Abstract
The cerebrospinal fluid (CSF) secretion of rat was monitored by longitudinal relaxation time-weighted magnetic resonance imaging (T1-weighted MRI) in combination with a ventricular injection of a T1-relaxation reagent: gadolinium-diethylene triamine-N,N,N′,N″,N″-pentaacetic acid (Gd-DTPA). A cannula was inserted in the left lateral ventricle, and 5 &mgr;l of 8.5 mM Gd-DTPA was injected as a CSF marker. Changes in the image intensity of the CSF were measured every 30 s, and the turnover rate of CSF (k) in the left lateral ventricle was obtained from the dilution of Gd-DTPA, based on the assumption of a single compartment model. In the control conditions, k was 0.158 ± 0.009 min−1 at an arterial blood CO2 tension (pCO2) of 38.6 ± 2.2 mmHg (n = 10), which corresponds to the CSF secretion rate of 3.6 μl min−1. The k value was decreased (0.078 ± 0.010 min−1, n = 4) by a carbonic-anhydrase inhibitor (acetazolamide). The turnover rate was decreased by hypocapnia (0.094 ± 0.019 min−1, pCO2 = 24.7 ± 2.9 mmHg, n = 4), and it increased gradually and reached a plateau level as a result of hypercapnia (0.194 ± 0.011 min−1, pCO2 = 104.5 ± 7.1 mmHg, n = 10). These results suggested that CO2 upregulates the secretion of CSF in the rat.
