Neurogenesis persists in certain adult brain regions including the dentate gyrus. Recent studies have shown that long-term potentiation (LTP) induction in the afferent pathway enhances adult neurogenesis in the dentate gyrus. Here, we investigated whether long-term depression (LTD) induction also affects adult neurogenesis. We induced LTD in the dentate gyrus in one hemisphere and compared the amount of progenitor proliferation with that in the other hemisphere. Unlike LTP induction, LTD induction per se did not affect progenitor cell proliferation in the dentate gyrus. However, when LTD was induced a day before LTP induction, neuronal progenitor cell proliferation facilitated by LTP induction was markedly blunted. These results show that two forms of synaptic plasticity, LTP and LTD, differentially influence hippocampal adult neurogenesis. NeuroReport 20:1279-1283 (C) 2009 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.