Fig. 2. Morphology of L1ir and L1ir-negative synapses. (A) Electron micrographs of consecutive ultrathin sections (1-11) and three-dimensional reconstruction demonstrating the L1ir orphan bouton (a), L1ir synapse (b) and L1ir-negative synapse (c) of the same microscopic field in NP^+/+ mice (12). (B) Complete three-dimensional reconstruction of L1ir orphan boutons (a), L1ir synapses (b) and L1ir-negative synapses (c) in NP^+/+ and NP^-/- mice. Reconstructed presynapses are green, postsynapses are blue, their PSDs are light blue and L1-immunoreactive sites are red. Bars, 600 nm for all panels.