Role of the potassium-chloride cotransporter type 2 (KCC2) in balancing excitation in the mouse hippocampus

In this study, I have investigated whether and how potassium-chloride cotransporter 2 (KCC2) influences extracellular potassium ([K+]o) levels during physiological synaptic activity in the mouse hippocampus. I have shown that KCC2 plays a crucial role in clearing excess [K+]o in the vicinity of synapses during neuronal activity by temporarily reversing its mode of operation and transporting K+ from extracellular space into spine. By manipulating KCC2 activity, I have observed changes in [K+]o clearance, impacting neuronal excitability and synaptic transmission. When KCC2 was blocked, there was an increase in [K+]o levels around synapses, affecting astrocytic and neuronal responses and leading to enhanced excitatory signals. Conversely, enhancing KCC2 function reduced perisynaptic [K+]o, decreasing astrocytic response and lowering the frequency of excitatory signals. I have also shown that these effects were activity dependent and were more pronounced when other mechanisms of [K+]o buffering, such as astrocytic Kir channels, were compromised. Additionally, my results suggest that KCC2 activity can determine the efficiency of synaptic plasticity. These findings highlight the significance of KCC2 at dendritic spines in regulating [K+]o levels during physiological synaptic activity and its potential impact on information processing and storage. This research adds to previous evidence of tight connection of KCC2 with excitation balance in the brain.In dieser Studie habe ich untersucht, ob und wie der Kalium-Chlorid-Cotransporter 2 (KCC2) die Konzentration des extrazellulären Kaliums ([K+]o) während physiologischer synaptischer Aktivität im Hippocampus der Maus beeinflusst. Ich habe gezeigt, dass KCC2 eine entscheidende Rolle bei der Wiederaufnahme von überschüssigem [K+]o in der Nähe von exzitatorischen Synapsen während neuronaler Aktivität spielt, indem es vorübergehend seinen Betriebsmodus umkehrt und K+ aus dem extrazellulären Raum in die Dornfortsätze neuronaler Dendriten transportiert. Nach Manipulation der KCC2-Aktivität habe ich Veränderungen in der [K+]o-Aufnahme beobachtet, die sich auf die neuronale Erregbarkeit und synaptische Übertragung auswirkten. Wenn KCC2 blockiert wurde, gab es einen Anstieg der [K+]o um die Synapsen, was astrozytäre und neuronale Reaktionen beeinflusste und zur Verstärkung erregender Signale führte. Umgekehrt reduzierte die Steigerung der KCC2-Funktion das perisynaptische [K+]o, verringerte die astrozytäre Reaktion und senkte die Häufigkeit erregender Signale. Ich habe auch gezeigt, dass diese Effekte von der exzitatorschen Aktivität abhängig und ausgeprägter waren, wenn andere Mechanismen der [K+]o-Pufferung, wie die astrozytären Kir-Kanäle, beeinträchtigt waren. Darüber hinaus legen meine Ergebnisse nahe, dass die KCC2-Aktivität die Effizienz der synaptischen Plastizität beeinflussen kann. Diese Ergebnisse betonen die Bedeutung von KCC2 an dendritischen Dornfortsätzen bei der Regulation der [K+]o während physiologischer synaptischer Aktivität und deren potenziellen Auswirkungen auf die Informationsverarbeitung und -speicherung. Diese Forschung erweitert frühere Erkenntnisse über die enge Verbindung von KCC2 mit dem Erregungsgleichgewicht zentralnervöser Netzwerke

Interferon-γ acutely augments inhibition of neocortical layer 5 pyramidal neurons

BACKGROUND: Interferon-γ (IFN-γ, a type II IFN) is present in the central nervous system (CNS) under various conditions. Evidence is emerging that, in addition to its immunological role, IFN-γ modulates neuronal morphology, function, and development in several brain regions. Previously, we have shown that raising levels of IFN-β (a type I IFN) lead to increased neuronal excitability of neocortical layer 5 pyramidal neurons. Because of shared non-canonical signaling pathways of both cytokines, we hypothesized a similar neocortical role of acutely applied IFN-γ. METHODS: We used semi-quantitative RT-PCR, immunoblotting, and immunohistochemistry to analyze neuronal expression of IFN-γ receptors and performed whole-cell patch-clamp recordings in layer 5 pyramidal neurons to investigate sub- and suprathreshold excitability, properties of hyperpolarization-activated cyclic nucleotide-gated current (Ih), and inhibitory neurotransmission under the influence of acutely applied IFN-γ. RESULTS: We show that IFN-γ receptors are present in the membrane of rat's neocortical layer 5 pyramidal neurons. As expected from this and the putative overlap in IFN type I and II alternative signaling pathways, IFN-γ diminished Ih, mirroring the effect of type I IFNs, suggesting a likewise activation of protein kinase C (PKC). In contrast, IFN-γ did neither alter subthreshold nor suprathreshold neuronal excitability, pointing to augmented inhibitory transmission by IFN-γ. Indeed, IFN-γ increased electrically evoked inhibitory postsynaptic currents (IPSCs) on neocortical layer 5 pyramidal neurons. Furthermore, amplitudes of spontaneous IPSCs and miniature IPSCs were elevated by IFN-γ, whereas their frequency remained unchanged. CONCLUSIONS: The expression of IFN-γ receptors on layer 5 neocortical pyramidal neurons together with the acute augmentation of inhibition in the neocortex by direct application of IFN-γ highlights an additional interaction between the CNS and immune system. Our results strengthen our understanding of the role of IFN-γ in neocortical neurotransmission and emphasize its impact beyond its immunological properties, particularly in the pathogenesis of neuropsychiatric disorders

