Range Of Stimulation Frequencies Research Articles

The Empirical Mode Decomposition-Decision Tree Method to Recognize the Steady-State Visual Evoked Potentials with Wide Frequency Range.

Background:The empirical mode decomposition (EMD) is a technique to analyze the steady-state visual evoked potential (SSVEP) which decomposes the signal into its intrinsic mode functions (IMFs). Although for the limited stimulation frequency range, choosing the effective IMF leads to good results, but extending this range will seriously challenge the method so that even the combination of IMFs is associated with error.Methods:Stimulation frequencies ranged from 6 to 16 Hz with an interval of 0.5 Hz were generated using Psychophysics toolbox of MATLAB. SSVEP signal was recorded from six subjects. The EMD was used to extract the effective IMFs. Two features, including the frequency related to the peak of spectrum and normalized local energy in this frequency, were extracted for each of six conditions (each IMF, the combination of two consecutive IMFs and the combination of all three IMFs).Results:The instantaneous frequency histogram and the recognition accuracy diagram indicate that for wide stimulation frequency range, not only one IMF, but also the combination of IMFs does not have desirable efficiency. Total recognition accuracy of the proposed method was 79.75%, while the highest results obtained from the EMD-fast Fourier transform (FFT) and the CCA were 72.05% and 77.31%, respectively.Conclusion:The proposed method has improved the recognition rate more than 2.4% and 7.7% compared to the CCA and EMD-FFT, respectively, by providing the solution for situations with wide stimulation frequency range.

A machine learning approach for automated wide-range frequency tagging analysis in embedded neuromonitoring systems.

EEG is a standard non-invasive technique used in neural disease diagnostics and neurosciences. Frequency-tagging is an increasingly popular experimental paradigm that efficiently tests brain function by measuring EEG responses to periodic stimulation. Recently, frequency-tagging paradigms have proven successful with low stimulation frequencies (0.5-6Hz), but the EEG signal is intrinsically noisy in this frequency range, requiring heavy signal processing and significant human intervention for response estimation. This limits the possibility to process the EEG on resource-constrained systems and to design smart EEG based devices for automated diagnostic. We propose an algorithm for artifact removal and automated detection of frequency tagging responses in a wide range of stimulation frequencies, which we test on a visual stimulation protocol. The algorithm is rooted on machine learning based pattern recognition techniques and it is tailored for a new generation parallel ultra low power processing platform (PULP), reaching performance of more that 90% accuracy in the frequency detection even for very low stimulation frequencies (<1Hz) with a power budget of 56mW.

Rate-Dependent Role of IKur in Human Atrial Repolarization and Atrial Fibrillation Maintenance

The atrial-specific ultrarapid delayed rectifier K+ current (IKur) inactivates slowly but completely at depolarized voltages. The consequences for IKur rate-dependence have not been analyzed in detail and currently available mathematical action-potential (AP) models do not take into account experimentally observed IKur inactivation dynamics. Here, we developed an updated formulation of IKur inactivation that accurately reproduces time-, voltage-, and frequency-dependent inactivation. We then modified the human atrial cardiomyocyte Courtemanche AP model to incorporate realistic IKur inactivation properties. Despite markedly different inactivation dynamics, there was no difference in AP parameters across a wide range of stimulation frequencies between the original and updated models. Using the updated model, we showed that, under physiological stimulation conditions, IKur does not inactivate significantly even at high atrial rates because the transmembrane potential spends little time at voltages associated with inactivation. Thus, channel dynamics are determined principally by activation kinetics. IKur magnitude decreases at higher rates because of AP changes that reduce IKur activation. Nevertheless, the relative contribution of IKur to AP repolarization increases at higher frequencies because of reduced activation of the rapid delayed-rectifier current IKr. Consequently, IKur block produces dose-dependent termination of simulated atrial fibrillation (AF) in the absence of AF-induced electrical remodeling. The inclusion of AF-related ionic remodeling stabilizes simulated AF and greatly reduces the predicted antiarrhythmic efficacy of IKur block. Our results explain a range of experimental observations, including recently reported positive rate-dependent IKur-blocking effects on human atrial APs, and provide insights relevant to the potential value of IKur as an antiarrhythmic target for the treatment of AF.

Shortening speed dependent force potentiation is attenuated but not eliminated in skeletal muscles without myosin phosphorylation.

We investigated the influence of shortening speed on concentric force potentiation at different frequencies in muscles devoid of skeletal myosin light chain kinase (skMLCK-/-) and unable to phosphorylate myosin. EDL muscles from skMLCK-/- mice were activated in vitro (25 °C) across a range of stimulation frequencies (10-100Hz) during shortening ramps at 0.10, 0.30, or 0.50 of maximum shortening velocity (Vmax) before and after a potentiating stimulus (PS). When collapsed across all frequencies, the PS increased relative (post/pre) concentric force to 1.27 ± 0.02 and 1.17 ± 0.02 of pre-PS values at 0.50 and 0.30 Vmax, respectively (n = 4, P < 0.05 for all speeds). In addition, potentiation was significantly greater at low and intermediate-than at high stimulus frequencies at both speeds. In contrast, during shortening at 0.10 Vmax, a posttetanic depression was observed as mean concentric forces were reduced to 0.85 ± 0.02 of pre-PS values. Thus, although reduced compared to published values for wildtype muscles (Gittings et al., J Muscle Res Cell Motil 33:359-368, 2012), skMLCK-/- muscles displayed a speed dependent potentiation of concentric force during moderate and fast shortening speed at all frequencies tested. Our data support the presence of a myosin phosphorylation-independent mechanism(s) for concentric force potentiation at moderate speeds of shortening, and also suggests that myosin phosphorylation may be necessary to prevent the concentric force depression that may be present at slow speeds of shortening. Although additive in nature, further work is needed to parse out the relative influence of myosin phosphorylation-independent and dependent potentiation mechanisms on wildtype contractile function during dynamic conditions.

P114 The automatic neuroscientist: Tailoring tACS using real-time fMRI and Bayesian optimization

Introduction The conventional tACS approach involves defining the frequency and phase of stimulation ad hoc and testing them on a cohort of subjects. However, this approach exhibits two limitations: (1) the brain networks targeted by the stimulation cannot be verified without simultaneous functional magnetic resonance imaging (fMRI); (2) those stimulation parameters may vary across subjects due to difference in anatomy or heterogeneity in disease. Yet, there is a combinatorial explosion in the biologically plausible range of stimulation frequencies and phases, resulting in thousands of possibilities. Identifying the optimal stimulation protocol for a given individual is like ‘finding a needle in a haystack’. Therefore, using conventional methodology makes tailoring tACS to an individual highly unfeasible. Methods To address this fundamental challenge, we combine tACS with an innovative framework that utilizes real-time fMRI and machine-learning: The Automatic Neuroscientist ( Lorenz, 2016 ). The framework starts with a target brain state and finds a set of tACS parameters (frequency and phase of stimulation) that maximally activates it. This is done in a closed-loop fashion ( Download : Download high-res image (417KB) Download : Download full-size image Fig. 1), i.e. real-time fMRI provides instantaneous information on how effective certain stimulation parameters are. Based on this, the Bayesian optimization approach proposes the combination of tACS parameters that will be applied in the next iteration. This cycle continues until the Automatic Neuroscientist identifies the sweet spot within the exhaustive parameter space (Fig. 2 Download : Download high-res image (178KB) Download : Download full-size image ) that maximally activates the target brain state. Results We could demonstrate the technical feasibility of novel neurotechnology that combines real-time fMRI, machine-learning and tACS in a fully automated manner. Moreover, we showed that our closed-loop framework is far more efficient that the standard approach. Conclusion We envision that our framework will advance personalized treatment by means of non-invasive brain stimulation. This will be of particular importance for neurological and psychiatric deficits that are diffuse and widely heterogeneous in their origin.

Acute effects and after-effects of acoustic coordinated reset neuromodulation in patients with chronic subjective tinnitus.

