Isograft and xenograft of the subcommissural organ into the lateral ventricle of the rat and the formation of Reissner's fiber

The subcommissural organ (SCO) secretes glycoproteins into the cerebrospina l fluid (CSF) that aggregate and form Reissner's fiber (RF). The factors in volved in this aggregation are not known. One factor may be the hydrodynami cs of the CSF when flowing through the aqueduct. This hypothesis was tested by isografting rat SCO and xenografting bovine SCO into the lateral ventri cle of rats. Xenografts were either fresh bovine SCO or explants cultured f or 30 days before transplantation. The grafts were investigated by electron microscopy and immunocytochemistry using antibodies against RF glycoprotei ns, serotonin and the glucose transporter I. Maximal time of transplantatio n was 43 days for isografts and 14 days for xenografts. The isografts were not reinnervated but were revascularized; they secreted into the ventricle RF glycoproteins that became progressively packed into pre-RE and RF struct ures identical to those formed by the SCO in situ. RF was confined to the h ost ventricle and at its distal end the constituent proteins disassembled. Xenografts were neither reinnervated nor revascularized and secreted into t he host ventricle a material that never formed an RE These findings indicat e that the CSF factor responsible for the formation of RF is species specif ic, and that this process does not depend on the hydrodynamics of the CSF. The blood vessels revascularizing the isografted SCO acquired the character istics of the vessels irrigating the SCO in situ, namely, a tight endotheli um displaying glucose transporter I, and a perivascular space containing lo ng-spacing collagen, thus indicating that basal release of glycoproteins ma y also occur in the grafted SCO.