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61.
Mutations induced by repeated EMS treatments were investigated by using mouse L5178Y cells. The frequency of TGr mutations increased linearly with the number of EMS treatments whereas the yield of BrdUrdr mutations showed a curvilinear dose-response curve. The BrdUrdr frequency was roughly proportional to the square of the TGr frequency and the results were compatible with the hypothesis that BrdUrdr cells were induced by two mutational events within a cell. Most of the BrdUrdr colonies isolated after 6 EMS treatments, however, were unstable. When BrdUrdr colonies that had arisen in BrdUrd medium after 2 weeks' incubation were isolated in normal medium, the descendant cells showed a nearly normal level of thymidine incorporation and low plating efficiencies of about 1% in BrdUrd medium. In contrast, after isolation of the same colonies in BrdUrd medium, a low level of thymidine incorporation and high plating efficiencies in BrdUrd medium were observed in the descendant cells.
Reverse selection from BrdUrdr to HATr was accomplished with frequencies of 10−6−10−3 for the descendants grown in BrdUrd medium, and AzaCyd treatment drastically increased the reversion frequency to nearly 10−1. Further re-revertants from HATr to BrdUrdr were also found with frequencies of 10−3−10−2 without treatment. These results indicate that the initial BrdUrdr cells did not result from inactivation of the thymidine-kinase gene but that the mode of gene expression was altered in some way. 相似文献
62.
The effect of Cr(III) administration on hepatic RNA synthesis in mice was studied. It was found that Cr accumulated in mouse liver. Forty-eight hours after intraperitoneal injection of CrCl3 (0.005-5 mg Cr/kg body weight) approximately 10% of the administered dose per g of tissue remained. The accumulated Cr was still retained 64 days after administration (5 mg Cr/kg) with only a slight decrease. Approximately 20% of the hepatic Cr was detected in the nuclei. By administering CrCl3. RNA synthesis in mouse liver was markedly enhanced without altering the pool size of nucleotides. This enhancement was dose-dependent and statistically significant at doses of 0.05 (p less than 0.05), 0.5 (p less than 0.01), and 5 mg Cr/kg (p less than 0.01), and remained so for at least 16 days after administration of 5 mg Cr/kg. The synthesis of DNA and protein in mouse liver were not significantly changed by CrCl3 administration. On the other hand, Cr(VI) administration did not enhance but rather inhibited RNA synthesis in mouse liver. These results suggest that Cr(III) specifically enhances RNA synthesis in mouse liver. 相似文献
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T Sato M Ohkusa Y Okada M Sasaki 《Comparative biochemistry and physiology. A, Comparative physiology》1983,76(2):233-239
Distribution density of the taste disks of the fungiform papillae in the frog tongue was larger at the proximal portion than at the apical and middle portions. The number of myelinated afferent nerve fibres and taste cells per cm2 area of the tongue increased in the order of proximal greater than middle greater than apical portion. The amplitudes of gustatory neural responses for 0.5 M NaCl, 0.5 M KCl, 0.5 M NH4Cl, 0.05 M CaCl2, 1 mM acetic acid and 1 mM quinine-HCl (Q-HCl) were significantly larger with lingual stimulation of the proximal region than with the stimulation of the apical region. With these stimuli the mean ratio of the apical response to the proximal response was 1.00:1.54. On the other hand, this ration with deionized water was 1.00:5.00. The mean magnitudes of receptor potentials in taste cells for 1 mM acetic acid and 10 mM Q-HCl were the same among the apical, middle and proximal portions of the tongue. The mean magnitudes of receptor potentials for 0.5 M NaCl were significantly larger at the apical portion than at the other portions, whereas those for deionized water tended to be the largest at the proximal portion. It is concluded that the larger magnitude of the gustatory neural responses at the proximal portion of the tongue is due to morphological and physiological properties of the taste organ. 相似文献
65.
A Okada M Ariizumi G Okamoto 《European journal of applied physiology and occupational physiology》1983,52(1):94-97
To investigate the effects of whole body vibration on the central nervous system, rats were exposed to various whole body vibrations and examined for changes in the levels of norepinephrine (NE) in whole brain or regions of the brain. Whole brain NE had decreased significantly (P less than 0.05) after an acceleration of 5.0G with a frequency of 20 Hz; and the decrease was also observed in the hypothalamus (P less than 0.01) and the hippocampus (P less than 0.10). Exposure to noise [100 dB (A)] caused a significant decrease in NE. This decrease related particularly to a significant decrease in midbrain NE (P less than 0.05) and a non-significant decrease of NE in the hypothalamus. 相似文献
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