MK-801 prevents the increased NMDA-NR1 and NR2B subunits mRNA expression observed in the hippocampus of rats tolerant to diazepam

A new specific GluN2B partial antagonist ameliorates brain injury caused by ischemic stroke in rats

Ischemic stroke is one of the top-ranked causes of death and disability in the world, but still lacking efficacy treatment options. Excitotoxicity caused by NMDA receptors (NMDARs) hyperactivation plays a key role in brain injury after ischemic stroke. GluN2B, the regulatory subunit of NMDARs, plays an important role in brain injury induced by ischemic stroke, and specific antagonists of GluN2B can ameliorate brain damage induced by ischemic stroke in rats. However, over half a century after Memantine (the first NMDA partial inhibitor for Alzheimer's clinical treatment) was identified, only a few additional NMDA partial inhibitors, especially those specifically targeting GluN2B, have been discovered. In this study, by using whole patch-clamp technique and multiple molecular biological methods, we discovered a new specific GluN2B partial antagonist, named FLY26, and further determined its effects on alleviating the brain injury caused by ischemic stroke in rats. Our experiment results showed FLY26 suppressed the excitotoxicity caused by overactivation of NMDARs in SH-SY5Y cells, and ameliorated brain damage of middle cerebral artery occlusion (MACO) rats, within the dosage range of 1.5-6.0 mg/kg, via BDNF/TrkB signaling pathway. Our results indicated that FLY26 is a promising lead compound for the development of novel, specific GluN2B partial antagonist. Our results indicated that FLY26 is a promising lead compound for the development of novel, specific GluN2B partial antagonist, which may offer better safety profile as a therapeutic intervention for ischemic stroke.

NMDA Receptors and NO:cGMP Signaling Pathway Mediate the Diazepam-Induced Sensitization to Withdrawal Signs in Mice

The goal of the present study was to examine the effects of N-methyl-aspartate (NMDA) receptor antagonists-memantine and ketamine and the drugs modifying the NO:cGMP pathway-NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), the endogenous precursor of NO-L-arginine, and the guanylyl cyclase inhibitor-methylene blue (MB) on the development of sensitization to withdrawal signs precipitated after chronic, interrupted treatment with diazepam, a benzodiazepine receptor agonist, in mice. To develop the sensitization, the mice were divided into groups: continuously and sporadically (with two diazepam-free periods) treated with diazepam (15 mg/kg, sc). To precipitate the withdrawal syndrome (clonic and tonic seizures, and death), pentylenetetrazole (55 mg/kg, sc) with the benzodiazepine receptor antagonist, flumazenil (5.0 mg/kg, ip), were administered after the last injection of diazepam or saline. Memantine (2.5, 5.0 mg/kg), and ketamine (2.5, 5.0 mg/kg), L-NAME (100, 200 mg/kg) and 7-NI (20 and 40 mg/kg), L-arginine (250, 500 mg/kg) and MB (5 and 10 mg/kg) were administered ip in sporadically diazepam-treated mice during the diazepam-free periods. Our results indicated that both NMDA receptor antagonists and drugs that inhibit the NO:cGMP pathway, except L-arginine (the endogenous donor of NO), attenuated the diazepam-induced sensitization to withdrawal signs in mice. Thus, NMDA receptors and the NO:cGMP pathway are involved in the mechanisms of sensitization to benzodiazepine withdrawal.

Effects of NMDA antagonists on the development and expression of tolerance to diazepam-induced motor impairment in mice

The goal of the study was to investigate the effects of ketamine and memantine on the development and expression of tolerance to diazepam (DZ)-induced motor impairment in mice. DZ-induced motor incoordination was assessed by the rotarod and chimney tests. It was found that (a) ketamine, at the dose of 5mg/kg (but not 2.5mg/kg), decreased the expression, but not the development, of tolerance to the motor impairing effects of DZ, (b) memantine, at the doses of 5 and 10mg/kg decreased both the development and expression of DZ tolerance in the rotarod test (also in the chimney test but at the higher dose of 10mg/kg) and (c) ketamine and memantine alone had no effect, either in the rotarod or the chimney test in mice. Those findings provided behavioral evidence that the glutamatergic system could contribute an important role in the development and/or expression of tolerance to DZ in mice.

Effects of midazolam, pentobarbital and ketamine on the mRNA expression of ion channels in a model organism Daphnia pulex

Background

Over the last few decades intensive studies have been carried out on the molecular targets mediating general anesthesia as well as the effects of general anesthetics. The γ-aminobutyric acid type A receptor (GABA_AR) has been indicated as the primary target of general anaesthetics such as propofol, etomidate and isoflurane, and sedating drugs including benzodiazepines and barbiturates. The GABA_AR is also involved in drug tolerance and dependence. However, the involvement of other ion channels is possible.

