The most common type of @entity302 in adults is @entity1315 . After @entity130 , dentate granule cell axons (mossy fibers) sprout and form new synaptic connections. Whether this synaptic reorganization strengthens recurrent inhibitory circuits or forms a novel recurrent excitatory circuit is unresolved. We labeled individual granule cells in vivo, reconstructed sprouted mossy fibers at the EM level, and identified postsynaptic targets with @entity1246 immunocytochemistry in the @entity2134 model of @entity1315 . Granule cells projected an average of 1.0 and 1.1 mm of axon into the granule cell and molecular layers, respectively. Axons formed an average of one synapse every 7 microm in the granule cell layer and every 3 microm in the molecular layer. Most synapses were with spines (76 and 98% in the granule cell and molecular layers, respectively). Almost all of the synapses were with @entity1246 -negative structures (93 and 96% in the granule cell and molecular layers, respectively). By integrating light microscopic and EM data, we estimate that sprouted mossy fibers form an average of over 500 new synapses per granule cell, but <25 of the new synapses are with GABAergic interneurons. These findings suggest that almost all of the synapses formed by mossy fibers in the granule cell and molecular layers are with other granule cells. Therefore, after epileptogenic treatments that kill hilar mossy cells, mossy fiber sprouting does not simply replace one recurrent excitatory circuit with another. Rather, it replaces a distally distributed and disynaptic excitatory feedback circuit with one that is local and monosynaptic.

Axon sprouting in a model of XXXX creates a predominantly excitatory feedback circuit.

@entity1246 :: ('MESH:D005680', 'Chemical') :: ['GABA'] @entity2134 :: ('MESH:D010862', 'Chemical') :: ['pilocarpine'] @entity1315 :: ('MESH:D004833', 'Disease') :: ['temporal lobe epilepsy'] @entity302 :: ('MESH:D004827', 'Disease') :: ['epilepsy'] @entity130 :: ('MESH:D014947', 'Disease') :: ['epileptogenic injuries']
@entity1315 :: (MESH:D004833,Disease) :: ['temporal lobe epilepsy']
