Ependymal lining of infundibular recess in perinatal rats: relationships with portal capillaries and permeability.

Structure and permeability of the ependymal lining the infundibular recess were studied in perinatal rats with silver impregnation, electron microscopy, radioautography, and tracer techniques. According to our data basal processes of ependymal cells reach the primary portal plexus linking the 3rd ventricle and the hypophysial portal system all through the perinatal period. After birth, some of the processes penetrate into the perivascular space of the primary portal plexus and abut there on the endothelium of capillaries. Ependymal cells of fetuses and neonates are joined by specialized junctions (tight junctions, gap junctions and zonulae adhaerentes). Intraventricularly injected ionic lanthanum crosses the ependymal lining of fetuses both trans- and extra-cellularly everywhere in the infundibular recess. By postnatal day 9 only the rostral portion of the recess remains readily permeable. Caudally, extracellular leakage becomes highly restricted, apparently due to the appearance of circumferential tight junctions. Finally, [3H]dopamine seems to penetrate through the ependymal lining in the same way as ionic lanthanum entering the portal capillaries. These findings suggest that the adenohypophysiotropic neurohormones can penetrate from the cerebrospinal fluid into the portal circulation from the very beginning of the establishment of the hypothalamo-hypophysial functional relationships during ontogenesis.