Molecular and Functional Investigation of Striatal Cholinergic Interneuron Diversity – MoFISCO

Exploring the molecular mechanisms that shape functionally distinct neuronal subpopulations is a major challenge for neuroscience. To date, most studies have considered the cholinergic interneurons of the striatum (CINs) as a homogeneous population; consequently, the organizational principles underlying their functional diversity remain unknown. However, CINs are known to be involved in a wide range of functions, and are recurrently implicated in many neurological disorders. Our driving hypothesis is that these diverse functions are underpinned by a heterogeneous population of CINs with distinct molecular properties. As these interneurons constitute a very rare population (1-2% of the striatal neuronal population) that cannot be viably captured by single-cell isolation procedure, there is no in-depth gene profiling of CINs at the single-cell level. Here, we have developed an approach that allows us to circumvent these problems; our preliminary Smart-seq results show the existence of several CIN subtypes associated with specific marker genes. We will then determine whether these molecularly-defined subpopulations have specific functions. For that, we will first perform in vitro electrophysiology combined with single-neuron RT-qPCR to test whether the distinct intrinsic and/or circuit properties of CINs map onto molecular subtypes. Secondly, we will characterize in vivo the functional diversity of CIN response in a Pavlovian conditioning task: we will record CIN activities in head-fixed mice to classify CINs according to the heterogeneity of their firing pattern responses to behaviorally salient stimuli. Juxtacellular labeling followed by post hoc in situ hybridization in these mice will determine whether functional groups of CINs can be identified by specific marker genes. Overall, this highly ambitious proposal will improve our understanding of the role of CINs in defining striatal network dynamics and striatal-related function.