| Abstract: | The ultrastructure and permeability of the CSF-brain barrier in the median eminence were studied during the perinatal period in rats with electron microscopy, electron-microscopic radioautography and electron-dense markers. It was shown that the ependymal cells forming the ventral portion of the 3rd ventricle (infundibular recess) are joined by the specialized junctions. The specialized junctions are similar in ultrastructure in different parts of infundibular recess all through the perinatal period. They consist of the tight junctions which are sometimes in series with the gap junctions and adhesion zones. An electron-dense marker, La3+, injected into the cerebral ventricles, penetrates through the foetal ependymal linins both via the ependymal cells and intercellularly in all parts of the infundibular recess. In neonatal rats La3+ penetrates in the same way in the rostral part of infundibular recess only, while in the caudal part its permeability is markedly limited, apparently by the tight junctions formed de novo around the cells. 3H-dopamine, introduced into the ventricles, crosses over the ependymal linins apparently in the same way as La3+. Then the labeled dopamine is transported into the pericapillary space of the primary portal plexus and, finally, into the capillary lumen. Thus, the results obtained point to the permeability of the CSF-brain barrier in the foetal median eminence for the markers including neurohormones. In the postnatal period the permeability of the ependyma becomes limited due to the formation of the tight junctions surrounding the ependymal cells. |
