A pool of postnatally-generated interneurons persists in an immature stage in the olfactory bulb

Calretinin (CR)-expressing periglomerular (PG) cells are the most abundant interneurons in the glomerular layer of the olfactory bulb. They are predominately generated postnatally from the septal and dorsal sub-ventricular zones that continue producing them well into adulthood. Yet, little is known about their properties and functions. Using transgenic approaches and patch-clamp recording we show that CR(+) PG cells of both septal and dorsal origin have homogenous morphological and electrophysiological properties. They express a surprisingly poor repertoire of voltage-activated channels and fire, at most, one action potential. They also receive little synaptic inputs and NMDA receptors predominate at excitatory synapses. These properties, that resemble those of immature neurons, persist over time and limit the contribution of CR(+) PG cells in network activity. Thus, postnatally-generated CR(+) PG cells continuously supply a pool of latent neurons that unlikely participate in olfactory bulb computation but may provide a so far unsuspected reservoir of plasticity.