Effects of emodin on synaptic transmission in rat hippocampal CA1 pyramidal neurons in vitro.
Rhubarb extracts provide neuroprotection after brain injury, but the mechanism of this protective effect is not known. The present study tests the hypothesis that rhubarb extracts interfere with the release of glutamate by brain neurons and, therefore, reduce glutamate excitotoxicity. To this end, the effects of emodin, an anthraquinone derivative extracted from Rheum tanguticum Maxim. Ex. Balf, on the synaptic transmission of CA1 pyramidal neurons in rat hippocampus were studied in vitro. The excitatory postsynaptic potential (EPSP) was depressed by bath-application of emodin (0.3-30 microM). Paired-pulse facilitation (PPF) of the EPSP was significantly increased by emodin. The monosynaptic inhibitory postsynaptic potential (IPSP) recorded in the presence of glutamate receptor antagonists (DNQX and AP5) was not altered by emodin. Emodin decreased the frequency, but not the amplitude, of the miniature EPSP (mEPSP). The inhibition of the EPSP induced by emodin was blocked by either 8-CPT, an adenosine A1 receptor antagonist, or by adenosine deaminase. These results suggest that emodin inhibits the EPSP by decreasing the release of glutamate from Schaffer collateral/commissural terminals via the activation of adenosine A1 receptors in rat hippocampal CA1 area and that the neuroprotective effects of rhubarb extracts may result from decreased glutamate excitotoxicity.
Department of Physiology, Kurume University School of Medicine, 67 Asahi-machi, Kurume 830-0011, Japan.
Jian-Wen
JW
Gu
Hiroshi
H
Hasuo
Mitsue
M
Takeya
Takashi
T
Akasu
D000241:Adenosine / Q000494:pharmacology; D000243:Adenosine Deaminase / Q000494:pharmacology; D000818:Animals; D001640:Bicuculline / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004594:Electrophysiology / Q000379:methods; D004642:Emodin / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D006624:Hippocampus / Q000166:cytology*; D066298:In Vitro Techniques; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects; D058915:Purinergic P1 Receptor Antagonists; D017966:Pyramidal Cells / Q000187:drug effects* / Q000502:physiology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D058915:Purinergic P1 Receptor Antagonists; D011810:Quinoxalines; C053907:8-cyclopentyl-1,3-dimethylxanthine; C017069:bicuculline methiodide; C056723:FG 9041; C056639:2-amino-5-phosphopentanoic acid; D013806:Theophylline; D000243:Adenosine Deaminase; D014633:Valine; D000241:Adenosine; D004642:Emodin; D001640:Bicuculline