Reissner fiber binds and transports away monoamines present in the cerebrospinal fluid.
The subcommissural organ (SCO) is a brain gland that secretes glycoproteins into the cerebrospinal fluid (CSF), where they subsequently aggregate to form Reissner fiber (RF). By addition of newly released glycoproteins to its cephalic end, RF grows constantly through the Sylvian aqueduct, fourth ventricle and central canal of the spinal cord. Disaggregation of RF-material and passage to blood occur when RF reaches the terminal ventricle at the filum. The present investigation was designed to test the hypothesis that RF binds, transports and clears away monoamines present in the CSF. Four experimental protocols were applied: (i) in vivo binding of labeled monoamines to the rat RF, studied by pulse and chase, and after perfusion for 7 days; (ii) identification of monoamines, by high-performance liquid chromatography (HPLC), naturally occurring in the bovine RF; (iii) in vitro binding of labeled and unlabeled monoamines to the isolated bovine RF; and (iv) tentative identification of the amine binding site(s) in RF-proteins by use of specific antibodies. The results obtained indicate that RF participates in the regulation of the CSF concentration of monoamines either by binding and transporting them away throughout the central canal of the spinal cord (L-DOPA, noradrenaline, adrenaline), or by transiently binding them and releasing them back to the CSF (serotonin). Furthermore, evidence was obtained that (i) adrenaline and noradrenaline share the same binding site, and that this site would correspond to a repeated sequence present in the SCO-spondin, the major protein component of RF; and (ii) serotonin has its own binding site in RF.