Chronic subjective tinnitus is an auditory phantom phenomenon characterized by abnormal neuronal synchrony in the central auditory system. As shown computationally, acoustic coordinated reset (CR) neuromodulation causes a long-lasting desynchronization of pathological synchrony by downregulating abnormal synaptic connectivity. In a previous proof of concept study acoustic CR neuromodulation, employing stimulation tone patterns tailored to the dominant tinnitus frequency, was compared to noisy CR-like stimulation, a CR version significantly detuned by sparing the tinnitus-related pitch range and including substantial random variability of the tone spacing on the frequency axis. Both stimulation protocols caused an acute relief as measured with visual analogue scale scores for tinnitus loudness (VAS-L) and annoyance (VAS-A) in the stimulation-ON condition (i.e. 15 min after stimulation onset), but only acoustic CR neuromodulation had sustained long-lasting therapeutic effects after 12 weeks of treatment as assessed with VAS-L, VAS-A scores and a tinnitus questionnaire (TQ) in the stimulation-OFF condition (i.e. with patients being off stimulation for at least 2.5 h). To understand the source of the long-lasting therapeutic effects, we here study whether acoustic CR neuromodulation has different electrophysiological effects on oscillatory brain activity as compared to noisy CR-like stimulation under stimulation-ON conditions and immediately after cessation of stimulation. To this end, we used a single-blind, single application, cross over design in 18 patients with chronic tonal subjective tinnitus and administered three different 16-minute stimulation protocols: acoustic CR neuromodulation, noisy CR-like stimulation and low frequency range (LFR) stimulation, a CR type stimulation with deliberately detuned pitch and repetition rate of stimulation tones, as control stimulation. We measured VAS-L and VAS-A scores together with spontaneous EEG activity pre-, during- and post-stimulation. Under stimulation-ON conditions acoustic CR neuromodulation and noisy CR-like stimulation had similar effects: a reduction of VAS-L and VAS-A scores together with a decrease of auditory delta power and an increase of auditory alpha and gamma power, without significant differences. In contrast, LFR stimulation had significantly weaker EEG effects and no significant clinical effects under stimulation-ON conditions. The distinguishing feature between acoustic CR neuromodulation and noisy CR-like stimulation were the electrophysiological after-effects.Acoustic CR neuromodulation caused the longest significant reduction of delta and gamma and increase of alpha power in the auditory cortex region. Noisy CR-like stimulation had weaker and LFR stimulation hardly any electrophysiological after-effects. This qualitative difference further supports the assertion that long-term effects of acoustic CR neuromodulation on tinnitus are mediated by a specific disruption of synchronous neural activity. Furthermore, our results indicate that acute electrophysiological after-effects might serve as a marker to further improve desynchronizing sound stimulation.

Functional circuit mapping of striatal output nuclei using simultaneous deep brain stimulation and fMRI

The substantia nigra pars reticulata (SNr) and external globus pallidus (GPe) constitute the two major output targets of the rodent striatum. Both the SNr and GPe converge upon thalamic relay nuclei (directly or indirectly, respectively), and are traditionally modeled as functionally antagonistic relay inputs. However, recent anatomical and functional studies have identified unanticipated circuit connectivity in both the SNr and GPe, demonstrating their potential as far more than relay nuclei. In the present study, we employed simultaneous deep brain stimulation and functional magnetic resonance imaging (DBS-fMRI) with cerebral blood volume (CBV) measurements to functionally and unbiasedly map the circuit- and network level connectivity of the SNr and GPe. Sprague-Dawley rats were implanted with a custom-made MR-compatible stimulating electrode in the right SNr (n=6) or GPe (n=7). SNr- and GPe-DBS, conducted across a wide range of stimulation frequencies, revealed a number of surprising evoked responses, including unexpected CBV decreases within the striatum during DBS at either target, as well as GPe-DBS-evoked positive modulation of frontal cortex. Functional connectivity MRI revealed global modulation of neural networks during DBS at either target, sensitive to stimulation frequency and readily reversed following cessation of stimulation. This work thus contributes to a growing literature demonstrating extensive and unanticipated functional connectivity among basal ganglia nuclei.

Applications of In Vivo Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair.

Despite the regenerative capacity of skeletal muscle, permanent functional and/or cosmetic deficits (e.g., volumetric muscle loss (VML) resulting from traumatic injury, disease and various congenital, genetic and acquired conditions are quite common. Tissue engineering and regenerative medicine technologies have enormous potential to provide a therapeutic solution. However, utilization of biologically relevant animal models in combination with longitudinal assessments of pertinent functional measures are critical to the development of improved regenerative therapeutics for treatment of VML-like injuries. In that regard, a commercial muscle lever system can be used to measure length, tension, force and velocity parameters in skeletal muscle. We used this system, in conjunction with a high power, bi-phase stimulator, to measure in vivo force production in response to activation of the anterior crural compartment of the rat hindlimb. We have previously used this equipment to assess the functional impact of VML injury on the tibialis anterior (TA) muscle, as well as the extent of functional recovery following treatment of the injured TA muscle with our tissue engineered muscle repair (TEMR) technology. For such studies, the left foot of an anaesthetized rat is securely anchored to a footplate linked to a servomotor, and the common peroneal nerve is stimulated by two percutaneous needle electrodes to elicit muscle contraction and dorsiflexion of the foot. The peroneal nerve stimulation-induced muscle contraction is measured over a range of stimulation frequencies (1-200 Hz), to ensure an eventual plateau in force production that allows for an accurate determination of peak tetanic force. In addition to evaluation of the extent of VML injury as well as the degree of functional recovery following treatment, this methodology can be easily applied to study diverse aspects of muscle physiology and pathophysiology. Such an approach should assist with the more rational development of improved therapeutics for muscle repair and regeneration.

