Identification of astrocytes as oligodendrocyte coupling partners in suprachiasmatic nucleus (A, B) and spinal cord (C). A, Stereoscopic image of an oligodendrocyte linked to the same astrocyte by one unlabeled gap junction (top left box, enlarged intop right inset) and by one Cx43-labeled gap junction (20 nm gold; bottom left box, enlarged in bottom right inset). The coupled astrocyte contained a small bundle of GFAP filaments in the cross-fractured cytoplasm (asterisk), and a square array was labeled for AQP4 (10 nm gold beads; white arrow). In oligodendrocyte E-faces, reciprocal patches (black arrow) contain both IMPs and pits. B, Stereoscopic image of one Cx43-labeled gap junction and one unlabeled mixed gap junction/reciprocal patch (arrow) in an oligodendrocyte E-face. GFAP filaments are in the cross-fractured cytoplasm (asterisk).C, Stereoscopic image of a gap junction in a spinal cord oligodendrocyte E-face in a sample that was double-labeled for Cx32 (10 nm gold; none present) and Cx30 (20 nm gold). Only Cx30 labeling was present in the plasma membrane of the oligodendrocyte coupling partner. Gap junctions often abut or intermingle with reciprocal patches (arrow).