EM and EM Golgi study on structure of nucleus rotundus in chicks.

The analysis of EM structure of nucleus rotundus completes the results got by Golgi study. The fine structure of neurons and neuropil of the nucleus and the synaptic relations were studied by EM. The fine structural details of principal neuron were described. Several synapses of symmetrical type with flattened vesicles in large terminals contacted the cell body and also the origin and proximal part of the main dendrites. In the neuropil synaptic junctions were formed by terminals that contained (1) spherical vesicles with occasionally very few dense core vesicles, (2) flattened synaptic vesicles. Terminals that contained spherical vesicles were associated with asymmetric synaptic densities, and terminals that contained flattened vesicles formed symmetric junctions. Synapses of asymmetric type associated mostly with terminal sections of dendrites forming glomerular-like structure. Synapses of symmetric type with flattened synaptic vesicles contacted the branching areas of dendritic terminals and side-branches, the origin of main dendrites and the cell surface of principal neuron.