Applications of &lt;em&gt;In Vivo&lt;/em&gt; Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair

Despite the regenerative capacity of skeletal muscle, permanent functional and/or cosmetic deficits (e.g., volumetric muscle loss (VML) resulting from traumatic injury, disease and various congenital, genetic and acquired conditions are quite common. Tissue engineering and regenerative medicine technologies have enormous potential to provide a therapeutic solution. However, utilization of biologically relevant animal models in combination with longitudinal assessments of pertinent functional measures are critical to the development of improved regenerative therapeutics for treatment of VML-like injuries. In that regard, a commercial muscle lever system can be used to measure length, tension, force and velocity parameters in skeletal muscle. We used this system, in conjunction with a high power, bi-phase stimulator, to measure in vivo force production in response to activation of the anterior crural compartment of the rat hindlimb. We have previously used this equipment to assess the functional impact of VML injury on the tibialis anterior (TA) muscle, as well as the extent of functional recovery following treatment of the injured TA muscle with our tissue engineered muscle repair (TEMR) technology. For such studies, the left foot of an anaesthetized rat is securely anchored to a footplate linked to a servomotor, and the common peroneal nerve is stimulated by two percutaneous needle electrodes to elicit muscle contraction and dorsiflexion of the foot. The peroneal nerve stimulation-induced muscle contraction is measured over a range of stimulation frequencies (1-200 Hz), to ensure an eventual plateau in force production that allows for an accurate determination of peak tetanic force. In addition to evaluation of the extent of VML injury as well as the degree of functional recovery following treatment, this methodology can be easily applied to study diverse aspects of muscle physiology and pathophysiology. Such an approach should assist with the more rational development of improved therapeutics for muscle repair and regeneration.

Shaping Intrinsic Neural Oscillations with Periodic Stimulation.

Rhythmic brain activity plays an important role in neural processing and behavior. Features of these oscillations, including amplitude, phase, and spectrum, can be influenced by internal states (e.g., shifts in arousal, attention or cognitive ability) or external stimulation. Electromagnetic stimulation techniques such as transcranial magnetic stimulation, transcranial direct current stimulation, and transcranial alternating current stimulation are used increasingly in both research and clinical settings. Currently, the mechanisms whereby time-dependent external stimuli influence population-scale oscillations remain poorly understood. Here, we provide computational insights regarding the mapping between periodic pulsatile stimulation parameters such as amplitude and frequency and the response dynamics of recurrent, nonlinear spiking neural networks. Using a cortical model built of excitatory and inhibitory neurons, we explored a wide range of stimulation intensities and frequencies systematically. Our results suggest that rhythmic stimulation can form the basis of a control paradigm in which one can manipulate the intrinsic oscillatory properties of driven networks via a plurality of input-driven mechanisms. Our results show that, in addition to resonance and entrainment, nonlinear acceleration is involved in shaping the rhythmic response of our modeled network. Such nonlinear acceleration of spontaneous and synchronous oscillatory activity in a neural network occurs in regimes of intense, high-frequency rhythmic stimulation. These results open new perspectives on the manipulation of synchronous neural activity for basic and clinical research. Oscillatory activity is widely recognized as a core mechanism for information transmission within and between brain circuits. Noninvasive stimulation methods can shape this activity, something that is increasingly capitalized upon in basic research and clinical practice. Here, we provide computational insights on the mechanistic bases for such effects. Our results show that rhythmic stimulation forms the basis of a control paradigm in which one can manipulate the intrinsic oscillatory properties of driven networks via a plurality of input-driven mechanisms. In addition to resonance and entrainment, nonlinear acceleration is involved in shaping the rhythmic response of our modeled network, particularly in regimes of high-frequency rhythmic stimulation. These results open new perspectives on the manipulation of synchronous neural activity for basic and clinical research.

