Microscale Physiological Events on the Human Cortical Surface.

Despite ongoing advances in our understanding of local single-cellular and network-level activity of neuronal populations in the human brain, extraordinarily little is known about their "intermediate" microscale local circuit dynamics. Here, we utilized ultra-high-density microelectrode arrays and a rare opportunity to perform intracranial recordings across multiple cortical areas in human participants to discover three distinct classes of cortical activity that are not locked to ongoing natural brain rhythmic activity. The first included fast waveforms similar to extracellular single-unit activity. The other two types were discrete events with slower waveform dynamics and were found preferentially in upper cortical layers. These second and third types were also observed in rodents, nonhuman primates, and semi-chronic recordings from humans via laminar and Utah array microelectrodes. The rates of all three events were selectively modulated by auditory and electrical stimuli, pharmacological manipulation, and cold saline application and had small causal co-occurrences. These results suggest that the proper combination of high-resolution microelectrodes and analytic techniques can capture neuronal dynamics that lay between somatic action potentials and aggregate population activity. Understanding intermediate microscale dynamics in relation to single-cell and network dynamics may reveal important details about activity in the full cortical circuit.

Emerging roles of extracellular vesicles in the intercellular communication for exercise-induced adaptations.

Complex organisms rely heavily on intercellular communication. The rapidly expanding field of extracellular vesicle biology has made it clear that the necessary intercellular communication occurs partly through their paracrine and endocrine actions. Extracellular vesicles are nanoscale lipid membranes (30-2,000 nm in diameter) that shuttle functional biological material between cells. They are released from numerous tissues and are isolated from nearly all biofluids and cell cultures. Although their biogenesis, cell targeting, and functional roles are incompletely understood, they appear to have crucial roles in physiological and disease processes. Their enormous potential to serve as sensitive biomarkers of disease and also new therapeutic interventions for diseases have gained them considerable attention in recent years. Regular physical exercise training confers systemic health benefits and consequently prevents many age-related degenerative diseases. Many of the molecular mechanisms responsible for the salubrious effects of exercise are known, yet a common underlying mechanism potentially responsible for the holistic health benefits of exercise has only recently been explored (i.e., via extracellular vesicle transport of biological material). Here, we provide an overview of extracellular vesicle biology before outlining the current evidence on the capacity for a single bout and chronic exercise to elicit changes in extracellular vesicle content and modulate their molecular cargo (e.g., small RNAs). We highlight areas for future research and emphasize their potential utility as biomarkers and therapeutic strategies of disease and its prevention.

Cell integrity indicators assessed by bioelectrical impedance: A systematic review of studies involving athletes.

INTRODUCTION: Bioelectrical impedance analysis (BIA) has been used to evaluate cellular health and integrity through bioelectrical indicators. In the sporting context, monitoring these indicators can be useful to assess the quality and vitality of cells and body tissues. OBJECTIVE: The aim of this systematic review was to investigate indicators of cellular health and integrity evaluated by BIA in athletes. METHODS: Searches were performed in December 2017 in the Lilacs, Medline, PubMed, Science Direct, Scielo, Scopus, SPORTDiscus, and Web of Science databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. RESULTS: The searches retrieved 31 articles (30 involving professional athletes and one involving university athletes). In longitudinal studies (n = 15), the bioelectrical parameters directly associated with cellular health and integrity were extracellular water (ECW), phase angle (PA), BIA vector analysis (BIVA), crude reactance data (Xc), resistance (R), and ECW/BCM ratio. Regarding the findings of cross-sectional studies (n = 16), the investigated parameters (ECW, PA, BIVA, Z, BCM, and ECW/BCM) were directly associated with gender, age, sports performance level, modality, and game position. CONCLUSIONS: In the included studies, the cellular health and integrity indicators were: Z, Xc, R, total water, intracellular water, ECW, PA, BIVA, BCM, and ECW/BCM.

Spatiotemporal model of tripartite synapse with perinodal astrocytic process.

