Andrey Zakharov

Spreading Depolarizations (SDs) induce a transient depression of cortical activity, including a depression of Direct Cortical Responses (DCRs). Here, we examined the spatiotemporal dynamics of DCR depression during SDs induced by high-potassium or pinprick, using ECoG arrays and intracortical silicon probes in the anesthetized rat cortex. While SDs consistently suppressed DCRs, somatosensory-evoked responses, and spontaneous activity, the spatiotemporal pattern of DCR depression specifically depended on the direction of SD propagation relative to the stimulation and recording sites. When the SD wave first invaded the stimulation site, it triggered a simultaneous, "blanket" inhibition of DCRs across all recording sites of the ECoG array, preceding the local DC shift and suppression of spontaneous and sensory-evoked activity. Conversely, when the SD first invaded the recording sites of the ECoG array, DCR depression followed a sequential, "wave-like" pattern with a concomitant DC shift, and depression of local activity. Comparing the DCR onset and offset times across the ECoG array with the SD-related DC shifts, we found that the spatiotemporal organization of DCR depression provides reliable estimates of SD propagation direction, and the algorithm proposed here could be useful for both SD detection and propagation direction assessment during multisite ECoG recordings.

Hyperhomocysteinemia (hHCY) is a metabolic disorder characterized by elevated levels of homocysteine in plasma. hHCY correlates with a high risk of migraine headaches, especially migraine with aura. Cortical spreading depression (CSD) is a wave of depolarization passing through neurons and glial cells of the cortex and is considered an electrophysiological correlate of migraine aura. The aim of the present study was to analyze neuronal activity and CSD in the somatosensory cortex of rats in vivo with prenatal hHCY and to assess cortex viability after 2 h of CSD generation. Female rats were fed a diet high in methionine, and their offspring with high homocysteine levels in plasma were further used in experiments. Recurrent CSD was evoked by local KCl application on the dura surface. Neuronal viability was assessed by measuring the activity of lactate dehydrogenase (LDH) in the brain and 2,3,5-triphenyltetrazolium chloride staining of the somatosensory cortex after two hours of CSD generation. Animals with hHCY exhibited higher neuronal activity, and more CSDs were generated in response to KCl, indicating higher cortical excitability. Propagation of recurrent CSD was impaired in supragranular cortical layers, and the recovery of multiple unit activity and evoked sensory potentials after CSD was delayed in the hHCY group. Finally, in animals with prenatal hHCY, an ischemic focus was identified as a consequence of multiple CSDs, along with elevated levels of LDH activity in brain tissues, suggestive of diminished neuronal viability. These findings imply that prolonged elevated levels of homocysteine may not only predispose to migraine with aura but also potentially elevate the risk of migrainous infarction.

Cardiac arrhythmias are common disorders that can be fatal. Modern methods of treating bradyarrhythmias include the implantation of pacemakers and cardioverter–defibrillators. However, implantable devices can cause various complications related to the electrodes installed inside the heart, including infection. Less invasive heart rhythm modulation could be beneficial for some cohorts of patients. Here, we demonstrate an alternative approach to heart pacing based on thermogenetics. We used adeno-associated viruses to deliver genetic human transient receptor potential subfamily V member 1 (TRPV1), a heat-sensitive cation channel, into isolated cardiomyocytes and the mouse heart. This allowed us to induce action potentials and control contractility using short heat pulses delivered by infrared laser illumination. Using this approach, we demonstrated the thermogenetic pacing of isolated cardiomyocytes in vitro and in the mouse heart in vivo . Our results demonstrate the potential of thermogenetics for developing therapeutic strategies for heart rhythm modulation.

Electrical resistance of brain tissue during terminal ischemia Электрическое сопротивление ткани мозга во время терминальной ишемии

BACKGROUND: Methods and tools for operating with multichannel electrophysiological signals need to develop and correspond to the speed of data traffic in contemporary experiments. Analyzing and visualizing experimental data with minimal delay and with minimized experimenter effort is a pressing task in the field of neurobiology and requires the use of complex approaches specifically selected for each specific type of experiment. Creating open-source programs that can be promptly adapted for different tasks is one of the approaches that provide the ability to perform complex scientific experiments with high quality. AIM: This work is aimed at creating open-source software for analytical and visualization support of neurobiological experiments. METHODS: Software development was performed in MATLAB environment. The program is built on a modular principle and includes an intuitive graphical interface that facilitates control of the signal processing and display. RESULTS: A software tool was created that allows to optimize and accelerate various stages of electrophysiological research, including preliminary analysis of the quality of the experiment being prepared, in-depth analysis of recorded signals, and preparation of illustrative material for publications. CONCLUSION: The resulting program has a number of advantages in comparison with similar products in terms of versatility, speed, and availability, and can be used to solve a wide class of research problems.