The mind simulator: Upper alpha and enhanced mental rotation

Event Abstract Back to Event The mind simulator: Upper alpha and enhanced mental rotation Miriam Reiner1, 2* 1 Technion, EDucation in Science and Technology, Israel 2 Stanford, biological science, United States One of the essential cognitive abilities in general for functioning and learning of science and technology in particular, is associated with imagery, and relates to predicting the position of a rotated object, i.e. imagining the act of rotation of an object, without actual rotation. This operation is known as mental rotation and it has been studied extensively over the years. The present study deals with electrical activity in the brain associated with mental rotation. More specifically we look at the neural correlates of mental rotation. We identify a potential neural model, and focus on the role of synchronized oscillations, then test the model with neurofeedback. Our purpose is to identify a mechanism and conditions to enhance performance of rotating bodies in imagination. Mental rotation is important for everyday spatial activities such as orientation in unfamiliar places or finding a route on a map, and has an important role in cognitive processes associated with learning – success in mathematics and physics is positively correlated with mental rotation skills (Delgado & Prieto, 2004). Literature indicates that brain waves in the frequency range of 10-12 Hz- Upper Alpha – are associated with mental rotation ability. Klimesch et al,.(2003) brought evidence that mental rotation can be enhanced with rapid-rate repetitive transcranial magnetic stimulation. The core idea of magnetic stimulation is to induce electrical activity in the cortex by a short series of magnetic pulses in the Upper Alpha frequency band. Results show that this range of stimulation frequencies can improve mental rotation. Here we test changes in mental rotation, after raising the upper band of the spectrum of waves known as alpha. The EEG alpha frequency band is positively correlated with cognitive performance. Especially Upper Alpha (UA) is correlated with mental rotation (Gruzelier 2013a/b). The purpose of the study is to explore whether Upper Alpha is correlated with the rotational speed, which has not yet been studied in previous studies, that examined only the relationship between Upper alpha and accuracy in mental rotation. To increase the ecological validity, we introduce here three-dimensional objects, in contrast to previous studies that used two-dimensional shapes such as alphanumeric characters and simple three-dimensional shapes such as a series of connected cubes. The test is based on a well validated test (Shepard & Metzler, 1971 , Jansen-Osmann.P & Heil.M, 2007, Neubauer et al., 2010) Procedure The study involved 44 students who were divided into two groups, the experimental group and a control group. In the first stage both groups were subjected to a mental rotation test. The aim of the test is to assess the cognitive performance of mental rotation. In the second stage only the experimental group underwent a series of neurofeedback training in order to increase the intensity of upper alpha (UA). At the third stage both groups took a mental rotation test to assess if there is improvement in cognitive abilities of mental rotation (rotation speed and accuracy). Thus, we examined whether research subjects can be trained to increase the the power of UA with neurofeedback training (NF), and whether the subjects who increased UA, performed a faster and a significantly more accurate mental rotation than subjects who did not undergo NF training. We first identified individual alpha, (to avoid low validity due to interpersonal variance in the range of upper alpha) at P4 and Pz, and recorded a baseline from all 32 electrodes. The experiment lasted four consecutive days. On the first we measures individual upper alpha, ran a mental rotation test, and 8blocks of neurofeedback upper alpha, measuring the amplitude of upper alpha too. We repeated the latter two stages on the second third and foruth day, and ran a mental rotation test on the fourth day too. Results The results indicated that the power of the UA is positively correlated with the progression of training and it is evidence that subjects increased their alpha activity after NFT In addition, findings show that subjects who underwent neurofeedback training and increased the power of UA, performed the task of mental rotation faster than the subjects who did not undergo training and the experimental group was more accurate than the control group, but the difference in accuracy between the two groups was not significant . To summarize, neurofeedback processes induced upper alpha, and upper alpha is correlated with enhanced mental rotation. References

Screening and Optimization of Nerve Targets and Parameters Reveals Inhibitory Effect of Pudendal Stimulation on Rat Bladder Hypersensitivity.

