Long-term potentiation of evoked presynaptic response at CA3-CA1 synapses by transient oxygen-glucose deprivation in rat brain slices.

Physiological activity-dependent long-term changes in synaptic transmission, as long-term potentiation (LTP) are thought to be the substrate of learning and memory. However, a form of postsynaptic pathological LTP at the CA3-CA1 synapses has been demonstrated following few minutes of anoxia and aglycemia in vitro. The ischemia LTP shared many molecular mechanisms with the physiological LTP, and was believed to be involved in the delayed neuronal death following ischemia. However, the role of the presynaptic component in this regard is not known. Here we show that a short period of oxygen-glucose deprivation can induce a form of LTP (lasting for hours) of the presynaptic response at the CA3-CA1 synapses. This form of LTP is independent of postsynaptic alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors, but Ca(2+) dependent. This presynaptic LTP may represent a presynaptic hyperexcitability of the afferent fibers following ischemia, and responsible for the excitotoxicity to the CA1 neurons (ischemia-induced increases of glutamate release that kills neurons) and the postsynaptic pathological ischemic LTP.