Functional calcium imaging in developing cortical networks

Apocynin reduces dihydroethidium fluorescence in naked mole-rat cortex independently of NADPH oxidase

Pharmacological agents that modulate cellular targets offer a powerful approach to interrogate the role of a given component in cellular signalling cascades. However, such drugs are often nonspecific and/or have unexpected off-target effects. One cellular target of interest is the NADPH oxidase (NOX) enzyme family, which consume oxygen and produce reactive oxygen species. Among the most widely used inhibitors of NOX is apocynin, but apocynin also has off-target effects that may interfere with detection assays of hydrogen peroxide (H₂O₂) or directly scavenge H₂O₂ in some cell lines. Nonetheless, apocynin remains widely used for in vivo studies of brain function. Therefore, we used apocynin and another widely-used NOX inhibitor - diphenyleneiodonium (DPI) - to study the role of NOX in ROS homeostasis of hypoxia-tolerant naked mole-rat cortical brain slices during a normoxia➔hypoxia➔reoxygenation protocol. Using fluorescence microscopy, we found that apocynin decreased dihydroethidium fluorescence from naked mole-rat cortex in all treatment conditions by 65-75% of pre-drug normoxic control. This change was rapid, occurring within minutes of drug perfusion, and reversed equally rapidly upon washout. Conversely, apocynin had no effect on 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H₂DCFDA) fluorescence. DPI also had no effect on either fluorescence signal, suggesting that the effect of apocynin is due to indirect actions of the drug and not due to modulation of NOX. Taken together, our results highlight the pitfalls of pharmacological neuroscience and add to the body of evidence suggesting that apocynin is not a useful compound for targeting NOX.

Activation of lactate receptor HCAR1 down-modulates neuronal activity in rodent and human brain tissue

Lactate can be used by neurons as an energy substrate to support their activity. Evidence suggests that lactate also acts on a metabotropic receptor called HCAR1, first described in the adipose tissue. Whether HCAR1 also modulates neuronal circuits remains unclear. In this study, using qRT-PCR, we show that HCAR1 is present in the human brain of epileptic patients who underwent resective surgery. In brain slices from these patients, pharmacological HCAR1 activation using a non-metabolized agonist decreased the frequency of both spontaneous neuronal Ca²⁺ spiking and excitatory post-synaptic currents (sEPSCs). In mouse brains, we found HCAR1 expression in different regions using a fluorescent reporter mouse line and in situ hybridization. In the dentate gyrus, HCAR1 is mainly present in mossy cells, key players in the hippocampal excitatory circuitry and known to be involved in temporal lobe epilepsy. By using whole-cell patch clamp recordings in mouse and rat slices, we found that HCAR1 activation causes a decrease in excitability, sEPSCs, and miniature EPSCs frequency of granule cells, the main output of mossy cells. Overall, we propose that lactate can be considered a neuromodulator decreasing synaptic activity in human and rodent brains, which makes HCAR1 an attractive target for the treatment of epilepsy.

Neuronal F-Box protein FBXO41 regulates synaptic transmission and hippocampal network maturation

FBXO41 is a neuron-specific E3 ligase subunit implicated in epileptic encephalopathies. Fbxo41 null mutant (KO) mice show behavioral deficits and early lethality. Here, we report that loss of FBXO41 causes defects in synaptic transmission and brain development. Cultured Fbxo41 KO neurons had normal morphology and showed no signs of degeneration. Single-cell electrophysiology showed a lower synaptic vesicle release probability in excitatory neurons. Inhibitory neurons exhibited reduced synaptophysin expression, a smaller readily releasable pool, and decreased charge transfer during repetitive stimulation. In Fbxo41 KO hippocampal slices at postnatal day 6, the dentate gyrus was smaller with fewer radial-glial-like cells and immature neurons. In addition, neuronal migration was delayed. Two-photon calcium imaging showed a delayed increase in network activity and synchronicity. Together, our findings point toward a role for FBXO41 in synaptic transmission and postnatal brain development, before behavioral deficits are detected in Fbxo41 KO mice.

