Dopamine transmission is involved in reward processing and motor control, and its impairment plays a central role in numerous neurological disorders. Despite its strong pathophysiological relevance, the molecular and structural organization of the dopaminergic synapse remains to be established. Here, we used targeted labelling and fluorescence activated sorting to purify striatal dopaminergic synaptosomes. We provide the proteome of dopaminergic synapses with 57 proteins specifically enriched. Beyond canonical markers of dopamine neurotransmission such as dopamine biosynthetic enzymes and cognate receptors, we validated 6 proteins not previously described as enriched. Moreover, our data reveal the adhesion of dopaminergic synapses to glutamatergic, GABAergic or cholinergic synapses in structures we named “dopamine hub synapses”. At glutamatergic synapses, pre- and postsynaptic markers are significantly increased upon association with dopamine synapses. Dopamine hub synapses may thus support local dopaminergic signalling, complementing volume transmission thought to be the major mechanism by which monoamines modulate network activity.

The vSNAREs VAMP2 and VAMP4 control recycling and intracellular sorting of post-synaptic receptors in neuronal dendrites Graphical abstract Highlights d VAMP2 and 4 mediate the exocytosis of somato-dendritic recycling endosomes (REs) d VAMP2 mediates the exocytosis of a small subset of REcontaining AMPARs d VAMP4 depletion accelerates GluA1 recycling and increases post-synaptic currents d Increased basal synaptic transmission partially occludes LTP expression

Highlights:1. Fluorescence Activated Synaptosome Sorting allows for the establishment of a molecular synaptome of striatal dopaminergic projections. 2. Dopaminergic varicosities adhere to receptor filled post-synaptic membranes. 3. Dopaminergic projections build hub synapses with excitatory and inhibitory projections. 4. SynCAM 2 is a strong candidate for the adhesion and differentiation of dopamineeffector hub synapses. SUMMARYDopamine transmission is a monoaminergic system involved in reward processing and motor control. Volume transmission is thought to be the main mechanism by which monoamines modulate effector transmission though synaptic structures are scarcely described. Here, we applied a fluorescence activated synaptosome sorting workflow to dopaminergic projections to the striatum and explored cellular and molecular features of the dopaminergic synaptome. This demonstrated that dopaminergic varicosities adhere to post-synaptic membrane baring cognate receptors. We further identified a specific bond of varicosities to glutamatergic or GABAergic synapses in structures we named dopaminergic "hub synapses". Finally, we showed that the synaptic adhesion protein SynCAM 2 is strongly expressed at dopaminergic hub synapses. Our data strongly suggest that neuromodulation frequently operates from hubsynapses on local receptors, presumably in conjunction with extra-synaptic volume transmission. We provide a new framework for the molecular exploration of dopaminergic synapses and more generally on discrete synapse populations ex-vivo.