A: Schematic representation of a secretory ependymal cell of the rat SCO. In the rough endoplasmic reticulum secretory proteins have N-linked, high mannose type oligosaccharides (1). In the Golgi cisternae glucosamine, galactose and sialic acid are conjugated to the saccharide core (2). In the secretory granules and in the released secretion, the backbone protein of the secretory glycoproteins undergoes cleavage (3, arrow) [12, 28]. The secretory glycoproteins released into the ventricle may become densely packed forming Reissner's fiber (RF) or may remains soluble in the cerebrospinal fluid (from Rodriguez et al. ). B: Schematic representation of a N-linked, complex type, oligosaccharide. The core of glucosamine and mannose are conjugated in the rough endoplasmic reticulum (RER); glucosamine, galactose and sialic acid are conjugated in the Golgi apparatus (GA). Concanavalin A (Con A) has affinity for internal and terminal mannose residues; wheat germ agglutinin (WGA) has affinity for terminal residues of glucosamine and sialic acid. C: Immunoblotting analysis of the subcommissural organ (SCO) using AFRU as primary antibody. Four immunoreactive polypeptides are detected in the adult bovine SCO, five in the PN30 rat SCO and four in the PN30 mouse SCO. Numbers: refer to molecular weight in kDa; arrows: secretory compounds; asterisk indicates the absence of 200 kDa compound. D: Immunoblotting analyses using AFRU as primary antibody of extracts of rat SCO and rat and mouse central canal (CC) at PN30. Numbers refer to molecular weight in kDa. Two polypeptides of 200 and 45 kDa were present in all samples. Asterisk: immunoreactive band of 120 kDa present only in the rat central canal. E: Western blot analysis of cisternal CSF collected from E18, E20, PN1, PN 7 and PN30 rats. Numbers refer to molecular weight in kDa. Eight immunoreactive polypeptides are detected in the CSF collected perinatally (E18, E20, PN1, PN7) (horizontal lines). Four of these compounds are missing from the CSF of PN30 rats (asterisks). F: Densitometric linear scannings of CSF immunoblots at E18, PN1 and PN30. The statistical analysis using four immunoblots each revealed a significant difference in luminescence value of the 120 kDa band between E18 and PN1 (*, P < 0.001), and between PN1 and PN30 (P < 0.001). Differences between E18 and PN30 in the 180, 164 and 145 kDa bands were also significant (◇, P < 0.05).