Glutamate Receptor Blockers Research Articles

Prospects for the use of perampanel in the treatment of epilepsy in patients with malignant gliomas of the brain

Epilepsy occurs in 35-95% of patients with malignant cerebral gliomas of low malignancy and in 29-71% of patients with gliomas of high malignancy. Seizures can be both the first manifestation of malignant cerebral glioma and appear in the postoperative period and during chemoradiotherapy. This requires the use of antiepileptic drugs, which should control the seizure syndrome, provide control and secondary prevention of seizures, without reducing the response of anti-tumour therapy and the the patient QoL. The processes of epileptogenesis and oncogenesis are closely interrelated through common developmental mechanisms in which glutamate plays a key role. Hypersecretion of glutamate is accompanied by increased expression and activation of its receptors, which increases convulsive readiness. This is accompanied by increased level of brain neurotrophic growth factor, the number of synapses between peritumoral neurons and glioma cells, and increased expression of a number of growth factors, which contributes to tumourous proliferation. In this regard, special attention when treating epilepsy in patients with malignant cerebral gliomas is given to perampanel, a glutamate receptor blocker, a 3rd generation antiepileptic drug. The findings show that perampanel not only effectively controls seizures in patients with malignant cerebral gliomas, but also suppresses tumourous proliferation. Perampanel is able to dose-dependently enhance apoptosis and disrupt cell migration in malignant glioma cell lines. The findings have revealed synergistic effect of perampanel in combination with temozolamide. In conditions of chemoradiation therapy perampanel has a protective effect on healthy peritumoral tissues. Undesirable drug reactions during the use of perampanel are infrequent and insignificant. Additional studies are needed to further research the anticonvulsant and antitumour efficacy of perampanel to treat epilepsy in patients with malignant brain tumours.

Acute lipopolysaccharide (LPS)-induced cell membrane hyperpolarization is independent of voltage gated and calcium activated potassium channels

The gram-negative toxin lipopolysaccharides (LPS) are known to trigger inflammatory cytokines in mammals, which can result in pathological responses. Upon treatment of bacterial sepsis with antibiotics, the lysing bacteria can present a surge in LPS, inducing a cytokine storm. However, LPS can also have direct cellular effects, including transient rapid hyperpolarizing of the membrane potential, blocking glutamate receptors and even promoting release of glutamate. The detailed mechanism of action for these immediate responses is still unresolved. In addressing the membrane hyperpolarization, voltage gated K+ channel blockers 4-aminopyridine (4-AP, 3 mM), quinidine hydrochloride monohydrate (0.1 mM) and tetraethylammonium (TEA, 20 mM) were examined along with RNAi knockdowns of potential calcium activated K+ channels. The immediate responses of LPS were not blocked. Even in the presence of glutamate, the membrane still hyperpolarizes with LPS. When the driving gradient for the ionotropic glutamate receptors is enhanced during hyperpolarization, spontaneous quantal responses are dampened in amplitude. Thus, glutamate receptors are blocked, and the mechanism of hyperpolarization remains unresolved. The larval Drosophila glutamatergic neuromuscular junction is used as a model synaptic preparation to address the direct rapid actions by LPS.

Newly Synthesized Indolylacetic Derivatives Reduce Tumor Necrosis Factor-Mediated Neuroinflammation and Prolong Survival in Amyotrophic Lateral Sclerosis Mice.

The debilitating neurodegenerative disease known as amyotrophic lateral sclerosis (ALS) is characterized by the progressive loss of motor neurons (MNs) in the brain, spinal cord, and motor cortex. The ALS neuroinflammatory component is being characterized and includes the overexpression of mediators, such as inducible nitric oxide synthase (iNOS) and tumor necrosis factor-α (TNF-α). Currently, there are no effective treatments for ALS. Indeed, riluzole, an N-methyl-D-aspartate (NMDA) glutamate receptor blocker, and edaravone, a reactive oxygen species (ROS) scavenger, are currently the sole two medications approved for ALS treatment. However, their efficacy in extending life expectancy typically amounts to only a few months. In order to improve the medicaments for the treatment of neurodegenerative diseases, preferably ALS, novel substituted 2-methyl-3-indolylacetic derivatives (compounds II-IV) were developed by combining the essential parts of two small molecules, namely, the opioids containing a 4-piperidinyl ring with indomethacin, previously shown to be efficacious in different experimental models of neuroinflammation. The synthesized compounds were evaluated for their potential capability of slowing down neurodegeneration associated with ALS progression in preclinical models of the disease in vitro and in vivo. Notably, we produced data to demonstrate that the treatment with the newly synthesized compound III: (1) prevented the upregulation of TNF-α observed in BV-2 microglial cells exposed to the toxin lipopolysaccharides (LPS), (2) preserved SHSY-5Y cell survival exposed to β-N-methylamino-l-alanine (L-BMAA) neurotoxin, and (3) mitigated motor symptoms and improved survival rate of SOD1G93A ALS mice. In conclusion, the findings of the present work support the potential of the synthesized indolylacetic derivatives II-IV in ALS treatment. Indeed, in the attempt to realize an association between two active molecules, we assumed that the combination of the indispensable moieties of two small molecules (the opioids containing a 4-piperidinyl ring with the FANS indomethacin) might lead to new medicaments potentially useful for the treatment of amyotrophic lateral sclerosis.

Excitotoxic Storms of Ischemic Stroke: A Non-neuronal Perspective.

Numerous neurological disorders share a fatal pathologic process known as glutamate excitotoxicity. Among which, ischemic stroke is the major cause of mortality and disability worldwide. For a long time, the main idea of developing anti-excitotoxic neuroprotective agents was to block glutamate receptors. Despite this, there has been little successful clinical translation to date. After decades of "neuron-centered" views, a growing number of studies have recently revealed the importance of non-neuronal cells. Glial cells, cerebral microvascular endothelial cells, blood cells, and so forth are extensively engaged in glutamate synthesis, release, reuptake, and metabolism. They also express functional glutamate receptors and can listen and respond for fast synaptic transmission. This broadens the thoughts of developing excitotoxicity antagonists. In this review, the critical contribution of non-neuronal cells in glutamate excitotoxicity during ischemic stroke will be emphasized in detail, and the latest research progress as well as corresponding therapeutic strategies will be updated at length, aiming to reconceptualize glutamate excitotoxicity in a non-neuronal perspective.

Alzheimer's disease: diagnosis and treatment, errors in patient management

Alzheimer's disease (AD) is the most common degenerative disease of the brain leading to dementia. AD is the most common cause of disability among age-related diseases. The diagnosis of AD is based on clinical findings and is confirmed by the presence of positive biological markers of the disease, which reflect the pathological formation of beta-amyloid and tau protein in the brain. Magnetic resonance imaging of the brain shows brain atrophy in AD and helps to rule out other diseases. Psychosocial and behavioral approaches form the basis for the treatment of patients with AD; cognitive training in combination with regular physical exercise is recommended. Acetylcholinesterase inhibitors and the glutamate receptor blocker memantine are used as drugs that improve the cognitive functions of patients with AD. Dispersible forms of memantine are used to treat dysphagia in patients with AD. The efficacy and safety of pathogenetic therapy aimed at eliminating cerebral beta-amyloid by passive immunization is under discussion. Unfortunately, AD is rarely diagnosed in our country; doctors are not sufficiently informed about the diagnosis and modern treatment methods of AD. Many AD patients are observed with the misdiagnosis of chronic cerebrovascular disease and do not receive effective therapy. A clinical observation of a patient with early-onset AD is presented, reflecting typical errors in patient management. Issues for optimizing the management of AD patients are discussed.

TRPM4 blocking antibody reduces neuronal excitotoxicity by specifically inhibiting glutamate-induced calcium influx under chronic hypoxia

Excitotoxicity arises from unusually excessive activation of excitatory amino acid receptors such as glutamate receptors. Following an energy crisis, excitotoxicity is a major cause for neuronal death in neurological disorders. Many glutamate antagonists have been examined for their efficacy in mitigating excitotoxicity, but failed to generate beneficial outcome due to their side effects on healthy neurons where glutamate receptors are also blocked. In this study, we found that during chronic hypoxia there is upregulation and activation of a nonselective cation channel TRPM4 that contributes to the depolarized neuronal membrane potential and enhanced glutamate-induced calcium entry. TRPM4 is involved in modulating neuronal membrane excitability and calcium signaling, with a complex and multifaceted role in the brain. Here, we inhibited TRPM4 using a newly developed blocking antibody M4P, which could repolarize the resting membrane potential and ameliorate calcium influx upon glutamate stimulation. Importantly, M4P did not affect the functions of healthy neurons as the activity of TRPM4 channel is not upregulated under normoxia. Using a rat model of chronic hypoxia with both common carotid arteries occluded, we found that M4P treatment could reduce apoptosis in the neurons within the hippocampus, attenuate long-term potentiation impairment and improve the functions of learning and memory in this rat model. With specificity to hypoxic neurons, TRPM4 blocking antibody can be a novel way of controlling excitotoxicity with minimal side effects that are common among direct blockers of glutamate receptors.

Mechanisms of initiation of cortical spreading depression

BackgroundThere is increasing evidence from human and animal studies that cortical spreading depression (CSD) is the neurophysiological correlate of migraine aura and a trigger of migraine pain mechanisms. The mechanisms of initiation of CSD in the brain of migraineurs remain unknown, and the mechanisms of initiation of experimentally induced CSD in normally metabolizing brain tissue remain incompletely understood and controversial. Here, we investigated the mechanisms of CSD initiation by focal application of KCl in mouse cerebral cortex slices.MethodsHigh KCl puffs of increasing duration up to the threshold duration eliciting a CSD were applied on layer 2/3 whilst the membrane potential of a pyramidal neuron located very close to the site of KCl application and the intrinsic optic signal were simultaneously recorded. This was done before and after the application of a specific blocker of either NMDA or AMPA glutamate receptors (NMDARs, AMPARs) or voltage-gated Ca2+ (CaV) channels. If the drug blocked CSD, stimuli up to 12–15 times the threshold were applied.ResultsBlocking either NMDARs with MK-801 or CaV channels with Ni2+ completely inhibited CSD initiation by both CSD threshold and largely suprathreshold KCl stimuli. Inhibiting AMPARs with NBQX was without effect on the CSD threshold and velocity. Analysis of the CSD subthreshold and threshold neuronal depolarizations in control conditions and in the presence of MK-801 or Ni2+ revealed that the mechanism underlying ignition of CSD by a threshold stimulus (and not by a just subthreshold stimulus) is the CaV-dependent activation of a threshold level of NMDARs (and/or of channels whose opening depends on the latter). The delay of several seconds with which this occurs underlies the delay of CSD initiation relative to the rapid neuronal depolarization produced by KCl.ConclusionsBoth NMDARs and CaV channels are necessary for CSD initiation, which is not determined by the extracellular K+ or neuronal depolarization levels per se, but requires the CaV-dependent activation of a threshold level of NMDARs. This occurs with a delay of several seconds relative to the rapid depolarization produced by the KCl stimulus. Our data give insights into potential mechanisms of CSD initiation in migraine.

Reducing of the respiratory effects of dizocilpine by recombinant interleukin-1β in experiment

BACKGROUND: For a deeper understanding of the pathogenesis of COVID-19, it is necessary to study the mechanisms that implement the influence of pro-inflammatory cytokines on the processes of regulation of the external respiratory system. In experiments on anesthetized rats, the effect of the pro-inflammatory cytokine interleukin-1 on the respiratory effects of dizocilpine (MK-801), which has an inhibitory effect on neurotransmitter systems involved in the control of the respiratory system, was studied. It was considered that, first of all, dizocilpine is a highly effective non-competitive NMDA-type glutamate receptor blocker.
 AIM: The objectives of the study were to identify the effect of the influence of dizocilpine on the parameters of the breathing pattern and to assess the degree of change in this effect when dizocilpine was administered against the background of an elevated systemic level of interleukin-1.
 MATERIALS AND METHODS: The study was performed on 24 anesthetized tracheostomy spontaneously breathing rats. To register the volume-time parameters of external respiration, a pneumotachographic technique was used. In the process of processing the obtained results, the value of the recorded parameter was determined immediately before the introduction of MK-801 and 1 min after its introduction
 RESULTS: At a dosage of 0.1 mg/kg, dizocilpine was found to cause a reversible short-term decrease in respiratory rate, tidal volume, and minute respiratory volume. It has been shown that this effect of dizocilpine does not appear after intravenous administration of interleukin-1 (at a dosage of 2 g/kg). The results obtained confirm the assumption about the effect of an elevated systemic level of interleukin-1 on the state of neurotransmitter systems involved in the control of respiration.
 CONCLUSIONS: Based on the correlation of the obtained results with the literature data, an assumption was made about a change in the state of NMDA-type glutamate receptors under the influence of pro-inflammatory cytokines, which may be one of the mechanisms of cardiorespiratory dysfunctions observed in a systemic inflammatory reaction accompanied by hypercytokinemia.

Hypothalamic PVN astrocytes fail to properly set glutamate tone in obese mice contributing to impaired glucose metabolism in this condition

The hypothalamus is key in the control of energy balance, but strategies targeting hypothalamic neurons have failed to provide viable options to treat most metabolic diseases. Conversely, the role of astrocytes in systemic metabolic control has remained largely unexplored. Here, we show that obesity promotes anatomically restricted exacerbated Ca 2+ activity in hypothalamic paraventricular nucleus (PVN) astrocytes. Bidirectional chemogenetic manipulation of astrocyte Ca 2+ activity in lean mice stimulated or inhibited the activity of neighboring parvocellular neurons. Importantly, these effects translated into bidirectional regulation of sympathetic activity, glucose metabolism, and energy balance. We found that the astrocyte-mediated effects on PVN neurons were blocked by the glutamate receptor blocker kynurenic acid, and the astrocyte glutamate transport blocker TBOA, suggesting that the astrocyte-neuron signaling and the effects on glucose metabolism involved the astrocytic control of ambient glutamate levels. Notably, we found that TBOA alone stimulated neurons in lean mice but failed to evoke a response in obese mice. This suggests that the astrocyte glutamate transporter activity is impaired in obese mice. Finally, we found that chemogenetic inhibition of astrocyte Ca 2+ activity in obese mice improved glucose metabolism in this condition. Together, our results indicate that exacerbated astrocyte Ca 2+ activity leads to impaired glutamate transporter activity, standing as a likely mechanism contributing to altered PVN neuronal activity and glucose homeostasis during this condition. Collectively, these findings highlight a yet unappreciated role for astrocytes in the direct control of systemic metabolism and suggest potential targets for anti-obesity strategy. NHLBI F32 HL158172 (MKK) NHLBI HL090948 (JES) NINDS NS094640 (JES) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Management of patients with cognitive impairment

The management of patients with cognitive impairment (CI) is one of the urgent problems of modern medicine. Issues of diagnostics and therapy of patients with CI and their high mortality during the period of coronavirus infection are discussed. A wide prevalence of patients with mild CI (MCI), an important role of neuropsychological research in establishing CI, and frequent diagnosis of CI only at the stage of dementia were noted. In our country, CI is poorly diagnosed, the most common cause of CI in the elderly – Alzheimer's disease (AD) – is rarely established, patients are observed for a long time with a diagnosis of cerebrovascular disease (CVD). Some non-drug and drug methods can reduce the manifestations of CI, improve the quality of life of both the patients themselves and those around them. In severe CI, socio-psychological methods, stimulating patients to feasible household and social, physical and mental activity, and avoiding prolonged hospitalization are of primary importance. In addition to lifestyle changes, much attention in CI is given to the prevention of stroke, the treatment of arterial hypertension and diabetes mellitus. At the stage of dementia, cholinomimetic drugs (acetylcholinesterase inhibitors, donepezil, rivastigmine, galantamine) and the glutamate receptor blocker memantine are used. The use of choline alfoscerate in CI and the results of the multicenter, placebo-controlled ASCOMALVA study are discussed, in which, in patients with AD and CVD, the addition of choline alfoscerate to donepezil reduced the severity of CI, manifestations of depression, anxiety, and apathy. A new oral form of choline alfoscerate (Cerpechol) is reported that may improve patient compliance and be used in patients with swallowing disorders.

Застосування амантадину при хворобі Паркінсона, паркінсонізмі та ускладненнях терапії леводопою

У статті подано науковий огляд сучасних уявлень про роль блокаторів глутаматних (NMDA) рецепторів у патогенезі та лікуванні хвороби Паркінсона, паркінсонічних синдромів і дискінетичних розладів як ускладнень леводопатерапії. Найбільша увага приділяється механізму дії, можливостям і перевагам застосування амантадину.

Electrophysiological and pharmacological characterization of spreading depolarization in the adult zebrafish tectum.

Spreading depolarization (SD) is a slowly propagating wave of neuronal and glial depolarization. A growing number of studies show that SD and SD-like phenomena play a role in neurological disorders such as migraine, stroke, and traumatic brain injury. Despite the clinical importance of SD, its underlying molecular and cellular mechanisms remain elusive, possibly because of insufficient animal model allowing genetic manipulation. Such a model would also allow high-throughput screening for SD-suppressing drug development. To address this, we developed a novel experimental system to study SD using zebrafish. Electrophysiological recordings in the immobilized adult zebrafish revealed that increasing extracellular potassium concentration elicited SD with a large and long-lasting negative shift of direct current (DC) potential in the optic tectum. It also reduced the oscillatory activity in the extracellular field potential and increased the expression of the immediate early gene c-fos. Pharmacological blocking of the N-methyl-d-aspartate (NMDA) glutamate receptor attenuated the propagation of SD, suggesting that glutamatergic neurotransmission mediated tectal SD in zebrafish. Our analyses revealed that the zebrafish tectum and rodent cortex had similar SD kinetics. The current study provides electrophysiological and pharmacological evidence that zebrafish SD and mammal SD are comparable. This zebrafish SD model is suitable for genetic manipulation and cost-effective high-throughput screening. It could pave the way to novel diagnostic and therapeutic methods applicable to SD-associated neurological disorders.NEW & NOTEWORTHY Previous studies have implicated spreading depolarization (SD) in stroke and migraine. Here, we demonstrate SD, for the first time, in the adult zebrafish tectum showing waveform kinetics, c-fos expression, and attenuation by N-methyl-d-aspartate glutamate receptor blocker as observed in the rodent cortex. Since the zebrafish is an animal model amenable to genetic manipulation and chemical screening, this result could pave the way to novel diagnostic and therapeutic methods applicable to SD-associated neurological disorders.

Chronic Ethanol Exposure Enhances Facial Stimulation-Evoked Mossy Fiber-Granule Cell Synaptic Transmission via GluN2A Receptors in the Mouse Cerebellar Cortex.

Sensory information is transferred to the cerebellar cortex via the mossy fiber–granule cell (MF–GC) pathway, which participates in motor coordination and motor learning. We previously reported that chronic ethanol exposure from adolescence facilitated the sensory-evoked molecular layer interneuron–Purkinje cell synaptic transmission in adult mice in vivo. Herein, we investigated the effect of chronic ethanol exposure from adolescence on facial stimulation-evoked MF–GC synaptic transmission in the adult mouse cerebellar cortex using electrophysiological recording techniques and pharmacological methods. Chronic ethanol exposure from adolescence induced an enhancement of facial stimulation-evoked MF–GC synaptic transmission in the cerebellar cortex of adult mice. The application of an N-methyl-D-aspartate receptor (NMDAR) antagonist, D-APV (250 μM), induced stronger depression of facial stimulation-evoked MF–GC synaptic transmission in chronic ethanol-exposed mice compared with that in control mice. Chronic ethanol exposure-induced facilitation of facial stimulation evoked by MF–GC synaptic transmission was abolished by a selective GluN2A antagonist, PEAQX (10 μM), but was unaffected by the application of a selective GluN2B antagonist, TCN-237 (10 μM), or a type 1 metabotropic glutamate receptor blocker, JNJ16259685 (10 μM). These results indicate that chronic ethanol exposure from adolescence enhances facial stimulation-evoked MF–GC synaptic transmission via GluN2A, which suggests that chronic ethanol exposure from adolescence impairs the high-fidelity transmission capability of sensory information in the cerebellar cortex by enhancing the NMDAR-mediated components of MF–GC synaptic transmission in adult mice in vivo.

Emergence of functional neuromuscular junctions in an engineered, multicellular spinal cord-muscle bioactuator.

Three-dimensional (3D) biomimetic systems hold great promise for the study of biological systems in vitro as well as for the development and testing of pharmaceuticals. Here, we test the hypothesis that an intact segment of lumbar rat spinal cord will form functional neuromuscular junctions (NMJs) with engineered, 3D muscle tissue, mimicking the partial development of the peripheral nervous system (PNS). Muscle tissues are grown on a 3D-printed polyethylene glycol (PEG) skeleton where deflection of the backbone due to muscle contraction causes the displacement of the pillar-like “feet.” We show that spinal cord explants extend a robust and complex arbor of motor neurons and glia in vitro. We then engineered a “spinobot” by innervating the muscle tissue with an intact segment of lumbar spinal cord that houses the hindlimb locomotor central pattern generator (CPG). Within 7 days of the spinal cord being introduced to the muscle tissue, functional neuromuscular junctions (NMJs) are formed, resulting in the development of an early PNS in vitro. The newly innervated muscles exhibit spontaneous contractions as measured by the displacement of pillars on the PEG skeleton. Upon chemical excitation, the spinal cord-muscle system initiated muscular twitches with a consistent frequency pattern. These sequences of contraction/relaxation suggest the action of a spinal CPG. Chemical inhibition with a blocker of neuronal glutamate receptors effectively blocked contractions. Overall, these data demonstrate that a rat spinal cord is capable of forming functional neuromuscular junctions ex vivo with an engineered muscle tissue at an ontogenetically similar timescale.

Sympathomotor activation by midbrain locomotor neurons is mediated through glutamate release in the rostral ventrolateral medulla

Our pilot data showed that a portion of neuronal cells in the mecencephalic locomotor region (MLR) sends axonal projections to the rostral ventrolateral medulla (RVLM) (MLR‐RVLM pathway), being capable of eliciting sympathomotor activation in rats. Here, we examined the effect of ionotropic glutamate receptor blockade in rat RVLM on sympathomotor activation by the MLR‐RVLM pathway. Male rats received microinjections bilaterally in the RVLM with a retrograde adeno‐associated virus that encoded a channelrhodopsin with green fluorescence protein. Under anesthesia, 473 nm wavelength laser illumination of the MLR after administration in the RVLM with a cocktail of AP5 and CNQX, NMDA and AMPA glutamate receptor blockers, respectively, elicited 29% less (P < 0.05) renal sympathoexcitation than that after saline administration. Likewise, under decerebration without anesthesia, ventral root fiber excitation in response to MLR photostimulation seen after saline administration in the RVLM was suppressed to a 35% extent (P < 0.05) by preliminarily administration of the glutamate receptor blockers. These observations suggest that glutamatergic neurons in the MLR‐RVLM pathway function in generating central command function.Support or Funding InformationSupported by JSPS KAKENHI 18H03151 (S. Koba).

Development of a high-throughput arrayed neural circuitry platform using human induced neurons for drug screening applications.

Proper brain function relies on the precise arrangement and flow of information between diverse neural subtypes. Developing improved human cell-based models which faithfully mimic biologically relevant connectivity patterns may improve drug screening efforts given the limited success of animal models to predict safety and efficacy of therapeutics in human clinical trials. To address this need, we have developed experimental models of defined neural circuitries through the compartmentalization of neuronal cell subtypes in a 96 well plate-based platform where each microwell is divided into two compartments connected by microchannels allowing high-throughput screening (HTS) of small molecules. We demonstrate that we can generate subtype-specific excitatory and inhibitory induced neuronal cells (iNs) from human stem cell lines and that these neurons form robust functional circuits with defined connectivity. Through the use of the genetically encoded calcium indicator GCaMP6f, we monitor calcium ion transients generated during neuronal firing between and within compartments. We further demonstrate functionality of the circuit by perturbing network activity through the addition of glutamate receptor blockers using automated liquid handling. Lastly, we show that we can stimulate network activity in defined neuronal subtypes through the expression of the designer receptor exclusively activated by designer drugs (DREADD) hM3Dq and application of the ligand clozapine-N-oxide (CNO). Our results demonstrate the formation of functional neural circuits in a high-throughput platform that is compatible with compound screening, representing an important step towards developing new screening platforms for studying and ultimately treating psychiatric brain disorders that arise from disordered neural circuit function.

Intraoperative Ketamine in Total Knee Arthroplasty Does Not Decrease Pain and Narcotic Consumption: A Prospective Randomized Controlled Trial

BackgroundMultiple studies have demonstrated that ketamine, a glutamate receptor blocker, may decrease postoperative pain in abdominal and orthopedic surgeries. However, its role with spinal anesthesia and total knee arthroplasty (TKA) remains unknown. The purpose of this study is to determine the efficacy of subanesthetic dosing of ketamine during TKA on postoperative pain and narcotic consumption. MethodsIn this prospective, randomized, double-blinded clinical trial, we enrolled 91 patients undergoing primary TKA with spinal anesthesia in a single institution from 2017 to 2018. Patients were randomized to receive intraoperative ketamine infusion at a rate of 6 mcg/kg/min for 75 minutes or a saline placebo. All patients received spinal anesthesia and otherwise identical surgical approaches, pain management, and rehabilitation protocols. Patient-reported visual analog pain scores were calculated preoperatively, postoperative days (POD) 0-7, and 2 weeks. Narcotic consumption was evaluated on POD 0 and 1. ResultsThere was no difference in average pain between ketamine and placebo at all time points except for at PODs 1 (45 vs 56, P = .041) and 4 (39 vs 49, P = .040). For least pain experienced, patients administered with ketamine experienced a reduction in pain only at POD 4 (22 vs 35, P = .011). There was no difference in maximum pain cohorts at all time points of the study or in-hospital morphine equivalents between the 2 cohorts. ConclusionAs part of multimodal pain management protocol, intraoperative ketamine does not result in a clinically significant improvement in pain and narcotic consumption following TKA.

Central Circuits Inhibiting Skeletal Muscle Shivering

BackgroundSkeletal muscle shivering is the most important source of thermogenesis in the human cold‐defensive maintenance of core body temperature (Tcore) and the elevated Tcore during fever. We have described the thermoregulatory reflex pathway through which skin and core cooling, or injection of prostaglandin E2 into the preoptic area of the hypothalamus, leads to activation of skeletal muscle shivering (J Physiol 589.14: 3641–3658, 2011). Here we describe brain regions containing neurons that can provide an inhibitory regulation of shivering.ResultsEMG activities in masseter, neck and gastrocnemius muscles were recorded in Inactin‐anesthetized rats during cold exposure or injection of PGE2 into the preoptic hypothalamus. Cold‐evoked and febrile shivering EMGs were eliminated by activation of neurons in the ventral part of the lateral preoptic nucleus (vLPO), or by increasing the discharge of neurons in the paraventricular hypothalamus, in the nucleus of the tractus solitarii, or in the ventrolateral medulla. Inhibiting neuronal discharge or blocking glutamate receptors in the vLPO elicited a sustained increase in shivering EMGs in warm rats.ConclusionThese results indicate the strong, tonic inhibitory influence of neurons in the vLPO on skeletal muscle shivering, likely through a GABAergic input to shivering premotor neurons in the rostral raphe pallidus. The discovery of the vLPO and other neuronal populations capable of inhibiting shivering supports the potential for the therapeutic control of shivering in the settings of neurogenic fever, brain injury, or induction of hypothermia.Support or Funding InformationSupported by NIH grants NS040987 and NS091066This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The role of the deeper layers of the superior colliculus in attentional modulations of prepulse inhibition

