Learning may reduce neurogenesis in adult rat dentate gyrus.

Neuron production carries on throughout adult life in granule cell layer of mammalian dentate gyrus. The acquisition of a hippocampus-dependent task enhances newborn cell survival in granule cell layer (GCL) during the period in which several newborn cells die. In this paper the effect of learning, occurring after the maximal period of newborn cell death, on newborn cells was investigated. Rats were trained for hippocampus-dependent learning in Morris water maze. 5-bromo-2'-deoxyuridine was administered 8-10 days before training beginning and labeled cells were counted after training. Learning decreased BrdU-labeled cell density in GCL, and increased TUNEL-positive cells. Moreover, learning diminished immature neuron density prevalently in the internal blade of GCL. Therefore, a different effect of learning on immature neuron survival, depending on the time elapsing from mitosis to learning, is suggested.