title: Opioid-dependent effects of inescapable shock on escape behavior and conditioned fear responding are mediated by the dorsal raphe nucleus.
abstract: Manipulations of the dorsal raphe nucleus (DRN) modulate the behavioral effects of exposure to inescapable shock (IS). Opiate agonists and antagonists also influence the impact of IS, but the role of the DRN in mediating these effects is unknown. The opiate antagonist naltrexone micro-injected into the region of the DRN immediately prior to IS prevented both the escape deficit and the enhancement of fear conditioning that occur 24 h later. Intra-DRN naltrexone administered at the time of later behavioral testing reduced, but did not eliminate, these effects of prior IS. Conversely, the opiate agonist morphine, in combination with a subthreshold number of 20 IS trials, induced an escape deficit and enhanced conditioned fear 24 h later. Microinjections of naltrexone into the dorsolateral periaqueductal gray area did not alter the effects of IS and electrolytic lesions of the DRN prevented the effect of the morphine-20 IS trial combination. The role of opioids in mediating the behavioral effects of IS is discussed.
authors.affiliation: Department of Psychology, University of Colorado, Boulder 80309, USA. rgrahn@clipr.colorado.edu
authors.forename: R E
authors.initials: RE
authors.lastname: Grahn
authors.forename: S
authors.initials: S
authors.lastname: Maswood
authors.forename: M B
authors.initials: MB
authors.lastname: McQueen
authors.forename: L R
authors.initials: LR
authors.lastname: Watkins
authors.forename: S F
authors.initials: SF
authors.lastname: Maier
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D002404:Catheterization; D003213:Conditioning, Psychological / Q000502:physiology*; D004597:Electroshock; D004924:Escape Reaction / Q000502:physiology*; D005239:Fear / Q000502:physiology*; D006380:Helplessness, Learned; D008297:Male; D008845:Microinjections; D009020:Morphine / Q000494:pharmacology; D009271:Naltrexone / Q000008:administration & dosage / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D018847:Opioid Peptides / Q000502:physiology*; D010487:Periaqueductal Gray / Q000502:physiology; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D012701:Serotonin / Q000502:physiology
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D018847:Opioid Peptides; D012701:Serotonin; D009271:Naltrexone; D009020:Morphine