title: Alpha(2)-noradrenergic antagonist administration into the central nucleus of the amygdala blocks stress-induced hypoalgesia in awake behaving rats.
abstract: Stress-induced hypoalgesia (SIH) is an adaptive behavioral phenomenon mediated in part by the amygdala. Acute stress increases amygdalar noradrenaline levels and focal application of alpha(2)-adrenoceptor agonists in the central nucleus of the amygdala (CeA) is antinociceptive. We hypothesized that alpha(2)-adrenoceptor antagonist administration into the CeA may block SIH. Bilateral microinjections of drug or saline via chronically implanted CeA cannulae were followed by either a period of restraint stress or rest. The nocifensive paw-withdrawal latency (PWL) to a focused beam of light was measured. PWLs were longer in restrained rats, constituting SIH. Microinjection of the alpha(2)-adrenoceptor antagonist idazoxan into the CeA prior to restraint blocked SIH. Idazoxan administration in unrestrained rats had no effect. Microinjection of the alpha(2)-adrenoceptor agonist clonidine in unrestrained rats caused dose dependent hypoalgesia, mimicking the effects of environmental stress. alpha(2)-Adrenoceptor function in the CeA is necessary for restraint-induced SIH.
authors.affiliation: Department of Neurological Surgery, Oregon Health & Science University, 3303 Southwest Bond Avenue, Portland, OR 97239, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Ortiz
authors.forename: L N
authors.initials: LN
authors.lastname: Close
authors.forename: M M
authors.initials: MM
authors.lastname: Heinricher
authors.forename: N R
authors.initials: NR
authors.lastname: Selden
mesh_terms: D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D000679:Amygdala / Q000502:physiology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D019329:Idazoxan / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D010147:Pain Measurement / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012149:Restraint, Physical; D013315:Stress, Psychological / Q000523:psychology*; D014851:Wakefulness / Q000502:physiology
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D019329:Idazoxan