Disinhibitory circuitry gates associative synaptic plasticity in olfactory cortex

Abstract

Inhibitory microcircuits play an essential role in regulating cortical responses to sensory stimuli. Interneurons that inhibit dendritic or somatic integration in pyramidal neurons act as gatekeepers for neural activity, synaptic plasticity and the formation of sensory representations. Conversely, interneurons that specifically inhibit other interneurons can open gates through disinhibition. In the rodent piriform cortex, relief of dendritic inhibition permits long-term potentiation (LTP) of the recurrent synapses between pyramidal neurons (PNs) thought to underlie ensemble odor representations. We used an optogenetic approach to identify the inhibitory interneurons and disinhibitory circuits that regulate LTP. We focused on three prominent inhibitory neuron classes-somatostatin (SST), parvalbumin (PV), and vasoactive intestinal polypeptide (VIP) interneurons. We find that VIP interneurons inhibit SST interneurons and promote LTP through subthreshold dendritic disinhibition. Alternatively, suppression of PV-interneuron inhibition promotes LTP but requires suprathreshold spike activity. Thus, we have identified two disinhibitory mechanisms to regulate synaptic plasticity during olfactory processing.