BRAIN SITES INVOLVED IN MU-OPIOID RECEPTOR-MEDIATED ACTIONS - A 2-DEOXYGLUCOSE STUDY

Brain regions that may be functionally involved in the neuropharmacolo gical actions of mu-opioid agonists have been examined in conscious ra ts using the quantitative [C-14]2-deoxyglucose autoradiographic techni que. At 0.5 mu g and 1 mu g intracerebroventricularly the highly selec tive mu-opioid receptor agonist D-Ala(2), MePhe(4), Gly-ol(5)-enkephal in effected statistically significant increases as well as statistical ly significant decreases in regional glucose utilization: in limbic st ructures, such as hippocampal formation, medial amygdala and lateral s eptum, glucose utilization was most prominently increased after D-Ala( 2), MePhe(4), Gly-ol(5)-enkephalin; glucose utilization was further in creased in the lateral habenular nucleus, the hypothalamus, ventromedi al nucleus and dorsal raphe; whereas decreases were found in the mamil lary body and anterior thalamus. Glucose utilization in structures ass ociated with somatosensory and nociceptive processing was increased in the central gray of the midbrain and decreased in the nucleus gelatin osus. Only increases in glucose utilization were produced by D-Ala(2), MePhe(4), Gly-ol(5)-enkephalin in brain regions involved in motor con trol, including the globus pallidus, the substantia nigra, pars reticu lata, the nucleus ruber and the cerebellum, and brain regions involved in visual processing - the visual cortex and superior colliculus deep layer. It is concluded that this pattern of regional changes underlie s the mu-opioid receptor-mediated antinociceptive-, epileptogenic-, me mory- and mood-modulating actions of mu-opioid agonists.