Neurotransmitter release during and after ischemic event is thought to be involved in excitotoxicity as a pathogenesis for the ischemic brain damage, which is mediated by excessive activation of glutamate receptors and attendant calcium overload. To ascertain the role of transmitter release from nerve terminals in promoting the ischemic neurodegeneration, we delivered antisense oligodeoxynucleotides (ODNs) to synaptotagmin I or synapsin I into the rat brain by using HVJ-liposome gene transfer technique. The antisense ODNs were injected into the lateralventricle in rats 4 days prior to transient forebrain ischemia of 20 min. With a single antisense treatment, long-lasting downregulation of the transmitter release relating protein levels at overall synaptic terminals was achieved. The antisense in vivo knockdown of synaptotagmin I prevented almost completely the ischemic damage of hippocampal CA1 neurons, while the in vivo knockdown of synapsin I markedly promoted the ischemic damage of CA1 pyramidal neurons and extended the injury to relatively resistant CA2/CA3 region. The modulation of ischemic hippocampal damage by the in vivo knockdown of synaptotagmin I or synapsin I suggests that transmitter release from terminals plays an important role in the evolution of ischemic brain damage and therefore the transmitter release strategy by the use of antisense ODNs-HVJ-liposome complex is reliable for neuroprotective therapies.