Unidirectional coupling of gap junctions between neuroglia.

Gap junctions permit the passage of ions and small molecules between cells, thereby providing a basis for direct intercellular communication. In the rabbit retina, the low molecular weight dyes Lucifer yellow and biocytin passed readily from astrocytes into adjacent astrocytes, oligodendrocytes, and Müller cells. However, the dyes rarely passed from either oligodendrocytes or Müller cells into astrocytes. Unidirectional passage of dye suggests the presence of an asymmetric barrier to the movement of molecules through heterologous gap junctions and indicates the potential for a hierarchy of command between interconnected cells.