Optimized SynActive tools to study structure and function of potentiated synapses (v1)

Synaptic engrams can be defined as the synapse population of neurons supporting a specific memory and are believed to represent the cellular basis of learning processes characterized by newly formed or potentiated spines. We developed a new platform (SA =SynActive toolbox) in which a prototypical pair of SA constructs was employed to tag and visualize translation-dependent potentiated dendritic spines, in a spatially localized and activity-dependent manner.

We created a series of new Adeno Associated Viruses (AAV)-derived constructs: 1) SA-eGRASP; 2) PHP.eB-SA; 3) AAV9-SA. Such vectors represent a fundamental advancement as compared with the original SA constructs both in terms of spatial resolution and in view of in vitro and in vivo use for specific CNS targeting.

The new pair was stereotaxically injected into the hippocampus. Injected mice were exposed to contextual fear conditioning to trigger synaptic plasticity and translation-dependent long-term potentiation (LTP) of synapses. We also infected organotypic hippocampal slices with the appropriate AAV pair, before stimulating with chemical or electrical LTP.

A specific SA signal (identifying translation-dependent potentiated synapses) was revealed following confocal imaging of hippocampus from perfused mice and fixed organotypic slices. Potentiated spines along the dendritic tree of hippocampal pyramidal neurons were quantified and their distribution was investigated. All these new datasets can be exploited for computational models of synaptic memory engrams.