Presynaptic activity in the period immediately after conditioning is not necessary for long-term potentiation.

The stratum radiatum of in vitro slices of rat hippocampus was tetanically stimulated to induce long-term potentiation (LTP) in CA1 neurons. One group of slices received test stimuli immediately after tetanisation, whilst another received no test stimuli until 30 min afterwards. No difference (P greater than 0.65) was found between the magnitude of LTP induced in the two groups of slices. This result demonstrates that the induction and maintenance of LTP does not require presynaptic release of transmitter or other neuroactive substances in the period immediately after tetanisation.