In Vitro Development of Human iPSC-Derived Functional Neuronal Networks on Laser-Fabricated 3D Scaffolds

Neural progenitor cells generated from human induced pluripotent stem cells (hiPSCs) are the forefront of ″brain-on-chip″ investigations. Viable and functional hiPSC-derived neuronal networks are shaping powerful in vitro models for evaluating the normal and abnormal formation of cortical circuits, understanding the underlying disease mechanisms, and investigating the response to drugs. They therefore represent a desirable instrument for both the scientific community and the pharmacological industry. However, culture conditions required for the full functional maturation of individual neurons and networks are still unidentified. It has been recognized that three-dimensional (3D) culture conditions can better emulate in vivo neuronal tissue development compared to 2D cultures and thus provide a more desirable in vitro approach. In this paper, we present the design and implementation of a 3D scaffold platform that supports and promotes intricate neuronal network development. 3D scaffolds were produced through direct laser writing by two-photon polymerization (2PP), a high-resolution 3D laser microstructuring technology, using the biocompatible and nondegradable photoreactive resin Dental LT Clear (DClear). Neurons developed and interconnected on a 3D environment shaped by vertically stacked scaffold layers. The developed networks could support different cell types. Starting at the day 50 of 3D culture, neuronal progenitor cells could develop into cortical projection neurons (CNPs) of all six layers, different types of inhibitory neurons, and glia. Additionally and in contrast to 2D conditions, 3D scaffolds supported the long-term culturing of neuronal networks over the course of 120 days. Network health and functionality were probed through calcium imaging, which revealed a strong spontaneous neuronal activity that combined individual and collective events. Taken together, our results highlight advanced microstructured 3D scaffolds as a reliable platform for the 3D in vitro modeling of neuronal functions.

Spontaneous synchronous network activity in the neonatal development of mPFC in mice

Spontaneous Synchronous Network Activity (SSA) is a hallmark of neurodevelopment found in numerous central nervous system structures, including neocortex. SSA occurs during restricted developmental time‐windows, commonly referred to as critical periods in sensory neocortex. Although part of the neocortex, the critical period for SSA in the medial prefrontal cortex (mPFC) and the underlying mechanisms for generation and propagation are unknown. Using Ca²⁺ imaging and whole‐cell patch‐clamp in an acute mPFC slice mouse model, the development of spontaneous activity and SSA was investigated at cellular and network levels during the two first postnatal weeks. The data revealed that developing mPFC neuronal networks are spontaneously active and exhibit SSA in the first two postnatal weeks, with peak synchronous activity at postnatal days (P)8–9. Networks remain active but are desynchronized by the end of this 2‐week period. SSA was driven by excitatory ionotropic glutamatergic transmission with a small contribution of excitatory GABAergic transmission at early time points. The neurohormone oxytocin desynchronized SSA in the first postnatal week only without affecting concurrent spontaneous activity. By the end of the second postnatal week, inhibiting GABA_A receptors restored SSA. These findings point to the emergence of GABA_A receptor‐mediated inhibition as a major factor in the termination of SSA in mouse mPFC.

Distinct Synchronous Network Activity During the Second Postnatal Week of Medial Entorhinal Cortex Development

The medial entorhinal cortex (MEC) contains specialized cell types whose firing is tuned to aspects of an animal’s position and orientation in the environment, reflecting a neuronal representation of space. The spatially tuned firing properties of these cells quickly emerge during the third postnatal week of development in rodents. Spontaneous synchronized network activity (SSNA) has been shown to play a crucial role in the development of neuronal circuits prior to week 3. SSNA in MEC is well described in rodents during the first postnatal week, but there are little data about its development immediately prior to eye opening and spatial exploration. Furthermore, existing data lack single-cell resolution and are not integrated across layers. In this study, we addressed the question of whether the characteristics and underlying mechanisms of SSNA during the second postnatal week resemble that of the first week or whether distinct features emerge during this period. Using a combined calcium imaging and electrophysiology approach in vitro, we confirm that in mouse MEC during the second postnatal week, SSNA persists and in fact peaks, and is dependent on ionotropic glutamatergic signaling. However, SSNA differs from that observed during the first postnatal week in two ways: First, EC does not drive network activity in the hippocampus but only in neighboring neocortex (NeoC). Second, GABA does not drive network activity but influences it in a manner that is dependent both on age and receptor type. Therefore, we conclude that while there is a partial mechanistic overlap in SSNA between the first and second postnatal weeks, unique mechanistic features do emerge during the second week, suggestive of different or additional functions of MEC within the hippocampal-entorhinal circuitry with increasing maturation.

