Enhanced synaptic plasticity in newly generated granule cells of the adult hippocampus

Neural stem cells in various regions of the vertebrate brain continuously generate neurons throughout life(1-4). In the mammalian hippocampus, a region important for spatial and episodic memory(5,6), thousands of new granule cells are produced per day(7), with the exact number depending on environmental conditions and physical exercise(1,8). The survival of these neurons is improved by learning and conversely learning may be promoted by neurogenesis(8-10). Although it has been suggested that newly generated neurons may have specific properties to facilitate learning(2,10,11), the cellular and synaptic mechanisms of plasticity in these neurons are largely unknown. Here we show that young granule cells in the adult hippocampus differ substantially from mature granule cells in both active and passive membrane properties. In young neurons, T-type Ca2+ channels can generate isolated Ca2+ spikes and boost fast Na+ action potentials, contributing to the induction of synaptic plasticity. Associative long-term potentiation can be induced more easily in young neurons than in mature neurons under identical conditions. Thus, newly generated neurons express unique mechanisms to facilitate synaptic plasticity, which may be important for the formation of new memories.