Distinctive Classes of GABAergic Interneurons Provide Layer-Specific Phasic Inhibition in the Anterior Piriform Cortex

The primary olfactory (or piriform) cortex is a trilaminar paleocortex that is seen increasingly as an attractive model system for the study of cortical sensory processing. Recent findings highlight the importance of gamma-amino butyric acid (GABA)-releasing interneurons for the function of the piriform cortex (PC), yet little is known about the different types of interneurons in the PC. Here, we provide the first detailed functional characterization of the major classes of GABAergic interneurons in the anterior piriform cortex (aPC) and show how these classes differentially engage in phasic synaptic inhibition. By measuring the electrical properties of interneurons and combining this with information about their morphology, laminar location, and expression of molecular markers, we have identified 5 major classes in the aPC of the mouse. Each layer contains at least one class of interneuron that is tuned to fire either earlier or later in a train of stimuli resembling the input received by the PC in vivo during olfaction. This suggests that the different subtypes of interneuron are specialized for providing synaptic inhibition at different phases of the sniff cycle. Thus, our results suggest mechanisms by which classes of interneurons play specific roles in the processing performed by the PC in order to recognize odors.