Fast-spiking interneuron detonation drives high-fidelity inhibition in the olfactory bulb

Inhibitory circuits in the mammalian olfactory bulb (OB) dynamically
reformat olfactory information as it propagates from peripheral receptors
to the downstream cortex. To gain mechanistic insight into how specific OB
interneuron types support this sensory processing, we examine unitary
synaptic interactions between excitatory mitral and tufted cells (MTCs),
the OB projection neurons and a conserved population of anaxonic external
plexiform layer interneurons (EPL-INs) using pair and quartet whole-cell
recordings in acute mouse brain slices. Physiological, morphological,
neurochemical, and synaptic analyses divide EPL-INs into distinct subtypes
and reveal that parvalbumin-expressing fast-spiking EPL-INs (FSIs)
perisomatically innervate MTCs with release-competent dendrites and
synaptically detonate to mediate fast, short-latency recurrent and lateral
inhibition. Sparse MTC synchronization supralinearly increases this
high-fidelity inhibition, while sensory afferent activation combined with
single-cell silencing reveals that individual FSIs account for a
substantial fraction of total network-driven MTC lateral inhibition. OB
output is thus powerfully shaped by detonation-driven high-fidelity
perisomatic inhibition.