Figure 8.

Synaptic activation of presynaptic KARs can both enhance and depress mossy fiber synaptic transmission. (A1) Schematic drawing of the experimental setup. A set of mossy fibers (stim-test) was stimulated, as was an independent set of associational/commissural fibers (stim-cond). The associational/commissural fibers were stimulated repetitively (3 or 10 pulses at 200 Hz) to release glutamate, whereas the mossy fiber responses were used to test the effects of synaptically released glutamate. (A2) In the presence of GYKI 53655, mossy fiber NMDAR-EPSCs were examined without conditioning (Left), after strong conditioning (10 pulses, Center), and after weak conditioning (three pulses, Right). Strong conditioning depresses the EPSC, whereas weak conditioning enhances it (Upper). These effects are abolished by CNQX (Lower). (A3) The EPSC amplitudes for the experiment in A2 are shown. (B) A summary of three experiments performed as described in A. [Reprinted with permission from ref. 22 (Copyright 2001, American Association for the Advancement of Science).]