Electrophysiological and Molecular Insights into Thalamocortical Rhythmicity and Hippocampal Theta Oscillations

Zusammenfassung Neuronale Netzwerke sind mit verschiedenen spannungsgesteuerten Kalziumkanälen verknüpft, die eine Schlüsselrolle in der Entstehung von Oszillationen im Hippocampus, aber auch in der thalamokortikalen Rhythmizität einnehmen. Innerhalb einer Vielzahl von Oszillationen konnte gezeigte werden, dass der Cav2.3 R-typ Kalziumkanal für die hippocampale Thetaaktivität maßgeblich verantwortlich ist. Thetaoszillationen im Frequenzbereich von 4-7 Hz repräsentieren ein spezifisches Aktivitätsmuster, das für kognitive Fertigkeiten, wie dem Abrufen von Gedächtnisinhalten, unerlässlich ist. Auf pharmakologischer Ebene werden zwei Subtypen von Thetaaktivität, der Atropin resistente Typ I und das Atropin sensitive Typ II Theta, differenziert. Typ II Theta wird dabei über eine durch den Cav2.3 R-typ Kalziumkanal vermittelte, muskarinerge Signalkaskade in der hippocampalen CA1 Region generiert. Interessanterweise treten Theta Oszillationen auch während des paradoxen bzw. REM (rapid eye movement) Schlafs auf, was daraufhin deutet, dass Thetaaktivität vom zirkadianen Rhythmus abhängt. Da Cav2.3 R-typ Kalziumkanäle ebenfalls im retikulär thalamischen Kern (RTN), der in die Schlafgenerierung eingebunden ist, exprimiert werden, kann vermutet werden, dass dem Cav2.3 Kalziumkanal eine regulatorische Funktion beim Schlaf zukommt. Bislang konnte allerdings nicht geklärt werden, welche genaue Rolle Cav2.3 R-typ Kalziumkanäle im thalamokortikalen Netzwerk übernehmen. Daher analysierten wir den Cav2.3 R-typ Kalziumkanal in spontanen und pharmakologisch induzierten Schlaf von Cav 2.3-/- Mäusen und Cav 2.3+/+ Kontrolltieren. Unsere Ergebnisse zeigen eine erhöhte Anzahl an Schlafübergängen sowie eine verminderte Gesamtwachdauer bei Cav 2.3-/- Mäusen und verdeutlichen folglich die tragende Rolle des Cav2.3 R-typ Kalziumkanals in Bezug auf die Schlafmodulation. Studien belegen, dass Cav2.3-/- Mäuse auch Absence-Epilepsien ausbilden können, was die Rolle des Cav2.3 R-typ Kalziumkanals in der Epileptogenese widerspiegelt. Pathologische Veränderungen in der zentralen Rhythmizität und eine damit einhergehende erhöhte Anfallswahrscheinlichkeit können unter anderem durch Akkumulation von Aß Plaques, wie sie bei der Alzheimererkrankung auftreten, gefördert werden. Dabei zeigte sich, dass in Mausmodellen der familiären Alzheimer-Demenz (FAD) erhöhte Aß Plaquebildung mit Veränderungen in der Proteinsynthese vom BACE1 Enzym (ß-site APP cleaving enzyme 1) einhergeht. In diesem Zusammenhang ist eine gesteigerte Translation des BACE1 Enzyms unmittelbar an die 6 Phosphorylierung vom Serin an Position 51 des eukaryotischen Translationsinitiationsfaktors 2 Alpha (elF2α) gebunden. Diese Tatsache wirft die Frage auf, ob eine Runterregulierung von elF2α zu einer geringeren Anfallswahrscheinlichkeit durch verminderte Plaquebildung beiträgt und somit den kognitiven Verfall in 5XFAD Mäusen verzögern kann. Dazu untersuchten wir mögliche präventive Effekte von elF2α auf die Epileptogenese, indem wir 5XFAD Mäuse mit einer elF2αS51A Knock-in Line kreuzten, bei denen, durch eine Substitution von Serin durch Alanin an Position 51 bedingt, elF2α nicht mehr phosphoryliert werden kann. Unsere Ergebnisse zeigen einen limitierten präventiven Effekt von elF2α auf motorische und kognitive Defizite in 5XFAD Mäusen. Veränderungen im Hippocampus gehen mit elektrophysiologischen Befunden einher, welche nicht-konvulsive Statusformen epileptiformer Aktivität bei 5XFAD Tieren mit elF2αS51A Allel belegen. Weiterhin untersuchten wir, wie sich Anfallsaktivität auf die muskaringere Signalkaskade in 5XFAD Mäusen auswirkt. Wir stellten fest, dass eine verstärkte muskarinerge Signalkaskade sowohl zu neuronaler Dysrhythmie, aber auch zu einer Erhöhung von Atropin sensitiven Typ II Theta beiträgt, die als möglicher Kompensationsmechanismus zu einem dysbalancierten neuronalen System bei Morbus Alzheimer in Betracht gezogen werden kann

