Maturation of prefrontal input to dorsal raphe nucleus increases behavioral persistence in mice

The ability to persist towards a desired objective is a fundamental aspect of behavioral control whose impairment is implicated in several behavioral disorders. One of the prominent features of behavioral persistence is that its maturation occurs relatively late in development. This is presumed to echo the developmental time course of a corresponding circuit within late-maturing parts of the brain, such as the prefrontal cortex, but the specific identity of the responsible circuits is unknown. Here, we describe the maturation of the projection from layer 5 neurons of the prefrontal cortex to the dorsal raphe nucleus in mice. We show using pathway-specific optogenetic stimulation that this connection undergoes a dramatic increase in synaptic potency between postnatal weeks 3 and 8, corresponding to the transition from juvenile to adult. We then show that this period corresponds to an increase in the behavioral persistence that mice exhibit in a foraging task. Finally, we use genetic targeting to selectively ablate this pathway in adulthood and show that mice revert to a behavioral phenotype similar to juveniles. These results suggest that the prefrontal to dorsal raphe pathway is a critical anatomical and functional substrate of the development and manifestation of behavioral control.