Fig. 1.6.12. Asymmetrical (Gray I) synapse with spherical vesicle-containing bouton (S) and symmetrical (Gray II) synapse with pleiomorphic vesicles in the bouton (F). Note the intermediate line and parallel filaments in the synaptic cleft of the Gray I synapse. Scale = 200 nm. (Rat, thalamus; hippocampus.) Download the high resolution image (a); Download the high resolution image (b).