title: Behavioral and neuroendocrine actions of the Met-enkephalin-related peptide MERF.
abstract: The effects and the mediation of the action of the proenkephalin derivative Met(5)-enkephalin-Arg(6)-Phe(7) (MERF) on the hypothalamo-pituitary-adrenal (HPA) system and open-field behavior were investigated in mice. Intracerebroventricular injection of the heptapeptide increased square crossing, rearing, and plasma corticosterone level. To characterize the receptors involved in these neuroendocrine processes, animals were pretreated either with the nonselective opioid antagonist naloxone or the kappa-antagonist nor-binaltorphimine (nor-BNI). Both antagonists dose-dependently attenuated the HPA activation elicited by MERF. Naloxone also blocked the behavioral responses, but nor-binaltorphimine did not elicit a significant inhibition. The dopamine antagonist haloperidol and a corticotropin-releasing hormone (CRH) antagonist were also preadministered to shed light on the transmission of the actions of MERF. Both the motor responses and the HPA activation were diminished by the preadministration of the CRH antagonist, while haloperidol attenuated only square crossing and rearing. To investigate the direct effect of MERF on the dopaminergic system, dopamine release of striatal slices was measured in a superfusion system. Neither the basal nor the electric impulse-evoked dopamine release was modified by MERF. The results suggest that opioid-mediation predominate in the neuroendocrine actions of MERF, and the effect of the heptapeptide on the HPA system seems to be mediated by kappa-receptors. In the behavioral responses evoked by MERF, both CRH release and the action of the dopaminergic neurons of the subcortical motor system might be involved. MERF also appears to activate the paraventricular CRH neurons, but dopaminergic transmission does not seem to play a significant role in its hypothalamic action.
authors.affiliation: Department of Pathophysiology, University of Szeged, Neurohumoral Research Group, Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: E
authors.initials: E
authors.lastname: Bujdosó
authors.forename: M
authors.initials: M
authors.lastname: Jászberényi
authors.forename: J
authors.initials: J
authors.lastname: Farkas
authors.forename: G
authors.initials: G
authors.lastname: Tóth
authors.forename: M
authors.initials: M
authors.lastname: Wollemann
authors.forename: G
authors.initials: G
authors.lastname: Telegdy
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D005106:Exploratory Behavior / Q000187:drug effects*; D006220:Haloperidol / Q000494:pharmacology; D006727:Hormone Antagonists / Q000494:pharmacology; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects*; D008297:Male; D051379:Mice; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D017072:Neostriatum / Q000187:drug effects / Q000378:metabolism; D009924:Organ Culture Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D010913:Pituitary-Adrenal System / Q000187:drug effects*
chemical_list: D006727:Hormone Antagonists; D009292:Narcotic Antagonists; D010446:Peptide Fragments; D009270:Naloxone; C051844:norbinaltorphimine; D004744:Enkephalin, Methionine; D009271:Naltrexone; C027511:enkephalin-Met, Arg(6)-Phe(7)-; D003346:Corticotropin-Releasing Hormone; C045089:corticotropin releasing hormone (9-41); D006220:Haloperidol; D004298:Dopamine