Long-Term Potentiation by Theta-Burst Stimulation Using Extracellular Field Potential Recordings in Acute Hippocampal Slices

Theta-burst direct electrical stimulation remodels human brain networks

Theta-burst stimulation (TBS), a patterned brain stimulation technique that mimics rhythmic bursts of 3-8 Hz endogenous brain rhythms, has emerged as a promising therapeutic approach for treating a wide range of brain disorders, though the neural mechanism of TBS action remains poorly understood. We investigated the neural effects of TBS using intracranial EEG (iEEG) in 10 pre-surgical epilepsy participants undergoing intracranial monitoring. Here we show that individual bursts of direct electrical TBS at 29 frontal and temporal sites evoked strong neural responses spanning broad cortical regions. These responses exhibited dynamic local field potential voltage changes over the course of stimulation presentations, including either increasing or decreasing responses, suggestive of short-term plasticity. Stronger stimulation augmented the mean TBS response amplitude and spread with more recording sites demonstrating short-term plasticity. TBS responses were stimulation site-specific with stronger TBS responses observed in regions with strong baseline stimulation effective (cortico-cortical evoked potentials) and functional (low frequency phase locking) connectivity. Further, we could use these measures to predict stable and varying (e.g. short-term plasticity) TBS response locations. Future work may integrate pre-treatment connectivity alongside other biophysical factors to personalize stimulation parameters, thereby optimizing induction of neuroplasticity within disease-relevant brain networks.

Receive, Retain and Retrieve: Psychological and Neurobiological Perspectives on Memory Retrieval

Memory and learning are interdependent processes that involve encoding, storage, and retrieval. Especially memory retrieval is a fundamental cognitive ability to recall memory traces and update stored memory with new information. For effective memory retrieval and learning, the memory must be stabilized from short-term memory to long-term memory. Hence, it is necessary to understand the process of memory retention and retrieval that enhances the process of learning. Though previous cognitive neuroscience research has focused on memory acquisition and storage, the neurobiological mechanisms underlying memory retrieval and its role in learning are less understood. Therefore, this article offers the viewpoint that memory retrieval is essential for selecting, reactivating, stabilizing, and storing information in long-term memory. In arguing how memories are retrieved, consolidated, transmitted, and strengthened for the long term, the article will examine the psychological and neurobiological aspects of memory and learning with synaptic plasticity, long-term potentiation, genetic transcription, and theta oscillation in the brain.

Repeated finasteride administration promotes synaptic plasticity and produces antidepressant- and anxiolytic-like effects in female rats

Finasteride is used in female-pattern hair loss, hirsutism, and polycystic ovarian syndrome. It inhibits 5α-reductase, which is an important enzyme in the biosynthesis of neurosteroids. The effects of finasteride treatment on mental health in female patients as well as the effects of repeated/chronic finasteride administration in female rodents are still unknown. Accordingly, in our study, we administered finasteride (10, 30, or 100 mg/Kg, s.c.) for 6 days in female rats and evaluated behavior, plasma steroid levels, and synaptic plasticity. Depression-like behavior was evaluated using forced swim test (FST) and splash test. Anxiety-like behavior was evaluated using novelty-suppressed feeding task (NSFT), elevated plus maze (EPM), open field test (OFT), and light-dark test (LDT). Plasma steroid levels were assessed using ELISA and synaptic plasticity by field potential recordings. We observed that finasteride decreased total immobility duration in FST, indicating antidepressant-like effect and decreased the latency to first bite in NSFT, showing anxiolytic-like effect. We also found a significant increase in plasma estradiol and a significant decrease in plasma corticosterone level. Furthermore, field potential recordings showed that finasteride increased hippocampal long-term potentiation. These results indicate that repeated finasteride administration in female rats may have antidepressant- and anxiolytic-like effect, which might be mediated by enhanced estradiol levels or decreased corticosterone levels. Further studies are required to validate the molecular mechanisms underlying the effects of finasteride in female rats. Understanding the mechanisms will help us in developing novel neurosteroid-based therapeutics in the treatment of neuropsychiatric disorders in women.

