High-frequency Stimulation Conditions Research Articles

Astrocyte Receptor Rebirth.

Conditional Knockout of mGluR5 From Astrocytes During Epilepsy Development Impairs High-Frequency Glutamate Uptake Umpierre AD, West PJ, White JA, et al. J Neurosci. 2019;39(4):727-742. doi:10.1523/JNEUROSCI.1148-18.2018Astrocyte expression of metabotropic glutamate receptor 5 (mGluR5) is consistently observed in resected tissue from patients with epilepsy and is equally prevalent in animal models of epilepsy. However, little is known about the functional signaling properties or downstream consequences of astrocyte mGluR5 activation during epilepsy development. In the rodent brain, astrocyte mGluR5 expression is developmentally regulated and confined in expression/function to the first weeks of life, with similar observations made in human control tissue. Herein, we demonstrate that mGluR5 expression and function dramatically increase in a mouse model of temporal lobe epilepsy. Interestingly, in both male and female mice, mGluR5 function persists in the astrocyte throughout the process of epileptogenesis following status epilepticus. However, mGluR5 expression and function are transient in animals that do not develop epilepsy over an equivalent time period, suggesting that patterns of mGluR5expression may signify continuing epilepsy development or its resolution. We demonstrate that, during epileptogenesis, astrocytes reacquire mGluR5-dependent calcium transients following agonist application or synaptic glutamate release, a feature of astrocyte–neuron communication absent since early development. Finally, we find that the selective and conditional knockout of mGluR5 signaling from astrocytes during epilepsy development slows the rate of glutamate clearance through astrocyte glutamate transporters under high-frequency stimulation conditions, a feature that suggests astrocyte mGluR5 expression during epileptogenesis may recapitulate earlier developmental roles in regulating glutamate transporter function.

Conditional Knock-out of mGluR5 from Astrocytes during Epilepsy Development Impairs High-Frequency Glutamate Uptake.

Astrocyte expression of metabotropic glutamate receptor 5 (mGluR5) is consistently observed in resected tissue from patients with epilepsy and is equally prevalent in animal models of epilepsy. However, little is known about the functional signaling properties or downstream consequences of astrocyte mGluR5 activation during epilepsy development. In the rodent brain, astrocyte mGluR5 expression is developmentally regulated and confined in expression/function to the first weeks of life, with similar observations made in human control tissue. Herein, we demonstrate that mGluR5 expression and function dramatically increase in a mouse model of temporal lobe epilepsy. Interestingly, in both male and female mice, mGluR5 function persists in the astrocyte throughout the process of epileptogenesis following status epilepticus. However, mGluR5 expression and function are transient in animals that do not develop epilepsy over an equivalent time period, suggesting that patterns of mGluR5 expression may signify continuing epilepsy development or its resolution. We demonstrate that, during epileptogenesis, astrocytes reacquire mGluR5-dependent calcium transients following agonist application or synaptic glutamate release, a feature of astrocyte-neuron communication absent since early development. Finally, we find that the selective and conditional knock-out of mGluR5 signaling from astrocytes during epilepsy development slows the rate of glutamate clearance through astrocyte glutamate transporters under high-frequency stimulation conditions, a feature that suggests astrocyte mGluR5 expression during epileptogenesis may recapitulate earlier developmental roles in regulating glutamate transporter function.SIGNIFICANCE STATEMENT In development, astrocyte mGluR5 signaling plays a critical role in regulating structural and functional interactions between astrocytes and neurons at the tripartite synapse. Notably, mGluR5 signaling is a positive regulator of astrocyte glutamate transporter expression and function, an essential component of excitatory signaling regulation in hippocampus. After early development, astrocyte mGluR5 expression is downregulated, but reemerges in animal models of temporal lobe epilepsy (TLE) development and patient epilepsy samples. We explored the hypothesis that astrocyte mGluR5 reemergence recapitulates earlier developmental roles during TLE acquisition. Our work demonstrates that astrocytes with mGluR5 signaling during TLE development perform faster glutamate uptake in hippocampus, revealing a previously unexplored role for astrocyte mGluR5 signaling in hypersynchronous pathology.

Locally induced neuronal synchrony precisely propagates to specific cortical areas without rhythm distortion

Propagation of oscillatory spike firing activity at specific frequencies plays an important role in distributed cortical networks. However, there is limited evidence for how such frequency-specific signals are induced or how the signal spectra of the propagating signals are modulated during across-layer (radial) and inter-areal (tangential) neuronal interactions. To directly evaluate the direction specificity of spectral changes in a spiking cortical network, we selectively photostimulated infragranular excitatory neurons in the rat primary visual cortex (V1) at a supra-threshold level with various frequencies, and recorded local field potentials (LFPs) at the infragranular stimulation site, the cortical surface site immediately above the stimulation site in V1, and cortical surface sites outside V1. We found a significant reduction of LFP powers during radial propagation, especially at high-frequency stimulation conditions. Moreover, low-gamma-band dominant rhythms were transiently induced during radial propagation. Contrastingly, inter-areal LFP propagation, directed to specific cortical sites, accompanied no significant signal reduction nor gamma-band power induction. We propose an anisotropic mechanism for signal processing in the spiking cortical network, in which the neuronal rhythms are locally induced/modulated along the radial direction, and then propagate without distortion via intrinsic horizontal connections for spatiotemporally precise, inter-areal communication.

Effect of low-frequency deep brain stimulation on sensory thresholds in Parkinson's disease.

OBJECTIVE Chronic pain is a major distressing symptom of Parkinson's disease (PD) that is often undertreated. Subthalamic nucleus (STN) deep brain stimulation (DBS) delivers high-frequency stimulation (HFS) to patients with PD and has been effective in pain relief in a subset of these patients. However, up to 74% of patients develop new pain concerns while receiving STN DBS. Here the authors explore whether altering the frequency of STN DBS changes pain perception as measured through quantitative sensory testing (QST). METHODS Using QST, the authors measured thermal and mechanical detection and pain thresholds in 19 patients undergoing DBS via HFS, low-frequency stimulation (LFS), and off conditions in a randomized order. Testing was performed in the region of the body with the most pain and in the lower back in patients without chronic pain. RESULTS In the patients with chronic pain, LFS significantly reduced heat detection thresholds as compared with thresholds following HFS (p = 0.029) and in the off state (p = 0.010). Moreover, LFS resulted in increased detection thresholds for mechanical pressure (p = 0.020) and vibration (p = 0.040) compared with these thresholds following HFS. Neither LFS nor HFS led to changes in other mechanical thresholds. In patients without chronic pain, LFS significantly increased mechanical pain thresholds in response to the 40-g pinprick compared with thresholds following HFS (p = 0.032). CONCLUSIONS Recent literature has suggested that STN LFS can be useful in treating nonmotor symptoms of PD. Here the authors demonstrated that LFS modulates thermal and mechanical detection to a greater extent than HFS. Low-frequency stimulation is an innovative means of modulating chronic pain in PD patients receiving STN DBS. The authors suggest that STN LFS may be a future option to consider when treating Parkinson's patients in whom pain remains the predominant complaint.

Modulation of Extracellular Levels of 5-HT in the Caudate Putamen of Freely Moving Rats by High Frequency Stimulation of the Subthalamic Nucleus

Electrical high frequency stimulation (HFS) in the subthalamic nucleus (STN) has been shown to have a thera- peutic effect in several movement disorders. But, debilitating psychiatric effects like depression and suicidality are occa- sionally seen and might be caused by the changes in the serotoninergic activity. Previous studies could show that HFS of the STN results in inhibition of the serotonergic neurons originating in the dorsal raphe nucleus. The aim of this study was to characterize the effect of HFS (124 Hz, 0.5 mA) in the STN, on the extracellular levels of serotonin, dopamine and their metabolites HIAA, DOPAC and HVA in the caudate-putamen (CPu) in conscious and freely moving rats. Extracellular levels of the neurotransmitters and their metabolites were quantified using high performance liquid chromatography with electrochemical detection. Under HFS conditions, a significant reduction in the extracellular levels of serotonin was ob- served. Cessation of HFS showed a recovery back to basal levels. Dopamine levels were not affected, although significant increase of its metabolites DOPAC and HVA were measured. In the case of low frequency stimulation (LFS), levels of se- rotonin and its metabolite HIAA remained unchanged, while the levels of dopamine metabolites, DOPAC and HVA, showed a significant decline. These results demonstrate evidence for a strong linkage between HFS in the STN and reduc- tion of the levels of serotonin in the caudate-putamen, which is likely responsible for psychiatric side effects seen in Park- insonian patients who are treated with STN stimulation.

