Non-competitive N-methyl-D-aspartic Acid Research Articles

Efficacy and Safety of Remimazolam Tosilate Combined With Esketamine for Analgesic Sedation in Mechanically Ventilated ICU Patients: A Single-Arm Clinical Study Protocol.

IntroductionPatients in the intensive care unit (ICU) frequently experience increased heart rate, blood pressure, and respiration rate as a product of anxiety and restlessness about their condition and treatments. Analgesia and sedation commonly involve benzodiazepines or opioids that lead to respiratory suppression and other adverse reactions. Remimazolam tosilate is a short-acting GABAA receptor agonist with reduced cardiovascular and respiratory inhibition compared to other commonly used benzodiazepines. Esketamine is a non-competitive N-methyl-D-aspartic acid (NMDA) receptor inhibitor that inhibits hyperalgesia and prolongs postoperative analgesia. It also reduces postoperative pain, delirium, and the use and acute tolerance of opioids. This study aims to assess the efficacy and safety of remimazolam tosilate combined with esketamine and sufentanil for sedation and analgesia in mechanically ventilated ICU patients.Methods and AnalysisThis prospective, single-arm, single-center, open-label clinical trial will be conducted from January 2022 to December 2023. The study will include 200 adult patients (≥ 18 years) from Shandong Provincial Hospital (affiliated with Shandong First Medical University) who are mechanically ventilated and admitted to the ICU between 24 and 72 h from the time of ventilation and who are administered analgesia and sedatives. Patients will undergo arterial blood gas analysis before administration. Remimazolam tosilate (0.2 mg/kg) will be injected intravenously within 30 s, followed by continuous infusion at a rate of 0.1 to 0.3 mg/kg/h via micropump. Esketamine (0.25 mg/kg) will be injected intravenously and maintained at 0.15 mg/kg/h, while sufentanil will be maintained at the rate of 0.1 to 0.2 μg/kg/h. The primary study outcome is the overall time required to maintain sedation. Secondary outcomes will include the total dosage used to reach the target sedation level, total mechanical ventilation time, awakening time, length of hospital stay, and incidence of cardiorespiratory-related adverse events and delirium. Adverse events (AEs) will be reported regardless of their relationship to the experimental drugs. AEs associated with adverse drug reactions will be classified as “affirmative correlation,” “possible relevance,” and “unable to determine.” A paired t-test or Wilcoxon signed-rank test will be used to compare the changes of observed indexes before and after treatment. A P < 0.05 will be considered statistically significant.Ethics and DisseminationThis study was approved by the local ethics committee at Shandong Provincial Hospital affiliatied to Shandong First Medical University. The results of this trial will be disseminated in peer-reviewed journals and at scientific conferences.Trial RegistrationThe trial is registered at the Chinese Clinical Trial Registry: ChiCTR2100053106; date of registration: 2021-11-10.

Effects of the co-administration of MK-801 and clozapine on MiRNA expression profiles in rats.

MiRNAs are small, non-coding RNAs that can silence the expression of various target genes by binding their mRNAs and thus regulate a wide range of crucial bodily functions. However, the miRNA expression profile of schizophrenia after antipsychotic mediation is largely unknown. Non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonists such as MK-801 have provided useful animal models to investigate the effects of schizophrenia-like symptoms in rodent animals. Herein, the hippocampal miRNA expression profiles of Sprague-Dawley rats pretreated with MK-801 were examined after antipsychotic clozapine (CLO) treatment. Total hippocampal RNAs from three groups were subjected to next-generation sequencing (NGS), and bioinformatics analyses, including differential expression and enrichment analyses, were performed. Eight miRNAs were differentially expressed between the MK-801 and vehicle (VEH) control groups. Interestingly, 14 miRNAs were significantly differentially expressed between the CLO+MK-801 and MK-801 groups, among which rno-miR-184 was the most upregulated. Further analyses suggested that these miRNAs modulate target genes that are involved in endocytosis regulation, ubiquitin-mediated proteolysis, and actin cytoskeleton regulation and thus might play important roles in the pathogenesis of schizophrenia. Our results suggest that differentially expressed miRNAs play important roles in the complex pathophysiology of schizophrenia and subsequently impact brain functions.

