Nucleus Tractus Solitarius- induced Suppression of the Jaw Opening Reflex and A Possible Interrelationship betweeen Antinociceptive and Cardiovascular Responses

다국어 초록 (Multilingual Abstract)

This study was performed to investigate the mechanisms of the nucleus tractus solitarius （NTS）-induced pain modulation in the orofacial area and a possible interrelationship between the antinociceptive and cardiovascular responses in rats. After 15 nM glutamate or 160 pM acetylcholine was microinjected into the NTS, arterial pressure was decreased in 57±3 and 45±2 mmHg, and heart rate was also decreased in 78±7 and 33±4 beats／min, respectively. Digastric electromyogram （dEMG） evoked by noxious electrical stimulation in the palatal mucosa was suppressed by the NTS application of glutamate to 20±4％ of the control. However, aCSF and acetylcholine did not affect the dEMG. Pentolinium blocked the depressor response resulting from the microinjection of 15 nM glutamate into the NTS, but had no significant effect on the suppression of dEMG response to NTS stimulation. Methysergide and phentolamine, but not naloxone, significantly inhibited the suppression of dEMG response to microinjection of glutamate into the NTS. These results suggest that the NTS is effective in the modulation of nociceptive transmission in orofacial area and have an interrelationship between antinociception and cardiovascular responses. The NTS-induced antinociception seems to be mediated by serotonergic and adrenergic pathways but not by opioid pathway.