Deletion of Voltage-Gated Calcium Channels in Astrocytes during Demyelination Reduces Brain Inflammation and Promotes Myelin Regeneration in Mice

To determine whether Cav1.2 voltage-gated Ca²⁺ channels contribute to astrocyte activation, we generated an inducible conditional knock-out mouse in which the Cav1.2 α subunit was deleted in GFAP-positive astrocytes. This astrocytic Cav1.2 knock-out mouse was tested in the cuprizone model of myelin injury and repair which causes astrocyte and microglia activation in the absence of a lymphocytic response. Deletion of Cav1.2 channels in GFAP-positive astrocytes during cuprizone-induced demyelination leads to a significant reduction in the degree of astrocyte and microglia activation and proliferation in mice of either sex. Concomitantly, the production of proinflammatory factors such as TNFα, IL1β and TGFβ1 was significantly decreased in the corpus callosum and cortex of Cav1.2 knock-out mice through demyelination. Furthermore, this mild inflammatory environment promotes oligodendrocyte progenitor cells maturation and myelin regeneration across the remyelination phase of the cuprizone model. Similar results were found in animals treated with nimodipine, a Cav1.2 Ca²⁺ channel inhibitor with high affinity to the CNS. Mice of either sex injected with nimodipine during the demyelination stage of the cuprizone treatment displayed a reduced number of reactive astrocytes and showed a faster and more efficient brain remyelination. Together, these results indicate that Cav1.2 Ca²⁺ channels play a crucial role in the induction and proliferation of reactive astrocytes during demyelination; and that attenuation of astrocytic voltage-gated Ca²⁺ influx may be an effective therapy to reduce brain inflammation and promote myelin recovery in demyelinating diseases.SIGNIFICANCE STATEMENT Reducing voltage-gated Ca²⁺ influx in astrocytes during brain demyelination significantly attenuates brain inflammation and astrocyte reactivity. Furthermore, these changes promote myelin restoration and oligodendrocyte maturation throughout remyelination.

Neuroprotective Effect of AM404 Against NMDA-Induced Hippocampal Excitotoxicity

Different studies have demonstrated that inflammation and alterations in glutamate neurotransmission are two events contributing to the pathophysiology of neurodegenerative or neurological disorders. There are evidences that N-arachidonoylphenolamine (AM404), a cannabinoid system modulator and paracetamol metabolite, modulates inflammation and exerts neuroprotective effects on Huntington's (HD) and Parkinson's diseases (PD), and ischemia. However, the effects of AM404 on the production of inflammatory mediators and excitotoxicity in brain tissue stimulated with N-methyl-D-aspartic acid (NMDA) are not elucidated. In this present study, we investigated the effects of AM404 on the production of inflammatory mediators and neuronal cell death induced by NMDA in organotypic hippocampal slices cultures (OHSC) using qPCR, western blot (WB), and immunohistochemistry. Moreover, to comprehend the mechanism of excitotoxicity, we evaluated the effects of AM404 on glutamate release in hippocampal synaptosomes and the NMDA-induced calcium responses in acute hippocampal slices. Our results showed that AM404 led to a significant decrease in cell death induced by NMDA, through a mechanism possibly involving the reduction of glutamate release and the calcium ions responses. Furthermore, it decreased the expression of the interleukin (IL)-1β. This study provides new significant insights about the anti-inflammatory and neuroprotection effects of AM404 on NMDA-induced excitotoxicity. To understand the effects of AM404 in these processes might contribute to the therapeutic potential of AM404 in diseases with involvement of neuroinflammation and neurodegeneration and might lead to a possible future treatment of neurodegenerative diseases.