Methods

Using reverse transcription and quantitative PCR techniques, we systematically investigated changes in the mRNA levels of ion channel genes in response to exposure to midazolam, pentobarbital and ketamine in a freshwater model animal, Daphnia pulex. To retrieve the sequences of Daphnia ion channel genes, Blast searches were performed based on known human or Drosophila ion channel genes. Retrieved sequences were clustered with the maximum-likelihood method. To quantify changes in gene expression after the drug treatments for 4 hours, total RNA was extracted and reverse transcribed into cDNA and then amplified using quantitative PCR.

Results

A total of 108 ion channel transcripts were examined, and 19, 11 and 11 of them are affected by midazolam (100 μM), pentobarbital (200 μM) and ketamine (100 μM), respectively, covering a wide variety of ion channel types. There is some degree of overlap with midazolam- and pentobarbital-induced changes in the mRNA expression profiles, but ketamine causes distinct changes in gene expression pattern.

In addition, flumazenil (10 μM) eliminates the effect of midazolam on the mRNA expression of the GABA_A receptor subunit Rdl, suggesting a direct interaction between midazolam and GABA_A receptors.

Conclusions

Recent research using high throughput technology suggests that changes in mRNA expression correlate with delayed protein expression. Therefore, the mRNA profile changes in our study may reflect the molecular targets not only in drug actions, but also in chronic drug addiction. Our data also suggest the possibility that hypnotic/anesthetic drugs are capable of altering the functions of the nervous system, as well as those non-nerve tissues with abundant ion channel expressions.

Mechanisms Underlying Tolerance after Long-Term Benzodiazepine Use: A Future for Subtype-Selective GABA(A) Receptor Modulators?

Despite decades of basic and clinical research, our understanding of how benzodiazepines tend to lose their efficacy over time (tolerance) is at least incomplete. In appears that tolerance develops relatively quickly for the sedative and anticonvulsant actions of benzodiazepines, whereas tolerance to anxiolytic and amnesic effects probably does not develop at all. In light of this evidence, we review the current evidence for the neuroadaptive mechanisms underlying benzodiazepine tolerance, including changes of (i) the GABA(A) receptor (subunit expression and receptor coupling), (ii) intracellular changes stemming from transcriptional and neurotrophic factors, (iii) ionotropic glutamate receptors, (iv) other neurotransmitters (serotonin, dopamine, and acetylcholine systems), and (v) the neurosteroid system. From the large variance in the studies, it appears that either different (simultaneous) tolerance mechanisms occur depending on the benzodiazepine effect, or that the tolerance-inducing mechanism depends on the activated GABA(A) receptor subtypes. Importantly, there is no convincing evidence that tolerance occurs with α subunit subtype-selective compounds acting at the benzodiazepine site.

Termination of pseudopregnancy in the rat alters the response to progesterone, chlordiazepoxide, and MK-801 in the elevated plus-maze

RATIONALE

Allopregnanolone, a neurosteroid-reduced metabolite of progesterone, is a well-documented positive modulator of the gamma-aminobutyric type A (GABA(A)) receptor. As has been reported for other positive modulators of the GABA(A) receptor, chronic exposure to neurosteroids is hypothesized to decrease GABA(A) receptor function. Drawing from the literature on chronic exposure to benzodiazepines or alcohol, putative changes in N-methyl-D-aspartate (NMDA) receptor function are also expected after chronic neurosteroid exposure.

OBJECTIVES

To assess the sensitivity of the GABA(A) and NMDA receptors after chronic elevation of neurosteroid produced by termination of pseudopregnancy in behavioral tests of anxiety and sensorimotor coordination.

METHODS

Female rats ovariectomized on day 10 of pseudopregnancy were tested in the elevated plus-maze and on the rotor rod after an acute injection of progesterone (4 mg/0.2 ml, s.c.), chlordiazepoxide (5 or 15 mg/kg, i.p.), or MK-801 (0.025, 0.05, or 0.1 mg/kg, i.p.).

RESULTS

Pseudopregnancy termination produced an anxiogenic-like response in the plus-maze; an acute injection of progesterone restored baseline levels of behavior in this test. Pseudopregnancy termination eliminated the anxiolytic-like, sedative, and ataxic effects of chlordiazepoxide. In contrast, pseudopregnancy termination produced an increased sensitivity to the anxiolytic-like and ataxic effects of MK-801.

CONCLUSIONS

The effects of pseudopregnancy termination on the behavioral response to positive modulators of the GABA(A) receptor are consistent with results from studies in which chronic exposure to neurosteroids decreases the response to acute neurosteroid and benzodiazepine administration. However, unlike the enhanced glutamatergic tone resulting from discontinuation of chronic benzodiazepine or alcohol exposure, the termination of pseudopregnancy apparently decreases NMDA receptor function.