Neuromodulation has been reported to reliably improve symptoms of bladder overactivity and sometimes pain. The effect of electrical stimulation of several nerve pathways demonstrated to alter cystometric responses to bladder distension was examined on nociceptive responses in models of bladder hypersensitivity. Bladder hypersensitivity was produced by several published methods including neonatal inflammation, acute inflammation, and chronic stress. Effects of different sites of stimulation (L6 and T13 nerve roots, proximal and distal pudendal nerves [PNs]) on nociceptive reflex responses to urinary bladder distension in urethane-anesthetized female rats were assessed and a parametric analysis of parameters of stimulation was performed. Bilateral biphasic stimulation of the proximal PNs resulted in statistically significant inhibition of visceromotor and cardiovascular responses to bladder distension in rats made hypersensitive by neonatal bladder inflammation. We found a range of optimal stimulation frequencies (5-10 Hz) which produced robust inhibitory effects when using short pulse widths (100-240 μs). Onset of inhibition was within minutes and persisted for several minutes after the stimulus was discontinued. Use of bilateral PN stimulation in acute inflammation and stress-induced hypersensitivity models as well as unilateral stimulation, very distal PN cutaneous branch stimulation, and stimulation of the T13 and L6 nerve roots all proved ineffective with the parameters used. This study suggests that inhibitory effects of bilateral PN stimulation can be evoked in a rodent hypersensitivity model at relatively low frequencies with short pulse widths. The onset of effect is rapid, which suggests the potential for treating episodic pain in painful bladder disorders.

Hyperammonemia results in reduced muscle function independent of muscle mass.

The mechanism of the nearly universal decreased muscle strength in cirrhosis is not known. We evaluated whether hyperammonemia in cirrhosis causes contractile dysfunction independent of reduced skeletal muscle mass. Maximum grip strength and muscle fatigue response were determined in cirrhotic patients and controls. Blood and muscle ammonia concentrations and grip strength normalized to lean body mass were measured in the portacaval anastomosis (PCA) and sham-operated pair-fed control rats (n = 5 each). Ex vivo contractile studies in the soleus muscle from a separate group of Sprague-Dawley rats (n = 7) were performed. Skeletal muscle force of contraction, rate of force development, and rate of relaxation were measured. Muscles were also subjected to a series of pulse trains at a range of stimulation frequencies from 20 to 110 Hz. Cirrhotic patients had lower maximum grip strength and greater muscle fatigue than control subjects. PCA rats had a 52.7 ± 13% lower normalized grip strength compared with control rats, and grip strength correlated with the blood and muscle ammonia concentrations (r(2) = 0.82). In ex vivo muscle preparations following a single pulse, the maximal force, rate of force development, and rate of relaxation were 12.1 ± 3.5 g vs. 6.2 ± 2.1 g; 398.2 ± 100.4 g/s vs. 163.8 ± 97.4 g/s; -101.2 ± 22.2 g/s vs. -33.6 ± 22.3 g/s in ammonia-treated compared with control muscle preparation, respectively (P < 0.001 for all comparisons). Tetanic force, rate of force development, and rate of relaxation were depressed across a range of stimulation from 20 to 110 Hz. These data provide the first direct evidence that hyperammonemia impairs skeletal muscle strength and increased muscle fatigue and identifies a potential therapeutic target in cirrhotic patients.

O044. Frequency-dependent habituation deficit of the nociceptive blink reflex in migraine with and without aura.

Background The habituation phenomenon is a frequency-dependent form of non-associative learning which reflects the excitability level of both sensory and pain systems. We previously demonstrated a frequency-dependent deficit of habituation of the conventional blink reflex in migraine[1]. We investigated the habituation of the trigeminal nociceptive system by studying the habituation of the late component (R2) of the nociceptive blink reflex (nBR) in a wide range of stimulation frequencies in subjects with migraine without aura (MWoA) and with aura (MWA).

O043. Frequency-dependent habituation deficit of the nociceptive blink reflex in cluster headache and paroxysmal hemicrania.

Background The habituation phenomenon is a frequency-dependent form of non-associative learning which reflects the excitability level of both sensory and pain systems. We previously demonstrated a frequency-dependent deficit of habituation of the conventional blink reflex in cluster headache (CH) [1]. We investigated the habituation of the trigeminal nociceptive system by studying the habituation of the late component (R2) of the nociceptive blink reflex (nBR) in a wide range of stimulation frequencies in CH and paroxysmal hemicrania (PH).

