BRAIN SITES INVOLVED IN DELTA-OPIOID RECEPTOR-MEDIATED ACTIONS

The brain sites which may be involved in delta-opioid receptor agonist -mediated actions in vivo were examined using quantitative [1-C-14]deo xyglucose autoradiography. For this purpose [D-Pen(2),D-Pen(5)]enkepha lin (DPDPE) - one of the most selective delta-opioid receptor agonists available - was employed. DPDPE was most effective at a dose of 25 mu g i.c.v. All of the motor regions measured displayed significant incr eases in glucose utilization. Further, increases were widespread in li mbic forebrain regions and were also detected in components of the lim bic midbrain. The ventroposterolateral thalamic nucleus, a region rela ying somatosensory information to the cerebral cortex, displayed the s trongest enhancement of glucose utilization. This regional pattern of changes is assumed to underlie the modulatory role in the processing o f somatosensory and nociceptive information of DPDPE, its rewarding pr operties and the behavioral arousal produced by the delta-opioid agoni st. A selective involvement of delta-opioid receptors in these effects was indicated by their antagonism by the delta-opioid receptor antago nist ICI 174,865 (N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH).