Rapid dendritic Ca2+ influx is associated with induction of homosynaptic long-term depression in adult rat hippocampus.

Homosynaptic long-term depression was induced in area CA1 of adult hippocampus by prolonged low-frequency stimulation (900 pulses at 2 Hz) in the presence of the GABAA receptor antagonist picrotoxin. Using ratio imaging with fura-2, we demonstrate that the induction of this long-term depression is associated with a rapid and transient (approximately 30 s) dendritic Ca2+ increase (approximately 500 nM) dependent on the activation of voltage-gated Ca2+ channels. This transient increase, by itself, was insufficient for long-term depression induction.