, 2000). In particular, constitutive TNFα has recently been implicated in control of the stability of neuronal networks in response to prolonged changes in activity via the phenomenon of synaptic scaling (Stellwagen and Malenka, 2006 and Turrigiano, 2008) and plays a specific role in ocular dominance plasticity upon monocular visual deprivation (Kaneko et al., 2008). The cytokine, released from astrocytes, was reported to strengthen excitatory synaptic transmission by promoting surface insertion of AMPA receptor (AMPAR) subunits GABA agonists list (Bains and Oliet, 2007, Beattie et al., 2002 and Stellwagen et al., 2005). In the present study, we find that TNFα is also an obligatory factor for the induction

of synaptically effective gliotransmission EGFR inhibitor review at GC synapses in the dentate gyrus, specifically controlling glutamate release from astrocytes. Notably, constitutive levels of the cytokine promote functional docking and rapid coordinated secretion of glutamatergic vesicles in cultured astrocytes. Indeed, TNFα most likely determines the kinetics of

P2Y1R-dependent glutamate release in situ and the local extracellular concentration of the amino acid, a critical factor in the activation of pre-NMDAR and, ultimately, in the potentiation of GC synapses. To investigate the role of TNFα in astrocyte-dependent synaptic modulation in hippocampal dentate gyrus, we planned studies on Tnf−/− mice ( Pasparakis et al., 1996). Our previous work in rats established that purinergic P2Y1R, strongly expressed in astrocytic processes around GC synapses, respond to stimulation with the agonist 2-methylthioadenosine-5′-diphosphate (2MeSADP, 10 μM) ADP ribosylation factor by inducing a highly reproducible increase in mEPSC frequency in GCs ( Jourdain et al., 2007). We therefore decided to utilize this stimulus paradigm and recorded mEPSCs from hippocampal dentate GCs in acute mouse hemibrain horizontal slices

from P18–P23 mice. Recordings were performed 50–90 μm deep in the slices, where astrocytes and the patched GCs retained their integral tridimensional structures, as confirmed by two-photon imaging of cells fluorescently labeled with specific markers ( Figure 1A). Initially, we used slices from wild-type (WT) mice and applied 2MeSADP either by bath perfusion or locally, within the volume of the recorded GC, via pressure ejection from a micropipette. In both cases the P2Y1R agonist increased mEPSC frequency in GCs (bath application: +37% ± 11%; p < 0.05; n = 14 cells; local application: +32% ± 10%, p < 0.05; n = 7 cells), with no effect on the amplitude or kinetics of the currents ( Figure 1B and see Figure S1 available online). The effect of the drug on mEPSC frequency was abolished in the presence of N6-methyl-2′-deoxyadenosine-3′,5′-bisphosphate (MRS2179 10 μM; n = 7 cells), a P2Y1R blocker, confirming the specific involvement of this purinergic receptor subtype.