets of serotonin receptors modulate the EOD in opposite directions. We found that the 5HT1AR agonist 8-OH-DPAT diminishes EOD duration and amplitude while the 5HT1AR antagonist WAY100635 increases these parameters. In contrast, the 5HT2R agonist alpha-Me-5-HT increases EOD amplitude but not duration, yet 5-HT-induced increases in EOD duration can be inhibited by blocking 5HT2A/2C-like receptors with ketanserin. These results show that 5-HT exerts bi-directional control of EOD modulations in B. pinnicaudatus via action at receptors similar to mammalian 5HT1A and 5HT2 receptors. The discordant amplitude and duration response suggests separate mechanisms for modulating these waveform parameters.  相似文献
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号