Differential cross-tolerance development between single and repeated immobilization stress on the antinociceptive effect induced by b-endorphin, @entity750 , @entity1286 , and @entity10024 in the inflammatory mouse XXXX mode.

@entity11982 @entity14651 @entity1337 @entity406 @entity10024 @entity14650 @entity750 @entity1286 @entity158
We have evaluated the possible underlying mechanisms of immobilization @entity1337 ( @entity1337 ) by behavioral cross-tolerance studies and molecular studies. In the behavioral studies, the cross-tolerance between single or repeated immobilization @entity1337 and the antinociceptive effects of b-endorphin, @entity1286 , @entity750 ( @entity750 ), or @entity10024 were assessed. Both single and repeated ( 7) immobilization stress significantly attenuated the b-endorphin and @entity750 -induced antinociception in the 2nd phase of @entity406 response, respectively. However, these cross-tolerances disappeared in prolonged repetition of the stress ( 14). Neither single nor repeated ( 7 and  14) immobilization stress affected the antinociceptive effect of @entity1286 or @entity10024 at all. We also found that immobilization stress activated hypothalamic proopiomelanocortin ( @entity11982 ) gene and b-endorphin expression. Since, it has potent inhibitory activity on the noxious stimuli-induced @entity11982 expression, immobilization stress seemed to dissipate the @entity11982 gene expression process. Meanwhile, we did not find any changes in the opioid receptors' (mu-, delta- and kappa-receptor) and the cannabinoid receptors' ( @entity14650 and @entity14651 ) expressions in the midbrain regions elicited by single or repeated stress. These results suggested that a single immobilization stress activates the descending @entity158 modulatory system, which is mainly mediated through endorphinergic and serotonergic activation. Moreover, the tolerance of @entity1337 induced by repeated stresses may be due to the prolonged activation of these systems induced by repeated immobilization.
