3D Functional Ultrastructure of Cortico-Striatal Dopamine Hub Synapses – UltraDopa

Dopamine (DA) neuromodulation in the brain finely regulates motivation, voluntary movements, reward-based learning and valence coding. Slow metabotropic DA signaling and the lack of characterization of DA synapses favored the hypothesis that DA transmission is volumic. We recently purified DA projection to the striatum with advanced subcellular fractionation and identified that DA varicosities bind onto existing synapses of dopaminoceptive systems in multipartite DA hub synapses (DHS). Cortico-striatal glutamatergic synapses are important dopaminoceptive elements in motor and reward circuits. Indeed, we showed that nearly half of cortico-striatal synapses are engaged into DHS and display significant molecular remodeling compared to those devoid of DA inputs. With this original model, UltraDopa aims at establishing a 3D-model of DA synapse and cortico-striatal DHS at the nanoscale. To that end we will implement corelative cryo-electron-tomography of nano-cellular to macro-molecular structures, and 3D STORM (STochastic Optical Reconstruction Microscopy) on isolated DHS, as well as correlative electron microscopy on high pressure frozen striatal slices. We will establish the nanoscale organization of synaptic vesicles, release sites, and synaptic adhesion sites at cortico-striatal DHS. We will then analyze the impact of the genetic loss of a synaptic adhesion molecule expressed at DHS on its structure. Finally, we will determine how exposure to cocaine, acting directly on DA neurotransmission, affects the structure of DHS. UltraDopa will pave the way for a redefinition of neurotransmission mechanisms between the volumic model classically attributed to modulators and the synaptic model to the excitatory/inhibitory systems. In addition, UltraDopa will generate a new framework of knowledge instrumental for translational research on addiction to psychostimulants that represent an increasing burden to the French social system.