Navegando por Autor "Hilscher, Markus M."
Agora exibindo 1 - 9 de 9
- Resultados por página
- Opções de Ordenação
Artigo Chrna2-Martinotti Cells Synchronize Layer 5 Type A Pyramidal Cells via Rebound Excitation(2017-02-09) Hilscher, Markus M.; Leão, Richardson Naves; Edwards, Steven J.; Leão, Emelie Katarina Svahn; Kullander, KlasMartinotti cells are the most prominent distal dendrite–targeting interneurons in the cortex, but their role in controlling pyramidal cell (PC) activity is largely unknown. Here, we show that the nicotinic acetylcholine receptor α2 subunit (Chrna2) specifically marks layer 5 (L5) Martinotti cells projecting to layer 1. Furthermore, we confirm that Chrna2-expressing Martinotti cells selectively target L5 thick-tufted type A PCs but not thin-tufted type B PCs. Using optogenetic activation and inhibition, we demonstrate how Chrna2-Martinotti cells robustly reset and synchronize type A PCs via slow rhythmic burst activity and rebound excitation. Moreover, using optical feedback inhibition, in which PC spikes controlled the firing of surrounding Chrna2-Martinotti cells, we found that neighboring PC spike trains became synchronized by Martinotti cell inhibition. Together, our results show that L5 Martinotti cells participate in defined cortical circuits and can synchronize PCs in a frequency-dependent manner. These findings suggest that Martinotti cells are pivotal for coordinated PC activity, which is involved in cortical information processing and cognitive control.Artigo Chrna2-OLM interneurons display different membrane properties and h-current magnitude depending on dorsoventral location(2019-07) Hilscher, Markus M.; Nogueira, Ingrid; Mikulovic, Sanja; Kullander, Klas; Leão, Richardson Naves; Leão, Emelie Katarina SvahnThe hippocampus is an extended structure displaying heterogeneous anatomical cell layers along its dorsoventral axis. It is known that dorsal and ventral regions show different integrity when it comes to functionality, innervation, gene expression, and pyramidal cell properties. Still, whether hippocampal interneurons exhibit different properties along the dorsoventral axis is not known. Here, we report electrophysiological properties of dorsal and ventral oriens lacunosum moleculare (OLM) cells from coronal sections of the Chrna2‐cre mouse line. We found dorsal OLM cells to exhibit a significantly more depolarized resting membrane potential compared to ventral OLM cells, while action potential properties were similar between the two groups. We found ventral OLM cells to show a higher initial firing frequency in response to depolarizing current injections but also to exhibit a higher spike‐frequency adaptation than dorsal OLM cells. Additionally, dorsal OLM cells displayed large membrane sags in response to negative current injections correlating with our results showing that dorsal OLM cells have more hyperpolarization‐activated current (Ih) compared to ventral OLM cells. Immunohistochemical examination indicates the h‐current to correspond to hyperpolarization‐activated cyclic nucleotide‐gated subunit 2 (HCN2) channels. Computational studies suggest that Ih in OLM cells is essential for theta oscillations in hippocampal circuits, and here we found dorsal OLM cells to present a higher membrane resonance frequency than ventral OLM cells. Thus, our results highlight regional differences in membrane properties between dorsal and ventral OLM cells allowing this interneuron to differently participate in the generation of hippocampal theta rhythms depending on spatial location along the dorsoventral axis of the hippocampus.Artigo Decreasing dorsal cochlear nucleus activity ameliorates noise-induced tinnitus perception in mice(Springer Science and Business Media LLC, 2022-05-12) Borges, Thawann Malfatti; Boerner, Barbara Ciralli; Hilscher, Markus M.; Leao, Richardson Naves; Leão, Emelie Katarina SvahnBackground: The dorsal cochlear nucleus (DCN) is a region known to integrate somatosensory and auditory inputs and is identified as a potential key structure in the generation of phantom sound perception, especially noise-induced tinnitus. Yet, how altered homeostatic plasticity of the DCN induces and maintains the sensation of tinnitus is not clear. Here, we chemogenetically decrease activity of a subgroup of DCN neurons, Ca2+/Calmodulin kinase 2 α (CaMKII α)-positive DCN neurons, using Gi-coupled human M4 Designer Receptors Exclusively Activated by Designer Drugs (hM4Di DREADDs), to investigate their role in noise-induced tinnitus. Results: Mice were exposed to loud noise (9–11kHz, 90dBSPL, 1h, followed by 2h of silence), and auditory brainstem responses (ABRs) and gap prepulse inhibition of acoustic startle (GPIAS) were recorded 2 days before