Information transfer may not be limited only to synapses. Therefore, the processes and dynamics of biological neuron-astrocyte coupling and intercellular interaction within this domain are worth investigating. Existing models of tripartite synapse consider an astrocyte as a point process. Here, we extended the tripartite synapse model by considering the astrocytic processes (synaptic and perinodal) as compartments. The scattered extrinsic signals in the extracellular space and the presence of calcium stores in different astrocytic sites create local transient [Ca2+]. We investigated the Ca2+ dynamics and found that the increase in astrocytic intracellular [Ca2+] enhances the probability of neurotransmitter release. However, the period in which the extrasynaptic glutamate lingers in the extracellular space may cause excitotoxicity. We propose further biological investigation on intercellular communication, considering that unconventional sources (nonsynaptic) of glutamate may improve information processing in neuron-astrocyte networks.

Refinement of Spatial Receptive Fields in the Developing Mouse Lateral Geniculate Nucleus Is Coordinated with Excitatory and Inhibitory Remodeling.

Receptive field properties of individual visual neurons are dictated by the precise patterns of synaptic connections they receive, including the arrangement of inputs in visual space and features such as polarity (On vs Off). The inputs from the retina to the lateral geniculate nucleus (LGN) in the mouse undergo significant refinement during development. However, it is unknown how this refinement corresponds to the establishment of functional visual response properties. Here we conducted in vivo and in vitro recordings in the mouse LGN, beginning just after natural eye opening, to determine how receptive fields develop as excitatory and feedforward inhibitory retinal afferents refine. Experiments used both male and female subjects. For in vivo assessment of receptive fields, we performed multisite extracellular recordings in awake mice. Spatial receptive fields at eye-opening were >2 times larger than in adulthood, and decreased in size over the subsequent week. This topographic refinement was accompanied by other spatial changes, such as a decrease in spot size preference and an increase in surround suppression. Notably, the degree of specificity in terms of On/Off and sustained/transient responses appeared to be established already at eye opening and did not change. We performed in vitro recordings of the synaptic responses evoked by optic tract stimulation across the same time period. These recordings revealed a pairing of decreased excitatory and increased feedforward inhibitory convergence, providing a potential mechanism to explain the spatial receptive field refinement.SIGNIFICANCE STATEMENT The development of precise patterns of retinogeniculate connectivity has been a powerful model system for understanding the mechanisms underlying the activity-dependent refinement of sensory systems. Here we link the maturation of spatial receptive field properties in the lateral geniculate nucleus (LGN) to the remodeling of retinal and inhibitory feedforward convergence onto LGN neurons. These findings should thus provide a starting point for testing the cell type-specific plasticity mechanisms that lead to refinement of different excitatory and inhibitory inputs, and for determining the effect of these mechanisms on the establishment of mature receptive fields in the LGN.

Understanding Qi Running in the Meridians as Interstitial Fluid Flowing via Interstitial Space of Low Hydraulic Resistance.

Qi, blood and the meridians are fundamental concepts in Chinese medicine (CM), which are components of the human body and maintain physiological function. Pathological changes of qi, blood and meridians may lead to discomfort and disease. Treatment with acupuncture or herbal medicine aims to regulate qi and blood so as to recover normal function of the meridians. This paper explores the nature of qi as well as compares and correlates them with the structures of the human body. We propose a conceptualization of qi as being similar to the interstitial fluid, and the meridians as being similar to interstitial space of low hydraulic resistance in the body. Hence, qi running in the meridians can be understood as interstitial fluid flowing via interstitial space of low hydraulic resistance.

Overcoming the difficulties in collecting apoplastic fluid from rice leaves by the infiltration-centrifugation method.

Physiological and biochemical studies on the leaf apoplast have been facilitated by the use of the infiltration-centrifugation technique to collect intercellular washing fluid (IWF). However, this technique has been difficult to implement in rice (Oryza sativa L.) for various reasons. We compared the collection efficiency of leaf IWF between two types of rice varieties (Indica and Japonica), as well as between rice and other species (spinach, snap bean and wheat). Although the extraction of IWF in most species took only 2-3 min, it took up to 35 min in rice. The difficulty in infiltration with rice was ascribed to the small stomatal aperture and hydrophobicity of the leaves. In this study, we have established an improved method for collecting IWF and determining the apoplastic air and water volumes in rice leaves. We have shortened the infiltration time to 8 min via the following improvements: (i) infiltration under outdoor shade in the daytime to prevent stomatal closure and a rise in temperature of the infiltration medium; (ii) soaking of leaves in a surfactant solution to decrease the leaf hydrophobicity; and (iii) continuous pressurization using a sealant injector to facilitate the infiltration. The rapid collection of IWF achieved using this technique will facilitate study of the leaf apoplast in rice.

