Figure 5

Inhibitory coupling between pairs of lamina II inhibitory interneurons. A. Example recordings from a pair of synaptically connected neurons. Top traces are from the presynaptic neuron showing a train of action potentials evoked by a 100 ms depolarizing current step. Bottom traces show simultaneous recordings of IPSCs from the postsynaptic cell. Note on the right, the release failure in response to the first action potential. Most IPSCs in this pair displayed fast decay kinetics with a slow component also visible in some events. B. Graph showing the probability p of release for each of the first five presynaptic action potentials in the train calculated from the pair of neurons shown in A (p defined as number of IPSCs per number of corresponding action potential in 50 consecutive trains delivered at 0.1 Hz). Note the dramatic increase in release probability in response to the 2nd action potential in the train. C. Probability of release for each of the first 4 action potentials in the train averaged for all 3 synaptically connected pairs studied. Values are means ± SEM. D. The probability p of release per train calculated for each train from the pair of neurons shown in A. The plot was smoothed with a running average of four values. Note the transient increase in probability after the initial trains.