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We conducted three experiments to examine variables that might influence the longevity of socially induced food preferences in Norway rats. The duration of social influence on the food choices of 42-day-old rats (1) increased with both increasing numbers of demonstrators and increasing numbers of demonstrations by a single demonstrator, (2) varied with the temporal distribution of demonstrations, but (3) did not vary with the age of demonstrators. The results suggest that a single episode of social learning produces short-term, but not long-term, effects on a Norway rat's food choices. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.  相似文献   
999.
Interactions of the beta subunit of the Oxytricha nova telomere binding protein with the telomeric DNA sequences, d(T4G4)2 and dT6(T4G4)2, have been investigated in vitro using Raman and fluorescence spectroscopies. Raman difference spectra show that the beta subunit binds to both d(T4G4)2 and dT6(T4G4)2 but promotes the formation of a parallel-stranded quadruplex only in dT6(T4G4)2, thus demonstrating the importance of the telomeric 5' tail for in vitro recognition and guanine quadruplex formation. While d(T4G4)2 is not a suitable substrate for quadruplex promotion by the beta subunit, the Raman spectra reveal other structural rearrangements of this DNA strand upon beta subunit binding, including changes in guanine glycosyl torsion angles from syn to anti and disruption of carbonyl hydrogen-bonding interactions. The conformation of d(T4G4)2 in the beta:d(T4G4)2 complex is suggested as a plausible intermediate along the pathway to formation of the parallel-stranded guanine quadruplex. Fluorescence band shifts indicate that at least one of the two tryptophans of the beta subunit is shielded from solvent as a consequence of DNA binding in both the beta:dT6(T4G4)2 and beta:d(T4G4)2 complexes. However, the Raman spectra of these complexes suggest no significant changes in the beta subunit secondary structure attendant with DNA binding. A model for beta subunit binding by Oxytricha telomeric DNA sequences and a mechanism for quadruplex formation are proposed. A key feature of this model is the use of a telomeric hairpin secondary structure as the recognition motif.  相似文献   
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OBJECTIVE: To quantify the number of extractions and/or restorations placed in chronically sick children under intubation general anaesthesia and compare these findings with healthy children. SETTING: Two large paediatric dentistry units in Central London: a tertiary referral centre dealing with severe chronic sickness in children and an undergraduate dental school with a large commitment to special needs dentistry in children. DESIGN: Prospective comparison of treatment received for (a) chronically sick children and (b) dentally anxious (otherwise fit) children receiving intubation general anaesthesia during July 1991 to June 1996 inclusive. The statistical tests used were the Shapiro-Wilks test for normality and the Mann Whitney U test for non-parametric comparison of independent groups. MAIN OUTCOME MEASURES: Mean total treatment tally (TTT)--the sum of extractions and restorations for each child presented as summary data. RESULTS: Different patterns of dental care were found between the healthy and chronically sick groups. For similar levels of disease, a significantly greater number of extractions were carried out for chronically sick children (P < 0.0001), and significantly fewer restorations (P < 0.0001). The number of pulpotomies and stainless steel crowns provided to sick children was significantly smaller than to healthy children (P < 0.0001). This paper discusses the influences of chronic ill health on dental treatment provided under general anaesthesia. CONCLUSION: The underlying medical disorder in chronically sick children significantly influences the pattern of treatment when this is provided under general anaesthesia.  相似文献   
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