Short-term frequency-dependent plasticity at recurrent mossy fiber synapses of the XXXX brain.

@entity1 @entity410 @entity2227 @entity2134 @entity4176 @entity1315 @entity143 @entity302 @entity35
The recurrent mossy fiber pathway of the dentate gyrus expands dramatically in @entity1 @entity1315 and in animal models of this disorder, creating monosynaptic connections among granule cells. This novel granule cell network can support reverberating excitation but is difficult to activate with low-frequency stimulation. This study used hippocampal slices from @entity2134 -treated @entity35 to explore the dependence of synaptic transmission in this pathway on stimulus frequency. Minimal electrically evoked EPSCs exhibited a high failure rate ( approximately 60%). Stimulus trains delivered at a frequency of <1 Hz depressed synaptic transmission, as evidenced by an increase in response failures. Conversely, stimulus trains delivered at higher frequencies reduced the percentage of response failures and increased the amplitude of compound EPSCs, including pharmacologically isolated @entity143 receptor-mediated EPSCs. Short-term frequency-dependent facilitation was of modest size compared with mossy fiber synapses on other neuronal types. Facilitation depended on the activation of @entity4176 receptors by released @entity2227 and was inhibited by feedback activation of type II metabotropic @entity2227 receptors. These results suggest that the recurrent mossy fiber pathway may be functionally silent during baseline asynchronous granule cell activity in vivo attributable, in part, to progressive transmission failure. The pathway may synchronize granule cell firing and may promote @entity410 propagation most effectively during the brief periods of high-frequency granule cell firing that occur during normal behavior, during the periods of hypersynchronous fast activity characteristic of @entity302 brain and, most importantly, during the period of increasing granule cell activity that precedes a spontaneous @entity410 .