Brain ischemia induces slow voltage shifts in the cerebral cortex, including waves of spreading depolarization (SD) and negative ultraslow potentials (NUPs), which are considered as brain injury markers. However, different electrode materials and locations yield variable SD and NUP features. Here, we compared terminal cortical events during isoflurane or sevoflurane euthanasia using intracortical linear iridium electrode arrays and Ag/AgCl-based electrodes in the rat somatosensory cortex. Inhalation of anesthetics caused respiratory arrest, associated with hyperpolarization and followed by SD and NUP on both Ir and Ag electrodes. Ag-NUPs were bell shaped and waned within half an hour after death. Ir-NUPs were biphasic, with the early fast phase corresponding to Ag-NUP, and the late absent on Ag electrodes, phase of a progressive depolarizing voltage shift reaching −100 mV by two hours after death. In addition, late Ir-NUPs were more ample in the deep layers than at the cortical surface. Thus, intracortical Ag and Ir electrodes reliably assess early manifestations of terminal brain injury including hyperpolarization, SD and the early phase of NUP, while the late, giant amplitude phase of NUP, which is present only on Ir electrodes, is probably related to the sensitivity of Ir electrodes to a yet unidentified factor related to brain death.

The development of ischemic lesions has primarily been studied in horizontal cortical space. However, how ischemic lesions develop through the cortical depth remains largely unknown. We explored this question using direct current coupled recordings at different cortical depths using linear arrays of iridium electrodes in the focal epipial endothelin-1 (ET1) ischemia model in the rat barrel cortex. ET1-induced impairments were characterized by a vertical gradient with (i) rapid suppression of the spontaneous activity in the superficial cortical layers at the onset of ischemia, (ii) compartmentalization of spreading depolarizations (SDs) to the deep layers during progression of ischemia, and (iii) deeper suppression of activity and larger histological lesion size in superficial cortical layers. The level of impairments correlated strongly with the rate of spontaneous activity suppression, the rate of SD onset after ET1 application, and the amplitude of giant negative ultraslow potentials (∼−70 mV), which developed during ET1 application and were similar to the tent-shaped ultraslow potentials observed during focal ischemia in the human cortex. Thus, in the epipial ET1 ischemia model, ischemic lesions develop progressively from the surface to the cortical depth, and early changes in electrical activity at the onset of ET1-induced ischemia reliably predict the severity of ischemic damage.

Objective: Cortical spreading depolarization (SD) and seizures are often co‐occurring electrophysiological phenomena. However, the cross‐layer dynamics of SD during seizures and the effect of SD on epileptic activity across cortical layers remain largely unknown.Methods: We explored the spatial‐temporal dynamics of SD and epileptic activity across layers of the rat barrel cortex using direct current silicone probe recordings during flurothyl‐induced seizures.Results: SD occurred in half of the flurothyl‐evoked seizures. SD always started from the superficial layers and spread downward either through all cortical layers or stopping at the L4/L5 border. In cases without SD, seizures were characterized by synchronized population firing across all cortical layers throughout the entire seizure. However, when SD occurred, epileptic activity was transiently silenced in layers involved with SD but persisted in deeper layers. During partial SD, epileptiform activity persisted in deep layers throughout the entire seizure, with positive signals at the cortical surface reflecting passive sources of population spikes generated in deeper cortical layers. During full SD, the initial phase of SD propagation through the superficial layers was similar to partial SD, with suppression of activity at the superficial layers and segregation of seizures to deep layers. Further propagation of SD to deep layers resulted in a wave of transient suppression of epileptic activity through the entire cortical column. Thus, vertical propagation of SD through the cortical column creates dynamic network states during which epileptiform activity is restricted to layers without SD.Significance: Our results point to the importance of vertical SD spread in the SD‐related depression of epileptiform activity across cortical layers.

Transmission of excitation from L4 to L2/3 is a part of a canonical circuit of cortical sensory signal processing. While synapses from L4 to L2/3 are mediated by both AMPA and NMDA glutamate receptors, previous studies suggested that sensory-evoked excitation of neurons in supragranular layers is almost entirely mediated by NMDA receptors. Here, we readdressed this question using extracellular recordings of sensory-evoked potentials (SEPs) and multiple unit activity (MUA) in the rat barrel cortex. We found that blockade of NMDA receptors using the selective antagonist dAPV profoundly inhibited the late part of L2/3 SEP, the associated sink, and MUA response but did not affect its initial part. Our results indicate that both non-NMDA and NMDA receptors are involved in sensory signal transmission from L4 to L2/3. While non-NMDA receptors mediate fast transmission of sensory signals, NMDA-Rs are importantly involved in the generation of the late phase of the sensory-evoked response in supragranular layers.