Ketamine Alleviates Postoperative Depression-Like Symptoms in Susceptible Mice: The Role of BDNF-TrkB Signaling.

Patients are more likely to suffer from central nervous system (CNS) complications after anesthesia and surgery. However, postoperative depression (POD) has not yet received sufficient attentions, and its pathogenesis and therapeutic strategies remain poorly understood. We here aimed to investigate whether brain derived neurotrophic factor (BDNF)-tropomyosin-related kinase B (TrkB) signaling plays an important role in POD. BDNF-TrkB signaling was altered in brain and peripheral tissues, including medial prefrontal cortex (mPFC), hippocampus, liver, and muscle, among control, POD susceptible, and resilient groups. Additionally, we demonstrated that 7,8-dihydroxyflavone (7,8-DHF), a TrkB agonist, could exert its pharmacologic property to alleviate POD-like symptoms. More importantly, ketamine, a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, also has significant antidepressant effects in POD model, associating with the improving effects on levels of BDNF-TrkB signaling in brain and peripheral tissues. Interestingly, the beneficial effects of ketamine on POD-like symptoms are fully attenuated by a TrkB antagonist. These findings suggest that abnormal expressions of BDNF-TrkB signaling in brain and peripheral tissues are implicated in the pathogenesis of POD, and that therapeutic agents targeting BDNF-TrkB, particularly ketamine, could favor the beneficial effects for POD.

Risperidone Reverses the Downregulation of BDNF in Hippocampal Neurons and MK801-Induced Cognitive Impairment in Rats.

MK-801, also known as dizocilpine, is a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist that induces schizophrenia-like symptoms. Our previous study showed that brain-derived neurotrophic factor (BDNF) signaling was upregulated in cultured hippocampal astrocytes in response to MK-801. However, dysfunctional NMDA receptors are mainly expressed in neurons. The effects of MK-801 on neuron-derived BDNF expression and of risperidone on MK-801-induced cognitive impairment and changes in BDNF expression are unclear. To address this issue, we examined BDNF expression in the hippocampus of rats that received repeated injections of MK-801 (0.5 mg/kg body weight for 6 days) and in primary cultured hippocampal neurons incubated with 20 μM MK-801 for 24 h. BDNF expression and cognitive function were also evaluated in rats receiving intraperitoneal injections of risperidone (1 mg/kg body weight) once daily for 7 days and in hippocampal neurons incubated with 10 μM risperidone following MK801 treatment. MK-801 treatment decreased BDNF expression in the rat hippocampus as well as the expression and secretion of BDNF in hippocampal neurons in vitro. However, risperidone reversed the effects of MK801 on BDNF level and improved cognitive function in rats treated with MK801. These findings suggest that risperidone may alleviate cognitive impairment caused by MK801 via upregulation of BNDF signaling in the hippocampus.

Controversies of the Effect of Ketamine on Cognition.

Controversies of the Effect of Ketamine on Cognition.

Distinct effects of ketamine and acetyl l-carnitine on the dopamine system in zebrafish

Ketamine, a noncompetitive N-methyl-d-aspartic acid (NMDA) receptor antagonist is commonly used as a pediatric anesthetic. We have previously shown that acetyl L-carnitine (ALCAR) prevents ketamine toxicity in zebrafish embryos. In mammals, ketamine is known to modulate the dopaminergic system. NMDA receptor antagonists are considered as promising anti-depressants, but the exact mechanism of their function is unclear. Here, we measured the levels of dopamine (DA) and its metabolites, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the zebrafish embryos exposed to ketamine in the presence and absence of 0.5mM ALCAR. Ketamine, at lower doses (0.1–0.3mM), did not produce significant changes in DA, DOPAC or HVA levels in 52h post-fertilization embryos treated for 24h. In these embryos, tyrosine hydroxylase (TH) mRNA expression remained unchanged. However, 2mM ketamine (internal embryo exposure levels equivalent to human anesthetic plasma concentration) significantly reduced DA level and TH mRNA indicating that DA synthesis was adversely affected. In the presence or absence of 2mM ketamine, ALCAR showed similar effects on DA level and TH mRNA, but increased DOPAC level compared to control. ALCAR reversed 2mM ketamine-induced reduction in HVA levels. With ALCAR alone, the expression of genes encoding the DA metabolizing enzymes, MAO (monoamine oxidase) and catechol-O-methyltransferase (COMT), was not affected. However, ketamine altered MAO mRNA expression, except at the 0.1mM dose. COMT transcripts were reduced in the 2mM ketamine-treated group. These distinct effects of ketamine and ALCAR on the DA system may shed some light on the mechanism on how ketamine can work as an anti-depressant, especially at sub-anesthetic doses that do not affect DA metabolism and suppress MAO gene expression.

