new neurons develop morphological features of granule cells. New granule cells grow characteristic dendritic trees extending toward the molecular layer (Ribak et al., 2004), elaborate axons toward the CA3 region of the hippocampus (Hastings & Gould, 1999; Zhao et al., 2006), and generate action potentials (van Praag et al., 2002). Initially, new neurons respond to GABA, the main inhibitory neurotransmitter of mature granule cells, with excitation (Ge et al., 2006). As new neurons mature, Cl- channels on the granule cell membrane mature and GABA has an inhibitory effect. New neurons also show enhanced synaptic plasticity during maturation (Snyder et al., 2001; Ge et al., 2007) compared to mature granule cells. This lack of inhibition and increased plasticity make new neurons an ideal substrate for influencing hippocampal function.