Shortening Speed Dependence of Concentric Force Potentiation in the Absence of Myosin Phosphorylation

Contraction‐induced elevation of myoplasmic Ca2+ leads to sequential activation of skeletal muscle myosin light chain kinase (skMLCK), an enzyme responsible for phosphorylating the myosin regulatory light chain (RLC). In wildtype (WT) mouse skeletal muscle containing skMLCK, force potentiation correlates with RLC phosphate content; although, these muscles may contain an RLC phosphorylation‐independent component. In this study, extensor digitorum longus (EDL) muscles from knockout (KO) C57BL/6 mice, devoid of skMLCK, were activated in vitro (25°C) across a range of stimulation frequencies (10, 25, 45, 70 and 100 Hz) and subjected to shortening ramps at 0.1, 0.3 or 0.5 of maximal shortening velocity (Vmax). This was performed before and after a standard conditioning stimulus (CS) that potentiated mean concentric force at 0.3 and 0.5 Vmax to 1.20 ± 0.03 and 1.30 ± 0.02 of unpotentiated (pre‐CS) values, respectively; however, mean forces were depressed to 0.84 ± 0.03 of pre‐CS values at 0.1 Vmax (n = 3, P &lt; 0.05). Increasing shortening speed augmented the frequency at which concentric force potentiation was maximal: 25 and 45 Hz at 0.3 and 0.5 Vmax, respectively. These results mirrored previous results from WT muscles (Gittings et al., 2012), except that concentric force potentiation was attenuated by ~50% across all frequencies at 0.3 and 0.5 Vmax, while force at 0.1 Vmax was reduced rather than unchanged. Thus, our data indicates the presence of an RLC phosphorylation‐independent mechanism for potentiation in skMLCK KO muscles that may complement the intact RLC phosphorylation mechanism in WT muscles.Supported by NSERC (2014‐05122).

0298 : Action potential shortening in the pig right ventricular outflow tract epicardium

The right ventricular outflow tract (RVOT) has a distinct embryological origin from the rest of the right ventricle (RV) and is a frequent origin for idiopathic and disease-related arrhythmias. We hypothesised that heterogeneous action potential duration (APD) across the right ventricle (RV) may contribute to RVOT arrhythmia generation. Pigs were anesthetized and monophasic action potentials (MAPs) recorded in sinus rhythm from the epicardium of the RV free wall and RVOT. The RV was isolated and perfused via both right and left anterior coronary arteries. The preparation was paced (1-5Hz) and the electrical activity optically mapped (di-4-ANEPPS, 10μM) on both epicardial (EPI) and endocardial (ENDO) surfaces. The expression of potassium channels was assessed by RT-PCR. In vivo, MAP durations measured at 20% and 80% repolarization were both significantly shorter in the RVOT than in the RV free wall EPI (P<0.05). Similar APD variations were observed ex vivo as RVOT APD20 and APD80 were decreased by 29% and 15% respectively compared to free wall (P<0.01). Interestingly, no APD difference was observed on the ENDO resulting in a larger transmural APD difference in the RVOT than in the RV free wall. The RVOT EPI APD80 shortening was preserved over a range of stimulation frequencies leading to a downward shift of the restitution curve and a significant decrease of its slope (P<0.05). In accordance with these results, expression level of mRNA coding for Kv4.3 (Ito) and Kv11.1 (IKr) were upregulated in the RVOT compared to the RV free wall epicardium (P<0.01) while no difference was found for Kv7.1 (IKs) or Kv4.2 (Ito). Moreover, no variation in K+ channel expression was observed across the RV endocardium. Action potentials are shorter in the RVOT than elsewhere in the RV EPI. This electrophysiological signature was mirrored by regional variations in specific K+ channels. The resulting APD dispersion may facilitate RV re-entrant arrhythmias in the context of a RVOT ectopy.

Glutamate mediated astrocytic filtering of neuronal activity.

Neuron-astrocyte communication is an important regulatory mechanism in various brain functions but its complexity and role are yet to be fully understood. In particular, the temporal pattern of astrocyte response to neuronal firing has not been fully characterized. Here, we used neuron-astrocyte cultures on multi-electrode arrays coupled to Ca2+ imaging and explored the range of neuronal stimulation frequencies while keeping constant the amount of stimulation. Our results reveal that astrocytes specifically respond to the frequency of neuronal stimulation by intracellular Ca2+ transients, with a clear onset of astrocytic activation at neuron firing rates around 3-5 Hz. The cell-to-cell heterogeneity of the astrocyte Ca2+ response was however large and increasing with stimulation frequency. Astrocytic activation by neurons was abolished with antagonists of type I metabotropic glutamate receptor, validating the glutamate-dependence of this neuron-to-astrocyte pathway. Using a realistic biophysical model of glutamate-based intracellular calcium signaling in astrocytes, we suggest that the stepwise response is due to the supralinear dynamics of intracellular IP3 and that the heterogeneity of the responses may be due to the heterogeneity of the astrocyte-to-astrocyte couplings via gap junction channels. Therefore our results present astrocyte intracellular Ca2+ activity as a nonlinear integrator of glutamate-dependent neuronal activity.

