Figure 9.

Mean ± SEM plasma corticosterone (ng/ml) obtained in vehicle-injected (aCSF, white bars) and muscimol-injected rats (black bars) after a 30 min exposure to the first (day 1) of 3 restraint (or no restraint) repeated exposures (24 h apart), and after the injection-free fourth restraint (or no restraint) exposure (test) conducted 48 h after the third restraint/no restraint episodes. All rats included in this histogram had verified rPH bilateral cannulae placements (3.3–3.5 mm posterior to bregma) and are represented in the same groups on day 1 and test. Leftmost bars of each day represent the values of injected rats never restrained to determine possible nonspecific effects of repeated muscimol injections on test day corticosterone release (Veh, n = 4; Musc, n = 3). Middle bars of each day tested the possibility that repeated muscimol injections significantly increased or decreased acute stress-induced corticosterone release on the test day (Veh, n = 5; Musc, n = 6). Rightmost bars of each day evaluated the effects of rPH muscimol injections on both acute and repeated restraint corticosterone release (Veh, n = 10; Musc, n = 12), similar to that tested for loud noise. *Significant within-group differences from day 1 (p < 0.05). ^∼Significantly different from the Vehicle group on day 1 and test, respectively (p < 0.05).