Synchronous 20 Hz rhythmic activity in hippocampal networks induced by activation of metabotropic glutamate receptors in vitro

Abstract

High frequency synchronized neuronal activity plays an important role in spatiotemporal processing of sensory inputs and possibly cognitive function. This activity, in the so called beta and gamma electroencephalographic frequency range is found in cortical areas and in the hippocampus. Here we show that activation of metabotropic glutamate receptors by the agonist 1-aminocyclopentane-(1S,3R)-dicarboxylate evokes synchronous 20 Hz rhythmic activity in rat hippocampal slices. Quisqualate was more potent than 1-aminocyclopentane-(1S,3R)-dicarboxylate which suggests involvement of either the metabotropic glutamate receptor subtypes I, V or both. The 20 Hz rhythmic activity was different from the theta-rhythmic effect induced by the cholinergic muscarinic receptor agonist carbachol which showed a dominant frequency of 9.0 +/- 0.5 Hz. The 20 Hz rhythmic activity is correlated with an increased firing rate of pyramidal neurons. The 20 Hz rhythmic activity was reduced by the GABA(A) receptor antagonist bicuculline, thus interneuron activity plays a major role in the 20 Hz oscillations. The 20 Hz rhythmic activity induced by activation of metabotropic glutamate receptors represents a new aspect of synchronized activity in the hippocampus and may be involved in the binding and representation of converging sensory inputs.