title: Long-lasting delayed hyperalgesia after chronic restraint stress in rats-effect of morphine administration.
abstract: Different effects upon the nociceptive response have been observed with exposure to acute and chronic stress in rats. In the present study we repeatedly submitted rats to restraint for 40 days, inducing hyperalgesia using the tail-flick test. A new session of acute stress was applied at the end of 40 days period, and the chronically-stressed animals demonstrated analgesia after forced swimming, but not after restraint. The effect of stress interruption for 14 or 28 days on the nociceptive threshold was then investigated. The basal tail-flick latency remained decreased for at least 28 days (hyperalgesic effect). Following the periods of suspension, the animals were submitted to new session of acute restraint, and stress-induced analgesia was observed only after 28 days of stress interruption. Thus, the mechanisms involved in the long-lasting hyperalgesia presented in this study are not exactly the same as those responsible for the analgesia induced by acute stressors. After 40 days of chronic stress treatment, morphine was injected i.p. (1.0, 5.0 mg/kg or saline). The repeatedly stressed rats displayed decreased morphine effects on nociception compared to unstressed controls. The tolerance of the response to morphine agrees with previous studies suggesting that chronic restraint stress could modify the activity of opioid systems.
authors.affiliation: Departamentos de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Ramiro Barcelos, 2600-Anexo, Lab. 32, 90035-003, RS, Porto Alegre, Brazil
authors.forename: Iraci Lucena
authors.initials: IL
authors.lastname: da Silva Torres
authors.forename: Simone N S
authors.initials: SN
authors.lastname: Cucco
authors.forename: Marcio
authors.initials: M
authors.lastname: Bassani
authors.forename: Marcelo S
authors.initials: MS
authors.lastname: Duarte
authors.forename: Patricia P
authors.initials: PP
authors.lastname: Silveira
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Vasconcellos
authors.forename: Angela Sampaio
authors.initials: AS
authors.lastname: Tabajara
authors.forename: Giovana
authors.initials: G
authors.lastname: Dantas
authors.forename: Fernanda U
authors.initials: FU
authors.lastname: Fontella
authors.forename: Carla
authors.initials: C
authors.lastname: Dalmaz
authors.forename: Maria Beatriz C
authors.initials: MB
authors.lastname: Ferreira
mesh_terms: D000818:Animals; D002908:Chronic Disease; D006930:Hyperalgesia / Q000188:drug therapy* / Q000209:etiology; D009020:Morphine / Q000008:administration & dosage*; D051381:Rats; D012149:Restraint, Physical; D013312:Stress, Physiological / Q000150:complications / Q000188:drug therapy*; D013995:Time
chemical_list: D009020:Morphine