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Welcome to Ali Khammanivong's
UST Web Page
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Background |
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University of St. Thomas
Graduate of 1998
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In Biology and Mathematics
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UST Independent Study
and Work
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Current Work outside of
School
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Current Contact
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Future
Plans |
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Educations
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Graduate Program in Genetics
and Immunology in Neuroscience at University of Minnesota
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Medical School
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Careers
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Cancer Research in Neuroscience
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Research in Human Higher Brain
Functions (extra interest)
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Medical Practioner in Cancer
Treatment
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Senior Executive and Director
of United Intelligence (UI)
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Submitted
Work |
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THE MOUSE CIRCADIAN
SYSTEM BECOMES UNRESPONSIVE TO LIGHT AFTER "SATURATING" LIGHT-INDUCED PHASE
DELAYS
Ali Khammanivong
and Dwight Nelson*, Department of Biology,
University of St. Thomas,
St. Paul, MN 55105
Society
for Neuroscience Abstract, 1998
Many
studies have examined the sensitivity of the circadian photic entrainment
pathway in mice using single light pulses. We have begun to characterize
changes in the light sensitivity in this pathway caused by an initial stimulation.
Mice (C57BL/6J) were entrained for at least 3 weeks to a 12:12 LD cycle
and then placed into single cages equipped to monitor running wheel activity
using a data acquisition system (Chronobiology Kit, Stanford Software).
After at least 1 more week in LD, mice were transferred to constant
darkness. After 7 days of DD, light pulses were individually presented
to mice at CT16. Mice (5-10 per group) were exposed to either one 15-min
pulse, one 30-min pulse, or two 15-min light pulses separated by durations
of darkness from 1-104 min. All stimuli were "saturating" white fluorescent
light of 640 µW (~5000 lux) and should have induced a maximum phase
delay at CT16. After 2 weeks the steady-state phase shift of the circadian
activity rhythm was measured for each animal. Results suggest that the
mouse circadian system is unresponsive to light following the initial light
pulse. The initial stimulus induced a phase delay of 104 ± 12 min
(0 ± SEM). Phase delays induced by 2 pulses separated by 1, 15 or
104 min were 85 ± 23, 114 ± 8 and 108 ± 9 min respectively
and were not differ significantly from shifts induced by a single pulse.
These results are similar to results obtained from hamsters using phase
advances and suggest that the light responsiveness of the mammalian photic
entrainment pathway is greatly reduced by an initial light stimulation
or by the response an initial stimulus induces in the circadian pacemaker.
The mechanism for this reduction in light sensitivity remains a mystery. |
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| Last Updated: 7/13/1998 |
© Ali Khammanivong, 1998 - All Rights
Reserved
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