title: Orphanin FQ/nociceptin suppresses motor activity through an action along the mesoaccumbens axis in rats.
abstract: OBJECTIVE
  Intracerebroventricular administration of orphanin FQ/nociceptin (OFQ/N), the endogenous agonist ligand of the opioid receptor-like (ORL-1) receptor, decreases extracellular levels of dopamine and suppresses motor activity. The presence of the ORL-1 receptor on mesoaccumbal and nigrostriatal dopaminergic neurons raises the possibility that an action along these pathways may be one means by which OFQ/N produces motor suppression. Thus, the present study used local administration of OFQ/N into the ventral tegmental area (VTA), the substantia nigra, the nucleus accumbens and the striatum to determine the contribution of cell-body regions and terminal fields of the dopaminergic neurons to the motor-suppressant effect of OFQ/N.
  
  
  METHODS
  Rats were implanted bilaterally with guide cannulae into one of the brain regions and tested 4 days later. First, the effect of a single dose of OFQ/N (30 microg/0.5 microL per side) on motor activity was determined after direct injection into the VTA, substantia nigra, nucleus accumbens or striatum. Rats were habituated to activity chambers for 1 hour and then injected with either artificial cerebrospinal fluid or OFQ/N into one of the brain regions, and motor activity was recorded for a further 1 hour. Next, the dose-response effect of intra-VTA or intranigral OFQ/N (3 microg or 30 microg/0.5 microL per side) on motor activity was examined. Finally, the effect of intra-VTA OFQ/N (3 microg or 30 microg/0.5 microL per side) on motor activity was determined in the presence of J-113397, an ORL-1 receptor antagonist.
  
  
  RESULTS
  OFQ/N suppressed motor activity when injected into the VTA and to a lesser extent after direct injection into the nucleus accumbens. However, OFQ/N failed to attenuate motor activity significantly after injection into the substantia nigra or the striatum. Subsequent dose-response studies showed that OFQ/N suppressed motor activity even at a 10-fold-lower dose after intrategmental but not intranigral administration. The motor-suppressant action of intra-VTA OFQ/N was attenuated by J-113397 (1.5 microg/0.5 microL per side) administered into the VTA 10 minutes before administration of OFQ/N.
  
  
  CONCLUSIONS
  Our results indicate that OFQ/N suppresses motor activity through activation of the ORL-1 receptor primarily through an action in the VTA.
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences, Neuropsychiatric Institute, UCLA, USA.
authors.forename: Shridhar
authors.initials: S
authors.lastname: Narayanan
authors.forename: Hoa
authors.initials: H
authors.lastname: Lam
authors.forename: F Ivy
authors.initials: FI
authors.lastname: Carroll
authors.forename: Kabirullah
authors.initials: K
authors.lastname: Lutfy
mesh_terms: D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects; D008124:Locomotion / Q000187:drug effects*; D008297:Male; D009714:Nucleus Accumbens / Q000187:drug effects*; D018847:Opioid Peptides / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000819:agonists*; D013378:Substantia Nigra / Q000187:drug effects; D000097629:Nociceptin
chemical_list: D018847:Opioid Peptides; D011957:Receptors, Opioid; D000097629:Nociceptin