ラット延髄後角の侵害受容細胞に対する扁桃体条件刺激の抑制効果にオピオイド受容体が関与するか?

抄録

We have shown that conditioning stimulation of the amygdaloid nucleus has an inhibitory effect on the nociceptive neurons in the tngermnal caudal nucleus and the medial reticular subnuclei of the rat The purpose of this study is to investigate whether the opioid receptor is involved in the inhibitory effect of amygdaloid stimulation of the nociceptive neurons
The animals were anesthetized with N₂O-O₂ (2・1) and 0.5%-halothane, and immobilized with pancuromum bromide. The peripheral test stimulus (a single rectangular pulse of 2.0 msec in duration) was applied to the facial skin in the receptive field of nociceptive neurons, and the ipsilateral amygdaloid conditioning stimuli to the recording site were trains of 33 pulses (0.5 msec in duration, 100-300 μA) delivered at 330Hz. Fifty-six wide dynamic range (WDR) neurons and 15 nociceptive specifc (NS) neurons were recorded WDR neurons were distributed in the superficial layer of the caudal nucleus and diffusely throughout the reticular subnucleus, whereas most of the NS neurons were distributed in the dorsal part of the reticular subnucleus The conditioning stimulation in the central nucleus, basomedial and basolateral nuclei markedly inhibited the activities in 8 of 8 nociceptive neurons (3 WDR and 5 NS neurons) The inhibitory effect was 73 6±12 8% (mean±S.D) at maximum Naloxone (2mg/kg, 1v.), opioid receptor antagonist, did not exert an influence on the amygdaloid inhibitory effect (n=4) The present results suggest that the amygdaloid nucleus inhibits the ascending nociceptive information at the 2nd order neurons through a receptor other than the opioid receptor. It has been known that the amygdaloid nucleus is a key structure for mediating stress responses Therefore, the amygdaloid antmociceptive effect may provide one of the neurophysiological bases for stress-induced analgesia (SIA), especially non-opioid type SIA.