and 2 weeks after noise exposure to identify animals with a significantly decreased inhibition of startle, indicating tinnitus but without permanent hearing loss. Neuronal activity of CaMKII α+ neurons expressing hM4Di in the DCN was lowered by administration of clozapine-N-oxide (CNO). We found that acutely decreasing firing rate of CaMKII α+ DCN units decrease tinnitus-like responses (p = 3e −3, n = 11 mice), compared to the control group that showed no improvement in GPIAS (control virus; CaMKII α-YFP + CNO, p = 0.696, n = 7 mice). Extracellular recordings confirmed CNO to decrease unit firing frequency of CaMKII α-hM4Di+ mice and alter best frequency and tuning width of response to sound. However, these effects were not seen if CNO had been previously administered during the noise exposure (n = 6 experimental and 6 control mice). Conclusion: We found that lowering DCN activity in mice displaying tinnitus-related behavior reduces tinnitus, but lowering DCN activity during noise exposure does not prevent noise-induced tinnitus. Our results suggest that CaMKII α-positive cells in the DCN are not crucial for tinnitus induction but play a significant role in maintaining tinnitus perception in miceArtigo Direct reprogramming of adult human somatic stem cells into functional neurons using Sox2, Ascl1, and Neurog2(2018-06-08) Araújo, Jessica Alves de Medeiros; Hilscher, Markus M.; Marques-Coelho, Diego; Golbert, Daiane C. F.; Cornelio, Deborah A.; Medeiros, Silvia R. Batistuzzo de; Leão, Richardson Naves; Costa, Marcos RomualdoReprogramming 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.Artigo Firing properties of Renshaw cells defined by Chrna2 are modulated by hyperpolarizing and small conductance ion currents Ih and ISK(2015) Perry, Sharn; Gezelius, Henrik; Larhammar, Martin; Hilscher, Markus M.; Lamotte d’Incamps, Boris; Leão, Emelie Katarina Svahn; Kullander, KlasRenshaw cells in the spinal cord ventral horn regulate motoneuron output through recurrent inhibition. Renshaw cells can be identified in vitro using anatomical and cellular criteria; however, their functional role in locomotion remains poorly defined because of the difficulty of functionally isolating Renshaw cells from surrounding motor circuits. Here we aimed to investigate whether the cholinergic nicotinic receptor alpha2 (Chrna2) can be used to identify Renshaw cells (RCs(α2)) in the mouse spinal cord. Immunohistochemistry and electrophysiological characterization of passive and active RCs(α2) properties confirmed that neurons genetically marked by the Chrna2-Cre mouse line together with a fluorescent reporter mouse line are Renshaw cells. Whole-cell patch-clamp recordings revealed that RCs(α2) constitute an electrophysiologically stereotyped population with a resting membrane potential of -50.5 ± 0.4 mV and an input resistance of 233.1 ± 11 MΩ. We identified a ZD7288-sensitive hyperpolarization-activated cation current (Ih) in all RCs(α2), contributing to membrane repolarization but not to the resting membrane potential in neonatal mice. Additionally, we found RCs(α2) to express small calcium-activated potassium currents (I(SK)) that, when blocked by apamin, resulted in a complete attenuation of the afterhyperpolarisation potential, increasing cellular firing frequency. We conclude that RCs(α2) can be genetically targeted through their selective Chrna2 expression and that they display currents known to modulate rebound excitation and firing frequency. The genetic identification of Renshaw cells and their electrophysiological profile is required for genetic and pharmacological manipulation as well as computational simulations with the aim to understand their functional role.Artigo Novel markers for OLM interneurons in the hippocampus(2015-06-02) Mikulovic, Sanja; Restrepo, C. Ernesto; Hilscher, Markus M.; Kullander, Klas; Leão, Richardson NavesOriens-lacunosum moleculare (OLM) cells are a major subclass of hippocampal interneurons involved in controlling synaptic plasticity in Shaffer collateral synapses (Leão et al., 2012) and electrogenesis in pyramidal cell (PC) dendrites (Lovett-Barron et al., 2012). Their firing phase is locked with theta oscillations, which imply a role for these cells in theta rhythmogenesis (Klausberger and Somogyi, 2008; Forro et al., 2015). OLM interneurons also appear to be key in the pathophysiology of epilepsy (Dugladze et al., 2007) and is the most vulnerable interneuron population in models of epilepsy (Dinocourt et al., 2003). Somatostatin has been frequently used as a molecular marker for identification of OLM cells (Forro et al., 2015). Two recent studies suggest that the OLM cell population is heterogeneous. First, the expression of cholinergic receptor, nicotinic, alpha