Functional Dendritic Features of Serotonin Neurons in the Dorsal Raphe Nucleus

Abstract

The relatively few serotonin (5-HT) neurons located in the Dorsal Raphe Nucleus (DRN) give rise to an extensive axonal network modulating a wide-range of brain functions and behaviors. In turn, the DRN receives inputs from several brain regions and therefore exhibits the characteristics of a hub network. While recent technological advancements have provided an unprecedented look at the neurobiology of the DRN, important knowledge gaps remain in understanding how the constellation of synaptic inputs to this region confers 5-HT neurons their unique coding features. As a first step towards characterizing the DRN's input processing strategy, we set out to explore the landscape of dendritic operation operating in DRN 5-HT neurons. Using multi-photon microscopy and in vitro electrophysical recordings, we conducted a morphological and electrophysiological survey of 5-HT neurons where we identified two structurally and morphologically distinct types of glutamatergic synapses both expressing small NMDAR-mediated conductance. Our initial findings provide valuable insights on local rules that govern how synaptic inputs to the DRN are being processed to ultimately confer 5-HT neurons their unique coding features.