title: Opioids affect acquisition of LiCl-induced conditioned taste aversion: involvement of OT and VP systems.
abstract: Aversive properties of lithium chloride (LiCl) are mediated via pathways comprising neurons of the nucleus of the solitary tract (NTS) and oxytocin (OT) and vasopressin (VP) cells in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. Because opioids act on brain regions that mediate effects of LiCl, we evaluated whether administration of opioids shortly before LiCl in rats influences 1) development of conditioned taste aversion (CTA) and 2) activation of NTS neurons and OT/VP cells. Neuronal activation was assessed by applying c-Fos immunohistochemical staining. Three opioids were used: morphine (MOR), a mu-agonist, butorphanol tartrate (BT), a mixed mu/kappa-agonist, and nociceptin/orphanin FQ (N/OFQ), which binds to an ORL1 receptor. BT and N/OFQ completely blocked acquisition of CTA. MOR alleviated but did not eliminate the aversive effects. Each of the opioids decreased LiCl-induced activation of NTS neurons as well as OT and VP cells in the PVN and SON. We conclude that opioids antagonize aversive properties of LiCl, presumably by suppressing activation of pathways that encompass OT and VP cells and NTS neurons.
authors.affiliation: Minnesota Obesity Center, Research Service Veterans Affairs Medical Center, Minneapolis 55417, USA.
authors.forename: P K
authors.initials: PK
authors.lastname: Olszewski
authors.forename: Q
authors.initials: Q
authors.lastname: Shi
authors.forename: C J
authors.initials: CJ
authors.lastname: Billington
authors.forename: A S
authors.initials: AS
authors.lastname: Levine
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D002077:Butorphanol / Q000494:pharmacology; D018021:Lithium Chloride / Q000494:pharmacology*; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018847:Opioid Peptides / Q000494:pharmacology; D010121:Oxytocin / Q000502:physiology*; D010286:Paraventricular Hypothalamic Nucleus / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000819:agonists; D013495:Supraoptic Nucleus / Q000502:physiology*; D013649:Taste; D014667:Vasopressins / Q000502:physiology*; D000097629:Nociceptin
chemical_list: D000701:Analgesics, Opioid; D002077:Butorphanol; D018021:Lithium Chloride; D009020:Morphine; D018847:Opioid Peptides; D010121:Oxytocin; D011957:Receptors, Opioid; D014667:Vasopressins; D000097629:Nociceptin