Ultrastructural identification of synapses between mitral/tufted cell dendrites

Asymmetrical, type 1 synapses between mitral and/or tufted (M/T) cell dendrites were observed in the glomerular layer (GL) and juxtaglomerular external plexiform layer (EPL) of Salamander olfactory bulb sections. The dendrites had electron-lucent cytoplasm containing regularly-arrayed microtubules and spherical translucent vesicles. The vesicles were clustered against a thin pre-synaptic density that was aligned with a 17-20 nm-wide synaptic cleft and a thicker post-synaptic density. These dendrodendritic synapses could be a source of the delayed, prolonged excitation that originates from the GL/EPL. During spatiotemporal encoding of odor stimuli, they could amplify or synchronize M/T cell responses. (C) 2000 Elsevier Science B.V. All rights reserved.