SPONTANEOUS CONGENITAL HYDROCEPHALUS IN THE MUTANT MOUSE HYH - CHANGES IN THE VENTRICULAR SYSTEM AND THE SUBCOMMISSURAL ORGAN

The subcommissural organ is an ependymal gland located at the entrance of the cerebral aqueduct., It secretes glycoproteins into the cerebro spinal fluid, where they aggregate to form Reissner's fiber. This fibe r grows along the aqueduct, fourth ventricle, and central canal. There is evidence that the subcommissural organ is involved in the pathogen esis of congenital hydrocephalus. This organ was investigated in the m utant mouse hyh developing a congenital hydrocephalus. The central ner vous system of normal and hydrocephalic hyh mice, 1 to 40 days old, wa s investigated using antibodies recognizing the subcommissural organ s ecretory glycoproteins, and by transmission and scanning electron micr oscopy. At birth, the affected mice displayed open communications betw een all ventricles, absence of a central canal in the spinal cord, epe ndymal denudation of the ventricles, stenosis of the rostral end of th e aqueduct, and hydrocephalus of the lateral and third ventricles and of the caudal end of the aqueduct. Around the 5th postnatal day, the c ommunication between the caudal aqueduct and fourth ventricle sealed, and hydrocephalus became severe. It is postulated that the hh mice car ry a genetic defect affecting the ependymal cell lineage. The subcommi ssural organ showed signs of increased secretory activity; it released to the stenosed aqueduct a material that aggregated, but it did not f orm a Reissner's fiber. A large area of the third ventricular wall dif ferentiated into a secretory ependyma synthesizing a material similar to that secreted by the subcommissural organ. It is concluded that the subcommissural organ changes during hydrocephalus; whether these chan ges preceed hydrocephalus needs to be investigated.