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981.
Abstract: To determine whether protein kinase C (PKC) mediates release of peptides from sensory neurons, we examined the effects of altering PKC activity on resting and evoked release of substance P (SP) and calcitonin gene-related peptide (CGRP). Exposing rat sensory neurons in culture to 10 or 50 n M phorbol 12,13-dibutyrate (PDBu) significantly increased SP and CGRP release at least 10-fold above resting levels, whereas the inactive 4α-PDBu analogue at 100 n M had no effect on release. Furthermore, 100 n M bradykinin increased peptide release approximately fivefold. Down-regulation of PKC significantly attenuated the release of peptides evoked by either PDBu or bradykinin. PDBu at 1 n M or 1-oleoyl-2-acetyl- sn -glycerol at 50 µ M did not alter resting release of peptides, but augmented potassium- and capsaicin-stimulated release of both SP and CGRP approximately twofold. This sensitizing action of PKC activators on peptide release was significantly reduced by PKC down-regulation or by pretreating cultures with 10 n M staurosporine. These results establish that activation of PKC is important in the regulation of peptide release from sensory neurons. The PKC-induced enhancement of peptide release may be a mechanism underlying the neuronal sensitization that produces hyperalgesia. 相似文献
982.
Michael R. Dohm Jack P. Hayes Theodore Garland 《Evolution; international journal of organic evolution》1996,50(4):1688-1701
We tested the hypothesis that locomotor speed and endurance show a negative genetic correlation using a genetically variable laboratory strain of house mice (Hsd:ICR: Mus domesticus). A negative genetic correlation would qualify as an evolutionary “constraint,” because both aspects of locomotor performance are generally expected to be under positive directional selection in wild populations. We also tested whether speed or endurance showed any genetic correlation with body mass. For all traits, residuals from multiple regression equations were computed to remove effects of possible confounding variables such as age at testing, measurement block, observer, and sex. Estimates of quantitative genetic parameters were then obtained using Shaw's (1987) restricted maximum-likelihood programs, modified to account for our breeding design, which incorporated cross-fostering. Both speed and endurance were measured on two consecutive trial days, and both were repeatable. We initially analyzed performances on each trial day and the maximal value. For endurance, the three estimates of narrow-sense heritabilities ranged from 0.17 to 0.33 (full ADCE model), and some were statistically significantly different from zero using likelihood ratio tests. The heritability estimate for sprint speed measured on trial day 1 was 0.17, but negative for all other measures. Moreover, the additive genetic covariance between speeds measured on the two days was near zero, indicating that the two measures are to some extent different traits. The additive genetic covariance between speed on trial day 1 and any of the four measures of endurance was negative, large, and always statistically significant. None of the measures of speed or endurance was significantly genetically correlated with body mass. Thus, we predict that artificial selection for increased locomotor speed in these mice would result in a decrease in endurance, but no change in body mass. Such experiments could lead to a better understanding of the physiological mechanisms leading to trade-offs in aspects of locomotor abilities. 相似文献
983.
984.
Michael W. Hart 《Evolution; international journal of organic evolution》1996,50(1):174-187
Species with large eggs and nonfeeding larvae have evolved many times from ancestors with smaller eggs and feeding larvae in numerous groups of aquatic invertebrates and amphibians. This change in reproductive allocation and larval form is often accompanied by dramatic changes in development. Little is known of this transformation because the intermediate form (a facultatively feeding larva) is rare. Knowledge of facultatively feeding larvae may help explain the conditions under which nonfeeding larvae evolve. Two hypotheses concerning the evolutionary loss of larval feeding are as follows: (1) large eggs evolve before modifications in larval development, and (2) the intermediate form (facultatively feeding larva) is evolutionarily short-lived. I show that larvae of a heart urchin, Brisaster latifrons, are capable of feeding but do not require food to complete larval development. Food for larvae appears to have little effect on larval growth and development. The development, form, and suspension feeding mechanism of these larvae are similar to those of obligate-feeding larvae of other echinoids. Feeding rates of Brisaster larvae are similar to cooccurring, obligate-feeding echinoid larvae but are low relative to the large size of Brisaster larvae. The comparison shows that in Brisaster large egg size, independence from larval food, and relatively low feeding rate have evolved before the heterochronies and modified developmental mechanisms common in nonfeeding echinoid larvae. If it is general, the result suggests that hypotheses concerning the origin of nonfeeding larval development should be based on ecological factors that affect natural selection for large eggs, rather than on the evolution of heterochronies and developmental novelties in particular clades. I also discuss alternative hypotheses concerning the evolutionary persistence of facultative larval feeding as a reproductive strategy. These hypotheses could be tested against a phylogenetic hypothesis. 相似文献
985.
986.
