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J. S. Lin, J. H. K. Liu; Circadian Variations of Intracranial Pressure and Translaminar Pressure Difference in Sprague-Dawley Rats. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1632. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the circadian (24-hour) change pattern of intracranial pressure (ICP) in Sprague-Dawley rats and to project its influence on the circadian change pattern of translaminar pressure difference, which is intraocular pressure (IOP) minus ICP.
Sprague-Dawley rats 10-12 weeks of age were entrained to a standard light-dark cycle. A telemetric pressure transmitter was implanted subcutaneously on the upper back of each light-dark entrained rat, and the pressure catheter tip was inserted into the lateral ventricle using a stereotaxic technique. Broadcasted ICP and locomotoractivity data were received at 120 Hz in conscious freely moving rats. Means of 2-minute data were recorded every 5 minutes for 2-10 days to generate the 24-hour ICP and activity patterns. The averages for the 12-hour light phase and the 12-hour dark phase were compared. The 24-hour change pattern of ICP was also determined under an acute 24-hour constant dark condition. A projection of the translaminar pressure difference was calculated based on a previously established 24-hour IOP pattern and on the ICP data collected in these Sprague-Dawley rats.
Under the standard light-dark condition, locomotor activity levels were higher during the dark phase than the light phase (P<0.01, paired t-test, N=9). Average ICP was 9.33±5.03 mmHg (mean±SD) during the light phase and 9.22±5.03 mmHg during the dark phase, with an average light-dark difference of -0.11±1.45 mmHg (P=0.823). Under the acute constant dark condition, the subjective light-dark difference in ICP remained not significant (-0.32±1.56 mmHg, P=0.636, N=6), indicating that the circadian ICP variation remained flat and independent of light-dark conditions. As a statistically significant light-dark elevation of 5.28±3.91 mmHg in IOP (P<0.01, N=11) was found in Sprague-Dawley rats housed under the same laboratory conditions, the light-dark variation in ICP was considered minimal. Average translaminar pressure difference was projected to be higher in the dark phase (14.26 mmHg) than in the light phase (8.84 mmHg), and the light-dark difference was mainly due to the change of IOP, not the change of ICP.
There is no statistically significant ICP variation between the light and dark phases in Sprague-Dawley rats. The circadian variation of translaminar pressure difference is mainly due to the circadian change in IOP, not ICP, in this species.
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