Establishing the conditions under which long-term depression (LTD) an be induced in vitro remains an important empirical issue. While heterosynaptic LTD is readily elicited in the hippocampus in vivo, the induction of homosynaptic LTD has been more problematic, both in CA1 and in the dentate gyrus. Our work has demonstrated, however, that 900 pulses at 1 Hz will reliably induce LTD in both area CA1 and the dentate gyrus of pentobarbital-anesthetized animals, when the stimulating and recording electrodes are in close proximity to each other.