EXTRACELLULAR SPACE IN RAT BRAIN AFTER FIXATION WITH 12-M FORMALDEHYDE

The ultrastructure of the central nervous system (CNS) of the rat is described with particular reference to its extracellular space (ECS) and the presence of tight junctions. Ultrathin sections were examined with the electron microscope after perfusion of the brain, via abdominal aorta, with a 38 % (12 M) solution of formaldehyde for 60-90 sec. Material so fixed shows excellent cytological preservation. The ECS is almost insignificant, except at the outermost regions of the molecular layer. Tight junctions were seen to exist in large numbers between processes filled with synaptic vesicles, but not between glial processes, which show, instead, a different kind of nexuses more similar to the so-called gap junctions. The conclusion is reached that the interneuronal tight junctions described by other authors in the mammalian CNS should not be interpreted as fixation artifacts. © 1969 Academic Press, Inc.