NMDA receptors as voltage sensors

© Springer Science+Business Media LLC 2017. The membrane potential is an essential parameter of a living cell. However, measurements of the membrane potential using conventional techniques are associated with a number of artifacts. Cell-attached recordings of the currents through NMDA receptor channels enable noninvasive measurements of the neuronal membrane potential. This approach overcomes the problem of a leak conductance introduced during intracellular sharp electrode recordings and whole-cell patch-clamp recordings. Here, we describe the procedures of using cell-attached recordings of NMDA receptor channels to measure the true membrane potential

How Relations are Built within a SNS World: Social Network Analysis on Mixi

Our purpose here is to (1) investigate the structure of the personal networks developed on mixi, a Japanese social networking service (SNS), and (2) to consider the governing mechanism which guides participants of a SNS to form an aggregate network. Our findings are as follows:the clustering coefficient of the network is as high as 0.33 while the characteristic path lenght is as low as 5.5. A network among central users (over 300 edges) consist of two cliques, which seems to be very fragile. Community-affiliation network suggests there are several easy-entry communities which later lead users to more high-entry, unique-theme communities. The analysis on connectedness within a community reveals the importance of real-world interaction. Lastly, we depict a probable image of the entire ecology on mixi among users and communities, which contributes broadly to social systems on the Web

Early patterns of activity in the developing cortex: Focus on the sensorimotor system

© 2017 Elsevier Ltd. Early development of somatotopic cortical maps occurs during the fetal period in humans and during the postnatal period in rodents. During this period, the sensorimotor cortex expresses transient patterns of correlated neuronal activity including delta waves, gamma- and spindle-burst oscillations. These early activity patterns are largely driven by the thalamus and triggered, in a topographic manner, by sensory feedback resulting from spontaneous movements. Early cortical activities are instrumental for competitive interactions between sensory inputs for the cortical territories, they prevent cortical neurons from apoptosis and their alteration may lead to disturbances in cortical network development in a number of neurodevelopmental diseases

Spontaneous activity in developing sensory circuits: Implications for resting state fMRI

The immature brain spontaneously expresses unique patterns of electrical activity that are believed to contribute to the development of neuronal networks. Certain electrographic features of this activity, particularly modulation on an infraslow time scale, resemble activity patterns observed in the mature brain at 'rest', loosely defined as the absence of an investigator imposed task. However, it is not clear whether the immature activity patterns observed at rest are precursors of the spontaneous neuronal activity that forms resting state networks in the adult. Here, we review recent studies that have explored the generative mechanisms of resting state activity during development in the primary sensory systems of premature human neonates and neonatal rodents. The remarkable hypothesis suggested by this work is that while resting state activity during the pre- and possibly near-term period can bear superficial resemblance to adult activity it is fundamentally different in terms of function and origin. During early development spontaneous thalamocortical activity in primary sensory regions is determined largely by transitory generators in the sensory periphery. This is in contrast to the adult, where spontaneous activity generated within thalamocortex, particularly by cortico-cortical connections, dominates. We therefore suggest a conservative interpretation of developmental mapping studies which are based on indirect measurement of activity (e.g. fMRI), or on the partitioning of EEG frequency using bands derived from adult studies. The generative mechanisms for brain activity at early ages are likely different from those of adults, and may play very different roles; for example in circuit formation as opposed to attention. © 2012 Elsevier Inc

Depolarizing GABA and developmental epilepsies

© 2014 John Wiley & Sons Ltd. Early in development, GABA, which is the main inhibitory neurotransmitter in adult brain, depolarizes immature neurons and exerts dual-excitatory and shunting/inhibitory-effects in the developing neuronal networks. The present review discusses some general questions, including the properties of excitation at depolarizing GABAergic synapse and shunting inhibition by depolarizing GABA; technical issues in exploration of depolarizing GABA using various techniques and preparations, including the developmental aspects of traumatic injury and what is known (or rather unknown) on the actions of GABA in vivo; complex roles of depolarizing GABA in developmental epilepsies, including a contribution of depolarizing GABA to enhanced excitability in the immature networks, caused by repetitive seizures accumulation of intracellular chloride concentration that increases excitatory GABA power and its synchronizing proconvulsive effects, and correction of chloride homeostasis as a potential strategy to treat neonatal seizures

