Figure 2.

Structural plasticity of mossy fiber presynaptic terminals. (A) Schematic diagram showing mossy fiber bouton (MFB) contacting thorny excrescence of CA3 pyramidal cell. Thick postsynaptic lines reflect postsynaptic densities. Note that filopodial extension of mossy terminal is specialized to innervate GABAergic interneurons. (B) Induction of long-term potentiation (LTP) in MF-PC synapses with high-frequency stimulation or forskolin leads to increase in MFB volume and in the number of release sites per MFB. Blue color reflects structural plastic changes. Additionally, LTP promotes development of small protrusions extending from the large complex spines into the presynaptic bouton. (C) Spatial learning or enriched-environment promotes an expansion of mossy fibers terminals in the stratum lucidum. Furthermore, housing mice in an enriched environment leads to an increased local complexity of MFBs with frequent appearance of satellite boutons with functional release sites. Additionally hippocampus-dependent learning increases the number of filopodia protruding from MFBs and contacting feedforward projecting PV+ interneurons. (D) MFB filopodia are characterized by a dynamic intrinsic structural plasticity in the adult hippocampus ex vivo. Filopodia undergo spatial rearrangement in shape in mature hippocampal slice cultures. Plasticity processes that increase MF transmission affect also filopodia motility.