In the mid 1970s and the early 1980s, Michael Kaplan and his colleagues reexamined the initial observations using the electron microscope and added substantial confidence that neurogenesis could occur in the adult brain. Combining electron microscopy and tritiated thymidine labeling, they showed that labeled cells in the rat dentate gyrus have ultrastructural characteristics of neurons, such as dendrites and synapses. Although they were able to demonstrate this in repeatable studies in primate cortex, most researchers at the time did not consider this to be evidence of significant neurogenesis in adult mammals.