Another possibility is that male and females experience stress differently, the study said. If females perceive the restraint as more traumatic, they may react more strongly to the stress associated with the induction of the foreign substance and have a stronger immune reaction.

Stressor simulates collapsed burrow The 120 rats in the study, 60 males and 60 females, were weaned 28 days after birth, and assigned to one of two groups: those that lived in their own cages (isolated) and those that lived in same-sex groups of five (non-isolated). The isolated and non-isolated groups had an equal number of males and females.

When the rats were 100 days old, the researchers subdivided the two groups. They placed half the isolated rats into the stressed group and half into the non-stressed group. They divided the non-isolated rats in the same way. The four resultant groups -- isolated and stressed, isolated and non-stressed, non-isolated and stressed, and non-isolated and non-stressed -- each had 15 females and 15 males.

The researchers then injected the two non-stressed groups, (isolated and non-isolated), with carrageenin (seaweed), a substance that doesn't harm the rats but does challenge their immune systems. The immune system responds by walling off the carrageenin with scar tissue, then neutralizing and reabsorbing it, Hermes explained.

The rats in the stressed groups, both isolated and non-isolated, however, weren't injected with the carrageenin at the 100-day mark. Instead, each was placed for 30 minutes in a restraint tube (the acute stressor). The restraint tube inhibits the rat from moving and simulates a collapsed burrow. The stressed animals were injected with carr
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Contact: Christine Guilfoy
cguilfoy@the-aps.org
301- 634-7253
American Physiological Society
27-Feb-2006