Direct Reprogramming of Adult Human Somatic Stem Cells Into Functional Neurons Using Sox2, Ascl1, and Neurog2

Reprogramming of somatic cells into induced pluripotent stem cells (iPS) or directly into cells from a different lineage, including neurons, has revolutionized research in regenerative medicine in recent years. Mesenchymal stem cells are good candidates for lineage reprogramming and autologous transplantation, since they can be easily isolated from accessible sources in adult humans, such as bone marrow and dental tissues. Here, we demonstrate that expression of the transcription factors (TFs) SRY (sex determining region Y)-box 2 (Sox2), Mammalian achaete-scute homolog 1 (Ascl1), or Neurogenin 2 (Neurog2) is sufficient for reprogramming human umbilical cord mesenchymal stem cells (hUCMSC) into induced neurons (iNs). Furthermore, the combination of Sox2/Ascl1 or Sox2/Neurog2 is sufficient to reprogram up to 50% of transfected hUCMSCs into iNs showing electrical properties of mature neurons and establishing synaptic contacts with co-culture primary neurons. Finally, we show evidence supporting the notion that different combinations of TFs (Sox2/Ascl1 and Sox2/Neurog2) may induce multiple and overlapping neuronal phenotypes in lineage-reprogrammed iNs, suggesting that neuronal fate is determined by a combination of signals involving the TFs used for reprogramming but also the internal state of the converted cell. Altogether, the data presented here contribute to the advancement of techniques aiming at obtaining specific neuronal phenotypes from lineage-converted human somatic cells to treat neurological disorders.

Conditional Deletion of the L-Type Calcium Channel Cav1.2 in Oligodendrocyte Progenitor Cells Affects Postnatal Myelination in Mice

To determine whether L-type voltage-operated Ca²⁺ channels (L-VOCCs) are required for oligodendrocyte progenitor cell (OPC) development, we generated an inducible conditional knock-out mouse in which the L-VOCC isoform Cav1.2 was postnatally deleted in NG2-positive OPCs. A significant hypomyelination was found in the brains of the Cav1.2 conditional knock-out (Cav1.2^KO) mice specifically when the Cav1.2 deletion was induced in OPCs during the first 2 postnatal weeks. A decrease in myelin proteins expression was visible in several brain structures, including the corpus callosum, cortex, and striatum, and the corpus callosum of Cav1.2^KO animals showed an important decrease in the percentage of myelinated axons and a substantial increase in the mean g-ratio of myelinated axons. The reduced myelination was accompanied by an important decline in the number of myelinating oligodendrocytes and in the rate of OPC proliferation. Furthermore, using a triple transgenic mouse in which all of the Cav1.2^KO OPCs were tracked by a Cre reporter, we found that Cav1.2^KO OPCs produce less mature oligodendrocytes than control cells. Finally, live-cell imaging in early postnatal brain slices revealed that the migration and proliferation of subventricular zone OPCs is decreased in the Cav1.2^KO mice. These results indicate that the L-VOCC isoform Cav1.2 modulates oligodendrocyte development and suggest that Ca²⁺ influx mediated by L-VOCCs in OPCs is necessary for normal myelination.

SIGNIFICANCE STATEMENT

Overall, it is clear that cells in the oligodendrocyte lineage exhibit remarkable plasticity with regard to the expression of Ca²⁺ channels and that perturbation of Ca²⁺ homeostasis likely plays an important role in the pathogenesis underlying demyelinating diseases. To determine whether voltage-gated Ca²⁺ entry is involved in oligodendrocyte maturation and myelination, we used a conditional knock-out mouse for voltage-operated Ca²⁺ channels in oligodendrocyte progenitor cells. Our results indicate that voltage-operated Ca²⁺ channels can modulate oligodendrocyte development in the postnatal brain and suggest that voltage-gated Ca²⁺ influx in oligodendroglial cells is critical for normal myelination. These findings could lead to novel approaches to intervene in neurodegenerative diseases in which myelin is lost or damaged.