Frequency-Dependent Effects of Ethanol on Dopamine Release in the Nucleus Accumbens

Ethanol (EtOH) is known to have excitatory effects on dopamine (DA) release, with moderate-to-high doses (0.5 to 2.5g/kg) of acute EtOH enhancing DA neuron firing rates in the ventral tegmental area (VTA) and DA levels in the nucleus accumbens (NAc). EtOH has also been shown to reduce DA activity, with moderate doses (1 to 2g/kg) attenuating electrically evoked release, and higher doses (5g/kg) decreasing NAc DA levels, demonstrating a biphasic effect of EtOH on DA release. The purpose of the current study was to evaluate EtOH's inhibitory effects on NAc DA terminal release under low- and high-frequency stimulation conditions. Using fast-scan cyclic voltammetry in NAc slices from C57BL/6J mice, we examined EtOH's (40 to 160mM) effects on DA release under several different stimulation parameters, varying frequency (5 to 125Hz), number of pulses (1 to 10), and stimulation intensity (50 to 350μA). Additionally, calcium concentrations were manipulated under high-frequency stimulation conditions (20Hz, 10 pulses, 350μA) to determine whether EtOH's effects were dependent upon calcium concentration, and by extension, the amount of DA release. Acute EtOH (40 to 160mM) inhibited DA release to a greater extent under high-frequency, multiple-pulse stimulation conditions, with increased sensitivity at 5 and 10 pulses and frequencies of 20Hz or higher. High-frequency, multiple-pulse stimulations also resulted in greater DA release compared with single-pulse release, which was controlled by reducing stimulation intensity. Under reduced DA conditions, high-frequency stimulations still showed increased EtOH sensitivity. Reducing calcium levels also decreased DA release at high-frequency stimulations, but did not affect EtOH sensitivity. EtOH appears to inhibit DA release at NAc terminals under high-frequency stimulation conditions that are similar to release events observed during phasic burst firing in DAergic neurons, suggesting that EtOH may provide inhibition of DA terminals selectively during phasic signaling, while leaving tonic DA terminal activity unaffected.

Induction of the perceptual correlate of human long-term potentiation (LTP) is associated with the 5-HTT genotype

The purpose of the present study was to examine how genetic variability in the promoter of the SLC6A4 gene encoding the serotonin transporter (5-HTT) may influence induction of long-term potentiation (LTP). The genotyping of the 53 healthy volunteers was performed by a combination of TaqMan assay and gel electrophoresis. Based on the transcription rates, the subjects were divided in 3 groups; 5-HTT SS, 5-HTT SLG/LALG/SLA and 5-HTT LALA. The intensity of pain to test stimuli was rated on a visual analog scale (VAS). High frequency stimulation (HFS) conditioning applied to one arm was used to induce LTP. Only a minor change in pain was observed following the HFS conditioning evoked by electrical test stimuli delivered through the conditioning electrode. Moreover, the change in pain evoked by test stimuli delivered through the conditioning electrode was not related to the 5-HTT genotype. However, we observed a clear increase in pain following the HFS conditioning evoked by mechanical pin-prick test stimuli delivered at the skin adjacent to the conditioning. Also, the 9 individuals with the 5-HTT SS genotype reported more pain than individuals with 5-HTT SLG/LALG/SLA genotype following HFS conditioning on mechanical pin-prick test stimuli. Thus, the present data show that induction of the perceptual correlate of human LTP is associated with the genetic variability in the gene encoding the 5-HTT. Taken together, this suggests that the expression of 5-HTT, may be important for induction of LTP in humans.

