Evidence that granule cells generated in the dentate gyrus of adult rats extend axonal projections.

Fully mature rats were injected intraperitoneally with 3H-TdR on postnatal day (P) 100. After an additional 28-32 days, a retrograde fluorescent tracer, either FB or DY, was injected into the regio inferior of the hippocampal formation to label granule cells of the dentate gyrus through their mossy fiber axons. Examination of autoradiographs from these brains reveals that 3H-TdR labeled cells within the granule cell layer of the dentate gyrus are often labeled with the retrograde tracer as well. This indicates that within the mature hippocampal formation, newly generated dentate granule cells are capable of extending axonal projections for considerable distances.