Scientists think that some of the neurotransmitters may be the same or similar chemicals as the hormones but acting in a different capacity. Some of the hormones travel throughout the body, altering the metabolism of food so that the brain and muscles have sufficient stores of metabolic fuel for activities, such as fighting or fleeing, that help the person cope with the source of the stress. In the brain, the neurotransmitters trigger emotions, such as aggression or anxiety, that prompt the person to undertake those activities. Normally, stress hormones are released in small amounts throughout the day, but when the body is under stress the level of these hormones increases dramatically. The release of stress hormones begins in the brain.
Cortisol travels throughout the body, helping it to cope with stress.
If the stressor is mild, when the cortisol reaches the brain and pituitary gland it inhibits the further release of CRF and ACTH, which return to their normal levels. But if the stressor is intense, signals in the brain for more CRF release outweigh the inhibitory signal from cortisol, and the stress hormone cycle continues. Researchers speculate that CRF and ACTH may be among the chemicals that serve dual purposes as hormones and neurotransmitters. The researchers posit that if, indeed, these chemicals also act as neurotransmitters, they may be involved in producing the emotional responses to stress. The stress hormone cycle is controlled by a number of stimulatory chemicals in addition to CRF and ACTH and inhibitory chemicals in addition to cortisol both in the brain and in the blood.