REGULATION OF HIPPOCAMPAL TRANSMITTER RELEASE DURING DEVELOPMENT AND LONG-TERM POTENTIATION

Developmental changes in rat hippocampal transmitter release and synap tic plasticity were investigated. Recordings from pairs of pyramidal n eurons in slices showed that an action potential in a CA3 neuron relea sed only a single quantum of transmitter onto a CAI neuron. Failures o f synaptic transmission reflected probabilistic transmitter release. T he probability of release (P-r) was 0.9 in 4- to 8-day-old rats and de creased to less than 0.5 at 2 to 3 weeks. Long-term potentiation (LTP) in 2- to 3-week-old rats was associated with an increase in P-r from a single synaptic site. The high initial P-r in 4- to 8-day-old rats n ormally occludes the expression of LTP at this stage.