Effects of pCO2 on the CSF Turnover Rate in Rats Monitored by Gd-DTPA Enhanced T1-Weighted Magnetic Resonance Imaging.

Abstract

Hypercapnia produces a vasodilatation of the cerebral vasculature with an increase in cerebral blood flow and hypocapnia causes vasoconstriction with a decrease in cerebral blood flow. The cerebrospinal fluid (CSF) pressure was increased by hypercapnia and decreased by hypocapnia [1]. This suggested that the formation of CSF might be altered by carbon dioxide. However, we have seen conflicting results in regard to the influence of hypercapnia and hypocapnia on CSF formation [2][3][4][5][6]. To confirm the effects of CO 2 , we developed a new method to measure local CSF turnover rate in the lateral ventricle of the rat brain.Several methods have been developed to measure the rate of CSF production, based on (i) drainage of CSF from the cisterna magna or aqueduct; (ii) clearance of injected substances, such as inulin or dextran; and (iii) ventriculocisternal perfusion. The drainage technique was the earliest, and it was a direct attempt to measure the CSF production rate [7]. This method was applied in experiments using large animals such as dogs and cats, but it is not suitable for small animals such as rats and mice. The ventriculocisternal perfusion method [8] employs an inflow-cannula, inserted into a lateral ventricle, and an outflow-cannula in the cisterna magna. An artificial CSF is pumped in Key words: 1 H MRI, production of cerebrospinal fluid, hypocapnia, hypercapnia, carbonic anhydrase inhibitor. Abstract:The cerebrospinal fluid (CSF) secretion of rat was monitored by longitudinal relaxation time-weighted magnetic resonance imaging (T 1 -weighted MRI) in combination with a ventricular injection of a T 1 -relaxation reagent: gadolinium-diethylene triamine-N,N,NЈ,NЉ,NЉ-pentaacetic acid (Gd-DTPA). A cannula was inserted in the left lateral ventricle, and 5 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 0.158Ϯ0.009 min Ϫ1 at an arterial blood CO 2 tension (pCO 2 ) of 38.6Ϯ2.2 mmHg (nϭ10), which corresponds to the CSF secretion rate of 3.6 l min Ϫ1. The k value was decreased (0.078Ϯ0.010 min Ϫ1, nϭ4) by a carbonic-anhydrase inhibitor (acetazolamide). The turnover rate was decreased by hypocapnia (0.094Ϯ0.019 min Ϫ1, pCO 2 ϭ24.7Ϯ 2.9 mmHg, nϭ4), and it increased gradually and reached a plateau level as a result of hypercapnia (0.194Ϯ0.011 min Ϫ1, pCO 2 ϭ104.5Ϯ7.1 mmHg, nϭ10). These results suggested that CO 2 upregulates the secretion of CSF in the rat.

Long-Term Relationships between Synaptic Tenacity, Synaptic Remodeling, and Network Activity

“…On the other hand, in the absence of perfusion, the long-term viability of these preparations was drastically impaired. Interestingly, media turnover rates (∼0.15%/min) were one to two orders of magnitudes lower than cerebrospinal fluid (CSF) turnover rates in the intact rat brain (1% to 16%/min; [55]), indicating that perfusion rates were not excessively high.…”

Leptin and post-prandial satiety: acute central leptin more potently reduces meal frequency than meal size in the rat

“…Real-time neuroimaging studies in the rat have revealed that material injected into the lateral ventricle appears almost simultaneously in the upper part of the third ventricle, which communicates with the lateral ventricles via the foramen of Monro, and peaks in the posterior third ventricle within 2 min of injection at a signal intensity 75-90% of that observed in the lateral ventricle (Bui et al 1999;Takamata et al 2001). Consistent with these observations, radiolabeled leptin has been shown to penetrate more than 200 μm into periventricular structures of the third ventricle within 2 min of infusion into the lateral ventricle (Maness et al 1998).…”

“…At the pretreatment interval used in the present study (30 min), leptin infused into the lateral ventricle would have penetrated more than 600 μm into structures that surround the third ventricle by the onset of testing (Maness et al 1998), thereby enveloping the arcuate nucleus, a putative site of action. Thus, while third versus lateral ventricle of administration might account for differences in potency, it is unlikely to result in different modes of action because of the substantial, rapid flow of CSF between the lateral and third ventricles (Maness et al 1998;Bui et al 1999;Takamata et al 2001).…”

The evolutionary and integrative roles of transthyretin in thyroid hormone homeostasis

“…In most mammals, it takes about 200 min for the secretion of an amount of CSF replacing the total volume of CSF in the ventricles (Cserr 1971). For rats, longitudinal relaxation timeweighted magnetic resonance imaging after intraventricular injection of the T 1 -relaxation reagent Gd-DTPA showed that the whole ventricular space is not a single compartment (Takamata et al 2001). Probably, the flow of CSF through the ventricular system involves both laminar and turbulent flow, the proportions of which differ from region to region.…”