Panoramic variation analysis of a family with neurodevelopmental disorders caused by biallelic loss-of-function variants in TMEM141, DDHD2, and LHFPL5

Highly clinical and genetic heterogeneity of neurodevelopmental disorders presents a major challenge in clinical genetics and medicine. Panoramic variation analysis is imperative to analyze the disease phenotypes resulting from multilocus genomic variation. Here, a Pakistani family with parental consanguinity was presented, characterized with severe intellectual disability (ID), spastic paraplegia, and deafness. Homozygosity mapping, integrated single nucleotide polymorphism (SNP) array, whole-exome sequencing, and whole-genome sequencing were performed, and homozygous variants in TMEM141 (c.270G>A, p.Trp90*), DDHD2 (c.411+767_c.1249-327del), and LHFPL5 (c.250delC, p.Leu84*) were identified. A Tmem141p.Trp90*/p.Trp90* mouse model was generated. Behavioral studies showed impairments in learning ability and motor coordination. Brain slice electrophysiology and Golgi staining demonstrated deficient synaptic plasticity in hippocampal neurons and abnormal dendritic branching in cerebellar Purkinje cells. Transmission electron microscopy showed abnormal mitochondrial morphology. Furthermore, studies on a human in vitro neuronal model (SH-SY5Y cells) with stable shRNA-mediated knockdown of TMEM141 showed deleterious effect on bioenergetic function, possibly explaining the pathogenesis of replicated phenotypes in the cross-species mouse model. Conclusively, panoramic variation analysis revealed that multilocus genomic variations of TMEM141, DDHD2, and LHFPL5 together caused variable phenotypes in patient. Notably, the biallelic loss-of-function variants of TMEM141 were responsible for syndromic ID.

Phenobarbital does not worsen outcomes of neonatal hypoxia on hippocampal LTP on rats

Introduction

Neonatal hypoxia is a common cause of early-life seizures. Both hypoxia-induced seizures (HS), and the drugs used to treat them (e.g., phenobarbital, PB), have been reported to have long-lasting impacts on brain development. For example, in neonatal rodents, HS reduces hippocampal long-term potentiation (LTP), while PB exposure disrupts GABAergic synaptic maturation in the hippocampus. Prior studies have examined the impact of HS and drug treatment separately, but in the clinic, PB is unlikely to be given to neonates without seizures, and neonates with seizures are very likely to receive PB. To address this gap, we assessed the combined and separate impacts of neonatal HS and PB treatment on the development of hippocampal LTP.

Methods

Male and female postnatal day (P)7 rat pups were subjected to graded global hypoxia (or normoxia as a control) and treated with either PB (or vehicle as a control). On P13-14 (P13+) or P29-37 (P29+), we recorded LTP of the Schaffer collaterals into CA1 pyramidal layer in acute hippocampal slices. We compared responses to theta burst stimulation (TBS) and tetanization induction protocols.

Results

Under the TBS induction protocol, female rats showed an LTP impairment caused by HS, which appeared only at P29+. This impairment was delayed compared to male rats. While LTP in HS males was impaired at P13+, it normalized by P29+. Under the tetanization protocol, hypoxia produced larger LTP in males compared to female rats. PB injection, under TBS, did not exacerbate the effects of hypoxia. However, with the tetanization protocol, PB - on the background of HS - compensated for these effects, returning LTP to control levels.

Discussion

These results point to different susceptibility to hypoxia as a function of sex and age, and a non-detrimental effect of PB when administered after hypoxic seizures.

Altered EEG, disrupted hippocampal long-term potentiation and neurobehavioral deficits implicate a delirium-like state in a mouse model of sepsis

Sepsis and systemic inflammation are often accompanied by severe encephalopathy, sleep disruption and delirium that strongly correlate with poor clinical outcomes including long-term cognitive deficits. The cardinal manifestations of delirium are fluctuating altered mental status and inattention, identified in critically ill patients by interactive bedside assessment. The lack of analogous assessments in mouse models or clear biomarkers is a challenge to preclinical studies of delirium. In this study, we utilized concurrent measures of telemetric EEG recordings and neurobehavioral tasks in mice to characterize inattention and persistent cognitive deficits following polymicrobial sepsis. During the 24-hour critical illness period for the mice, slow-wave EEG dominance, sleep disruption, and hypersensitivity to auditory stimuli in neurobehavioral tasks resembled clinical observations in delirious patients in which alterations in similar outcome measurements, although measured differently in mice and humans, are reported. Mice were tested for nest building ability 7 days after sepsis induction, when sickness behaviors and spontaneous activity had returned to baseline. Animals that showed persistent deficits determined by poor nest building at 7 days also exhibited molecular changes in hippocampal long-term potentiation compared to mice that returned to baseline cognitive performance. Together, these behavioral and electrophysiological biomarkers offer a robust mouse model with which to further probe molecular pathways underlying brain and behavioral changes during and after acute illness such as sepsis.

