Chemical LTD in the CA1 field of the hippocampus from young and mature rats

Within the hippocampal formation, two forms of long-lasting synaptic plasti city, long-term potentiation (LTP) and long-term depression (LTD), can be i nduced which require the activation of NMDA receptors. Interestingly, it ha s been shown that both LTP and LTD are reduced in adult animals. Recently, a new chemical protocol has been described which elicits LTD in the CA1 fie ld of the hippocampus. Application of 20 mu M NMDA for 3 min results in a s table and long-lasting decrease in the evoked synaptic responses. We used t his protocol to induce LTD in hippocampal slices from young and adult rats and show that this form of LTD is AP5-sensitive and can be blocked by the p rotein phosphatase inhibitor cyclosporin A in slices from adult animals. In contrast to electrical LTD (induced by prolonged low frequency stimulation ), the extent of chemical LTD was not different between the young and adult rats. These findings indicate that the intracellular signal transduction c ascades involved in long-lasting synaptic depression are still intact in ad ult animals.