Evaluation of doxorubicin toxicity on cardiomyocytes using a dual functional extracellular biochip.

Nowadays, cardiotoxicity induced by clinical drugs presents a high prevalence and has aroused great attention onto the effective and reliable drug evaluation before clinical treatment. Doxorubicin (Adriamycin), as a type of anthracycline chemotherapy agent for cancer treatment, was restricted in the clinical use because of its cardiotoxicity. In the present work, a dual functional biochip ExCell integrated with microelectrode arrays and interdigitated electrodes was designed to study the electrophysiological function and physical state of cardiomyocytes under the treatment of doxorubicin. Extracellular field potentials and cell-substrate impedance were measured to respectively express these two functions simultaneously in the same culture. The result detected by ExCell presented a portrait of cardiotoxicity induced by doxorubicin. The amplitude of extracellular field potentials decreased to 93%, 82% and 50% at 50 min treatment of doxorubicin with concentrations of 20 µM, 100 µM and 200 µM, respectively. Successively, beating rate decrease, beat-to-beat variation and Ca(2+) flux manifested severe abnormality. The cell-substrate impedance declined continuously in the depressing process of electrophysiological function and cell death was induced in high concentration treatment. All these result indicate that the biochip ExCell has the potential to be a fast-response and subtle tool for high-throughput drug evaluation assays.

Magnesium modulates amyloid-beta protein precursor trafficking and processing.

Alzheimer's disease (AD), the most common form of dementia, is characterized by the presence of excessive deposits of aggregated amyloid-beta (Abeta), which is derived from the amyloid-beta protein precursor (AbetaPP) following processing by beta- and gamma-secretase. Metal elements are implicated in the pathophysiology of AD. Magnesium affects many biochemical mechanisms vital for neuronal properties and synaptic plasticity, and magnesium levels were reported to be decreased in various tissues including brain of AD patients. However, the exact role of magnesium in the neurodegenerative process of AD remains elusive. In this study, we investigated the effects of physiological (0.8 mM, as normal control), low (0-0.4 mM), and high (1.2-4.0 mM) concentrations of extracellular magnesium ([Mg2+]o) on AbetaPP processing and Abeta secretion. Here we show the effects of varying [Mg2+]o on AbetaPP processing is time- and dose-dependent. After 24 h treatment, high [Mg2+]o increased C-terminal fragment-alpha (CTFalpha) levels and soluble alpha-secretase cleaved AbetaPP (sAbetaPPalpha) release via enhancing retention of AbetaPP on plasma membrane. In contrast, low [Mg2+]o enhanced CTFbeta accumulation and Abeta secretion, and reduced cell surface AbetaPP level. Varying [Mg2+]o did not alter protein contents of full length AbetaPP. However, decreased total intracellular magnesium level by magnesium deprivation over 24 hr impaired cell viability. Normal AbetaPP processing could be restored when magnesium was adjusted back to physiological concentration. These data demonstrate that AbetaPP processing can be modulated by magnesium and at high [Mg2+]o, AbetaPP processing favors the alpha-secretase cleavage pathway. Our findings suggest that supplementation of magnesium has a therapeutic potential for preventing AD.

Predicting stimulus-locked single unit spiking from cortical local field potentials.

The rapidly increasing use of the local field potential (LFP) has motivated research to better understand its relation to the gold standard of neural activity, single unit (SU) spiking. We addressed this in an in vivo, awake, restrained mouse auditory cortical electrophysiology preparation by asking whether the LFP could actually be used to predict stimulus-evoked SU spiking. Implementing a Bayesian algorithm to predict the likelihood of spiking on a trial by trial basis from different representations of the despiked LFP signal, we were able to predict, with high quality and fine temporal resolution (2 ms), the time course of a SU's excitatory or inhibitory firing rate response to natural species-specific vocalizations. Our best predictions were achieved by representing the LFP by its wide-band Hilbert phase signal, and approximating the statistical structure of this signal at different time points as independent. Our results show that each SU's action potential has a unique relationship with the LFP that can be reliably used to predict the occurrence of spikes. This "signature" interaction can reflect both pre- and post-spike neural activity that is intrinsic to the local circuit rather than just dictated by the stimulus. Finally, the time course of this "signature" may be most faithful when the full bandwidth of the LFP, rather than specific narrow-band components, is used for representation.

