Astrocytes are critical participants in synapse development and function, but their role in synaptic plasticity is unclear. Eph receptors and their ephrin ligands have been suggested to regulate neuron-glia interactions and EphA4-mediated ephrin reverse signaling is required for synaptic plasticity in the hippocampus. Here we show that long-term potentiation (LTP) at the CA3-CA1 synapse is modulated by EphA4 in the postsynaptic CA1 cell and by ephrinA3, a ligand of EphA4 that is found in astrocytes. Lack of EphA4 increases the levels of glial glutamate transporters and ephrinA3 modulates transporter currents in astrocytes. Pharmacological inhibition of glial glutamate transporters rescues the LTP defects in EphA4 and ephrinA3 mutant mice. Transgenic overexpression of ephrinA3 in astrocytes reduces glutamate transporter levels and produces focal dendritic swellings possibly caused by glutamate excitotoxicity. These results suggest that EphA4/ephrinA3 signaling is a critical mechanism for astrocytes to regulate synaptic function and plasticity.

Learning and memory formation involve long-term potentiation (LTP) of synaptic strength. A fundamental feature of LTP induction in the brain is the need for coincident pre- and postsynaptic activity. This restricts LTP expression to activated synapses only (homosynaptic LTP) and leads to its input specificity. In the spinal cord, we discovered a fundamentally different form of LTP that is induced by glial cell activation and mediated by diffusible, extracellular messengers, including d-serine and tumor necrosis factor (TNF), and that travel long distances via the cerebrospinal fluid, thereby affecting susceptible synapses at remote sites. The properties of this gliogenic LTP resolve unexplained findings of memory traces in nociceptive pathways and may underlie forms of widespread pain hypersensitivity.

Sensory nerve fibers differ not only with respect to their sensory modalities and conduction velocities, but also in their relative roles for pain hypersensitivity. It is presently largely unknown which types of sensory afferents contribute to various forms of neuropathic and inflammatory pain hypersensitivity. Vesicular glutamate transporter 3-positive (VGluT3

BackgroundThe identification of factors that compromise neurogenesis is aimed at improving stem cell-based approaches in the field of regenerative medicine. Interferon gamma (IFNγ) is a main pro-inflammatory cytokine and up-regulated during several neurological diseases. IFNγ is generally thought to beneficially enhance neurogenesis from fetal or adult neural stem/precursor cells (NSPCs).ResultsWe now provide direct evidence to the contrary that IFNγ induces a dysfunctional stage in a substantial portion of NSPC-derived progeny in vitro characterized by simultaneous expression of glial fibrillary acid protein (GFAP) and neuronal markers, an abnormal gene expression and a functional phenotype neither typical for neurons nor for mature astrocytes. Dysfunctional development of NSPCs under the influence of IFNγ was finally demonstrated by applying the microelectrode array technology. IFNγ exposure of NSPCs during an initial 7-day proliferation period prevented the subsequent adequate differentiation and formation of functional neuronal networks.ConclusionsOur results show that immunocytochemical analyses of NSPC-derived progeny are not necessarily indicating the correct cellular phenotype specifically under inflammatory conditions and that simultaneous expression of neuronal and glial markers rather point to cellular dysregulation. We hypothesize that inhibiting the impact of IFNγ on NSPCs during neurological diseases might contribute to effective neurogenesis and regeneration.