Spinal long‐term potentiation is associated with reduced opioid neurotransmission in the rat brain

Neuronal events leading to development of long-term potentiation (LTP) in the nociceptive pathways may be a cellular mechanism underlying hyperalgesia. In the present study, we examine if induction of spinal LTP may be associated with functional changes in the supraspinal opioidergic system. The opioid receptors (ORs) play a key role in nociceptive processing and controlling the descending modulatory system to the spinal cord. Spinal LTP was induced by electrical high-frequency stimulation (HFS) conditioning applied to the sciatic nerve, and the excitability at spinal level was verified by spinal field potential recordings. To study supraspinal changes in opioid neurotransmission following the same HFS conditioning, we used small animal positron emission tomography (PET) and [(11)C]Phenethyl-Orvinol ([(11)C]PEO). All rats included in the PET study were scanned at baseline and 150 min after HFS, and specific binding was calculated with a reference tissue model. A clear C-fibre LTP, i.e. increased C-fibre response and reduced C-fibre threshold, was observed 150 min after HFS conditioning (t-test, P<0.05, n = 6). Moreover, increased OR binding, relative to baseline, was observed after the same type of HFS conditioning ipsilaterally in the amygdala, hippocampus, somatosensory cortex and superior colliculus, and bilaterally in the nucleus accumbens, caudate putamen and hypothalamus (paired t-test, HFS>baseline, P<0.05, n = 8). HFS conditioning of the sciatic nerve resulted in both spinal LTP and functional changes in supraspinal opioidergic signalling. Our findings suggest that induction of spinal LTP may be associated with reduced opioid neurotransmission in brain regions involved in pain modulation and affective-emotional responses.

Spinal cord long-term potentiation (LTP) is associated with increased dorsal horn gene expression of IL-1β, GDNF and iNOS

Previous data show that spinal cord long-term potentiation (LTP) can be induced by electrical high-frequency stimulation (HFS) conditioning applied to the sciatic nerve. It has been suggested that the cellular events leading to this form of plasticity may contribute to central hyperalgesia. In the present study, extracellular recordings from single dorsal horn neurons and quantitative real-time reverse-transcriptase polymerase chain reaction (RT-PCR) on rat dorsal horn tissue were used to examine whether maintenance of spinal LTP is associated with changes in gene expression of the proinflammatory interleukin-1β (IL-1β), glial cell-line derived neurotrophic factor (GDNF), inducible nitric oxide synthase (iNOS), p38 mitogen-activated protein kinase (p38 MAPK), cyclooxygenase 2 (COX2) and tumor necrosis factor α (TNFα). The data demonstrated that the HFS conditioning induced a robust increase in the dorsal horn C-fibre responses, which outlasted the duration of the experiments of 6 h ( p < 0.05, HFS vs. control). Moreover, a significant increase in the expression of mRNA for IL-1β, GDNF and iNOS were observed 6 h following the HFS conditioning ( p < 0.05, HFS vs. control). For the first time we show that spinal cord LTP is associated with an increased dorsal horn expression of the genes for IL-1β, GDNF and iNOS.

Spinal cord long‐term potentiation is attenuated by the NMDA‐2B receptor antagonist Ro 25‐6981

The NR2B-containing N-methyl-d-aspartate (NMDA) receptors may be involved in a variety of phenomena including synaptic plasticity, memory formation and pain perception. Here we used the NMDA-2B receptor antagonist Ro 25-6981 to investigate the role of the NR2B-containing NMDA receptors in spinal nociception. Extracellular single unit recordings were performed from dorsal horn wide dynamic range (WDR) neurones in intact urethane-anaesthetized Sprague-Dawley rats. The responses of the WDR neurones evoked by C-fibre activation after sciatic nerve stimulation were defined according to latencies. To block the dorsal horn NMDA-2B receptors, the antagonist Ro 25-6981 was applied topically onto the spinal cord. High-frequency stimulation (HFS) of the sciatic nerve was used to induce spinal long-term potentiation (LTP). Spinal administration of the NMDA-2B receptor antagonist Ro 25-6981 had a clear antinociceptive effect at the spinal level (P < 0.05, C-fibre evoked responses after 4 mm Ro 25-6981 vs. C-fibre evoked responses in baseline). Moreover, spinal administration of this antagonist clearly attenuated the magnitude of spinal cord LTP after HFS conditioning (P < 0.05, C-fibre evoked responses after HFS vs. C-fibre evoked responses after 8 mm Ro 25-6981 + HFS). The present study indicates that expression of full LTP in dorsal horn neurones obtained by HFS conditioning may be dependent on the NMDA receptors containing the NR2B subunit. This suggests that activation of dorsal horn NR2B-containing NMDA receptors may be involved in use-dependent sensitization at the spinal level.