Effects of the neuropeptide S receptor antagonist RTI-118 on abuse-related facilitation of intracranial self-stimulation produced by cocaine and methylenedioxypyrovalerone (MDPV) in rats

Neuropeptide S (NPS) is a neurotransmitter that activates the NPS receptor to modulate biological functions including anxiety-like behaviors, feeding, and drug reinforcement. RTI-118 is a novel NPS receptor antagonist that decreased cocaine self-administration in rats at doses that had little or no effect on food-maintained responding. To build on these previous findings, this study examined effects of RTI-118 on cocaine-induced facilitation of intracranial self-stimulation (ICSS) in rats. To provide a context for data interpretation, effects of RTI-118 were compared to effects of the kappa opioid receptor agonist U69,593, because the kappa opioid receptor is another peptide neurotransmitter receptor reported to modulate abuse-related cocaine effects. RTI-118 effects were also examined on ICSS facilitation produced by methylenedioxypyrovalerone (MDPV), a novel designer drug of abuse with some cocaine-like effects. Male Sprague–Dawley rats (n=12) with electrodes targeting the medial forebrain bundle responded under a fixed-ratio 1 schedule for range of brain stimulation frequencies. Under control conditions, brain stimulation maintained a frequency-dependent increase in ICSS rates. Cocaine (1.0–10mg/kg) and MDPV (3.2mg/kg) facilitated ICSS. RTI-118 (3.2–32mg/kg) alone produced little effect on ICSS but dose dependently blocked cocaine-induced ICSS facilitation. U69,593 (0.25–0.5mg/kg) also attenuated cocaine effects, but blockade of cocaine effects was incomplete even at a U69,593 dose that alone depressed ICSS. RTI-118 (32mg/kg) failed to block MDPV-induced ICSS facilitation. These results support further consideration of NPS receptor antagonists as candidate treatments for cocaine abuse and provide evidence for differential effects of a candidate treatment on abuse-related effects of cocaine and MDPV.

Effects of the novel, selective and low-efficacy mu opioid receptor ligand NAQ on intracranial self-stimulation in rats.

Low-efficacy mu opioid receptor agonists may be useful for some clinical indications, but clinically available low-efficacy mu agonists also have low selectivity for mu vs. kappa opioid receptors. NAQ (17-cyclopropylmethyl-3,14ß-dihydroxy-4,5α-epoxy-6α-[(3'-isoquinolyl)acetamido]morphinan) is a novel opioid receptor ligand with low-efficacy at mu receptors and greater mu-receptor selectivity than existing low-efficacy agonists. This study examined behavioral effects of NAQ in rats using an intracranial self-stimulation (ICSS) procedure that has been used previously to examine other opioids. NAQ effects were examined before, during, and after chronic morphine treatment, and effects of NAQ were compared to effects of nalbuphine and naltrexone. Adult male Sprague-Dawley rats were trained to respond for electrical brain stimulation delivered via electrodes implanted in the medial forebrain bundle. A range of brain stimulation frequencies maintained a wide range of baseline ICSS rates. Effects of NAQ (0.32-10 mg/kg), nalbuphine (1.0 mg/kg), and naltrexone (0.1 mg/kg) were determined before morphine treatment and during treatment with 3.2 and 18 mg/kg/day morphine. NAQ effects were also redetermined beginning 2 weeks after termination of morphine treatment. NAQ produced weak ICSS facilitation in morphine-naïve rats but more robust ICSS facilitation during and after morphine treatment and also reversed morphine withdrawal-associated depression of ICSS. These effects were similar to effects of nalbuphine. These results agree with the in vitro characterization of NAQ as a low-efficacy mu agonist. Opioid exposure may enhance abuse-related effects of NAQ, but NAQ may also serve as a low-efficacy and relatively safe option for treatment of opioid withdrawal or dependence.