A substantial number of asymmetric axosomatic synapses is a characteristic of the granule cells of the hippocampal dentate gyrus.

The types of axosomatic synapses for pyramidal neurons of the Ammon's horn and granule cells of the dentate gyrus were investigated in the rat hippocampus. Local circuit neurons in both of these regions were also included. The mean number of axosomatic synapses was higher for pyramidal neurons than granule cells. Practically all of these synaptic contacts were symmetric for the pyramidal neurons of the CA1 area, whereas the percentage of asymmetric axosomatic synapses for granule cells and local circuit neurons was 21% and 26%, respectively. This finding is interesting because granule cells appear to be the only known projection neuron type to possess such a high percentage of asymmetric axosomatic synapses.