Gamma rhythms are known to contribute to the process of memory encoding.
However, little is known about the underlying mechanisms at the molecular,
cellular and network levels. Using local field potential recording in awake
behaving mice and concomitant field potential and whole-cell recordings in
slice preparations we found that gamma rhythms lead to activity-dependent
modification of hippocampal networks, including alterations in sharp wave-
ripple complexes. Network plasticity, expressed as long-lasting increases in
sharp wave-associated synaptic currents, exhibits enhanced excitatory synaptic
strength in pyramidal cells that is induced postsynaptically and depends on
metabotropic glutamate receptor-5 activation. In sharp contrast, alteration of
inhibitory synaptic strength is independent of postsynaptic activation and
less pronounced. Further, we found a cell type-specific, directionally biased
synaptic plasticity of two major types of GABAergic cells, parvalbumin- and
cholecystokinin-expressing interneurons. Thus, we propose that gamma frequency
oscillations represent a network state that introduces long-lasting synaptic
plasticity in a cell-specific manner
