Low levels of Na, K-ATPase and carbonic anhydrase II during choroid plexus development suggest limited involvement in early CSF secretion.
In the adult, cerebrospinal fluid (CSF) is produced by the actions of numerous transporters and enzymes creating ion gradients that drive the entry of water into the ventricles via the aquaporin-1 water channels (AQP1). It is not known when in development CSF secretion starts but, in the rat, it has been postulated to occur around the time of birth. However, recent evidence suggests that the secretion may start much earlier, as soon as the lateral choroid plexuses first appear (around E14).


OBJECTIVE
To investigate the developmental profiles of two major enzymes responsible for CSF secretion in the adult, Na, K-ATPase (NKA) and carbonic anhydrase II (CAII).


METHODS
The developmental profiles of both enzymes were investigated using immunohistochemistry and Western Blot analysis in tissue from embryonic day (E) 15, 18, postnatal day (P) 0, 9 and adult rats.


RESULTS
Western Blot analysis showed low levels of NKA at E15 followed by a progressive increase with age. Immunohistochemistry confirmed the presence of NKA on the apical membrane of the lateral ventricular choroid plexus epithelium from E15 onwards. Western Blot analysis of CAII was complicated by its presence in blood, but the amount of protein increased with age. Immunohistochemically, CAII appeared in the lateral ventricular choroid plexus between P0 and P9.


CONCLUSIONS
The low levels of NKA and CAII during early choroid plexus development indicate that other mechanisms, such as the previously described specific protein transfer across epithelial cells, may be involved in early CSF secretion and movement of water into the cerebral ventricles.
Johansson
Pia
P
Department of Pharmacology, University of Melbourne, Parkville, Victoria 3010, Australia. piaaj@unimelb.edu.au
Dziegielewska
Katarzyna
K
Saunders
Norman
N
D000818:Animals; D015153:Blotting, Western; D024402:Carbonic Anhydrase II / Q000096:biosynthesis*; D002555:Cerebrospinal Fluid / Q000502:physiology*; D002831:Choroid Plexus / Q000196:embryology* / Q000201:enzymology*; D015870:Gene Expression; D007150:Immunohistochemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis*
D024402:Carbonic Anhydrase II; D000254:Sodium-Potassium-Exchanging ATPase