p h y s o o g y . o r g / b y l i l 1 0 . 2 2 0 . 3 3 . 3 o n S e p t e m b e r 1 6 , 2 0 1 6 April 1971 CHOROID PLEXUS PHYSIOLOGY 295 insight et al. from exposed of fluid pia). Although ions, exchange into (120) the characteristics of extrachoroidal compared et al. and Ames plexus with CSF obtained choroid (4) have circulation (i.e., fluid differences that that has come into regional difference in composition can unequivocally the only processes is for potassium. exchange processes, Rougemont collected of CSF route along the and the ependyma for several the composition from contact sites further with have been observed be ascribed to extrachoroidal CSF obtained respect to only one of mixed from to four the cisterna magna ions plexus and K+), while the plexus concentrations it was calculated and choroid

Samples (Table similar fluid being the lateral fell while Clthat bicarbonate estimated Ca++, 5) differed with with ventricle regard to concentration fluid plexus 5) differed with with ventricle regard to concentration fluid plexus (Cl-, Mg++, (Na+). During of circulation the cisterna magna, rose. On and Ca++ balance, also differed of choroid K+, Mg++, the basis of charge magna concentration and cisterna The HCOSregard to fluid was with plexus CSF choroid concentration. to be 7 mM greater that of cisternal than for differences ventricle, Thus CSF (4). CSF and between choroidal fluid exchange third cisterna magna In seeking from lateral the plexus of the processes must be considered. may differ fourth ventricular the exposed net extrachoroidal may arise to location explanations both and extrachoroidal and from fluids produced of the by the plexuses fluid from differences significantly plexus in composition collected in composition ventricles

from In contrast the plexuses observed changes the concentration intrawithin exchange processes. the cisterna magna considered, just in to ex trachoroidal composition fluid means space may f ound (120) were ventricular the Rougemont and concentration (17) subsequently the cortical The tration indicate In suggested and K+* 9 space, somewhat in CSF cerebral and Na+ and Clinterstitial differences be ascribed in cats similar lower that subarachnoid samples and Clfrom concentration, that CSF in Na+ et al. while K+ and Davson through to dogs. the concencisterna pericallosa was significantly confirmed in Bito circulation the observation further the cisterna pericallosa. falls during that K+ concentration subarachnoid decrease space of cats and also extended [K+] this observation from observed takes CSF in concentration filtrate; in a plasma consequently potassium to interpreted has been

have for exchange be at must permeable, that extrachoroidal that Bito transport the pia is relatively view of evidence that further, they suggest less than and Davson processes the subarachnoid the blood-brain in order that that barrier is the site of active loss of K+ within to explain the net at a value variations interstitial in CSF. Concurrent fluid K+ concentration is maintained that regional the view with CSF of that CSF and between the uniformity to differences be ascribed fluid, may in composition composition Bito suggest interstitial concentrations are similar and Davson the subarachnoid to that indicates within with space ions. fluid two similarities of potassium, plexus Possible respect variations homeostasis these and composition and in CSF of regional out In a discussion it calis a charthe in that restricted should cium acteristic also be pointed magnesium, alone, to choroid but differences