In this article, seventy nociceptive ullit8 of dorsal horn and five preqaDg1ioDic 8ympatheticunits of spina1 cord in forty-four anesthetized cats homobi1ized with Flaxedil were stUdied-Tbe resu1ts observed were:1. Eleetroplioretic administration of noradrenaline(NA) induced a remarkable depreB8ionof both evoked and sPontaneous diseharges of nocieoptive units. Sitalar effects could beprodused by electric sthoulation of noradrenergic Al nuc1ei or hijection of amphetuche orlia1ul pressing of’ ’Znsanlj,, (one form of ac upuncture) respeetively.2. The effect of 5-hydroxytrrotamine (5-HT) on evoked nooieeptive discharge was sim-i1ar to NA, but on sponhaeous diwharge of nociceptive unitB was excitment.3. Effeets of the above*mentioned factors on the nociceptive di8eharges of preganglionicsympathetic lleurons were 8hailar to the nociceptive units too.4. On the contrary, the astivity of inboited neuron by lloxious stimulation was augInentedby administration of NA, amphetamine, the stimulation of Al nuclei and the deep musele.It is suggested that the noradrenergie nuclei in lower braill stem may p1ny an boortantrole in desc8nding iAniBitory circuits of nociceptive spinal reflex. In this article, seventy nociceptive ullit8 of dorsal horn and five preqaDg1ioDic 8ympatheticunits of spina1 cord in forty-four anesthetized cats homobi1ized with Flaxedil were stUdied-Tbe resu1ts observed were: 1. Eleetroplioretic administration of noradrenaline (NA) induced a remarkable depreB8ion of both evoked and sPontaneous diseharges of nocieoptive units. Sitalar effects could beproduced by electric sthoulation of noradrenergic Al nuc1ei or hijection of amphetuche or lilul pressing of ’Znsanlj ,, (one form of acupuncture) respeetively. 2. The effect of 5-hydroxytrrotamine (5-HT ) on evoked nooieeptive discharge was sim-i1ar to NA, but on sponhaeous diwharge of nociceptive unitB was excitment.3. Effeets of the above * mentioned factors on the nociceptive di8eharges of preganglionicicsympathetic lleurons were 8hailar to the nociceptive units too.4. On the contrary, the astivity of inboited neuron by lloxious stimulation was augment administered by NA, amphetamine, the stimulation o f Al nuclei and the deep musele. It is suggested that the noradrenergie nuclei in lower braill stem may p1ny an boortantrole in desc8nding iAniBitory circuits of nociceptive spinal reflex.