p < 0.0001; Fig. 3-2B), reaching asymptote by day 4, with no significant between-groups

differences or group by time interaction effect.

 Exposure to acute social defeat (NC/A and C/A) produced significant elevations in

circulating ACTH concentrations when compared with the ACTH concentrations in the

control rats (NC/NA) (F (5, 30) = 3.874, p < 0.0079; Fig. 3-3A). Circulating ACTH

concentrations were not elevated in the chronically, but not acutely, stressed rats (C/NA).

Exposure to social defeat stress for all groups (including C/NA) produced significant

elevations in circulating CORT concentrations when compared with the CORT

concentrations in the control rats (F (5, 30) = 20.79, p < 0.0001; Fig. 3-3B).

 Exposure to social defeat significantly decreased thymus masses in Groups C/A-10

and C/A-30, but not for the other groups (F (2, 15) = 5.651, p < 0.0148; Fig. 3-4A).

There were no significant differences in adrenal masses between the rats in the stressed

groups and the rats in the control group (F (5, 30) = 0.9299, p < 0.4756; Fig. 3-4B).