Research Highlight: Astrocytes gate Hebbian synaptic plasticity in the striatum

Astrocytes control the strength and timing of synaptic inputs by fast glutamate uptake via EAAT2 glutamate transporter. However, whether astrocytes contribute to the fine temporal detection of incoming inputs important for plasticity expression is yet unknown. Spike-timing-dependent plasticity (STDP) is a synaptic Hebbian learning rule allowing for associative storage of relevant firing patterns. Temporal coding via STDP in the striatum may be essential for the association of sensory and motor events during procedural learning. ENP group leader Laurent Venance and his colleague Silvana Valtcheva, now demonstrate that EAAT2 sets the appropriate glutamate dynamics for the optimal temporal contingency between pre- and postsynaptic activity required for STDP emergence. In brief, the authors use ex vivo whole-cell recordings of striatal output neurons and pharmacological manipulations of EAAT2 activity to demonstrate the role of astrocytes as gatekeepers for Hebbian synaptic plasticity such as STDP in the striatum. Thus, the efficiency of glutamate uptake, most through astrocytic EAAT2, gates the expression of Hebbian synaptic plasticity in the striatum.

Check out the article:

Astrocytes gate Hebbian synaptic plasticity in the striatum, Silvana Valtcheva and Laurent Venance, Nature communications, 7:13845 (published 20 dec 2016). 

DOI: 10.1038/ncomms13845

Figure. Impact of astrocytes, via EAAT2, on Hebbian plasticity. Schematic representation of the role of astrocytes, via EAAT2, on Hebbian plasticity in the striatum. (A: black trace and B: left panel) Transient EAAT2 blockade prevents the expression of STDP, instead favoring non-Hebbian plasticity (timing-independent LTP). This LTP is mediated by extrasynaptic NMDAR and LTD is dependent on the activation of striatal GABAergic microcircuits. In these conditions, unpaired activity is sufficient to induce LTP. (A: blue trace and B: middle panel) The physiological expression and activity of EAAT2 allows the emergence of Hebbian plasticity (bidirectional STDP). Depending on the order of pre- and postsynaptic activity, NMDAR-mediated t-LTP or endocannabinoid-mediated t-LTD is induced. (A: pink trace and B: right panel) EAAT2 overexpression by limiting glutamate spillover prevents STDP expression.