It is known that dendrites of hippocampal pyramidal cells amplify clustered glutamatergic input. This involves N-methyl-D-aspartate receptors (NMDARs), whose activity also depends on the presence of NMDAR co-agonists such as D-serine.
In our recent study by Bohmbach et al., we discovered an unexpected frequency-dependent excitatory feedback loop between pyramidal cell activity and dendritic amplification of synaptic input. It is mediated by NMDAR co-agonists and astrocytes. Importantly, disrupting this feedback loop at the level of astrocytes impairs spatial memory.
K. Bohmbach, N. Masala, E.M. Schönhense, K. Hill, A.N. Haubrich, A. Zimmer, T. Opitz, H. Beck, C. Henneberger (2022) An astrocytic signaling loop for frequency-dependent control of dendritic integration and spatial learning. Nat. Commun. 13(1):7932. (link)