GluA4 Dependent Plasticity Mechanisms Contribute to Developmental Synchronization of the CA3-CA1 Circuitry in the Hippocampus

During the course of development, molecular mechanisms underlying activity-dependent synaptic plasticity change considerably. At immature CA3-CA1 synapses in the hippocampus, PKA-driven synaptic insertion of GluA4 AMPA receptors is the predominant mechanism for synaptic strengthening. However, the physiological significance of the developmentally restricted GluA4-dependent plasticity mechanisms is poorly understood. Here we have used microelectrode array (MEA) recordings in GluA4 deficient slice cultures to study the role of GluA4 in early development of the hippocampal circuit function. We find that during the first week in culture (DIV2-6) when GluA4 expression is restricted to pyramidal neurons, loss of GluA4 has no effect on the overall excitability of the immature network, but significantly impairs synchronization of the CA3 and CA1 neuronal populations. In the absence of GluA4, the temporal correlation of the population spiking activity between CA3-CA1 neurons was significantly lower as compared to wild-types at DIV6. Our data show that synapse-level defects in transmission and plasticity mechanisms are efficiently compensated for to normalize population firing rate at the immature hippocampal network. However, lack of the plasticity mechanisms typical for the immature synapses may perturb functional coupling between neuronal sub-populations, a defect frequently implicated in the context of developmentally originating neuropsychiatric disorders.Peer reviewe

Plasma etched carbon microelectrode arrays for bioelectrical measurements

Carbon-based materials have attracted much attention in biological applications like interfacing electrodes with neurons and cell growth platforms due to their natural biocompatibility and tailorable material properties. Here we have fabricated sputtered carbon thin film electrodes for bioelectrical measurements. Reactive ion etching (RIE) recipes were optimized with Taguchi method to etch the close field unbalanced magnetron sputtered carbon thin film (nanocarbon, nC) consisting of nanoscale crystalline sp(2)-domains in amorphous sp(3)-bonded backbone. Plasma etching processes used gas mixtures of Ar/O-2/SF6/CHF3 for RIE and O-2/SF6 for ICP-RIE. The highest achieved etch rate for nanocarbon was >> 389 nm/min and best chromium etch mask selectivity was 135:1. Biocompatibility of the material was tested with rat neuronal cultures. Next, we fabricated multielectrode arrays (MEA) with carbon recording electrodes and metal wiring. Organotypic brain slices grown on the MEAs were viable and showed characteristic spontaneous electrical network activity. The results demonstrate that interactions with nanocarbon substrate support neuronal survival and maturation of functional neuronal networks. Thus the material can have wide applications in biomedical research.Peer reviewe

Neuroimmune crosstalk in the central nervous system and its significance for neurological diseases

The central nervous system (CNS) is now known to actively communicate with the immune system to control immune responses both centrally and peripherally. Within the CNS, while studies on glial cells, especially microglia, have highlighted the importance of this cell type in innate immune responses of the CNS, the immune regulatory functions of other cell types, especially neurons, are largely unknown. How neuroimmune cross-talk is homeostatically maintained in neurodevelopment and adult plasticity is even more elusive. Inspiringly, accumulating evidence suggests that neurons may also actively participate in immune responses by controlling glial cells and infiltrated T cells. The potential clinical application of this knowledge warrants a deeper understanding of the mutual interactions between neurons and other types of cells during neurological and immunological processes within the CNS, which will help advance diagnosis, prevention, and intervention of various neurological diseases. The aim of this review is to address the immune function of both glial cells and neurons, and the roles they play in regulating inflammatory processes and maintaining homeostasis of the CNS.Peer reviewe