The Ca-V 2.3 R-Type Voltage-Gated Ca2+ Channel in Mouse Sleep Architecture

Study Objectives: Voltage-gated Ca2+ channels (VGCCs) are key elements in mediating thalamocortical rhythmicity. Low-voltage activated (LVA) Ca(V)3 T-type Ca2+ channels have been related to thalamic rebound burst firing and to generation of non-rapid eye movement (NREM) sleep. High-voltage activated (HVA) Ca(V)1 L-type Ca2+ channels, on the opposite, favor the tonic mode of action associated with higher levels of vigilance. However, the role of the HVA Non-L-type Ca(V)2.3 Ca2+ channels, which are predominantly expressed in the reticular thalamic nucleus (RTN), still remains unclear. Recently, Ca(V)2.3(-/-) mice were reported to exhibit altered spike-wave discharge (SWD)/absence seizure susceptibility supported by the observation that Ca(V)2.3 mediated Ca2+ influx into RTN neurons can trigger small-conductance Ca2+-activated K+-channel type 2 (SK2) currents capable of maintaining thalamic burst activity. Based on these studies we investigated the role of Ca(V)2.3 R-type Ca2+ channels in rodent sleep. Methods: The role of Ca(V)2.3 Ca2+ channels was analyzed in Ca(V)2.3(-/-) mice and controls in both spontaneous and artificial urethane-induced sleep, using implantable video-EEG radiotelemetry. Data were analyzed for alterations in sleep architecture using sleep staging software and time-frequency analysis. Results: Ca(V)2.3 deficient mice exhibited reduced wake duration and increased slow-wave sleep (SWS). Whereas mean sleep stage durations remained unchanged, the total number of SWS epochs was increased in Ca(V)2.3(-/-) mice. Additional changes were observed for sleep stage transitions and EEG amplitudes. Furthermore, urethane-induced SWS mimicked spontaneous sleep results obtained from Ca(V)2.3 deficient mice. Quantitative Real-time PCR did not reveal changes in thalamic Ca(V)3 T-type Ca2+ channel expression. The detailed mechanisms of SWS increase in Ca(V)2.3(-/-) mice remain to be determined. Conclusions: Low-voltage activated Ca(V)2.3 R-type Ca2+ channels in the thalamocortical loop and extra-thalamocortical circuitries substantially regulate rodent sleep architecture thus representing a novel potential target for pharmacological treatment of sleep disorders in the future

EEG Radiotelemetry in Small Laboratory Rodents: A Powerful State-of-the Art Approach in Neuropsychiatric, Neurodegenerative, and Epilepsy Research

EEG radiotelemetry plays an important role in the neurological characterization of transgenic mouse models of neuropsychiatric and neurodegenerative diseases as well as epilepsies providing valuable insights into underlying pathophysiological mechanisms and thereby facilitating the development of new translational approaches. We elaborate on the major advantages of nonrestraining EEG radiotelemetry in contrast to restraining procedures such as tethered systems or jacket systems containing recorders. Whereas a main disadvantage of the latter is their unphysiological, restraining character, telemetric EEG recording overcomes these disadvantages. It allows precise and highly sensitive measurement under various physiological and pathophysiological conditions. Here we present a detailed description of a straightforward successful, quick, and efficient technique for intraperitoneal as well as subcutaneous pouch implantation of a standard radiofrequency transmitter in mice and rats. We further present computerized 3D-stereotaxic placement of both epidural and deep intracerebral electrodes. Preoperative preparation of mice and rats, suitable anaesthesia, and postoperative treatment and pain management are described in detail. A special focus is on fields of application, technical and experimental pitfalls, and technical connections of commercially available radiotelemetry systems with other electrophysiological setups

Spontaneous long-term and urethane induced hippocampal EEG power, activity and temperature data from mice lacking the Ca(v)3.2 voltage-gated Ca2+ channel