Reactive Transformation and Increased BDNF Signaling by Hippocampal Astrocytes in Response to MK-801.

MK-801, also known as dizocilpine, is a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist that induces schizophrenia-like symptoms. While astrocytes have been implicated in the pathophysiology of psychiatric disorders, including schizophrenia, astrocytic responses to MK-801 and their significance to schizotypic symptoms are unclear. Changes in the expression levels of glial fibrillary acid protein (GFAP), a marker of astrocyte activation in response to a variety of pathogenic stimuli, were examined in the hippocampus of rats treated with the repeated MK-801 injection (0.5 mg/10ml/kg body weight for 6 days) and in primary cultured hippocampal astrocytes incubated with MK-801 (5 or 20 μM for 24 h). Moreover, the expression levels of BDNF and its receptors TrkB and p75 were examined in MK-801-treated astrocyte cultures. MK-801 treatment enhanced GFAP expression in the rat hippocampus and also increased the levels of GFAP protein and mRNA in hippocampal astrocytes in vitro. Treatment of cultured hippocampal astrocytes with MK-801 enhanced protein and mRNA levels of BDNF, TrkB, and p75. Collectively, our results suggest that hippocampal astrocytes may contribute to the pathophysiology of schizophrenia symptoms associated with NMDA receptor hypofunction by reactive transformation and altered BDNF signaling.

Opposing effects of ketamine and acetyl l-carnitine on the serotonergic system of zebrafish

Ketamine, a pediatric anesthetic, is a noncompetitive N-methyl-d-aspartic acid (NMDA) receptor antagonist. Studies show that ketamine is neurotoxic in developing mammals and zebrafish. In both mammals and zebrafish, acetyl l-carnitine (ALCAR) has been shown to be protective against ketamine toxicity. Ketamine is known to modulate the serotonergic system in mammals. Here, we measured the levels of serotonin (5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in the embryos exposed to ketamine in the presence and absence of ALCAR. Ketamine, at lower doses, did not produce significant changes in the 5-HT or 5-HIAA levels in 3 dpf (day post-fertilization) embryos. However, 2mM ketamine (internal embryo exposure levels comparable to human anesthetic plasma concentration) significantly reduced 5-HT level, and 5-HIAA was not detectable indicating that 5-HT metabolism was abolished. In the presence or absence of 2mM ketamine, ALCAR by itself did not significantly alter 5-HT or 5-HIAA levels compared to the control. Ratios of metabolite/5-HT indicated that 2mM ketamine inhibited 5-HT metabolism to 5-HIAA whereas lower doses (0.1–0.3mM) of ketamine did not have any effect. ALCAR reversed the effects of 2mM ketamine not only by restoring 5-HT and 5-HIAA levels but also 5-HT turnover rate to control levels. Whole mount immunohistochemical studies showed that 2mM ketamine reduced the serotonergic area in the brain whereas ALCAR expanded it with increased axonal sprouting and branching. These results indicate that ketamine and ALCAR have opposing effects on the zebrafish serotonergic system.

Repeated ketamine administration alters N-methyl-D-aspartic acid receptor subunit gene expression: implication of genetic vulnerability for ketamine abuse and ketamine psychosis in humans.

For more than 40 years following its approval by the Food and Drug Administration (FDA) as an anesthetic, ketamine, a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, has been used as a tool of psychiatric research. As a psychedelic drug, ketamine induces psychotic symptoms, cognitive impairment, and mood elevation, which resemble some symptoms of schizophrenia. Recreational use of ketamine has been increasing in recent years. However, little is known of the underlying molecular mechanisms responsible for ketamine-associated psychosis. Recent animal studies have shown that repeated ketamine administration significantly increases NMDA receptor subunit gene expression, in particular subunit 1 (NR1 or GluN1) levels. This results in neurodegeneration, supporting a potential mechanism where up-regulation of NMDA receptors could produce cognitive deficits in chronic ketamine abuse patients. In other studies, NMDA receptor gene variants are associated with addictive behavior. Here, we focus on the roles of NMDA receptor gene subunits in ketamine abuse and ketamine psychosis and propose that full sequencing of NMDA receptor genes may help explain individual vulnerability to ketamine abuse and ketamine-associated psychosis.

