Role of hilar mossy cells in the CA3-dentate gyrus network during sharp wave-ripple activity in vitro

Der Gyrus dentatus (DG) des Hippokampus wird als Eingangsstation für Informationen aus dem entorhinalen Kortex betrachtet. In das DG-Netzwerk sind zwei exzitatorische Zelltypen eingebettet: Körnerzellen, die Signale von dem entorhinalen Kortex empfangen, und Hilus-Mooszellen (MCs), die Signale von Körnerzellen als auch von feedback-Projektionen von CA3-Pyramidenzellen (PCs) empfangen. Postsynaptische Ziele von MC-Projektionen umfassen DG Körnerzellen und verschiedene Interneurone in der selben und in der kontralateralen Hemisphäre des Gehirns. Die Rolle von MCs während rhythmischer Populationsaktivität, und insbesondere während Sharp-Wave / Ripple-Komplexen (SWRs), ist bisher weitgehend unerforscht. SWRs sind prominente Ereignisse im Hippocampus während des Tiefschlafs (Slow wave sleep) und des ruhigen Wachzustandes, und sie sind an der Gedächtniskonsolidierung beteiligt. In der vorliegenden Arbeit, untersuchen wir mithilfe eines in-vitro-Modells von SWRs, inwieweit Mooszellen an SWRs in CA3 beteiligt sind. Mit CA3-Feldpotential-Ableitungen und gleichzeitigen ‚cell-attached‘ Messungen von einzelnen MCs konnten wir beobachten, dass ein wesentlicher Anteil von MCs (47%) während der SWRs in das aktive neuronale Netzwerk rekrutiert werden. Darüber hinaus fanden wir in MCs SWR-assoziierte synaptische Aktivität, bei denen sowohl die exzitatorischen als auch die inhibitorischen Komponenten phasenkohärent und verzögert zur Ripple Oszillation in CA3 auftreten. Simultane Patch-clamp Messungen von CA3-Pyramidenzellen und MCs zeigten längere exzitatorische und inhibitorische Latenzzeiten bei MCs, was die Hypothese einer von CA3 ausgehenden Feedback-Rekrutierung unterstützt. Unsere Daten zeigen zusätzlich, dass das Verhältnis exzitatorischer zu inhibitorischer Aktivität in MCs höher ist als in CA3-Pyramidenzellen, wodurch die MCs mit höherer Wahrscheinlichkeit während SWRs überschwellig aktiviert werden. Schließlich zeigen wir, dass ein signifikanter Anteil (66%) der getesteten Körnerzellen SWR-assoziierte exzitatorische Signale erhalten, im Vergleich zu MCs zeitlich verzögert, was auf eine indirekte Aktivierung von Körnerzellen durch CA3 PCs über MCs hinweist. Zusammengefasst zeigen unsere Daten die aktive Beteiligung von Mooszellen an SWRs und deuten auf eine funktionelle Bedeutung als Schaltstelle für das CA3- Gyrus dentatus Netzwerk in diesem wichtigen physiologischen Netzwerkzustand hin.The dentate gyrus (DG) is considered as the hippocampal input gate for the information arriving from the entorhinal cortex. Embedded into the DG network are two excitatory cell types –granule cells (GCs), which receive inputs from the entorhinal cortex, and hilar mossy cells (MCs), which receive input from GCs and feedback projections from CA3 pyramidal cells (PCs). The postsynaptic targets of MC projections are the GCs and hilar interneurons in both ipsilateral and contralateral hemispheres of the brain. The role of MCs during rhythmic population activity, and in particular during sharp-wave/ripple complexes (SWRs), has remained largely unexplored. SWRs are prominent field events in the hippocampus during slow wave sleep and quiet wakefulness, and are involved in memory consolidation and future planning. In this study, we sought to understand whether MCs participate during CA3 SWRs using an in vitro model of SWRs. With simultaneous CA3 field potential– and cell-attached recordings from MCs, we observed that a significant fraction of MCs (47%) are recruited into the active neuronal network during SWRs. Moreover, MCs receive pronounced, compound, ripple-associated synaptic input where both excitatory and inhibitory components are phase-coherent with and delayed to the CA3 ripple. Simultaneous patch recordings from CA3 pyramidal neurons and MCs revealed longer excitatory and inhibitory latencies in MCs, supporting a feedback recruitment from CA3. Our data also show that the excitatory to inhibitory charge transfer (E/I) ratio in MCs is higher than in the CA3 PCs, making the MCs more likely to spike during SWRs. Finally, we demonstrate that a significant fraction (66%) of tested GCs receive SWR-associated excitatory inputs that are delayed compared to MCs, indicating an indirect activation of GCs by CA3 PCs via MCs. Together, our data suggest the involvement of mossy cells during SWRs and their importance as a relay for CA3-dentate gyrus networks in this important physiological network state

Nanodiamonds-induced effects on neuronal firing of mouse hippocampal microcircuits

Fluorescent nanodiamonds (FND) are carbon-based nanomaterials that can efficiently incorporate optically active photoluminescent centers such as the nitrogen-vacancy complex, thus making them promising candidates as optical biolabels and drug-delivery agents. FNDs exhibit bright fluorescence without photobleaching combined with high uptake rate and low cytotoxicity. Focusing on FNDs interference with neuronal function, here we examined their effect on cultured hippocampal neurons, monitoring the whole network development as well as the electrophysiological properties of single neurons. We observed that FNDs drastically decreased the frequency of inhibitory (from 1.81 Hz to 0.86 Hz) and excitatory (from 1.61 Hz to 0.68 Hz) miniature postsynaptic currents, and consistently reduced action potential (AP) firing frequency (by 36%), as measured by microelectrode arrays. On the contrary, bursts synchronization was preserved, as well as the amplitude of spontaneous inhibitory and excitatory events. Current-clamp recordings revealed that the ratio of neurons responding with AP trains of high-frequency (fast-spiking) versus neurons responding with trains of low-frequency (slow-spiking) was unaltered, suggesting that FNDs exerted a comparable action on neuronal subpopulations. At the single cell level, rapid onset of the somatic AP ("kink") was drastically reduced in FND-treated neurons, suggesting a reduced contribution of axonal and dendritic components while preserving neuronal excitability.Comment: 34 pages, 9 figure

Anti-epileptic effect of Ganoderma lucidum polysaccharides by inhibition of intracellular calcium accumulation and stimulation of expression of CaMKII a in epileptic hippocampal neurons

Purpose: To investigate the mechanism of the anti-epileptic effect of Ganoderma lucidum polysaccharides (GLP), the changes of intracellular calcium and CaMK II a expression in a model of epileptic neurons were investigated. Method: Primary hippocampal neurons were divided into: 1) Control group, neurons were cultured with Neurobasal medium, for 3 hours; 2) Model group I: neurons were incubated with Mg2+ free medium for 3 hours; 3) Model group II: neurons were incubated with Mg2+ free medium for 3 hours then cultured with the normal medium for a further 3 hours; 4) GLP group I: neurons were incubated with Mg2+ free medium containing GLP (0.375 mg/ml) for 3 hours; 5) GLP group II: neurons were incubated with Mg2+ free medium for 3 hours then cultured with a normal culture medium containing GLP for a further 3 hours. The CaMK II a protein expression was assessed by Western-blot. Ca2+ turnover in neurons was assessed using Fluo-3/AM which was added into the replacement medium and Ca2+ turnover was observed under a laser scanning confocal microscope. Results: The CaMK II a expression in the model groups was less than in the control groups, however, in the GLP groups, it was higher than that observed in the model group. Ca2+ fluorescence intensity in GLP group I was significantly lower than that in model group I after 30 seconds, while in GLP group II, it was reduced significantly compared to model group II after 5 minutes. Conclusion: GLP may inhibit calcium overload and promote CaMK II a expression to protect epileptic neuron

Widespread depolarization during expiration: A source of respiratory drive?

Respiration influences various pacemakers and rhythms of the body during inspiration and expiration but the underlying mechanisms are relatively unknown. Understanding this phenomenon is important, as breathing disorders, breath holding, and hyperventilation can lead to significant medical conditions. We discuss the physiological modulation of heart rhythm, blood pressure, sympathetic nerve activity, EEG, and other changes observed during inspiration and expiration. We also correlate the intracellular mitochondrial respiratory metabolic processes with real-time breathing and correlate membrane potential changes with inspiration and expiration. We propose that widespread minor hyperpolarization occurs during inspiration and widespread minor depolarization occurs during expiration. This depolarization is likely a source of respiratory drive. Further knowledge of intracellular and extracellular ionic changes associated with respiration will enhance our understanding of respiration and its role as a modulator of cellular membrane potential. This could expand treatment options for a wide range of health conditions, such as breathing disorders, stress-related disorders, and further our understanding of the Hering–Breuer reflex and respiratory sinus arrhythmia