Tooth-pulp-evoked rostral spinal trigeminal nucleus neuron activity is inhibited by conditioning sciatic nerve stimulation in the rat: possible role of 5-HT3 receptor mediated GABAergic inhibition.
The purpose of the present study was to determine whether modulation of the trigeminal spinal nucleus oralis (TSNO) neurons related to tooth-pulp (TP)-evoked jaw-opening reflex (JOR) after electrical stimulation of the sciatic nerve (SN) is mediated by the descending serotonergic (5-HT(3)) inhibitory system activated by inhibitory GABAergic interneurons. In 30 anesthetized rats, the activity of TSNO neurons (87.5%, 35/40) and all digastric muscle electromyograms (dEMG, n=30) in response to TP stimulation (at an intensity of 3.5 times the threshold for JOR) were inhibited by conditioning stimulation of the SN (5.0 mA x 0.5 ms, 1 Hz, conditioning-test intervals; 50 ms). The inhibitory effects were significantly attenuated after intravenous administration of the 5-HT(3) receptor antagonist ICS 205-930 (n=6). Using multibarrel electrodes, iontophoretic application of ICS 205-930 into the TSNO significantly reduced the SN stimulation-induced inhibition of TP-evoked TSNO neuronal excitation (n=6), and in the same neurons, iontophoretic application of the GABA(A) receptor antagonist bicuculline into the TSNO greatly inhibited their effect. On the other hand, we found the expression of 5-HT(3) receptor immunoreactive neurons in the TSNO. These results suggest that SN stimulation may activate the descending serotonergic (5-HT(3)) inhibitory system through activation of inhibitory GABAergic interneurons, which inhibit excitatory responses of the TSNO neurons to TP stimulation.
Oshima
Katsuo
K
General Dentistry of University Hospital, The Nippon Dental University, School of Dentistry at Tokyo, Chiyoda-ku, Tokyo 102-8158, Japan. oshima-k@tky.ndu.ac.jp
Takeda
Mamoru
M
Tanimoto
Takeshi
T
Katsuumi
Ichiroh
I
Matsumoto
Shigeji
S
D000200:Action Potentials / Q000187:drug effects / Q000528:radiation effects; D000818:Animals; D003782:Dental Pulp; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000528:radiation effects; D007150:Immunohistochemistry / Q000379:methods; D007211:Indoles / Q000494:pharmacology; D007568:Jaw; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D044406:Receptors, Serotonin, 5-HT3 / Q000502:physiology*; D012018:Reflex / Q000502:physiology* / Q000528:radiation effects; D012584:Sciatic Nerve / Q000502:physiology* / Q000528:radiation effects; D012702:Serotonin Antagonists / Q000494:pharmacology; D014279:Trigeminal Nucleus, Spinal / Q000166:cytology*; D000077526:Tropisetron; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D007211:Indoles; D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists; D005680:gamma-Aminobutyric Acid; D000077526:Tropisetron