Junctions in the central nervous system of the cat

Summary Fixed and unfixed astrocytic membranes from the CNS of the cat were studied by means of the freeze-etching technique.A variable number of gap junctions was detected in astrocytic membranes. They are characterized by the well known hexagonal composition of their subunits. Besides this type of highly ordered membrane-bound particles, a second one was found. It is composed of four single particles (diameter 5 nm) which form an orthogonal subunit with a side length of about 10 nm. These membrane-associated orthogonal particle complexes (MOPC) could be observed in different stages of aggregation and expansion. They reveal an accumulation in membranes of the marginal glia layers and in the perivascular astrocytic end-feet. Unfixed, glycerol treated membranes, however, do not show these structures. After glycerol treatment of the unfixed membranes by immersion, the MOPC disintegrate to single particles which form clusters of various extension. The clustering phenomenon is dependent on the length of the time of exposure to glycerol. Shortening of the glycerol treatment by intravasal perfusion of the cryoprotectant agent causes an decrease of the clusters. Fragments and transient forms of the MOPC become visible. By variation of different physico-chemical parameters of the washing solution a similar effect on the MOPC was not achieved. The discussion deals with probable functional aspects of the MOPC. They are considered to act as membrane-bound functional multienzyme complexes which a) might play a role in mediating transmembrane passage of metabolites, or b) are essential for CSF control mechanisms, or c) have a functional relation to the nexus.Presented in part at the IIIth European Congress of Anatomists, Manchester, September 1973.Supported by Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 114(Bionach).