Motor Neuron Transdifferentiation of Neural Stem Cell from Adipose-Derived Stem Cell Characterized by Differential Gene Expression

Adipose-derived stem cells (ADSC) are adult stem cells which can be induced into motor neuron-like cells (MNLC) with a preinduction-induction protocol. The purpose of this study is to generate MNLC from neural stem cells (NSC) derived from ADSC. The latter were isolated from the perinephric regions of Sprague-Dawley rats, transdifferentiated into neurospheres (NS) using B27, EGF, and bFGF. After generating NSC from the NS, they induced into MNLC by treating them with Shh and RA, then with GDNF, CNTF, BDNF, and NT-3. The ADSC lineage was evaluated by its mesodermal differentiation and was characterized by immunostaining with CD90, CD105, CD49d, CD106, CD31, CD45, and stemness genes (Oct4, Nanog, and Sox2). The NS and the NSC were evaluated by immunostaining with nestin, NF68, and Neurod1, while the MNLC were evaluated by ISLET1, Olig2, and HB9 genes. The efficiency of MNLC generation was more than 95 ± 1.4 % (mean ± SEM). The in vitro generated myotubes were innervated by the MNLC. The induced ADSC adopted multipolar motor neuron morphology, and they expressed ISLET1, Olig2, and HB9. We conclude that ADSC can be induced into motor neuron phenotype with high efficiency, associated with differential expression of the motor neuron gene. The release of MNLC synaptic vesicles was demonstrated by FM1-43, and they were immunostained with synaptophysin. This activity was correlated with the intracellular calcium ion shift and membrane depolarization upon stimulation as was demonstrated by the calcium indicator and the voltage-sensitive dye, respectively.

Adult axolotls can regenerate original neuronal diversity in response to brain injury

The axolotl can regenerate multiple organs, including the brain. It remains, however, unclear whether neuronal diversity, intricate tissue architecture, and axonal connectivity can be regenerated; yet, this is critical for recovery of function and a central aim of cell replacement strategies in the mammalian central nervous system. Here, we demonstrate that, upon mechanical injury to the adult pallium, axolotls can regenerate several of the populations of neurons present before injury. Notably, regenerated neurons acquire functional electrophysiological traits and respond appropriately to afferent inputs. Despite the ability to regenerate specific, molecularly-defined neuronal subtypes, we also uncovered previously unappreciated limitations by showing that newborn neurons organize within altered tissue architecture and fail to re-establish the long-distance axonal tracts and circuit physiology present before injury. The data provide a direct demonstration that diverse, electrophysiologically functional neurons can be regenerated in axolotls, but challenge prior assumptions of functional brain repair in regenerative species.

DOI:http://dx.doi.org/10.7554/eLife.13998.001

Humans and other mammals have a very limited ability to regenerate new neurons in the brain to replace those that have been injured or damaged. In striking contrast, some animals like fish and salamanders are capable of filling in injured brain regions with new neurons. This is a complex task, as the brain is composed of many different types of neurons that are connected to each other in a highly organized manner across both short and long distances.

The extent to which even the most regenerative species can build new brain regions was not known. Understanding any limitations will help to set realistic expectations for the success of potential treatments that aim to replace neurons in mammals.

Amamoto et al. found that the brain of the axolotl, a species of salamander, could selectively regenerate the specific types of neurons that were damaged. This finding suggests that the brain is able to somehow sense which types of neurons are injured. The new neurons were able to mature into functional neurons, but they were limited in their ability to reconnect to their original, distant target neurons.

More research is now needed to investigate how the axolotl brain recognizes which types of neurons have been damaged. It will also be important to understand which cells respond to the injury to give rise to the new neurons that fill the injury site, and to uncover the molecules that are important for governing this regenerative process.

DOI:http://dx.doi.org/10.7554/eLife.13998.002

Ubiquitin ligase TRIM3 controls hippocampal plasticity and learning by regulating synaptic γ-actin levels

TRIM3 regulates synaptic γ-actin levels. TRIM3-deficient mice consequently have higher hippocampal spine densities, increased long-term potentiation, and enhanced contextual fear memory consolidation, indicating that temporal control of ACTG1 levels by TRIM3 is required to constrain hippocampal plasticity within physiological boundaries.