polypeptide 2 (Chrna2) seems to be restricted to OLM interneurons neurons of CA1 (Leão et al., 2012). Second, a subset of OLM interneurons that expresses the 5HT3a receptor is derived from the caudal ganglionic eminence and do not entrain to gamma oscillations. In contrast, OLM interneurons derived from the medial ganglionic eminence partially phase lock to in vitro gamma oscillations and do not express 5HT3a receptors (Chittajallu et al., 2013). Further, other dendritic targeting interneurons in the hippocampus also express somatostatin (Lovett-Barron et al., 2014). Hence, functional studies of OLM cell in hippocampal function have been targeting a relatively heterogenous cell population.Artigo OLMα2 cells bidirectionally modulate learning(2018-07) Siwani, Samer; França, Arthur S. C.; Mikulovic, Sanja; Reis, Amilcar; Hilscher, Markus M.; Edwards, Steven J.; Leão, Richardson Naves; Tort, Adriano Bretanha Lopes; Kullander, KlasInhibitory interneurons participate in mnemonic processes. However, defined roles for identified interneuron populations are scarce. A subpopulation of oriens lacunosum-moleculare (OLM) interneurons genetically defined by the expression of the nicotinic receptor α2 subunit has been shown to gate information carried by either the temporoammonic pathway or Schaffer collaterals in vitro. Here we set out to determine whether selective modulation of OLMα2 cells in the intermediate CA1 affects learning and memory in vivo. Our data show that intermediate OLMα2 cells can either enhance (upon their inhibition) or impair (upon their activation) object memory encoding in freely moving mice, thus exerting bidirectional control. Moreover, we find that OLMα2 cell activation inhibits fear-related memories and that OLMα2 cells respond differently to nicotine in the dorsoventral axis. These results suggest that intermediate OLMα2 cells are an important component in the CA1 microcircuit regulating learning and memory processes.Artigo A role for solute carrier family 10 member 4, or vesicular aminergic-associated transporter, in structural remodelling and transmitter release at the mouse neuromuscular junction(2015) Patra, Kalicharan; Lyons, David J.; Bauer, Pavol; Hilscher, Markus M.; Sharma, Swati; Leão, Richardson Naves; Kullander, KlasThe solute carrier and presynaptic vesicle protein solute carrier family 10 member 4, or vesicular aminergic-associated transporter (VAAT), was recently proven to have a modulatory role in central cholinergic signalling. It is currently unknown whether VAAT also affects peripheral cholinergic synapses. Here we demonstrated a regulatory role for the presynaptic vesicle protein VAAT in neuromuscular junction (NMJ) development and function. NMJs lacking VAAT had fewer branch points, whereas endplates showed an increased number of islands. Whereas the amplitude of spontaneous miniature endplate potentials in VAAT-deficient NMJs was decreased, the amplitude of evoked endplate potentials and the size of the readily releasable pool of vesicles were both increased. Moreover, VAAT-deficient NMJs displayed aberrant short-term synaptic plasticity with enhanced synaptic depression in response to high-frequency stimulation. Finally, the transcript levels of cholinergic receptor subunits in VAAT-deficient muscles were increased, indicating a compensatory postsynaptic sensitization. Our results suggested that VAAT modulates NMJ transmission efficiency and, as such, may represent a novel target for treatment of disorders affecting motor neurons.Artigo Synchronization through nonreciprocal connections in a hybrid hippocampus microcircuit(2013-07-23) Hilscher, Markus M.; Leão, Emelie Katarina Svahn; Leão, Richardson NavesSynchronizationamongneuronsisthoughttoarisefromtheinterplaybetweenexcitationandinhibition;however,theconnectivityrulesthatcontributetosynchronizationarestillunknown.WestudiedtheseissuesinhippocampalCA1microcircuitsusingpairedpatchclamprecordingsandrealtimecomputing.Byvirtuallyconnectingamodelinterneuronwithtwopyramidalcells(PCs),wewereabletotesttheimportanceofconnectivityinsynchronizingpyramidalcellactivity.OurresultsshowthatacircuitwithanonreciprocalconnectionbetweenpyramidalcellsandnofeedbackfromPCstothevirtualinterneuronproducedthegreatestlevelofsynchronizationandmutualinformationbetweenPCspikingactivity.Moreover,weinvestigatedtheroleofintrinsicmembranepropertiescontributingtosynchronizationwheretheapplicationofaspecificionchannelblocker,ZD7288dramaticallyimpairedPCsynchronization.Additionally,backgroundsynapticactivity,inparticulararisingfromNMDAreceptors,hasalargeimpactonthesynchronyobservedintheaforementionedcircuit.Ourresultsgivenewinsightstothebasicconnectionparadigmsofmicrocircuitsthatleadtocoordinationandtheformationofassemblies.