Can DCEMRI assess the effect of green tea on the angiogenic properties of rodent prostate tumors?

The purpose of this research was to test whether dynamic contrast enhanced MRI could assess the effect of green tea on the angiogenic properties of transplanted rodent tumors. Copenhagen rats bearing AT6.1 prostate tumors inoculated in the hind limbs were randomly assigned to cages in which they were allowed to only drink either plain water (control group) or water containing green tea extract (treated group). Assignments were made after a baseline MRI experiment (week 0) was performed on each rat at 4.7T. All the rats were subsequently imaged at day 7 (week 1) and day 14 (week 2) to follow tumor growth and vascular development. The two-compartment pharmacokinetic model was used to analyze the dynamic contrast Gd-DTPA enhanced MRI data on a pixel-by-pixel basis over the tumor area to obtain the volume transfer constant (K(trans)) and extravascular extracellular space (v(e)). An identity Chi-squared test showed that the distributions of averaged histograms (n=6) of K(trans) and v(e) were significantly different from week 0 to both weeks 1 and 2 (p<0.001) in both the control and the treated rats due to increasing areas of tumor necrosis. However, the tumor growth rate was statistically indistinguishable between control and treated rats. There was no significant difference in the distributions of K(trans) and v(e) between control and treated rats. The results showed that no effects of green tea on tumor micro-vasculature were measurable by dynamic Gd-DTPA enhanced MRI.

Reciprocal modulation of I (h) and I (TASK) in thalamocortical relay neurons by halothane.

By combining electrophysiological, immunohistochemical, and computer modeling techniques, we examined the effects of halothane on the standing outward current (I (SO)) and the hyperpolarization-activated current (I (h)) in rat thalamocortical relay (TC) neurons of the dorsal lateral geniculate nucleus (dLGN). Hyperpolarizing voltage steps elicited an instantaneous current component (I (i)) followed by a slower time-dependent current that represented I (h). Halothane reduced I (h) by shifting the voltage dependency of activation toward more negative potentials and by reducing the maximal conductance. Moreover, halothane augmented I (i) and I (SO). During the blockade of I (h) through Cs+, the current-voltage relationship of the halothane-sensitive current closely resembled the properties of a current through members of the TWIK-related acid-sensitive K+ (TASK) channel family (I (TASK)). Computer simulations in a single-compartment TC neuron model demonstrated that the modulation of I (h) and I (TASK) is sufficient to explain the halothane-induced hyperpolarization of the membrane potential observed in current clamp recordings. Immunohistochemical staining revealed protein expression of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel proteins HCN1, HCN2, and HCN4. Together with the dual effect of halothane on I (h) properties, these results suggest that I (h) in TC neurons critically depends on HCN1/HCN2 heterodimers. It is concluded that the reciprocal modulation of I (h) and I (TASK) is an important mechanism of halothane action in the thalamus.

Pharmacologically induced and stimulus evoked rhythmic neuronal oscillatory activity in the primary motor cortex in vitro.

