Yi-Ruu Lin

Differential inhibitory effects of honokiol and magnolol on excitatory amino acid-evoked cation signals and NMDA-induced seizures

The effects of honokiol and magnolol, two major bioactive constituents of the bark of Magnolia officinalis, on Ca(2+) and Na(+) influx induced by various stimulants were investigated in cultured rat cerebellar granule cells by single-cell fura-2 or SBFI microfluorimetry. Honokiol and magnolol blocked the glutamate- and KCl-evoked Ca(2+) influx with similar potency and efficacy, but did not affect KCl-evoked Na(+) influx. However, honokiol was more specific for blocking NMDA-induced Ca(2+) influx, whereas magnolol influenced with both NMDA- and non-NMDA activated Ca(2+) and Na(+) influx. Moreover, the anti-convulsant effects of these two compounds on NMDA-induced seizures were also evaluated. After honokiol or magnolol (1 and 5 mg/kg, i.p.) pretreatment, the seizure thresholds of NMRI mice were determined by tail-vein infusion of NMDA (10 mg/ml). Data showed that both honokiol and magnolol significantly increased the NMDA-induced seizure thresholds, and honokiol was more potent than magnolol. These results demonstrated that magnolol and honokiol have differential effects on NMDA and non-NMDA receptors, suggesting that the distinct therapeutic applications of these two compounds for neuroprotection should be considered.

Antinociceptive actions of honokiol and magnolol on glutamatergic and inflammatory pain

The antinociceptive effects of honokiol and magnolol, two major bioactive constituents of the bark of Magnolia officinalis, were investigated on animal paw licking responses and thermal hyperalgesia induced by glutamate receptor agonists including glutamate, N-methyl-D-aspartate (NMDA), and metabotropic glutamate 5 receptor (mGluR5) activator (RS)-2-chloro-5-hydroxyphenylglycine (CHPG), as well as inflammatory mediators such as substance P and prostaglandin E2 (PGE2) in mice. The actions of honokiol and magnolol on glutamate-induced c-Fos expression in the spinal cord dorsal horn were also examined. Our data showed that honokiol and magnolol blocked glutamate-, substance P- and PGE2-induced inflammatory pain with similar potency and efficacy. Consistently, honokiol and magnolol significantly decreased glutamate-induced c-Fos protein expression in superficial (I-II) laminae of the L4-L5 lumbar dorsal horn. However, honokiol was more selective than magnolol for inhibition of NMDA-induced licking behavioral and thermal hyperalgesia. In contrast, magnolol was more potent to block CHPG-mediated thermal hyperalgesia. These results demonstrate that honokiol and magnolol effectively decreased the inflammatory pain. Furthermore, their different potency on inhibition of nociception provoked by NMDA receptor and mGluR5 activation should be considered.

The mechanism of honokiol-induced and magnolol-induced inhibition on muscle contraction and Ca2+ mobilization in rat uterus.

The effects of honokiol and magnolol extracted from the Magnolia officinalis on muscular contractile responses and intracellular Ca2+ mobilization were investigated in the non-pregnant rat uterus. Honokiol and magnolol (1–100xa0μmol/l) were observed to inhibit spontaneous and uterotonic agonists (carbachol, PGF2α, and oxytocin)-, high K+-, and Ca2+ channel activator (Bay K 8644)-induced uterine contractions in a concentration-dependent manner. The inhibition rate of honokiol on spontaneous contractions appeared to be slower than that of magnolol-induced response. The time periods that were required for honokiol and magnolol, at 100xa0μmol/l, to abolish 50% spontaneous contractions were approximately 6xa0min. Furthermore, honokiol and magnolol at 10xa0μmol/l also blocked the Ca2+-dependent oscillatory contractions. Consistently, the increases in intracellular Ca2+ concentrations ([Ca2+]i) induced by PGF2α and high K+ were suppressed by both honokiol and magnolol at 10xa0μmol/l. After washout of these treatments, the rise in [Ca2+]i induced by PGF2α and high K+ was still partially abolished. In conclusion, the inhibitory effects of honokiol and magnolol on uterine contraction may be mediated by blockade of external Ca2+ influx, leading to a decrease in [Ca2+]i. Honokiol and magnolol may be considered as putative Ca2+ channel blockers and be of potential value in the treatment of gynecological dysfunctions associated with uterine muscular spasm and dysmenorrhea.

Toluene exposure during brain growth spurt and adolescence produces differential effects on N-methyl-d-aspartate receptor-mediated currents in rat hippocampus

Toluene, an industrial organic solvent, is voluntarily inhaled as drug of abuse. Because inhibition of N-methyl-d-aspartate (NMDA) receptors is one of the possible mechanisms underlying developmental neurotoxicity of toluene, the purpose of the present study was to examine the effects of toluene exposure during two major neurodevelopmental stages, brain growth spurt and adolescence, on NMDA receptor-mediated current. Rats were administered with toluene (500 mg/kg, i.p.) or corn oil daily over postnatal days (PN) 4-9 (brain growth spurt) or PN 21-26 (early adolescence). Intracellular electrophysiological recordings employing in CA1 pyramidal neurons in the hippocampal slices were performed during PN 30-38. Toluene exposure during brain growth spurt enhanced NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) by electrical stimulation, but impaired the paired-pulse facilitation and NMDA response by exogenous application of NMDA. Toluene exposure during adolescence resulted in an increase in NMDA receptor-mediated EPSCs and a decrease in exogenous NMDA-induced currents, while lack of any effect on paired-pulse facilitation. These findings suggest that toluene exposure during brain growth spurt and adolescence might result in an increase in synaptic NMDA receptor responsiveness and a decrease in extrasynaptic NMDA receptor responsiveness, while only toluene exposure during brain growth spurt can produce presynaptic modulation in CA1 pyramidal neurons. The functional changes in NMDA receptor-mediated transmission underlying developmental toluene exposure may lead to the neurobehavioral disturbances.

Aliphatic chlorinated hydrocarbons alter the contractile responses of tracheal smooth muscle in piglet.

Aliphatic chlorinated hydrocarbons (ACHs) are widely used in several industrial processes and are also found in many commercial household products. They are classified as hazardous air pollutants, since ACHs exposure induces respiratory complications including airway hyperactivity. However, the contribution of airway smooth muscle tone to ACH-induced respiratory dysfunction has not been elucidated. Thus, the effects of ACHs such as dichloromethane (DCM), dichloroethane (DCE), and trichloromethane (TCM), on the basal and stimulant-induced contractile responses in piglet tracheal smooth muscle were investigated. ACHs at 100-1000 ppm were found to evoke the basal contraction of tracheal smooth muscle strips. Although DCM, DCE, and TCM enhanced the muscle tone precontracted by KCl, they exerted differential effects on acetylcholine- or histamineinduced muscle contraction. DCE did not alter the muscle tone activated by acetylcholine and histamine. DCM at 1000 ppm enhanced the muscle tension precontracted by acetylcholine but not by histamine. TCM at 30-1000 ppm increased the histamine-induced muscle contraction, but at 1000 ppm relaxed the muscle precontracted by acetylcholine. DCE and TCM at the highest concentration (1000 ppm) provoked a biphasic response with an initial increase in KCl-induced muscle tension followed by a decrease. Furthermore, pretreatment with DCE potentiated the acetylcholine-, histamine-, and KCl-induced muscle contractile responses. Pretreatment with TCM potentiated the histamine-, and KCl-induced response, but DCM only potentiated the KCl-induced response. The results suggest that ACH exposure altering the basal and spasmogen-induced contractile responses might participate in airway impairment with hyperresponsiveness.

Effects of sarcosine and N, N-dimethylglycine on NMDA receptor-mediated excitatory field potentials

BackgroundSarcosine, a glycine transporter type 1 inhibitor and an N-methyl-D-aspartate (NMDA) receptor co-agonist at the glycine binding site, potentiates NMDA receptor function. Structurally similar to sarcosine, N,N-dimethylglycine (DMG) is also N-methyl glycine-derivative amino acid and commonly used as a dietary supplement. The present study compared the effects of sarcosine and DMG on NMDA receptor-mediated excitatory field potentials (EFPs) in mouse medial prefrontal cortex brain slices using a multi-electrode array system.ResultsGlycine, sarcosine and DMG alone did not alter the NMDA receptor-mediated EFPs, but in combination with glutamate, glycine and its N-methyl derivatives significantly increased the frequency and amplitude of EFPs. The enhancing effects of glycine analogs in combination with glutamate on EFPs were remarkably reduced by the glycine binding site antagonist 7-chlorokynurenate (7-CK). However, DMG, but not sarcosine, reduced the frequency and amplitude of EFPs elicited by co-application of glutamate plus glycine. D-cycloserine, a partial agonist at the glycine binding site on NMDA receptors, affected EFPs in a similar manner to DMG. Furthermore, DMG, but not sarcosine, reduced the frequencies and amplitudes of EFPs elicited by glutamate plus D-serine, another endogenous ligand for glycine binding site.ConclusionsThese findings suggest that sarcosine acts as a full agonist, yet DMG is a partial agonist at glycine binding site of NMDA receptors. The molecular docking analysis indicated that the interactions of glycine, sarcosine, and DMG to NMDA receptors are highly similar, supporting that the glycine binding site of NMDA receptors is a critical target site for sarcosine and DMG.