The Effects of the Fraction Isolated from Iranian Buthotus shach Scorpion Venom on Synaptic Plasticity, Learning, Memory, and Seizure Susceptibility

Epilepsy, as a neurological disease, can be defined as frequent seizure attacks. Further, it affects many other aspects of patients' mental activities, such as learning and memory. Scorpion venoms have gained notice as compounds with potential antiepileptic properties. Among them, Buthotus schach (BS) is one of the Iranian scorpions studied by Aboutorabi et al., who fractionated, characterized, and tested this compound using electrophysiological techniques in brain slices (patch-clamp recording). In the present study, the fraction obtained from gel electrophoresis was investigated through behavioral and electrophysiological assays. At first, ventricular cannulation was performed in rats, and then the active fraction (i.e., F3), carbamazepine, and the vehicle were microinjected into the brain before seizure induction by the subcutaneous (SC) injection of pentylenetetrazol (PTZ). Seizure behaviors were scaled according to Racine stages. Memory and learning were evaluated using the Y-maze and passive avoidance tests. Other groups entered evoked field potential recording after microinjection and seizure induction. Population spike (PS) and field excitatory postsynaptic potential (fEPSP) were measured. The F3 fraction could prevent the fifth stage and postpone the third stage of seizure compared to the control (carbamazepine) group. There was no significant improvement in memory and learning in the group treated with the F3 fraction. Also, PS amplitude and fEPSP slope increased significantly, and long-term potentiation was successfully formed after the high-frequency stimulation of the performant pathway. Our results support the antiepileptic effects of the F3 fraction of BS venom, evidenced by behavioral and electrophysiological studies. However, the effects of this fraction on memory and learning were not in the same direction, suggesting the involvement of two different pathways.

John EK, Potesta CV, Gallagher MJ, Zhou C. Artificial sleep-like up/down-states induce synaptic plasticity in cortical neurons from mouse brain slices

During non-rapid eye movement (NREM) sleep, cortical neuron activity alternates between a depolarized (firing, up-state) and a hyperpolarized state (down-state) coinciding with delta electroencephalogram (EEG) slow-wave oscillation (SWO, 0. 5-4 Hz) in vivo. Recently, we have found that artificial sleep-like up/down-states can potentiate synaptic strength in layer V cortical neurons ex vivo. Using mouse coronal brain slices, whole cell voltage-clamp recordings were made from layer V cortical pyramidal neurons to record spontaneous excitatory synaptic currents (sEPSCs) and inhibitory synaptic currents (sIPSCs). Artificial sleep-like up/down-states (as SWOs, 0.5 Hz, 10 min, current clamp mode) were induced by injecting sinusoidal currents into layer V cortical neurons. Baseline pre-SWO recordings were recorded for 5 min and post-SWO recordings for at least 25-30 min. Compared to pre-SWO sEPSCs or sIPSCs, post-SWO sEPSCs or sIPSCs in layer V cortical neurons exhibited significantly larger amplitudes and a higher frequency for 30 min. This finding suggests that both sEPSCs and sIPSCs could be potentiated in layer V cortical neurons by the low-level activity of SWOs, and sEPSCs and sIPSCs maintained a balance in layer V cortical neurons during pre- and post-SWO periods. Overall, this study presents an ex vivo method to show SWO's ability to induce synaptic plasticity in layer V cortical neurons, which may underlie sleep-related synaptic potentiation for sleep-related memory consolidation in vivo.

Enriched environment ameliorates chronic temporal lobe epilepsy-induced behavioral hyperexcitability and restores synaptic plasticity in CA3-CA1 synapses in male Wistar rats

Temporal lobe epilepsy (TLE) is the most common form of focal epilepsies. Pharmacoresistance and comorbidities pose significant challenges to its treatment necessitating the development of non-pharmacological approaches. In an earlier study, exposure to enriched environment (EE) reduced seizure frequency and duration and ameliorated chronic epilepsy-induced depression in rats. However, the cellular basis of beneficial effects of EE remains unknown. Accordingly, in the current study, we evaluated the effects of EE in chronic epilepsy-induced changes in behavioral hyperexcitability, synaptic transmission, synaptophysin (SYN), and calbindin (CB) expression, hippocampal subfield volumes and cell density in male Wistar rats. Epilepsy was induced by lithium-pilocarpine-induced status epilepticus. Chronic epilepsy resulted in behavioral hyperexcitability, decreased basal synaptic transmission, increased paired-pulse facilitation ratio, decreased hippocampal subfields volumes. Moreover, epileptic rats showed decreased synaptophysin and CB expression in the hippocampus. Six weeks post-SE, epileptic rats were exposed to EE for 2 weeks, 6 hr/day. EE significantly reduced the behavioral hyperexcitability and restored basal synaptic transmission correlating with increased expression of SYN and CB. Our results reaffirm the beneficial effects of EE on behavior in chronic epilepsy and establishes some of the putative cellular mechanisms. Since drug resistance and comorbidities are a major concern in TLE, we propose EE as a potent non-pharmacological treatment modality to mitigate these changes in chronic epilepsy.

