Facilitatory actions of serotonin type 3 receptors on GABAergic inhibitory synaptic transmission in the spinal superficial dorsal horn.
Analgesic effects of serotonin (5-hydroxytryptamine [5-HT]) type 3 (5-HT3) receptors may involve the release of gamma-aminobutyric acid (GABA) in the spinal dorsal horn. However, the precise synaptic mechanisms for 5-HT3 receptor-mediated spinal analgesia are not clear. In this study, we investigated whether GABAergic neurons in the superficial dorsal horn (SDH) express functional 5-HT3 receptors and how these 5-HT3 receptors affect GABAergic inhibitory synaptic transmission in the SDH, by using slice preparations from adult glutamate decarboxylase 67-green fluorescent protein (GAD67-GFP) knock-in mice. Tight-seal whole cell recordings from GFP-positive and -negative neurons showed that 5-HT3 receptor-specific agonist 2-methyl-serotonin (2-Me-5-HT) induced inward currents in a substantial population of both GFP-positive and -negative neurons. Additionally, we confirmed expression of 5-HT3 receptors in both types of neurons by single-cell reverse transcription-polymerase chain reaction (RT-PCR) analysis. Further, GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs)-both those evoked by electrical stimulation and those occurring spontaneously in tetrodotoxin (i.e., miniature IPSCs [mIPSCs])-were recorded from GFP-negative neurons. 2-Me-5-HT increased the amplitude of the evoked IPSCs and the frequency of mIPSCs. The amplitude of mIPSCs was not affected by 2-Me-5-HT, suggesting that 5-HT augments GABAergic synaptic transmission via presynaptic mechanisms. The present observations indicate that 5-HT3 receptors are expressed on both somadendritic regions and presynaptic terminals of GABAergic neurons and regulate GABAA receptor-mediated inhibitory synaptic transmission in the SDH. Taken together, these results provide clues for the underlying mechanisms of the antinociceptive actions of 5-HT3 receptors in the spinal dorsal horn.
Fukushima
Teruyuki
T
Department of Physiology and Biological Information, Dokkyo Medical University School of Medicine, Kitakobayashi 880, Mibu, Tochigi 321-0293, Japan.
Ohtsubo
Toshiki
T
Tsuda
Masayuki
M
Yanagawa
Yuchio
Y
Hori
Yuuichi
Y
D000704:Analysis of Variance; D000818:Animals; D001645:Biguanides / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D005968:Glutamate Decarboxylase / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009433:Neural Inhibition / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D017294:Ondansetron / Q000494:pharmacology; D018408:Patch-Clamp Techniques / Q000379:methods; D020671:Posterior Horn Cells / Q000166:cytology*; D044406:Receptors, Serotonin, 5-HT3 / Q000502:physiology*; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology; D058827:Serotonin 5-HT3 Receptor Agonists; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D001645:Biguanides; D044406:Receptors, Serotonin, 5-HT3; D058827:Serotonin 5-HT3 Receptor Agonists; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D049452:Green Fluorescent Proteins; D012701:Serotonin; D017294:Ondansetron; D005680:gamma-Aminobutyric Acid; C045918:2-methyl-5-HT; C065734:1-(3-chlorophenyl)biguanide; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1