Ultrastructural features of primate granule cell bodies show important differences from those of rats: axosomatic synapses, somatic spines and infolded nuclei.

Granule cells of the primate dentate gyrus were examined in the electron microscope where they displayed significantly less axosomatic synapses than granule cells in rodents. In addition, primate granule cells frequently had infolded cell nuclei and somal spines which are features that are both rare in rodents. Since the granule cell body is an important site for gamma-aminobutyric acid (GABA)ergic inhibitory control, the reduced number of axosomatic synapses in monkeys suggests that local inhibitory connections of primate granule cells are less than that of rodents. Together, these differences may indicate that the primate granule cells are physiologically more active than rat granule cells.