Fig. 3. Electron micrographs showing the dendrodendritic gap junctions. a, Two PV-ir dendrites (D) receiving multiple presynaptic terminals (asterisks) make direct contact with each other. b, Enlargement of the contact site ina. A gap junction is formed between the two PV-ir dendrites. Note the close apposition of the plasma membranes of the two contacting cells as demarcated by arrows. A synaptic bouton (asterisk) forming a synapse of asymmetrical type is located in close vicinity to the gap junction. c, Electron micrograph of a specimen without immunoreaction, demonstrating a profile similar to a. The contacting dendrites (D) receive presynaptic terminals (asterisks). d, Enlargement of the contact site in c with the same magnification as inb, g, and i to facilitate comparison. Plasma membranes of the two cells are closely apposed, as demarcated by arrows. Note a layer of cytoplasmic semidense material (arrowheads) undercoating either side of the junction, which is characteristic of neuronal gap junctions.e, Further enlargement of the contact site ind, showing a narrow central gap, 2.7 nm wide, between the outer leaflets of the apposed unit membranes. f–i, Other examples of gap junctions formed between PV-ir dendrites (D). The contact sites in f andh are enlarged in g and i, respectively, with the same magnification as in b andd. Scale bars: a, c,f, h, 1 μm; b,d, e, g, i, 0.1 μm.