TITLE:
Sex Differences in Antinociceptive Effects Induced by Gravity Stress in Rats
AUTHORS:
Mari Kimoto, Jorge Lopes Zeredo, Zenro Nihei, Hiromi Yamashita, Kei Kaida, Kazuo Toda
KEYWORDS:
Gravity; Stress; Sex; Nociception; Opioid; Rat
JOURNAL NAME:
Journal of Behavioral and Brain Science,
Vol.3 No.2,
May
22,
2013
ABSTRACT: A number of studies have demonstrated that sex
differentially affects responses to stress and pain. In this study, sex-related
differences in pain responding were investigated in a gravity-induced analgesia
model, where the effects of stressful high-gravity loading (1.5G or 2.0G for 10
min) on nociceptive behavior in male and female rats were investigated.
In each rat, eight sites (nose, both forepaws, upper and lower back, both hind paws
and tail) were selected to apply noxious stimuli using a von Frey-type
needle stimulator. The threshold values of the withdrawal responses were
measured. In order to confirm the involvement of endogenous opioids in
gravity-induced antinociceptive effects, naloxone-HCl (an
opioid antagonist) was used. Effective analgesic effects could be induced by
strong (2.0G) gravity loading, and clear sex differences were observed.
Gravity-induced analgesic effects were more effective in males than in females,
indicating that males are more sensitive to stress than females judging from
nociceptive modulation. Naloxone-HCl produced a more pronounced suppression
of nociceptive behavior in male rats, suggesting that gravity loading may
activate endogenous opioids more readily in males than in females.