Parkinson's disease (PD) is associated with enhanced synchronization of neuronal network activity in the beta (15-30 Hz) frequency band across several nuclei of the basal ganglia (BG). Deep brain stimulation of the subthalamic nucleus (STN) appears to reduce this pathological oscillation, thereby alleviating PD symptoms. However, direct stimulation of primary motor cortex (M1) has recently been shown to be effective in reducing symptoms in PD, suggesting a role for cortex in patterning pathological rhythms. Here, we examine the properties of M1 network oscillations in coronal slices taken from rat brain. Oscillations in the high beta frequency range (layer 5, 27.8+/-1.1 Hz, n=6) were elicited by co-application of the glutamate receptor agonist kainic acid (400 nM) and muscarinic receptor agonist carbachol (50 microM). Dual extracellular recordings, local application of tetrodotoxin and recordings in M1 micro-sections indicate that the activity originates within deep layers V/VI. Beta oscillations were unaffected by specific AMPA receptor blockade, abolished by the GABA type A receptor (GABA(A)R) antagonist picrotoxin and the gap-junction blocker carbenoxolone, and modulated by pentobarbital and zolpidem indicating dependence on networks of GABAergic interneurons and electrical coupling. High frequency stimulation (HFS) at 125 Hz in superficial layers, designed to mimic transdural/transcranial stimulation, generated gamma oscillations in layers II and V (incidence 95%, 69.2+/-7.3 Hz, n=17) with very fast oscillatory components (VFO; 100-250 Hz). Stimulation at 4 Hz, however, preferentially promoted theta activity (incidence 62.5%, 5.1+/-0.6 Hz, n=15) that effected strong amplitude modulation of ongoing beta activity. Stimulation at 20 Hz evoked mixed theta and gamma responses. These data suggest that within M1, evoked theta, gamma and fast oscillations may coexist with and in some cases modulate pharmacologically induced beta oscillations.

Excitatory actions of vasoactive intestinal peptide on mouse thalamocortical neurons are mediated by VPAC2 receptors.

Thalamic nuclei can generate intrathalamic rhythms similar to those observed at various arousal levels and pathophysiological conditions such as absence epilepsy. These rhythmic activities can be altered by a variety of neuromodulators that arise from brain stem regions as well as those that are intrinsic to the thalamic circuitry. Vasoactive intestinal peptide (VIP) is a neuropeptide localized within the thalamus and strongly attenuates intrathalamic rhythms via an unidentified receptor subtype. We have used transgenic mice lacking a specific VIP receptor, VPAC(2), to identify its role in VIP-mediated actions in the thalamus. VIP strongly attenuated both the slow, 2-4 Hz and spindle-like 5-8 Hz rhythmic activities in slices from wild-type mice (VPAC(2)(+/+)) but not in slices from VPAC(2) receptor knock-out mice (VPAC(2)(-/-)), which suggests a major role of VPAC(2) receptors in the antioscillatory actions of VIP. Intracellular recordings revealed that VIP depolarized all relay neurons tested from VPAC(2)(+/+) mice. In VPAC(2)(-/-) mice, however, VIP produced no membrane depolarization in 80% of neurons tested. In relay neurons from VPAC(2)+/+ mice, VIP enhanced the hyperpolarization-activated mixed cation current, I(h), via cyclic AMP activity, but VIP did not alter I(h) in VPAC(2)-/- mice. In VPAC(2)-/- mice, pituitary adenylate cyclase activating-polypeptide (PACAP) depolarized the majority of relay neurons via I(h) enhancement presumably via PAC(1) receptor activation. Our findings suggest that VIP-mediated actions are predominantly mediated by VPAC(2) receptors, but PAC(1) receptors may play a minor role. The excitatory actions of VIP and PACAP suggest these peptides may not only regulate intrathalamic rhythmic activities, but also may influence information transfer through thalamocortical circuits.

Phenytoin reverses the chronic stress-induced impairment of memory consolidation for water maze training and depression of LTP in rat hippocampal CA1 region, but does not affect motor activity.

Previous studies have shown that phenytoin can protect hippocampal structure from damage by chronic stress, while whether it can reverse the hippocampal malfunction induced by chronic stress is unknown. We investigated the effects of phenytoin on motor activity of stressed rats and on the long-term memory of water maze spatial training, which is known to depend on hippocampal function. We also explored whether phenytoin could protect long-term potentiation (LTP) in hippocampal CA1 region from depression of chronic stressed rats. Isolated hippocampal slices of rats were used to observe the changes of LTP in hippocampal CA1 field with electrophysiological technique. The results showed that the motor activity of chronic forced-swimming rats was markedly higher than that of control rats, and phenytoin could not affect this change. The performance of water maze spatial training indicated that chronic stress damages long-term memory but not short-term memory, and phenytoin could reverse this long-term memory deficit. The increases of LTP after HFS in control and stress-phenytoin groups were significantly greater than those in stress-saline group (P < 0.05). There were no significant differences between control group and stress-phenytoin group (P > 0.05) and between control and control-phenytoin groups (P > 0.05). These findings provided the first evidence with behavioral and electrophysiological technique that phenytoin could reverse the hippocampal-dependent memory deficit and depression of LTP induced by chronic stress, which may be helpful for exploring the pathogenesis and improving the therapy of depression.