P.1.a.004 The association of promotor polymorphism in synapsin III gene with schizophrenia

The purpose of the present study was to examine how genetic variability in the promoter of the SLC6A4 gene encoding the serotonin transporter (5-HTT) may influence induction of long-term potentiation (LTP). The genotyping of the 53 healthy volunteers was performed by a combination of TaqMan assay and gel electrophoresis. Based on the transcription rates, the subjects were divided in 3 groups; 5-HTT SS, 5-HTT SLG/LALG/SLA and 5-HTT LALA. The intensity of pain to test stimuli was rated on a visual analog scale (VAS). High frequency stimulation (HFS) conditioning applied to one arm was used to induce LTP. Only a minor change in pain was observed following the HFS conditioning evoked by electrical test stimuli delivered through the conditioning electrode. Moreover, the change in pain evoked by test stimuli delivered through the conditioning electrode was not related to the 5-HTT genotype. However, we observed a clear increase in pain following the HFS conditioning evoked by mechanical pin-prick test stimuli delivered at the skin adjacent to the conditioning. Also, the 9 individuals with the 5-HTT SS genotype reported more pain than individuals with 5-HTT SLG/LALG/SLA genotype following HFS conditioning on mechanical pin-prick test stimuli. Thus, the present data show that induction of the perceptual correlate of human LTP is associated with the genetic variability in the gene encoding the 5-HTT. Taken together, this suggests that the expression of 5-HTT, may be important for induction of LTP in humans.

Diagnosis of ascites

Astrocyte expression of metabotropic glutamate receptor 5 (mGluR5) is consistently observed in resected tissue from patients with epilepsy and is equally prevalent in animal models of epilepsy. However, little is known about the functional signaling properties or downstream consequences of astrocyte mGluR5 activation during epilepsy development. In the rodent brain, astrocyte mGluR5 expression is developmentally regulated and confined in expression/function to the first weeks of life, with similar observations made in human control tissue. Herein, we demonstrate that mGluR5 expression and function dramatically increase in a mouse model of temporal lobe epilepsy (TLE). Interestingly, in both male and female mice, mGluR5 function persists in the astrocyte throughout the process of epileptogenesis following status epilepticus. However, mGluR5 expression and function is transient in animals that do not develop epilepsy over an equivalent time period, suggesting that patterns of mGluR5 expression may signify continuing epilepsy development or its resolution. We demonstrate that during epileptogenesis, astrocytes re-acquire mGluR5-dependent calcium transients following agonist application or synaptic glutamate release—a feature of astrocyte-neuron communication absent since early development. Finally, we find that the selective and conditional knockout of mGluR5 signaling from astrocytes during epilepsy development slows the rate of glutamate clearance through astrocyte glutamate transporters under high-frequency stimulation conditions, a feature that suggests astrocyte mGluR5 expression during epileptogenesis may recapitulate earlier developmental roles in regulating glutamate transporter function. <b>SIGNIFICANCE STATEMENT</b> In development, astrocyte mGluR5 signaling plays a critical role in regulating structural and functional interactions between astrocytes and neurons at the tripartite synapse. Notably, mGluR5 signaling is a positive regulator of astrocyte glutamate transporter expression and function—an essential component of excitatory signaling regulation in hippocampus. After early development, astrocyte mGluR5 expression is downregulated, but re-emerges in animal models of TLE development and patient epilepsy samples. We explored the hypothesis that astrocyte mGluR5 re-emergence recapitulates earlier developmental roles during TLE acquisition. Our work demonstrates that astrocytes with mGluR5 signaling during TLE development perform faster glutamate uptake in hippocampus, revealing a previously unexplored role for astrocyte mGluR5 signaling in hypersynchronous pathology.