ADENOSINE MEDIATES SPINAL NOREPINEPHRINE-PRODUCED ANTINOCICEPTION AS REVEALED BY NOCICEPTIVE DISCHARGES IN PARAFASCICULAR NEURONS IN RATS

The effects of intrathecal pretreatment with aminophylline on intrathe cal norepinephrine-produced or serotonin-produced suppression of noxio usly evoked discharges in thalamic parafascicular neurons were in inve stigated in 35 urethane-anesthetized rats. The results showed that: (1 ) both intrathecal norepinephrine (15 nmol) or serotonin (20 nmol) pro duced significant suppression of noxiously evoked discharges in parafa scicular neurons; (2) intrathecal aminophylline (120 nmol) blocked the norepinephrine-produced suppression of noxiously evoked discharges, w hile the same dose of aminophylline exhibited no significant effect on the serotonin-produced suppression of these discharges in parafascicu lar neurons. The results suggest that spinal norepinephrine-produced, but not serotonin-produced, antinociceptive effects maybe mediated by adenosine as one of successive chemical Links in the spinal dorsal hor n circuitry. (C) 1998 Elsevier Science B.V. All rights reserved.