Coordinated electrical activity in the olfactory bulb gates the oscillatory entrainment of entorhinal networks in neonatal mice

ABSTRACT While the developmental principles of sensory and cognitive processing have been extensively investigated, their synergy has been largely neglected. During early life, most sensory systems are still largely immature. As a notable exception, the olfactory system reaches full maturity during intrauterine life, controlling mother-offspring interactions and neonatal survival. Here, we elucidate the structural and functional principles underlying the communication between olfactory bulb (OB) and lateral entorhinal cortex (LEC) – the gatekeeper of limbic circuitry – during neonatal mouse development. Combining optogenetics, pharmacology, and electrophysiology in vivo with axonal tracing, we show that mitral cell-dependent discontinuous theta bursts in OB drive network oscillations and time the firing in LEC via axonal projections confined to upper cortical layers. Pharmacological silencing of OB activity diminishes entorhinal oscillations. Moreover, odor exposure boosts OB-entorhinal coupling at fast frequencies. Thus, early OB activity shapes the maturation of entorhinal circuits.