ラット扁桃体へのグルタメイト微量注入による延髄後角の侵害受容細胞に対する抑制効果

抄録

We have shown that conditioning electrical stimulation of the amygdala has an inhibitory effect on the nociceptive neurons in the medullary dorsal horn of the rat. The purpose of this study is to investigate whether the inhibitory effect depends on the activation of cell bodies or passing fibers by the glutamate microinjection into the amygdala. The animals were anesthetized with N_2O-O_2 (2:1) and 0.5%-halothane, and immobilized with pancuronium 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, 100-300μA) delivered at 330Hz. Thirty-five wide dynamic range (WDR) neurons and 11 nociceptive specific (NS) neurons were recorded. Both neurons were distributed in the superficial layers of the caudal nucleus and diffusely throughout the dorsal part of the reticular subnucleus. The conditioning stimulation in the central nucleus, basomedial and basolateral nuclei markedly inhibited the activities in 13 of 17 nociceptive neurons (10 WDR and 3 NS neurons). The inhibitory effect was 68.0±15.3% (mean±S.D.) at maximum. Microinjection of 0.5M monosodium glutamate (5μl) into the amygdala resulted in inhibition of medullary nociceptive neurons (5 WDR and 2 NS neurons). These findings suggest that the excitation of cell bodies in the amygdala contribute to the inhibitory effects on the 2nd order nociceptive neurons. Because it has been known that the amygdala is a key structure for mediating stress responses, the antinociceptive effect may provide one of the neurophysiological basis for the stress-induced analgesia (SIA).