Goldfish ependymins: cerebrospinal fluid proteins of meningeal origin

Ependymins are unique secretory proteins from the goldfish brain which have calcium binding capacity. They are synthesized in the leptomeninx and appear subsequently as the predominant protein constituents in the cerebrospinal fluid (CSF). In contrast, the serum is nearly devoid of ependymins. The perimeningeal fluid (PMF) between the meninx and the skull represents a mixture of CSF and serum. The different composition of PMF and CSF implies that there is no open communication between these two compartments. Separation is probably achieved by an arachnoid-like meningeal barrier as proposed from ultrastructural studies. This basic CSF system of fish is compared with that of higher vertebrates.