title: Etorphine increases the number of mu-opioid receptor-positive cells in the cerebral cortex.
abstract: Imunocytochemical techniques were used to determine whether agonist-induced activation of mu-opioid receptors alters the number and distribution of mu-opioid receptor-positive cells in the rat cerebral cortex. In untreated rats, mu-opioid receptor immunoreactivity was localized to neuronal perikarya and dendrites and to neuropilar punctate structures. mu-Opioid receptor-positive neurons were mostly in layers II and III and exhibited a bipolar or bitufted morphology. In rats treated with the mu-opioid receptor agonist etorphine (0.1mg/kg intraperitoneally) and perfused after different survival periods, there was an enhancement of immunostaining for mu-opioid receptors observed at 15min, reaching a maximum at 60min, and which returned to normal at 480min. Etorphine-induced effects included an increase in the intensity of cellular and neuropil staining; statistical analysis showed that the number of mu-opioid receptor-positive cells in etorphine-treated groups was significantly higher than in controls or saline-treated rats. In animals that received both etorphine and the mu-opioid receptor antagonist naloxone, the pattern of mu-opioid receptors immunoreactivity was similar to that of untreated animals. This study shows that the number of mu-opioid receptor-positive cells is significantly increased following etorphine treatment and suggests that agonist treatment may be exploited to increased immunostaining of mu-opioid receptors and also of other G-protein coupled receptors.
authors.affiliation: Institute of Human Physiology, University of Ancona, I-60020, Ancona, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Melone
authors.forename: N C
authors.initials: NC
authors.lastname: Brecha
authors.forename: C
authors.initials: C
authors.lastname: Sternini
authors.forename: C
authors.initials: C
authors.lastname: Evans
authors.forename: F
authors.initials: F
authors.lastname: Conti
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D005048:Etorphine / Q000494:pharmacology*; D007158:Immunologic Techniques; D009294:Narcotics / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D012016:Reference Values
chemical_list: D009294:Narcotics; D017450:Receptors, Opioid, mu; D005048:Etorphine