Pentobarbital induces thalamic oscillations in brain slices, modulated by GABA and glycine receptors.

We studied the effects of pentobarbital and antagonists of glutamate, gamma-aminobutyrate (GABA), and glycine receptors on extracellular activity in ventrobasal thalamic slices. Pentobarbital at sedative-hypnotic concentration (20 microM) reversibly induced 1-15 Hz oscillations. Sustained oscillations required electrical stimulation of internal capsule, but not elevated temperature or low [Mg2+]. Anesthetic concentration (200 microM) of pentobarbital evoked only transient oscillations. Kynurenate-sensitive glutamate receptors were essential for oscillations. GABA(A) antagonism (bicuculline, 50 microM or gabazine, 20 microM) suppressed oscillations at 5-15 Hz. GABA(B) antagonism (CGP 35348, 100 nM), or antagonism of glycine receptors (strychnine, 1 microM) suppressed oscillations at 1-4 and 11-15 Hz. GABA and glycine receptors modulated oscillation frequency. For elimination, oscillations required GABA antagonists and strychnine. Receptors for glutamate and glycine mediated oscillations during GABA receptor blockade in ventrobasal nuclei, or on disconnection from nRT. Glycine receptors were critical for oscillations in dorsal thalamic network, divested of GABAergic inhibition. Glutamate and GABA receptors mediated pentobarbital-induced oscillations in nRT, disconnected from ventrobasal nuclei. Hence, pentobarbital oscillogenesis occurred in isolated networks of the ventrobasal and reticularis nuclei mediated by glutamate receptors, with frequency modulation by GABA(A), GABA(B), and glycine receptors. These stationary oscillations represent a model of sedation-hypnosis, amenable to pharmacological analysis.

Can the use of methylprednisolone, vitamin C, or alpha-trinositol prevent cold-induced fluid extravasation during cardiopulmonary bypass in piglets?

OBJECTIVE: Hypothermic cardiopulmonary bypass is associated with capillary fluid leakage, resulting in edema and occasionally organ dysfunction. Systemic inflammatory activation is considered responsible. In some studies methylprednisolone has reduced the weight gain during cardiopulmonary bypass. Vitamin C and alpha-trinositol have been demonstrated to reduce the microvascular fluid and protein leakage in thermal injuries. We therefore tested these three agents for the reduction of cold-induced fluid extravasation during cardiopulmonary bypass. METHODS: A total of 28 piglets were randomly assigned to four groups of 7 each: control group, high-dose vitamin C group, methylprednisolone group, and alpha-trinositol-group. After 1 hour of normothermic cardiopulmonary bypass, hypothermic cardiopulmonary bypass was initiated in all animals and continued to 90 minutes. The fluid level in the extracorporeal circuit reservoir was kept constant at the 400-mL level and used as a fluid gauge. Fluid needs, plasma volume, changes in colloid osmotic pressure in plasma and interstitial fluid, hematocrit, and total water contents in different tissues were recorded, and the protein masses and the fluid extravasation rate were calculated. RESULTS: Hemodilution was about 25% after start of normothermic cardiopulmonary bypass. Cooling did not cause any further changes in hemodilution. During steady-state normothermic cardiopulmonary bypass, the fluid need in all groups was about 0.10 mL/(kg.min), with a 9-fold increase during the first 30 minutes of cooling (P <.001). This increased fluid need was due mainly to increased fluid extravasation from the intravascular to the interstitial space at a mean rate of 0.6 mL/(kg.min) (range 0.5-0.7 mL/[kg.min]; P <.01) and was reflected by increased total water content in most tissues in all groups. The albumin and protein masses remained constant in all groups throughout the study. CONCLUSION: Pretreatment with methylprednisolone, vitamin C, or alpha-trinositol was unable to prevent the increased fluid extravasation rate during hypothermic cardiopulmonary bypass. These findings, together with the stability of the protein masses throughout the study, support the presence of a noninflammatory mechanism behind the cold-induced fluid leakage seen during cardiopulmonary bypass.