Problem
You are examining stress responses by measuring circulating ACTH levels in the blood in the following three groups of animals:
1. Group 1: Animals undergo surgery for implantation of a stimulating electrode in the dorsomedial prefrontal cortex. After recovery, the brain region is stimulated at the same time the animal is exposed to a stressor.
2. Group 2: Animals undergo surgery for implantation of a stimulating electrode in the dorsomedial prefrontal cortex. After recovery, the animal is exposed to a stressor, but the brain region is not simulated.
3. Group 3: Animals do not undergo the surgery nor are they exposed to a stressor.
For all graphs: Circulating ACTH is measured 30 minutes after manipulation. Asterisk * indicates significantly different from the non-stressed control animals, plus sign + indicates significantly different from the non-stimulated sham animals.