Presynaptic mechanisms involved in the expression of STP and LTP at CA1 synapses in the hippocampus.

The study of long-term potentiation (LTP) has for many years been the centre of a raging debate as to whether the process is expressed by presynaptic or postsynaptic mechanisms. Here we present evidence that two forms of synaptic plasticity at CA3-CA1 synapses in the hippocampus are expressed by presynaptic changes. One form is short-term potentiation (STP) and the other a neonatal form of early-LTP (E-LTP). We review recent experimental data that suggests that this latter form of LTP involves an increase in the probability of neurotransmitter release (Pr). We describe how this is caused by the rapid down-regulation of a high affinity kainate receptor, which otherwise responds to ambient levels of l-glutamate by depressing Pr.