09 November 2006

Breeding season affects stress-induced analgesia in mice

Sex differences in the expression and antagonism of swim stress-induced analgesia in deer mice vary with the breeding season
Kavaliers and Galea
Summary (you might want to skip to the underlined part)
Swim stress-induced analgesia (SSIA) was examined in photoperiodically induced 'breeding'
(reproductive) and 'non-breeding' (non-reproductive) adult male and female deer mice, Perornyscus maniculatus.
Nociceptive responses (50°C, hot-plate) of breeding and non-breeding deer mice were determined after either a 1-
or 3-min swim in 20°C water. The 1-min swim induced an immediate and relatively short-lasting naloxone (1.0
mg/kg) insensitive 'non-opioid'-mediated SSIA that was antagonized by the N-methyl-D-aspartate (NMDA)
antagonist, MK-801 (0.10 mg/kg) in all of the groups of mice except the breeding (reproductive) females. Breeding
females displayed a non-opioid analgesia that was insensitive to MK-801. The 3-min swim induced a relatively more
prolonged mixed opioid and 'non-opioid' SSIA of which the initial portion was sensitive to antagonism by MK-801
in all groups of the mice except the breeding females, while the latter portion (15 min after swim) was reduced by
naloxone in all of the groups of mice. Overall, the breeding males displayed greater levels of SSIA than the breeding
females, with no consistent sex differences in the non-breeding mice. Within sexes, the breeding males displayed
greater levels of opioid and non-opioid SSIA than the non-breeding males, while the non-breeding females
displayed greater levels of SSIA than the breeding females. These results show that both sex and reproductive status
affect the expression and neurochemical mediation of non-opioid SSIA. These findings also suggest that reproductive
females may have an unique or novel hormonally (estrogen) dependent mechanism associated with the
expression of SSIA

(c) 1995 Elsevier Science

Pain 65 (1995) 327-334
Categories: ,