Subanesthetic Ketamine Treatment Promotes Abnormal Interactions between Neural Subsystems and Alters the Properties of Functional Brain Networks

Acute treatment with subanesthetic ketamine, a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, is widely utilized as a translational model for schizophrenia. However, how acute NMDA receptor blockade impacts on brain functioning at a systems level, to elicit translationally relevant symptomatology and behavioral deficits, has not yet been determined. Here, for the first time, we apply established and recently validated topological measures from network science to brain imaging data gained from ketamine-treated mice to elucidate how acute NMDA receptor blockade impacts on the properties of functional brain networks. We show that the effects of acute ketamine treatment on the global properties of these networks are divergent from those widely reported in schizophrenia. Where acute NMDA receptor blockade promotes hyperconnectivity in functional brain networks, pronounced dysconnectivity is found in schizophrenia. We also show that acute ketamine treatment increases the connectivity and importance of prefrontal and thalamic brain regions in brain networks, a finding also divergent to alterations seen in schizophrenia. In addition, we characterize how ketamine impacts on bipartite functional interactions between neural subsystems. A key feature includes the enhancement of prefrontal cortex (PFC)-neuromodulatory subsystem connectivity in ketamine-treated animals, a finding consistent with the known effects of ketamine on PFC neurotransmitter levels. Overall, our data suggest that, at a systems level, acute ketamine-induced alterations in brain network connectivity do not parallel those seen in chronic schizophrenia. Hence, the mechanisms through which acute ketamine treatment induces translationally relevant symptomatology may differ from those in chronic schizophrenia. Future effort should therefore be dedicated to resolve the conflicting observations between this putative translational model and schizophrenia.

Mapping the central effects of chronic ketamine administration in an adolescent primate model by functional magnetic resonance imaging (fMRI)

Ketamine, a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, is capable of triggering excessive glutamate release and subsequent cortical excitation which may induce psychosis-like behavior and cognitive anomalies. Growing evidence suggests that acute ketamine administration can provoke dose-dependent positive and negative schizophrenia-like symptoms. While the acute effects of ketamine are primarily linked to aberrant activation of the prefrontal cortex and limbic structures with elevated glutamate and dopamine levels, the long-term effects of ketamine on brain functions and neurochemical homeostasis remain incompletely understood. In recent years, reports of ketamine abuse, especially among young individuals, have surged rapidly, with profound socioeconomic and health impacts. We herein investigated the chronic effects of ketamine on brain function integrity in an animal model of adolescent cynomolgus monkeys (Macaca fascicularis) by functional magnetic resonance imaging (fMRI). Immunohistochemical study was also conducted to examine neurochemical changes in the dopaminergic and cholinergic systems in the prefrontal cortex following chronic ketamine administration. Our results suggest that repeated exposure to ketamine markedly reduced neural activities in the ventral tegmental area, substantia nigra in midbrain, posterior cingulate cortex, and visual cortex in ketamine-challenged monkeys. In contrast, hyperfunction was observed in the striatum and entorhinal cortex. In terms of neurochemical and locomotive changes, chronically ketamine-challenged animals were found to have reduced tyrosine hydroxylase (TH) but not choline acetyltransferase (ChAT) levels in the prefrontal cortex, which was accompanied by diminished total movement compared with the controls. Importantly, the mesolimbic, mesocortical and entorhinal-striatal systems were found to be functionally vulnerable to ketamine's chronic effects. Dysfunctions of these neural circuits have been implicated in several neuropsychiatric disorders including depression, schizophrenia and attention deficit disorder (ADD). Collectively, our results support the proposition that repeated ketamine exposure can be exploited as a pharmacological paradigm for studying the central effects of ketamine relevant to neuropsychiatric disorders.

Cortical ionotropic glutamate receptor antagonism protects against methamphetamine-induced striatal neurotoxicity

Binge administration of the psychostimulant drug, methamphetamine (mAMPH), produces long-lasting structural and functional abnormalities in the striatum. mAMPH binges produce nonexocytotic release of dopamine (DA), and mAMPH-induced activation of excitatory afferent inputs to cortex and striatum is evidenced by elevated extracellular glutamate (GLU) in both regions. The mAMPH-induced increases in DA and GLU neurotransmission are thought to combine to injure striatal DA nerve terminals of mAMPH-exposed brains. Systemic pretreatment with either competitive or noncompetitive N-methyl-D-aspartic acid (NMDA) antagonists protects against mAMPH-induced striatal DA terminal damage, but the locus of these antagonists' effects has not been determined. Here, we applied either the NMDA receptor antagonist, (dl)-amino-5-phosphonovaleric acid (AP5), or the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, dinitroquinoxaline-2,3-dione (DNQX), directly to the dura mater over frontoparietal cortex to assess their effects on mAMPH-induced cortical and striatal immediate-early gene (c-fos) expression. In a separate experiment we applied AP5 or DNQX epidurally in the same cortical location of rats during a binge regimen of mAMPH and assessed mAMPH-induced striatal dopamine transporter (DAT) depletions 1 week later. Our results indicate that both ionotropic glutamate receptor antagonists reduced the mAMPH-induced Fos expression in cerebral cortex regions near the site of epidural application and reduced Fos immunoreactivity in striatal regions innervated by the affected cortical regions. Also, epidural application of the same concentration of either antagonist during a binge mAMPH regimen blunted the mAMPH-induced striatal DAT depletions with a topography similar to its effects on Fos expression. These findings demonstrate that mAMPH-induced dopaminergic injury depends upon cortical NMDA and AMPA receptor activation and suggest the involvement of the corticostriatal projections in mAMPH neurotoxicity.

Anabasine, a selective nicotinic acetylcholine receptor agonist, antagonizes MK-801-elicited mouse popping behavior, an animal model of schizophrenia

The expression of the α 7-nicotinic acetylcholine receptor is diminished in selected brain areas of patients with schizophrenia. This diminished expression may account for the pathophysiological deficits of sensory inhibition and smooth pursuit eye movement performance in these patients. Furthermore, the deficits in sensory inhibition and smooth pursuit eye movement performance in schizophrenia appear to be inherited in an autosomal dominant fashion; thus, the “α 7-nicotinic acetylcholine receptor-deficiency” may be a necessary condition for expression of schizophrenia. This deficit has encouraged speculation about the possible therapeutic benefit of selective α 7-nicotinic acetylcholine receptor agonist interventions in this disorder. In view of this, we sought to examine the effect of anabasine, a selective α 7-nicotinic acetylcholine receptor agonist, on popping behavior in mice elicited by MK-801. MK-801, a high affinity analogue of phencyclidine (PCP), is a noncompetitive N-methyl- d-aspartic acid (NMDA) receptor antagonist that binds to the hydrophobic domain of this ligand-gated channel. PCP is known to precipitate a schizophreniform psychosis in susceptible individuals, causing productive (e.g. hallucinations) deficit (e.g. affective blunting, amotivation, and social withdrawal), cognitive and motor symptoms similar to those seen in naturally-occurring schizophrenia. Behaviors elicited by MK-801 in mice reflect a pharmacologically-induced state of NMDA receptor hypofunction (NRH), which has been proposed to exist in schizophrenia. Compounds that attenuate MK-801-elicited behaviors, which are identified in this animal model, may have the potential to treat schizophrenia, including deficit and cognitive symptoms. In the current study, anabasine attenuated MK-801-elicited popping at a dose that did not cause clonic seizures. The development of α 7-nicotinic acetylcholine receptor agonist interventions for schizophrenia must consider their potential liability to elicit seizure activity.

Involvement of the glutamatergic system in behavioral disorders in senescence-accelerated mice (SAMP8)

We previously reported that senescence-accelerated mice (SAMP8) showed age-related behavioral disorders such as learning and memory deficits and low anxiety-like behavior. To investigate the involvement of the brain glutamatergic system in the behavioral disorders observed in SAMP8, we examined the effects of MK-801, a non-competitive N-methyl- d-aspartic acid (NMDA) antagonist, on the behavior of a senescence-resistant control, SAMR1/TaSlc (SAMR1), and we tested the effects of D-cycloserine (DCS), a glycine site partial agonist, on behavioral disorders in SAMP8/TaSlc (SAMP8). In the elevated plus-maze test, MK-801 significantly increased the number of entries into open arms and the time spent on open arms compared with the control group treated with saline. Furthermore, in the passive avoidance task, MK-801 caused dose-dependent decreases in avoidance latency in SAMR1. SAMP8 showed significant impairment in the acquisition of the passive avoidance response compared with SAMR1, even though they were trained repeatedly. DCS (3 or 10 mg/kg, intraperitoneally) tended to reduce the increased time spent on the open arms in SAMP8, and the administration of DCS (10 mg/kg, intraperitoneally) before each trial also tended to extend the avoidance latencies observed in SAMP8. These results indicate that the MK-801-induced behavioral disorders in SAMR1 are similar to those in SAMP8 and suggest that the glutamatergic system might be involved in the behavioral disorders observed in SAMP8.

Cyclic Voltammetry as an Indicator of Antioxidant Activity

A series of compounds based around combining the neuroprotective properties of non-competitive N-methyl D-aspartic acid (NMDA) receptor antagonists with antioxidant functionalities have been prepared. The redox chemistry of these compounds has been evaluated using cyclic voltammetry, and the results have been compared with their radical-scavenging properties obtained from two standard biological assays, the inhibition of lipid peroxidation (thiobarbituric acid reacting substances assay) and the Sapphire colorimetric assay. Results from these different methods show general concordance. The most effective antioxidants were substituted phenols, e.g. Trolox�. The antioxidant activity of a series of pyrimidines was shown to be dependent on the presence of three amino substituents.

Cyclic Voltammetry as an Indicator of Antioxidant Activity

A series of compounds based around combining the neuroprotective properties of non-competitive N-methyl D-aspartic acid (NMDA) receptor antagonists with antioxidant functionalities have been prepared. The redox chemistry of these compounds has been evaluated using cyclic voltammetry, and the results have been compared with their radical-scavenging properties obtained from two standard biological assays, the inhibition of lipid peroxidation (thiobarbituric acid reacting substances assay) and the Sapphire colorimetric assay. Results from these different methods show general concordance. The most effective antioxidants were substituted phenols, e.g. Trolox�. The antioxidant activity of a series of pyrimidines was shown to be dependent on the presence of three amino substituents.

MK-801, a non-competitive NMDA receptor antagonist, prevents postischemic decrease of inositol 1,4,5-trisphosphate receptor mRNA expression in mongolian gerbil brain

Changes of inositol 1,4,5-trisphosphate receptor (IP 3R) mRNA expression after transient brain ischemia and the effect of MK-801, a non-competitive N-methyl- d-aspartic acid (NMDA) receptor antagonist, on the IP 3R mRNA expression was studied in mongolian gerbil brain by in situ hybridization. Transient ischemia was induced by ligating left common carotid artery for 10 min, and the animals were allowed recovery from 15 min to 24 h. MK-801 was introduced intraperitoneally 30 min before ischemia. IP 3R mRNA expression was decreased in dentate gyrus and hippocampus from 90 min until 24 h after ischemia. MK-801 pretreatment prevented the change of IP 3R mRNA expression after ischemia. These results suggest that IP 3R mRNA expression in ischemia may be related with NMDA receptor.

NG-nitro-L-arginine methyl ester (L-NAME) prevents tachyphylaxis to local anesthetics in a dose-dependent manner.

A model of local anesthetic tachyphylaxis was developed in our group previously using repeated sciatic nerve blocks in rats. In this model, thermal hyperalgesia accelerated tachyphylaxis, and the noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, MK-801, prevented both hyperalgesia and tachyphylaxis. Nitric oxide is thought to be a second messenger for NMDA pathways in the spinal cord, and appears to be involved in spinal mechanisms of hyperalgesia. We hypothesized that nitric oxide synthase inhibitors would also inhibit the development of tachyphylaxis. Repeated rat sciatic nerve blocks were placed by percutaneous injection of 2-chloroprocaine. Block duration was tested by measuring hot-plate latency at 56 degrees C. Two hours before the first nerve block, rats received intraperitoneal injections with saline or one of six concentrations of NG-nitro-L-arginine methyl ester (L-NAME) in a randomized, blinded pattern. Control rats developed tachyphylaxis as seen previously: the duration of the third block was 30% that of the first. L-NAME inhibited the development of tachyphylaxis in a dose-dependent manner; tachyphylaxis was inhibited by 50% using L-NAME at 0.2mg/kg and completely abolished by 50 mg/kg. Nitric oxide pathways may be involved in the development of tachyphylaxis to local anesthetic nerve block.

