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161.
Developing taste buds in the anterior mandibular floor of perihatching
chicks were studied by high voltage electron microscopic autoradiography in
order to identify proliferating gemmal cell types. Montaged profiles of 29
taste buds in five cases euthanized between embryonic day 21 and
posthatching day 2 were analyzed after a single [3H]thymidine injection
administered on embryonic day 16, 17 or 18. Results showed that dark cells
comprised 55% of identified (n = 900 cells) and 62% of labeled (n = 568
cells) gemmal cells as compared with light, intermediate, basal or
perigemmal bud cells. Dark cells had both a greater (P < 0.05) number of
labeled cells and a greater amount of label (grains/nucleus) than the other
four bud cell types, irrespective of injection day. The nuclear area
(micron 2) of dark cells was not significantly larger (P > 0.05) than
that of the other gemmal cell types and therefore cannot account for the
greater amount for label in the dark cells. Interestingly, only dark cells
showed a positive correlation (P < 0.003) between amount of label and
nuclear area. Results suggest that, during the perihatching period of
robust cell proliferation, dividing dark cells may give rise primarily, but
not exclusively, to dark cell progeny.
相似文献
162.
The major rivers of the South African ‘Lowveld’ (low-latitude savanna) suffer numerous impacts from upstream economic activities. Whereas monitoring these rivers is required to detect biodiversity losses, record pollution events and devise mitigation strategies, current monitoring programmes are inadequate. In 2009, the South African Earth Observation Network initiated an intensive long-term research programme on the Lowveld reaches of the Olifants River. Physico-chemical parameters, aquatic macroinvertebrates and fish abundances were recorded at four Lowveld sites in the Olifants River. We review six years of this programme. The results suggest deterioration in the ecological condition of the Olifants River with no discernible improvement through protected areas. Trends could not be detected. The parameters measured, sampling methods and/or sampling frequency might be responsible for the limited trends observed, or alternatively the results simply reflect stable conditions despite on-going pollution. Real time monitoring and an expansion in the parameters monitored would add value to the monitoring programme. 相似文献
163.
164.
165.
Bradford N. Bunnell Daniel R. Kenshalo Jr. Joseph D. Allen Frederick J. Manning Frank J. Sodetz 《Primates; journal of primatology》1979,20(1):77-86
The performance of 22 adult male rhesus monkeys on a Fixed Interval 1-min reinforcement schedule was examined under conditions
where the reinforcement probabilities were either 1.00 or .80. The results were then related to the social rank of animals
at the time that they were taken from their social groups. Both high and low ranked animals reached criterion performance
in the same number of trials. In general, high ranking animals responded at lower rates than low ranking animals when the
reinforcement probability was 1.00. When the reinforcement probability was shifted to .80, all animals showed an increase
in responding after nonreinforced intervals as compared with responses after reinforced intervals. The higher ranked animals
tended to have a higher ratio of nonreinforced to reinforced responses than lower ranked animals.
Supported by USAMRDC Contract No. DADA 17-73-C-3007. 相似文献
166.