Prepulse inhibition (PPI) is the suppression of the startle reflex, when a weaker non-startling sensory stimulus (the prepulse) precedes the intense startling stimulus. Although the basic PPI neural circuitry resides in the brainstem, PPI can be enhanced by selective attention to the prepulse, indicating that this sensorimotor-gating process is influenced by higher-order perceptual/cognitive processes. Along with the auditory cortex, the brain structures involved in attentional modulations of PPI include both the lateral nucleus of the amygdala (LA), which contributes to the fear-conditioning modulation, and the posterior parietal cortex (PPC), which contributes to the spatially attentional modulation. The deeper layers of the superior colliculus (DpSC), which has been suggested as a midbrain component in the PPI circuitry, receive descending axonal projections from some forebrain structures associated with auditory perception, emotional conditioning, or spatial attention. This study was to examine whether the DpSC are also involved in attentional modulations of PPI in rats. The results showed that both fear conditioning of a prepulse sound and precedence-effect-induced perceptual separation between the conditioned prepulse and a noise masker facilitated selective attention to the prepulse and consequently enhanced PPI. Reversibly blocking glutamate receptors in the DpSC with 2-mM kynurenic acid eliminated both the conditioning-induced and the perceptual-separation-induced PPI enhancements. However, the baseline magnitudes of startle and PPI were not affected. The results suggest that the DpSC play a role in mediating the attentional enhancements of PPI, probably through both receiving top-down signals from certain forebrain structures and modulating the midbrain representations of prepulse signals.

Sympathoexcitation by hypothalamic paraventricular nucleus neurons projecting to the rostral ventrolateral medulla.

Causal relationships between central cardiovascular pathways and sympathetic vasomotor tone have not been evidenced. This study aimed to verify the sympathoexcitatory role of hypothalamic paraventricular nucleus neurons that project to the rostral ventrolateral medulla (PVN-RVLM neurons). By using optogenetic techniques, we demonstrated that stimulation of PVN-RVLM glutamatergic neurons increased renal sympathetic nerve activity and arterial pressure via, at least in part, stimulation of RVLM C1 neurons in rats. This monosynaptic pathway may function in acute sympathetic adjustments to stressors and/or be a component of chronic sympathetic hyperactivity in pathological conditions such as heart failure. The rostral ventrolateral medulla (RVLM), which is known to play an important role in regulating sympathetic vasomotor tone, receives axonal projections from the hypothalamic paraventricular nucleus (PVN). However, no studies have proved that excitation of the PVN neurons that send axonal projections to the RVLM (PVN-RVLM neurons) causes sympathoexcitation. This study aimed to directly examine the sympathoexcitatory role of PVN-RVLM neurons. Male rats received microinjections into the PVN with an adeno-associated virus (AAV) vector that encoded a hybrid of channelrhodopsin-2/1 with the reporter tdTomato (ChIEF-tdTomato), or into the RVLM with a retrograde AAV vector that encoded a channelrhodopsin with green fluorescent protein (ChR2-GFPretro ). Under anaesthesia with urethane and α-chloralose, photostimulation (473nm wavelength) of PVN-RVLM neurons, achieved by laser illumination of either RVLM of ChIEF-tdTomato rats (n= 8) or PVN of ChR2-GFPretro rats (n= 4), elicited significant renal sympathoexcitation. Immunofluorescence confocal microscopy showed that RVLM adrenergic C1 neurons of ChIEF-tdTomato rats were closely associated with tdTomato-labelled, PVN-derived axons that contained vesicular glutamate transporter 2. In another subset of anaesthetized ChIEF-tdTomato rats (n= 6), the renal sympathoexcitation elicited by photostimulation of the PVN was suppressed by administering ionotropic glutamate receptor blockers into the RVLM. These results demonstrate that excitation of PVN-RVLM glutamatergic neurons leads to sympathoexcitation via, at least in part, stimulation of RVLM C1 neurons.