Antinociceptive mechanisms of Dipsacus saponin C administered intracerebroventricularly in the mouse

1. 1. Dipsacus saponin C (DSC) administered intracerebroventricularly (ICV) showed an antinociceptive effect in a dose-dependent (from 3.75 to 30 μg) manner as measured by the tailflick assay. The antinociception induced by DSC at the dose of 30 μg was maintained at least I h. 2. 2. Sulfated cholecystokinin (CCK, from 0.1 to 0.5 ng); muscimol (a GABA A receptor agonist, from 50 to 200 ng); MK-801 [(±)-5-methyl-10, 11-dihydro-5H-dibenzo (a,d) cyclohepten-5, 10-imine maleate, from 0.1 to 1 μg], a noncompetitive N-methyl- d-aspartic acid (NMDA) receptor antagonist; or CNQX (6-cyano-7-nitroquinoxaline-2,3-dione, from 0.1 to 0.5 μg), a non-NMDA receptor antagonist, injected ICV significantly reduced the inhibition of the tail-flick response induced by DSC (30 μg) administered ICV. However, naloxone (an opioid receptor antagonist, 2 μg) or baclofen (a GABA B receptor antagonist, 10 ng) did not affect the inhibition of the tail-flick response induced by DSC. 3. 3. The intrathecal (IT) injection of yohimbine (an α 2-adrenergic receptor antagonist, from 5 to 20 μg) and methysergide (a serotonin receptor antagonist, from 5 to 20 μg) but not naloxone (from 2 to 8 μg), significantly attenuated inhibition of the tail-flick response induced by DSC (30 μg) administered ICV. 4. 4. Our results suggest that DSC has an antinociceptive effect when it is administered supraspinally and GABA A, NMDA and non-NMDA receptors, but not opioid and GABA B receptors located at the supraspinal level, may be involved in DSC-induced antinociception. Furthermore, DSC administered supraspinally may produce antinociception by stimulating descending α 2-adrenergic and serotonin pathways but not the opioidergic pathway.

Multiplicative interaction between intrathecally and intracerebroventricularly administered morphine for antinociception in the mouse: Involvement of supraspinal nmda but not non-nmda receptors

Concurrent administration of morphine to both supraspinal and spinal sites produced a multiplicative (synergistic) interaction for antinociception. The purpose of this study was to determine if supraspinal glutaminergic receptors are involved in the multiplicative interaction for antinociception induced by morphine. The antinociception was assessed by the tail-flick test. Effect of MK-801 [(+/-)-5-methyl-10, 11-dihydro-5H-dibenzo (a,d)cyclohepten-5,10-imine maleate], a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, or CNQX (6-Cyano-7-nitroquinoxaline-2,3-dione), a competitive non-NMDA receptor antagonist on inhibition of the tail-flick response induced by a combined i.t. and i.c.v. administration of morphine was studied. Either i.t. or i.c.v. administration of morphine alone at the dose of 0.2 microgram slightly increased inhibition of the tail-flick response. However, concurrent i.t. and i.c.v. injections of morphine at the dose of 0.2 microgram increased the inhibition of the tail-flick response in a synergistic manner. Various doses of MK-801 (0.01-1 microgram) or CNQX (0.05-0.5 microgram) pretreated i.c.v. alone did not show any antinociceptive effect. MK-801 pretreated i.c.v. for 10 min dose-dependently attenuated the inhibition of the tail-flick response induced by concurrent i.t. and i.c.v. injections of morphine. However, CNQX pretreated i.c.v. for 10 min did not affect the inhibition of the tail-flick response induced by concurrent i.t. and i.c.v. injections of morphine. Our results suggest that supraspinal NMDA but not non-NMDA receptors are involved in mediating the antinociception produced by morphine-induced multiplicative interaction between spinal and supraspinal sites.