Early gamma oscillations

Gamma oscillations have long been considered to emerge late in development. However, recent studies have revealed that gamma oscillations are transiently expressed in the rat barrel cortex during the first postnatal week, a "critical" period of sensory-dependent barrel map formation. The mechanisms underlying the generation and physiological roles of early gamma oscillations (EGOs) in the development of thalamocortical circuits will be discussed in this review. In contrast to adult gamma oscillations, synchronized through gamma-rhythmic perisomatic inhibition, EGOs are primarily driven through feedforward gamma-rhythmic excitatory input from the thalamus. The recruitment of cortical interneurons to EGOs and the emergence of feedforward inhibition are observed by the end of the first postnatal week. EGOs facilitate the precise synchronization of topographically aligned thalamic and cortical neurons. The multiple replay of sensory input during EGOs supports long-term potentiation at thalamocortical synapses. We suggest that this early form of gamma oscillations, which is mechanistically different from adult gamma oscillations, guides barrel map formation during the critical developmental period. © 2013 IBRO

Enhanced Excitability of the Neonatal Rat Hippocampus After Acute Exposure to Ethanol

© 2016, Springer Science+Business Media New York.Enhanced excitability manifested by seizures and epilepsy is one of the characteristic features of the fetal alcohol spectrum disorders (FASD). Here, we examined network excitability using a high-potassium model in the hippocampal slices prepared from the postnatal days of P7–9 rats treated with ethanol. Ethanol was administered at 6 g/kg intraperitoneally 12 h before the slice preparation. The extracellular field potential recordings from the hippocampal slices using multishank silicon probes placed along CA3-CA1 axis were performed in the interface chamber. We found that elevation of the extracellular potassium from 3.5 to 6 mM evoked seizure-like clonic or tonic-clonic discharges in 77 % of the slices from the ethanol-treated animals and only in 15 % of the slices from the control animals. Further elevation of the extracellular potassium to 8.5 mM evoked epileptiform activity in 92 and 69 % of the slices from the ethanol-treated and the control animals, respectively. The current source density profile and the multiple unit activity analysis pointed on the CA3 hippocampal region as a generator of the epileptiform activity. Thus, the hippocampal slices from the ethanol-treated neonatal rats display enhanced excitability and could serve as a FASD model to study the early epileptiform transformations following exposure to ethanol

Impairments to the Giant Depolarizing Potentials After the Third Trimester Equivalent Ethanol Exposure in the Neonatal Rat

© 2016, Springer Science+Business Media New York.Ethanol exerts multiple adverse effects in the developing hippocampus resulting in the life-long neurological and behavioral deficits. However, the early disturbances in the hippocampal network function after exposure to ethanol remain largely unknown. Here, we examined the properties of the neonatal CA3 hippocampal network-driven giant depolarizing potentials using extracellular recordings of the local field potential and multiple units from the hippocampal slices prepared from the 5–11-day-old rats treated by ethanol in vivo (6 g/kg, intraperitoneally), 12 h before the slice preparation. Activity in hippocampal slices from the ethanol-treated animals displayed several abnormalities including a threefold increase in overall neuronal firing and profound, by nearly sevenfold, reduction of synchronization of CA3 units in giant depolarizing potentials. Thus, alterations in the hippocampal network function emerge shortly after the ethanol exposure and manifest in the enhanced excitation and severe impairments to the giant depolarizing potentials

Enhanced Excitability of the Neonatal Rat Hippocampus After Acute Exposure to Ethanol

© 2016, Springer Science+Business Media New York.Enhanced excitability manifested by seizures and epilepsy is one of the characteristic features of the fetal alcohol spectrum disorders (FASD). Here, we examined network excitability using a high-potassium model in the hippocampal slices prepared from the postnatal days of P7–9 rats treated with ethanol. Ethanol was administered at 6 g/kg intraperitoneally 12 h before the slice preparation. The extracellular field potential recordings from the hippocampal slices using multishank silicon probes placed along CA3-CA1 axis were performed in the interface chamber. We found that elevation of the extracellular potassium from 3.5 to 6 mM evoked seizure-like clonic or tonic-clonic discharges in 77 % of the slices from the ethanol-treated animals and only in 15 % of the slices from the control animals. Further elevation of the extracellular potassium to 8.5 mM evoked epileptiform activity in 92 and 69 % of the slices from the ethanol-treated and the control animals, respectively. The current source density profile and the multiple unit activity analysis pointed on the CA3 hippocampal region as a generator of the epileptiform activity. Thus, the hippocampal slices from the ethanol-treated neonatal rats display enhanced excitability and could serve as a FASD model to study the early epileptiform transformations following exposure to ethanol