Methylene blue inhibits Caspase-6 activity, and reverses Caspase-6-induced cognitive impairment and neuroinflammation in aged mice

Activated Caspase-6 (Casp6) is associated with age-dependent cognitive impairment and Alzheimer disease (AD). Mice expressing human Caspase-6 in hippocampal CA1 neurons develop age-dependent cognitive deficits, neurodegeneration and neuroinflammation. This study assessed if methylene blue (MB), a phenothiazine that inhibits caspases, alters Caspase-6-induced neurodegeneration and cognitive impairment in mice. Aged cognitively impaired Casp6-overexpressing mice were treated with methylene blue in drinking water for 1 month. Methylene blue treatment did not alter Caspase-6 levels, assessed by RT-PCR, western blot and immunohistochemistry, but inhibited fluorescently-labelled Caspase-6 activity in acute brain slice intact neurons. Methylene blue treatment rescued Caspase-6-induced episodic and spatial memory deficits measured by novel object recognition and Barnes maze, respectively. Methylene blue improved synaptic function of hippocampal CA1 neurons since theta-burst long-term potentiation (LTP), measured by field excitatory postsynaptic potentials (fEPSPs) in acute brain slices, was successfully induced in the Schaffer collateral-CA1 pathway in methylene blue-treated, but not in vehicle-treated, Caspase-6 mice. Increased neuroinflammation, measured by ionized calcium binding adaptor molecule 1 (Iba1)-positive microglia numbers and subtypes, and glial fibrillary acidic protein (GFAP)-positive astrocytes, were decreased by methylene blue treatment. Therefore, methylene blue reverses Caspase-6-induced cognitive deficits by inhibiting Caspase-6, and Caspase-6-mediated neurodegeneration and neuroinflammation. Our results indicate that Caspase-6-mediated damage is reversible months after the onset of cognitive deficits and suggest that methylene blue could benefit Alzheimer disease patients by reversing Caspase-6-mediated cognitive decline.

Optogenetics in the Era of Cerebral Organoids

The human brain has been deemed the most complex organ and has captivated neuroscientists for decades. Most studies of this organ have relied on reductionist model systems. Although all model systems are essentially wrong, cerebral organoids so far represent the closest recapitulation of human brain development and disease both in terms of cell diversity and organization. The optogenetic technique can be used in this context to study the functional neuroanatomy of the brain, to examine the neural circuits, and to determine the etiology of neurological disorders. In this opinion article, we suggest ways in which optogenetics can be combined with cerebral organoids to allow unprecedented precision and accuracy in studying normal and aberrant neurodevelopmental processes and, as well, neurodegenerative diseases.

Using Multiple Whole-Cell Recordings to Study Spike-Timing-Dependent Plasticity in Acute Neocortical Slices

This protocol provides a method for quadruple whole-cell recording to study synaptic plasticity of neocortical connections, with a special focus on spike-timing-dependent plasticity (STDP). It also describes how to morphologically identify recorded cells from two-photon laser-scanning microscopy (2PLSM) stacks.

In Vitro Investigation of Synaptic Plasticity

A classical in vitro model for investigation of information storage in the brain is based on the acute hippocampal slice. Here, repeated high-frequency stimulation of excitatory Schaeffer collaterals making synapses onto pyramidal cells in the hippocampal CA1 region leads to strengthening of evoked field-recording responses-long-term potentiation (LTP)-in keeping with Hebb's postulate. This model remains tremendously influential for its reliability, specificity, and relative ease of use. More recent plasticity studies have explored various other brain regions including the neocortex, which often requires more laborious whole-cell recordings of synaptically connected pairs of neurons, to ensure that the identities of recorded cells are known. In addition, with this experimental approach, the spiking activity can be controlled with millisecond precision, which is necessary for the study of spike-timing-dependent plasticity (STDP). Here, we provide protocols for in vitro study of hippocampal CA1 LTP using field recordings, and of STDP in synaptically connected pairs of layer-5 pyramidal cells in acute slices of rodent neocortex.