This article provides raw relative electroencephalographic (EEG) power, temperature and activity data from controls and Ca-v 3.2 deficient mice. Radiotransmitter implantation was carried out in male experimental mice under ketamine/xylazine narcosis. Following a recovery period, radiotelemetric EEG recordings from the hippocampal CA1 region were obtained under spontaneous 24 h long-term conditions and post urethane injection. Relative EEG power values (%) for 2 s epochs were analysed for the following frequency ranges: delta 1 (81 , 0.5-4 Hz), delta 2 (82 , 1-4 Hz), theta 1 (01 , 4-8 Hz), theta 2 (02 , 4-12 Hz), alpha (alpha, 8-12 Hz), sigma (sigma, 12- 16 Hz), beta 1 (beta 1 , 12-30 Hz), beta 2 (beta 2 , 16-24 Hz), beta 3 (beta 3 , 16-30 Hz), gamma low (gamma(low) , 30-50 Hz), gamma mid (gamma(mid) , 50-70 Hz), gamma high (gamma(high) , 70-100 Hz), gamma rip-ples (yripples, 80-200 Hz), and gamma fast ripples (y(fast) ripples, 20 0-50 0 Hz). In addition, subcutaneous temperature and rel-ative activity data were analysed for both the light and dark cycle of two long-term recordings. The same type of data was obtained post urethane injection. Detailed information is provided for the age and body weight of the experimen-tal animals, the technical specifications of the radiofrequency transmitter, the stereotaxic coordinates for the intracerebral, deep and epidural, surface EEG electrodes, the electrode fea-tures, the filtering and sampling characteristics, the analysed EEG frequency bands and the data acquisition parameters. EEG power data, temperature and activity data are avail-able at MENDELEY DATA (doi: 10.17632/x53km5sby6.1 , URL: http://dx.doi.org/10.17632/x53km5sby6.1 ). Raw EEG data are available at zenodo (https://zenodo.org/ ). (C) 2021 The Authors. Published by Elsevier Inc

Altered Theta Oscillations and Aberrant Cortical Excitatory Activity in the 5XFAD Model of Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by impairment of memory function. The 5XFAD mouse model was analyzed and compared with wild-type (WT) controls for aberrant cortical excitability and hippocampal theta oscillations by using simultaneous video-electroencephalogram (EEG) monitoring. Seizure staging revealed that 5XFAD mice exhibited cortical hyperexcitability whereas controls did not. In addition, 5XFAD mice displayed a significant increase in hippocampal theta activity from the light to dark phase during nonmotor activity. We also observed a reduction in mean theta frequency in 5XFAD mice compared to controls that was again most prominent during nonmotor activity. Transcriptome analysis of hippocampal probes and subsequent qPCR validation revealed an upregulation of Plcd4 that might be indicative of enhanced muscarinic signalling. Our results suggest that 5XFAD mice exhibit altered cortical excitability, hippocampal dysrhythmicity, and potential changes in muscarinic signaling

Enhanced hippocampal type II theta activity AND altered theta architecture in mice lacking the Ca(v)3.2 T-type voltage-gated calcium channel

T-type Ca2+ channels are assumed to contribute to hippocampal theta oscillations. We used implantable video-EEG radiotelemetry and qPCR to unravel the role of Ca(v)3.2 Ca2+ channels in hippocampal theta genesis. Frequency analysis of spontaneous long-term recordings in controls and Ca(v)3.2(-/-) mice revealed robust increase in relative power in the theta (4-8 Hz) and theta-alpha (4-12 Hz) ranges, which was most prominent during the inactive stages of the dark cycles. Urethane injection experiments also showed enhanced type II theta activity and altered theta architecture following Ca(v)3.2 ablation. Next, gene candidates from hippocampal transcriptome analysis of control and Ca(v)3.2(-/-) mice were evaluated using qPCR. Dynein light chain Tctex-Type 1 (Dynlt1b) was significantly reduced in Ca(v)3.2(-/-) mice. Furthermore, a significant reduction of GABA A receptor delta subunits and GABA B1 receptor subunits was observed in the septohippocampal GABAergic system. Our results demonstrate that ablation of Ca(v)3.2 significantly alters type II theta activity and theta architecture. Transcriptional changes in synaptic transporter proteins and GABA receptors might be functionally linked to the electrophysiological phenotype