Spiking induces synaptic plasticity in hippocampal neurogliaform cells by Gengyu Li, Robert Stewart, Marco Canepari & Marco Capogna, J. Neuroscience 34(4): 1280-1292, 2014.
The hippocampus contains more than 20 types of inhibitory interneurons that express different proteins and target different regions of pyramidal cells to regulate spatiotemporal integration of excitation and define temporal windows for spiking. Neurogliaform cells (NGFCs, top panel) express neuronal nitric oxide synthase (nNOS) and fire during theta oscillations in vivo. Li et al. published a “featured article” in the Journal of Neuroscience reporting a novel physiological role for nNOS. Theta-associated firing replayed in NGFCs induced inhibitory synaptic plasticity (bottom panel). This “firing-induced suppression of inhibition” (FSI) required back-propagation of action potentials (middle panel), calcium influx through L-type calcium channels, nNOS activity, and activation of NO-sensitive guanylyl cyclase (NO-sGC) receptors, which are present on presynaptic terminals. FSI also indirectly strengthened incoming excitatory postsynaptic potentials. Thus FSI enhances spatial and temporal summation of excitatory inputs to NGFCs, regulating their inhibition of pyramidal cells.