A new automated 3D detection of synaptic contacts reveals the formation of cortico-striatal synapses upon cocaine treatment in vivo
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Addiction can be considered as a form of neuronal adaptation within the reward circuitry. Upon psychostimulant administration, long-term behavioral adaptations are associated with synaptic plasticity and morphological changes of medium spiny neurons (MSN) from the striatum. Increased spine density onto MSN in response to chronic cocaine exposure in mice has been described for more than a decade, but no evidence indicates that these newly formed spines establish connections. We developed a method for labeling, automated detection and morphological analysis of synaptic contacts. Individual labeling of neurons in mice that express the Vesicular GLUtamate Transporter-1 fused to Venus allows visualization of both dendritic spines and axonal boutons. Automated three-dimensional segmentation and morphometric analysis retrieve information on thousands of synapses at high resolution. We used this method to demonstrate that new cortico-striatal connections are formed in the striatum upon chronic cocaine. We also show that the cortical input weight is preserved over other cerebral inputs and that the newly formed spines contact pre-existing axonal boutons. Our results pave the way for other studies, since our method can be applied to any other neuronal type as demonstrated herein for glutamatergic connections on pyramidal neurons and Purkinje cells.
KeywordsCocaine Striatum Dendritic spine Axonal bouton 3D segmentation VGLUT1
This work was supported by Centre National pour la Recherche Scientifique (CNRS), Institut National de la Santé et de la Recherche Médicale (INSERM), University Pierre and Marie Curie (UPMC), Agence Nationale pour la Recherche (ANR, ANR-08-BLAN-0287) and Fondation Jérôme Lejeune and the Labex Bio-Psy cluster of excellence. We wish to thank Dr. Susanne Bolte and Richard Schwartzmann from the Cellular Imaging facility of the IBPS (Institut de Biologie Paris-Seine) for expert assistance on microscopy and metrological analysis of the setup. We thank Dr. Kätlin Slim the care of the VGLUT1venus mouse line and Dr. Ann Lohof for intracellular filling of Purkinje cells.
Conflict of interest
The authors declare no competing financial interests.
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