Paper Information

Title: 

EFFECTS OF C-FIBERS REDUCTION ON HEAT PAIN THRESHOLD, MORPHINE ANALGESIA AND HYPERALGESIA

Type: POSTER
Author(s): ALIZADEH ZAHRA*,FEREYDOUNI MASOUD,BEHNAM RASOULI MORTEZA
 
 *DEPARTMENT OF BIOLOGY, FACULTY OF SCIENCES, FERDOWSI UNIVERSITY OF MASHHAD
 
Name of Seminar: IRANIAN CONGRESS OF PHYSIOLOGY AND PHARMACOLOGY
Type of Seminar:  CONGRESS
Sponsor:  PHYSIOLOGY AND PHARMACOLOGY SOCIETY, MASHHAD UNIVERSITY OF MEDICAL SCIENCE
Date:  2009Volume 19
 
 
Abstract: 

Because morphine shows its analgesic effect at the dose of 10 mg/kg and hyperalgesic effect at the dose of 1μg/kg in rat, and the presence of opioid receptors on the afferent nerves, specially C-fibers, present research had studied the effect of C-fibers reduction on heat pain threshold and analgesic and hyperalgesic effects of morphine using tail flick test. Male Wistar rats weighting 180-200 g were used (n=7). Adults animals were assigned in two groups: sham-control (received capsaicin vehicle at neonatal stage: C-normal) and experimental (received neonatal capsaicin: C-lesion). Each of them was divided by three subgroups. The subgroups were i.p. injected a single dose of saline, 10 mg/kg or 1μg/kg morphine separately. The results of tail flick tests were compared between the groups, before and 30 minute after the drug injections. In C-normal group morphine showed analgesic effect at the dose of 10 mg/kg while showed a hyperalgesic effect at the dose of 1μg/kg (P<0.001). In C-lesion group, pain threshold was elevated (P<0.001), in the same condition, analgesic effect of 10 mg/kg morphine was increased and hyperalgesic effect of 1μg/kg morphine was decreased (p<0.01). It seems that C-fibers have an important role on heat pain transmission because the reduction of these fibers using capsaicin significantly reduced the sensitivity to heat pain. Alleviation of morphine analgesic effect at usual dosage after the reduction of C-fibers suggests that analgesic effect of morphine is not mediated only presynapticaly and via C- fibers, nociceptor afferents like as Ad fibers and also post synaptic effects of morphine have to be considered. Morphine ultra low dose hyperalgesia was disappeared by reduction of C-fibers, thus it is probable that morphine hyperalgesia is mediated presynapticaly and via C- fibers.

 
Keyword(s): CAPSAICIN, C-FIBER, ANALGESIC, HYPERALGESIA, MORPHINE, TAIL FLICK TEST
 
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