Metabotropic glutamate receptors control gating of spike transmission in the hippocampus area CA1

Abstract

Signal transmission in the brain is regulated by a number of filters and modulatory systems. In particular, theta rhythm modulates local inhibition of networks and facilitates the induction of synaptic plastic processes. Additionally, the transmission of spikes in the network is controlled by pulse facilitation as a noise filter. Metabotropic glutamate receptors (mGluRs) that are found on interneurons in area CA1 of the hippocampus play a role in the fine-tuning of inhibitory circuits and in the transmission of spikes through the network. It was found that the mGluR agonist 1S,3S-1-amino-cyclo-pentyl-1,3-dicarboxylic acid (1S,3S-ACPD) blocked the induction of long-term potentiation (LTP) by high-frequency stimulation (HFS). In addition, theta-patterned stimulation was blocked by the drug. However, learning of spatial tasks in the water maze or radial arm maze was not inhibited by 1S,3S-ACPD. Yet, when stimulating with short bursts phase-locked with theta rhythm at the low inhibition phase, 1S,3S-ACPD did not inhibit the development of LTP. This suggests that burst transmission is not blocked in the network, while high-frequency trains are reduced to prevent overexcitation and the transmission of nonphysiologic stimuli patterns.