The tight epithelium of the Mongolian gerbil subcommissural organ as revealed by freeze-fracturing.

Examination of neonatal Mongolian gerbil subcommissural organ (SCO) by freeze-fracture electron microscopy reveals that the epithelial layer (the ependyma) possesses distinctive and very complex tight junctions which connect the apical portions of adjacent ependymal cells. The tight junction network of the Mongolian gerbil is more extensive neonatally than in the adult, and is in general, more conspicuous than in other animal species. The consistent finding of such very complex tight junctions at the interface between the C.S.F. and the SCO suggests that the SCO ependyma, at least in neonatal Monglian gerbils, might function as a tight epithelium with an ability to maintain steep solute gradients and high potential differences. The sealing-off of the SCO towards the C.S.F. (the C.S.F.--SCO barrier) and the effective blood-brain barrier in the organ (the blood-SCO barrier) might well be of functional significance, perhaps in relation to mechanisms involved in the control and/or detection of the stability of the internal environment of the brain.