What's more, activating the aggression system turns on the adrenocortical stress response without actual fighting--or even someone to fight. A hypothetical picture emerges: First, as has long been known, a signal from the nervous system (via pituitary hormone ACTH) signals the adrenals to produce a corticosteroid response that prepares the body for an emergency response, popularly called "fight or flight." Second, in this new finding, the same corticosteroid signal also feeds back to the brain, which lowers attack thresholds and facilitates fighting. Fighting, itself a stressor, then further activates the stress response. And so it goes.
Catecholamines are produced in chromaffin cells in the medulla of the adrenal gland, from tyrosine , a non-essential amino acid derived from food or produced from phenylalanine in the liver. The enzyme tyrosine hydroxylase converts tyrosine to L-DOPA in the first step of catecholamine synthesis. L-DOPA is then converted to dopamine before it can be turned into noradrenaline. In the cytosol , noradrenaline is converted to epinephrine by the enzyme phenylethanolamine N-methyltransferase (PNMT) and stored in granules. Glucocorticoids produced in the adrenal cortex stimulate the synthesis of catecholamines by increasing the levels of tyrosine hydroxylase and PNMT.