Figure 4.

Synaptic release of glutamate by brief stimulus trains to mossy fibers causes the heterosynaptic activation of presynaptic KARs. (A1) Schematic drawing of the experimental setup. Two independent sets of mossy fibers were stimulated. The independence was verified by the lack of a refractory period when the two pathways were stimulated at a close interval. One set (stim-cond.) was stimulated repetitively (10 pulses at 200 Hz) to release glutamate, whereas the other set (stim-test) was used to test the effects of synaptically released glutamate. (A2) Traces from a representative experiment are shown. A conditioning train caused a decrease in latency and an increase in amplitude of the test afferent volley as clearly shown in the expanded superimposed traces. All these effects are reversed after a short application of CNQX. (B) Summary graph of six experiments done in the same way as shown in A. (Upper) Responses of the test afferent volley during the experiment (arrow designates start of conditioning). (Lower) The first volley during the conditioning train. [Reprinted with permission from ref. 16 (Copyright 2000, Elsevier Science).]