Kathleen D. Murray Eleanor Groden Francis A. Drummond A. Randall Alford Richard H. Storch Michael D. Bentley 《Entomologia Experimentalis et Applicata》1996,80(3):503-510
The effects of citrus limonoids, applied topically to potato (Solanum tuberosum L. var. Katahdin) foliage, on Colorado potato beetle (Leptinotarsa decemlineata) (Say) (Chrysomelidae) larval development, growth, and survival were quantified in laboratory assays and a small-plot field test. In laboratory assays, survival, development rate, and body weight decreased with increasing limonoid concentration, however these measures of larval response did not significantly differ among varying periods of limonoid exposure (three, six, or nine days). Significant limonoid application concentration and frequency effects on survival, development rate, and defoliation were observed in the field test. These results indicate the potential utility of lethal and non-lethal effects of citrus limonoids for management of the Colorado potato beetle. 相似文献
987.
Genetic studies have uncovered many genes that are involved in the first steps of neuronal development inDrosophila.Less is known about the intermediate steps during which individual precursor cells follow either the neuronal pathway or the glial pathway. We report the identification of a novel bHLH gene,biparous,expressed in neuronal and glial precursors inDrosophila.Unlike most bHLH genes,biparousexpression continues to the final stages of neurogenesis in the embryo. Expression ofbiparousis not observed in end stage postmitotic neurons and precedes the expression ofrepo,a gene activated in later stages of glial differentiation. The bHLH domain is sufficiently different from previously described bHLH domains to imply a novel function. 相似文献
988.
Chromosomal polymorphism was assessed in the southern short-tailed shrew (Blarina carolinensis) using standard metaphase chromosome and G-banding techniques. Twenty-one animals (11 males, 10 females) from the Meeman Biological Station in Shelby Co., Tennessee, were examined for diploid number. Results showed diploid numbers of 35, 36, 37, 38, 39, 40 and 41 and fundamental numbers of 41, 42, 43, 44 and 45. No diploid numbers or fundamental numbers were unique to a specific collecting locality. The first G-banded karyotypes are reported for the species. These results indicate that Robertsonian polymorphisms, inversions, and possibly other events are responsible for chromosomal variation in B. carolinensis. 相似文献
989.
Michael J. Tyler Margaret Davies Graeme F. Watson David J. Williams 《Hydrobiologia》1996,318(3):135-137
The program BIOCLIM predicts the total geographic distribution of species, based upon the biogeoclimatic characteristics common to the localities at which they are known to occur. Field studies in the Northern Territory have located the Shield Shrimp Triops australiensis at localities substantially north of its known and predicted geographic distribution. 相似文献
990.
Michael Schaub 《Journal of Ornithology》1996,137(2):213-227
Zusammenfassung In der Brutsaison 1994 wurde das Jagdverhalten von fünf Rotkopfwürgerpaaren in der Nordschweiz beobachtet, das Nahrungsangebot mit der Sichtkreismethode erfaßt. Bei warmem und trockenem Wetter waren die Insekten aktiver und somit das Nahrungsangebot für die Rotkopfwürger günstiger. In hoher Vegetation gab es mehr Insekten als in niedriger. Die Rotkopfwürger jagten entweder am Boden (64% der Jagdflüge) oder in der Luft (36%). Die Bodenjagden waren energetisch günstiger, da die Beute durchschnittlich größer und die Jagddistanz kleiner war. Bodenjagden fanden vorzugsweise in Flächen mit kurzer Vegetation (durchschnittliche Vegetationshöhe: 7 cm) statt. Gejagt wurden ausschließlich Arthropoden und zwar gezielt große. Bei schlechten Wetterbedingungen mußten auch kleinere Beutetiere gefangen werden. Der Fluganteil am Gesamtzeitbudget war während der Nestlingszeit am größten. Zur Bebrütungs- und Nestlingszeit wurden die Jagdaktivitäten bei schlechtem Wetter gegenüber gutem tendenziell gesteigert, vor dem Brüten und nach dem Flüggewerden der Jungen aber eher gesenkt. Der Fluganteil beim Jagen über kurzer Vegetation schien kleiner als beim Jagen über hoher Vegetation.
Hunting behavior and time budget of Woodchat ShrikesLanius senator in Northern Switzerland
The hunting behavior of Woodchat Shrike in Northern Switzerland was studied by visual observations of five pairs in 1994. Data on food supply were collected by standardized observations in half-circles of 1 m radius. During warm and dry weather the activity of the insects increased. More insects were seen in high than in short vegetation. The Woodchat Shrikes either hunted on the ground (64% of all hunting flights) or in the air (36%). The energy gain in ground-huntings was higher than in flycatching due to larger average prey size and a shorter hunting distance. Ground huntings occured mainly in areas with short vegetation (7 cm high on average). The birds only fed on arthropods, preferring larger seizes. During bad weather they were dependant also on smaller prey. The proportion of time the adults spent in flight was longest during the nestling season. In bad weather, hunting activity was slightly increased during incubation and nestling stage but low before incubation and after fledging of the young. For hunting over short vegetation the birds seemed to spent less time in flight than for hunting over high vegetation.相似文献