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 [1-14C]deoxyglucose autoradiography. For this purpose [D-Pen2,D-Pen5]enkephalin (DPDPE)--one of the most selective delta-opioid receptor agonists available--was employed. DPDPE was most effective at a dose of 25 micrograms i.c.v. All of the motor regions measured displayed significant increases in glucose utilization. Further, increases were widespread in limbic forebrain regions and were also detected in components of the limbic midbrain. The ventroposterolateral thalamic nucleus, a region relaying somatosensory information to the cerebral cortex, displayed the strongest enhancement of glucose utilization. This regional pattern of changes is assumed to underlie the modulatory role in the processing of somatosensory and nociceptive information of DPDPE, its rewarding properties and the behavioral arousal produced by the delta-opioid agonist. A selective involvement of delta-opioid receptors in these effects was indicated by their antagonism by the delta-opioid receptor antagonist ICI 174,865 (N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH).