Estrogen-serotonin axis

Estrogen activates the enzyme tryptophan hydroxylase, which converts tryptophan into serotonin, and inhibits the enzyme monoamine oxidase type A, which breaks down serotonin, thereby increasing serotonin levels in the brain 2. This relationship between estrogen and serotonin is bidirectional, as estrogen also decreases the binding of serotonin to its receptors and inhibits its degradation 4. Estrogen's effects on serotonin are mediated through its activation of the corticotropin release hormone, CRH, which promotes inflammation and activates the pituitary and adrenal glands 1.

The interaction between estrogen and serotonin is complex and influenced by other hormones, such as progesterone, which inhibits tryptophan hydroxylase and increases the breakdown of serotonin 2. Progesterone has a protective effect against serotonin's inflammatory and stress-promoting effects 6. The relationship between estrogen and serotonin is also influenced by the concentration of dopamine and other neurotransmitters in the brain 4.

Research has shown that estrogen selectively increases tryptophan hydroxylase-2 mRNA expression in distinct subregions of the rat midbrain raphe nucleus, which is associated with anxiety behavior 5. Estrogen also regulates the release of insulin-like growth factor-I, oxytocin, and progesterone, which are involved in various physiological processes 5.

The activation of estrogen receptors by serotonin has been observed, and antagonist of these hormones can have opposite effects 8. This highlights the complex and bidirectional relationship between estrogen and serotonin, which is influenced by various hormones and neurotransmitters.

It is worth noting that the pharmaceutical industry's manipulation of information about estrogen has been more extreme than its treatment of serotonin, and that the myth about serotonin as a "happy hormone" has led to a misunderstanding of its effects on the brain 1.