Figure 1. Test day time line for experiments 3 and 4.

Early in the morning of the test day (4–5 d after surgical implantation of indwelling jugular vein catheters), adrenal-intact rats were transferred to a test room (within their home cage) and connected to an extension catheter line that permitted subsequent jugular vein CORT/vehicle infusion and serial blood samples without handling of the rat. Experimental manipulations were initiated approximately 2 hours later. Rats were given an iv infusion of CORT (0.31 mg/kg) or vehicle 60 minutes (experiment 3), 15 minutes (experiment 3), or 30 seconds (experiments 3 and 4) prior to or 5 minutes after (experiments 3 and 4) placement of rats in Plexiglas restraint tubes. Blood samples were taken 5 minutes before restraint onset (baseline) and 5, 15, and 30 minutes after restraint onset. Immediately after the 30-minute blood sample, rats were decapitated and trunk blood (experiment 3) or tissue (experiment 4) was collected. The putative glucocorticoid-negative feedback time domains for fast feedback, delayed feedback, and an intervening silent period are depicted (12).