Transparent, low-autofluorescence microECoG device for simultaneous Ca2+ imaging and cortical electrophysiology in vivo.

OBJECTIVE: Multimodal neuroimaging approaches are beneficial to discover brain functionalities at high spatial and temporal resolution. In our work, a novel material composition of a microECoG device relying on Parylene HT and indium-tin-oxide (ITO) is presented, which facilitates two-photon imaging of Ca2+ signals and concurrent recording of cortical EEG. APPROACH: Long-term stability of the interfaces of the transparent microdevice is confirmed in vitro by electrochemical and mechanical tests. The outstanding optical properties, like high transmittance and low auto-fluorescent are proven by fluorimetric measurements. Spatial resolution of fluorescent two-photon imaging through the microECoG device is presented in transgenic hippocampal slices, while concurrent recording of Ca2+ signals and cortical EEG is demonstrated in vivo. Photoartefacts and photodegradation of the materials are also investigated in detail to provide safety guidelines for further use in two-photon in vivo imaging schemes. MAIN RESULTS: Two-photon imaging of Ca signals can be safely performed through the proposed transparent ECoG device, without significant distortion in the dimensions of detected neuronal structures or in the temporal signaling. In chronic use, we demonstrated that fluorescent Ca signals of individual neurons can be clearly recorded even after 51 d. SIGNIFICANCE: Our results give a firm indication that highly transparent microECoG electrode arrays made of Parylene HT/ITO/Parylene HT multilayer are excellent candidates for synergetic recording of optical signals and EEG from intact brains with high resolution and are free of electrical and optical artefacts.

Role of nonsynaptic GluN2B-containing NMDA receptors in excitotoxicity: evidence that fluoxetine selectively inhibits these receptors and may have neuroprotective effects.

In acute ischaemic brain injury and chronic neurodegeneration, the primary step leading to excitotoxicity and cell death is the excessive and/or prolonged activation of glutamate (Glu) receptors, followed by intracellular calcium (Ca(2+)) overload. These steps lead to several effects: a persistent depolarisation of neurons, mitochondrial dysfunction resulting in energy failure, an increased production of reactive oxygen species (ROS), an increase in the concentration of cytosolic Ca(2+) [Ca(2+)]i, increased mitochondrial Ca(2+) uptake, and the activation of self-destructing enzymatic mechanisms. Antagonists for NMDA receptors (NMDARs) are expected to display neuroprotective effects, but no evidence to support this hypothesis has yet been reported. A number of clinical trials using NMDAR antagonists have failed to demonstrate neuroprotective effects, either by reducing brain injury or by preventing neurodegeneration. Recent advances in NMDAR research have provided an explanation for this phenomenon. Synaptic and extrasynaptic NMDARs are composed of different subunits (GluN2A and GluN2B) that demonstrate opposing effects. Synaptic GluN2A-containing and extrasynaptic GluN2B-containing NMDARs have different co-agonists: d-serine for synaptic NMDARs and glycine for extrasynaptic NMDARs. Both co-agonists are of glial origin. The mechanisms of cell destruction or cell survival in response to the activation of NMDAR receptors depend in part on [Ca(2+)]i and the route of entry of this ion and more significantly on the subunit composition and localisation of the NMDARs. While synaptic NMDAR activation is involved in neuroprotection, the stimulation of extrasynaptic NMDARs, which are composed of GluN2B subunits, triggers cell destruction pathways and may play a key role in the neurodegeneration associated with Glu-induced excitotoxicity. In addition, it has been found that synaptic and extrasynaptic NMDA receptors have opposing effects in determining the fate of neurons. This result has led to the targeting of nonsynaptic GluN2B-containing NMDARs as promising candidates for drug research. Under hypoxic conditions, it is likely that the failure of synaptic glutamatergic transmission, the impairment of the GluN2A-activated neuroprotective cascade, and the persistent over-activation of extrasynaptic GluN2B-containing NMDARs lead to excitotoxicity. Fluoxetine, a drug widely used in clinical practice as an antidepressant, has been found to selectively block GluNR2B-containing NMDARs. Therefore, it seems to be a potential candidate for neuroprotection.