Figure 7.

Synaptically released glutamate regularly coactivates neighboring synapses to a small extend. (A) AMPA receptor-mediated population synaptic responses in hippocampal slices are enhanced by glutamate acting on neighboring synapses. Left panel, summary of the first slopes of fEPSPs recorded in CA1 Str. rad. Note the slight, but statistically a significant decrease in fEPSPs upon application of the glutamate scavenger system (GPT, n = 9; “no drug” control experiment with placebo solution exchange, n = 11). Middle panel, the inhibitory effect of GPT is more pronounced on the second, facilitated fEPSPs, which is associated with a higher spatial density of releasing synapses. The letters “a” and “b” denote the times of the example traces illustrated in the right panel. Right panel, example traces illustrating the effect of GPT on population synaptic responses. (B) The glutamate scavenger system GPT is too slow to inactivate glutamate immediately after release in the synaptic cleft; the amplitude of miniature EPSCs remains unaffected. Miniature EPSCs were recorded in dissociated cultured neurons. As the nearest neighbor distance of synapses in cultured neurons is too large (≥1 μm) to allow for cross-talk, the amplitude of these currents is a measure of intrasynaptic AMPA receptor activation only. The letters “a” and “b” denote the times of the example traces illustrated in the right panel.