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).