KCC2 reverse mode helps to clear postsynaptically released potassium at glutamatergic synapses

Summary: Extracellular potassium [K+]o elevation during synaptic activity retrogradely modifies presynaptic release and astrocytic uptake of glutamate. Hence, local K+ clearance and replenishment mechanisms are crucial regulators of glutamatergic transmission and plasticity. Based on recordings of astrocytic inward rectifier potassium current IKir and K+-sensitive electrodes as sensors of [K+]o as well as on in silico modeling, we demonstrate that the neuronal K+-Cl- co-transporter KCC2 clears local perisynaptic [K+]o during synaptic excitation by operating in an activity-dependent reversed mode. In reverse mode, KCC2 replenishes K+ in dendritic spines and complements clearance of [K+]o, therewith attenuating presynaptic glutamate release and shortening LTP. We thus demonstrate a physiological role of KCC2 in neuron-glial interactions and regulation of synaptic signaling and plasticity through the uptake of postsynaptically released K+

KCC2 reverse mode helps to clear postsynaptically released potassium at glutamatergic synapses

Extracellular potassium [K+]o elevation during synaptic activity retrogradely modifies presynaptic release and astrocytic uptake of glutamate. Hence, local K+ clearance and replenishment mechanisms are crucial regulators of glutamatergic transmission and plasticity. Based on recordings of astrocytic inward rectifier potassium current IKir and K+-sensitive electrodes as sensors of [K+]o as well as on in silico modeling, we demonstrate that the neuronal K+-Cl- co-transporter KCC2 clears local perisynaptic [K+]o during synaptic excitation by operating in an activity-dependent reversed mode. In reverse mode, KCC2 replenishes K+ in dendritic spines and complements clearance of [K+]o, therewith attenuating presynaptic glutamate release and shortening LTP. We thus demonstrate a physiological role of KCC2 in neuron-glial interactions and regulation of synaptic signaling and plasticity through the uptake of postsynaptically released K+

Interferon-γacutely augments inhibition of neocortical layer 5 pyramidal neurons

Background Interferon-γ (IFN-γ, a type II IFN) is present in the central nervous system (CNS) under various conditions. Evidence is emerging that, in addition to its immunological role, IFN-γ modulates neuronal morphology, function, and development in several brain regions. Previously, we have shown that raising levels of IFN-β (a type I IFN) lead to increased neuronal excitability of neocortical layer 5 pyramidal neurons. Because of shared non-canonical signaling pathways of both cytokines, we hypothesized a similar neocortical role of acutely applied IFN-γ. Methods We used semi-quantitative RT-PCR, immunoblotting, and immunohistochemistry to analyze neuronal expression of IFN-γ receptors and performed whole-cell patch-clamp recordings in layer 5 pyramidal neurons to investigate sub- and suprathreshold excitability, properties of hyperpolarization-activated cyclic nucleotide-gated current (Ih), and inhibitory neurotransmission under the influence of acutely applied IFN-γ. Results We show that IFN-γ receptors are present in the membrane of rat’s neocortical layer 5 pyramidal neurons. As expected from this and the putative overlap in IFN type I and II alternative signaling pathways, IFN-γ diminished Ih, mirroring the effect of type I IFNs, suggesting a likewise activation of protein kinase C (PKC). In contrast, IFN-γ did neither alter subthreshold nor suprathreshold neuronal excitability, pointing to augmented inhibitory transmission by IFN-γ. Indeed, IFN-γ increased electrically evoked inhibitory postsynaptic currents (IPSCs) on neocortical layer 5 pyramidal neurons. Furthermore, amplitudes of spontaneous IPSCs and miniature IPSCs were elevated by IFN-γ, whereas their frequency remained unchanged. Conclusions The expression of IFN-γ receptors on layer 5 neocortical pyramidal neurons together with the acute augmentation of inhibition in the neocortex by direct application of IFN-γ highlights an additional interaction between the CNS and immune system. Our results strengthen our understanding of the role of IFN-γ in neocortical neurotransmission and emphasize its impact beyond its immunological properties, particularly in the pathogenesis of neuropsychiatric disorders