ラットの三叉神経脊髄路核尾側核および網様亜核の侵害受容細胞に対する扁桃体条件刺激の抑制効果

抄録

We have shown that conditioning stimulation of the amygdaloid nucleus has an inhibitory effect on the nociceptive responses of the somatosensory cortex. The purpose of this study is to investigate whether amygdaloid conditioning stimulation exerts influence on the nociceptive neurons in the medullary dorsal horn in the rat. 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 receptive field of nociceptive neurons, and the ipsilateral amygdaloid conditioning stimulation were trains of 33 pulses (0.5 msec in duration, 300 μA) delivered at 330Hz. Fifty-five WDR neurons were distributed in the superficial layers of the caudal nucleus and diffusely throughout the reticular subnucleus, whereas most of NS neurons (13/17) were distributed in the dorsal part of reticular subnucleus. The conditioning stimulation in the central nucleus, basomedial nucleus and basolateral nucleus, markedly inhibited the activities in 24 of 43 nociceptive neurons. The inhibitory effect was 45.3±16.1% (n=24) at maximum. The conditioning stimulation had almost no effect on the discharges of non-nociceptive neurons. In contrast, the conditioning stimulation in the lateral amygdaloid nucleus had no effect on the nociceptive and non-nociceptive neurons. The present results suggest that amygdaloid nucleus inhibits the ascending nociceptive information at the second order neurons. This amygdaloid antinociceptive effect may provide one of the neurophysiological bases for the stress-induced analgesia (SIA) observed in the presence of stress and fear.