Synaptic plasticity requires remodeling of the actin cytoskeleton. Although two actin isoforms, β- and γ-actin, are expressed in dendritic spines, the specific contribution of γ-actin in the expression of synaptic plasticity is unknown. We show that synaptic γ-actin levels are regulated by the E3 ubiquitin ligase TRIM3. TRIM3 protein and Actg1 transcript are colocalized in messenger ribonucleoprotein granules responsible for the dendritic targeting of messenger RNAs. TRIM3 polyubiquitylates γ-actin, most likely cotranslationally at synaptic sites. Trim3^−/− mice consequently have increased levels of γ-actin at hippocampal synapses, resulting in higher spine densities, increased long-term potentiation, and enhanced short-term contextual fear memory consolidation. Interestingly, hippocampal deletion of Actg1 caused an increase in long-term fear memory. Collectively, our findings suggest that temporal control of γ-actin levels by TRIM3 is required to regulate the timing of hippocampal plasticity. We propose a model in which TRIM3 regulates synaptic γ-actin turnover and actin filament stability and thus forms a transient inhibitory constraint on the expression of hippocampal synaptic plasticity.

Golli Myelin Basic Proteins Modulate Voltage-Operated Ca(++) Influx and Development in Cortical and Hippocampal Neurons

The golli proteins, products of the myelin basic protein gene, are widely expressed in oligodendrocyte progenitor cells and neurons during the postnatal development of the brain. While golli appears to be important for oligodendrocyte migration and differentiation, its function in neuronal development is completely unknown. We have found that golli proteins function as new and novel modulators of voltage-operated Ca(++) channels (VOCCs) in neurons. In vitro, golli knock-out (KO) neurons exhibit decreased Ca(++) influx after plasma membrane depolarization and a substantial maturational delay. Increased expression of golli proteins enhances L-type Ca(++) entry and processes outgrowth in cortical neurons, and pharmacological activation of L-type Ca(++) channels stimulates maturation and prevents cell death in golli-KO neurons. In situ, Ca(++) influx mediated by L-type VOCCs was significantly decreased in cortical and hippocampal neurons of the golli-KO brain. These Ca(++) alterations affect cortical and hippocampal development and the proliferation and survival of neural progenitor cells during the postnatal development of the golli-KO brain. The CA1/3 sections and the dentate gyrus of the hippocampus were reduced in the golli-KO mice as well as the density of dendrites in the somatosensory cortex. Furthermore, the golli-KO mice display abnormal behavior including deficits in episodic memory and reduced anxiety. Because of the expression of the golli proteins within neurons in learning and memory centers of the brain, this work has profound implication in neurodegenerative diseases and neurological disorders.

Rapid generation of sub-type, region-specific neurons and neural networks from human pluripotent stem cell-derived neurospheres

Stem cell-based neuronal differentiation has provided a unique opportunity for disease modeling and regenerative medicine. Neurospheres are the most commonly used neuroprogenitors for neuronal differentiation, but they often clump in culture, which has always represented a challenge for neurodifferentiation. In this study, we report a novel method and defined culture conditions for generating sub-type or region-specific neurons from human embryonic and induced pluripotent stem cells derived neurosphere without any genetic manipulation. Round and bright-edged neurospheres were generated in a supplemented knockout serum replacement medium (SKSRM) with 10% CO2, which doubled the expression of the NESTIN, PAX6 and FOXG1 genes compared with those cultured with 5% CO2. Furthermore, an additional step (AdSTEP) was introduced to fragment the neurospheres and facilitate the formation of a neuroepithelial-type monolayer that we termed the "neurosphederm". The large neural tube-type rosette (NTTR) structure formed from the neurosphederm, and the NTTR expressed higher levels of the PAX6, SOX2 and NESTIN genes compared with the neuroectoderm-derived neuroprogenitors. Different layers of cortical, pyramidal, GABAergic, glutamatergic, cholinergic neurons appeared within 27 days using the neurosphederm, which is a shorter period than in traditional neurodifferentiation-protocols (42-60 days). With additional supplements and timeline dopaminergic and Purkinje neurons were also generated in culture too. Furthermore, our in vivo results indicated that the fragmented neurospheres facilitated significantly better neurogenesis in severe combined immunodeficiency (SCID) mouse brains compared with the non-fragmented neurospheres. Therefore, this neurosphere-based neurodifferentiation protocol is a valuable tool for studies of neurodifferentiation, neuronal transplantation and high throughput screening assays.

Detection of silent cells, synchronization and modulatory activity in developing cellular networks

Developing networks in the immature nervous system and in cellular cultures are characterized by waves of synchronous activity in restricted clusters of cells. Synchronized activity in immature networks is proposed to regulate many different developmental processes, from neuron growth and cell migration, to the refinement of synapses, topographic maps, and the mature composition of ion channels. These emergent activity patterns are not present in all cells simultaneously within the network and more immature "silent" cells, potentially correlated with the presence of silent synapses, are prominent in different networks during early developmental periods. Many current network analyses for detection of synchronous cellular activity utilize activity-based pixel correlations to identify cellular-based regions of interest (ROIs) and coincident cell activity. However, using activity-based correlations, these methods first underestimate or ignore the inactive silent cells within the developing network and second, are difficult to apply within cell-dense regions commonly found in developing brain networks. In addition, previous methods may ignore ROIs within a network that shows transient activity patterns comprising both inactive and active periods. We developed analysis software to semi-automatically detect cells within developing neuronal networks that were imaged using calcium-sensitive reporter dyes. Using an iterative threshold, modulation of activity was tracked within individual cells across the network. The distribution pattern of both inactive and active, including synchronous cells, could be determined based on distance measures to neighboring cells and according to different anatomical layers.

Tools, methods, and applications for optophysiology in neuroscience

The advent of optogenetics and genetically encoded photosensors has provided neuroscience researchers with a wealth of new tools and methods for examining and manipulating neuronal function in vivo. There exists now a wide range of experimentally validated protein tools capable of modifying cellular function, including light-gated ion channels, recombinant light-gated G protein-coupled receptors, and even neurotransmitter receptors modified with tethered photo-switchable ligands. A large number of genetically encoded protein sensors have also been developed to optically track cellular activity in real time, including membrane-voltage-sensitive fluorophores and fluorescent calcium and pH indicators. The development of techniques for controlled expression of these proteins has also increased their utility by allowing the study of specific populations of cells. Additionally, recent advances in optics technology have enabled both activation and observation of target proteins with high spatiotemporal fidelity. In combination, these methods have great potential in the study of neural circuits and networks, behavior, animal models of disease, as well as in high-throughput ex vivo studies. This review collects some of these new tools and methods and surveys several current and future applications of the evolving field of optophysiology.

Forebrain engraftment by human glial progenitor cells enhances synaptic plasticity and learning in adult mice

Human astrocytes are larger and more complex than those of infraprimate mammals, suggesting that their role in neural processing has expanded with evolution. To assess the cell-autonomous and species-selective properties of human glia, we engrafted human glial progenitor cells (GPCs) into neonatal immunodeficient mice. Upon maturation, the recipient brains exhibited large numbers and high proportions of both human glial progenitors and astrocytes. The engrafted human glia were gap-junction-coupled to host astroglia, yet retained the size and pleomorphism of hominid astroglia, and propagated Ca2+ signals 3-fold faster than their hosts. Long-term potentiation (LTP) was sharply enhanced in the human glial chimeric mice, as was their learning, as assessed by Barnes maze navigation, object-location memory, and both contextual and tone fear conditioning. Mice allografted with murine GPCs showed no enhancement of either LTP or learning. These findings indicate that human glia differentially enhance both activity-dependent plasticity and learning in mice.

Living Brain Optical Imaging: Technology, Methods and Applications

Within the last few decades, optical imaging methods have yielded revolutionary results when applied to all parts of the central nervous system. The purpose of this review is to analyze research possibilities and limitations of several novel imaging techniques and show some of the most interesting achievements obtained by these methods. Here we covered intrinsic optical imaging, voltage-sensitive dye, photoacoustic, optical coherence tomography, near-infrared spectroscopy and some other techniques. All of them are mainly applicable for experimental neuroscience but some of them also suitable for the clinical studies.