Unpredictable sound stress evokes PMA, hind paw mechanical
allodynia, and grimacing pain behavior
We first determine the development of nociception post stress in the 1,
3, 7, 10, and 14 days and address whether there would be a sexually
dimorphic effect. We observed in this stress model, that on day 1 after
stress induction there was an enhancement in the plasma corticosterone
level, but not after 7 days of stress exposure (data not shown), as
described before for this model using rats (Khasar et al., 2008).
Male and female mice showed hind paw mechanical allodynia in the 3-, 7-,
and 10-days post stress induction. Mice returned to baseline withdrawal
thresholds in 14 days post stress induction (Fig. 2 A and B). Similarly,
when verifying PMA, in both sexes, the allodynic effect of stress
started on the first-day post-stress and was maintained until the
10th day (Fig 2. D and E). To measure spontaneous non
evoked pain in these animals, we assessed grimace. We observed that both
males and females ST, compared to NST mice had grimacing pain behavior
on the first and 7th-day post stress (Fig 2. G and H).
Thus, we verified that the nociceptive peak was on the 7th-day
post-stress for PMA, hind paw mechanical allodynia, and grimacing pain
behavior. Interestingly, on the nociceptive peak, it was observed a
sexual dimorphism for hind paw mechanical allodynia, PMA, and grimacing
pain behavior. These data showed that among the ST animals, females had
higher nociception compared to males in
the 7th-day post-stress induction
(Fig. 2 C, F, I). However, male and female mice had similar development
of nociception at 1-, 3-, 10-, and 14-days post-stress induction (data
not shown).