Human embryonic stem cell -derived neural co-cultures

ABSTRACT Background and aims: Human embryonic stem cells are pluripotent stem cells with the potential to differentiate into any cell types of the human body. Differentiation of these stem cells into neuronal and glial cells enables the formation of different type of neural cell grafts. These grafts can be used in the treatment of different neurological disorders or injuries, such as spinal cord injuries. Traditionally neural cell transplantations have focused on the transplantation of only single cell types. In this study the aim was to form co-cultures of both neuronal and oligodendroglial cells, in order to mimic the in vivo myelination. Methods: Human embryonic stem cells were differentiated into neurons and oligodendrocytes. Both of these cell populations were purified with fluorescence activated cell sorting and then cultured together. These co-cultures were aimed to form neural networks with myelinated axons. The gene and protein expression in co-cultures was studied. Results: Maturation of oligodendrocyte precursors in co-cultures was detected, indicating that the cells were matured into myelinating oligodendrocytes. Conclusions: Both neurons and oligodendrocytes did survive in the used co-culture conditions, and oligodendrocytes were able to mature into cells with myelinating capacity. Still, the design of co-culture formation and the myelin detection should be reconsidered in order to form successfully myelinating cultures. This study serves as a valuable base for the future optimization. Asiasanat:Key words: oligodendrocyte, oligodendrocyte precursor, neural co-culture, human embryonic stem cell, fluorescence activated cell sortin

Human embryonic stem cell -derived neural co-cultures

ABSTRACT Background and aims: Human embryonic stem cells are pluripotent stem cells with the potential to differentiate into any cell types of the human body. Differentiation of these stem cells into neuronal and glial cells enables the formation of different type of neural cell grafts. These grafts can be used in the treatment of different neurological disorders or injuries, such as spinal cord injuries. Traditionally neural cell transplantations have focused on the transplantation of only single cell types. In this study the aim was to form co-cultures of both neuronal and oligodendroglial cells, in order to mimic the in vivo myelination. Methods: Human embryonic stem cells were differentiated into neurons and oligodendrocytes. Both of these cell populations were purified with fluorescence activated cell sorting and then cultured together. These co-cultures were aimed to form neural networks with myelinated axons. The gene and protein expression in co-cultures was studied. Results: Maturation of oligodendrocyte precursors in co-cultures was detected, indicating that the cells were matured into myelinating oligodendrocytes. Conclusions: Both neurons and oligodendrocytes did survive in the used co-culture conditions, and oligodendrocytes were able to mature into cells with myelinating capacity. Still, the design of co-culture formation and the myelin detection should be reconsidered in order to form successfully myelinating cultures. This study serves as a valuable base for the future optimization. Asiasanat:Key words: oligodendrocyte, oligodendrocyte precursor, neural co-culture, human embryonic stem cell, fluorescence activated cell sortin

Kainaattireseptorit kehittyvän hermoverkon synkronisessa aktiivisuudessa

Kainaattireseptorit (KARt) ovat glutamaattireseptoreita, jotka muokkaavat ja säätelevät hermosolujen viestintää aivoissa. KAR:n toiminta riippuu niiden alayksikkökokoonpanosta sekä sijainnista hermosolussa. Näiden reseptorien ilmentäminen muuttuu yksilön kehityksen myötä, erityisen voimakkaasti niitä ilmennetään heti syntymän jälkeen. Onkin esitetty, että ensimmäisten elinviikkojen aikana KARt edistävät hermoverkkojen aktiivisuusriippuvaista kehitystä. Vaikka KAR:ta on tutkittu laajalti, niiden hermoston kehityksen aikainen toiminta ymmärretään vielä huonosti. Tässä työssä selvitimme miten kehittyvän hippokampuksen verkkoaktiivisuus muuttuu, kun KAR alayksikkö GluK1:n ilmentämistä lisättiin osassa CA3 pyramidaalisoluja. Tutkimuksen hypoteesina oli, että GluK1 säätelee hermoverkon toiminnallista kytkentää sekä synkronista aktiivisuutta. Työssä käytettiin monikanavamittauksia, joiden avulla tutkittiin hippokampusleikeviljelmien sähköistä toimintaa. Tässä osoitamme, että paikallinen GluK1 lisäys vaikuttaa leikkeiden jaksottaiseen spontaaniaktiviisuteen sekä edistää populaatiotason aktiivisuuden leviämistä hermoverkkoon tehokkaammin. Lisäksi näytämme, että toiminnallinen korrelaatio GluK1:ä ilmentavän hermosolupopulaation ja hippokampuksen muiden osien välillä on lisääntynyt. Työn tulokset viittaavat, että GluK1:n ilmentäminen edistää hermoverkon synkronista aktiivisuutta ja vahvistaa pyramidaalisolujen toiminnallisia yhteyksiä muihin hermosoluihin. Löydökset tukevat ja täydentävät aiempaa tutkittua tietoa KARn merkityksestä hermosoluyhteyksien aktiivisuusriippuvaisessa kehityksessä.Kainate type glutamatergic receptors (KARs) modulate synaptic transmission and neuronal excitability depending on their subunit composition and localization. Developmental expression of KARs in the immature hippocampus is suggested to promote activity dependent synchronization of neuronal networks, yet the exact mechanisms are still unclear. Here we asked how local manipulation of KAR subunit GluK1 at CA3 pyramidal cells modulates synchronous network activity in postnatal hippocampus in vitro. We hypothesized that local KAR enhancement will promote functional connectivity and synchronous activity in the networks. Multichannel recordings were used to study spatio-temporal profile of network activity in organotypic hippocampal slice cultures. We show, that local GluK1 enhancement is affecting spontaneous activity patterns and that the population discharges recruit the whole network more efficiently compared to control. In addition, the activities at the site of GluK1 overexpression are more correlated to CA1 and DG regions. Our data suggests that facilitated spatial propagation of population discharges promote synchronization of network activity in KAR expressing slices. These findings support and supplement the previous hypothesis that KARs might play essential role in the functional integration of neurons in hippocampal circuitries

Structured PDMS chambers for enhanced human neuronal cell activity on MEA platforms

Structured poly(dimethylsiloxane) (PDMS) chambers were designed and fabricated to enhance the signaling of human embryonic stem cell (hESC) - derived neuronal networks on microelectrode array (MEA) platforms. The structured PDMS chambers enable cell seeding on restricted areas and thus, reduce the amount of needed coating materials and cells. In addition, the neuronal cells formed spontaneously active networks faster in the structured PDMS chambers than in control chambers. In the PDMS chambers, the neuronal networks were more active and able to develop their signaling into organized signal trains faster than control cultures. The PDMS chamber design enables much more repeatable analysis and rapid growth of functional neuronal network in vitro. Moreover, due to its easy and cheap fabrication process, new configurations can be easily fabricated based on investigator requirements.Peer reviewe

Plasma etched carbon microelectrode arrays for bioelectrical measurements

Carbon-based materials have attracted much attention in biological applications like interfacing electrodes with neurons and cell growth platforms due to their natural biocompatibility and tailorable material properties. Here we have fabricated sputtered carbon thin film electrodes for bioelectrical measurements. Reactive ion etching (RIE) recipes were optimized with Taguchi method to etch the close field unbalanced magnetron sputtered carbon thin film (nanocarbon, nC) consisting of nanoscale crystalline sp2-domains in amorphous sp3-bonded backbone. Plasma etching processes used gas mixtures of Ar/O2/SF6/CHF3 for RIE and O2/SF6 for ICP-RIE. The highest achieved etch rate for nanocarbon was ≫389 nm/min and best chromium etch mask selectivity was 135:1. Biocompatibility of the material was tested with rat neuronal cultures. Next, we fabricated multielectrode arrays (MEA) with carbon recording electrodes and metal wiring. Organotypic brain slices grown on the MEAs were viable and showed characteristic spontaneous electrical network activity. The results demonstrate that interactions with nanocarbon substrate support neuronal survival and maturation of functional neuronal networks. Thus the material can have wide applications in biomedical research.Peer reviewe