PRL and migraine disorder: For example, an acute citalopram challenge can induce arousal and a neuroendocrine stress response through the release of prolactin, adrenocorticotropic hormone, and cortisol through activation of the hypothalamic-pituitary-adrenal (HPA) axis.2,5,31,34 The challenge already provided compelling evidence for altered tryptophan and kynurenine metabolism18 and increased neuronal stress sensitivity in migraine without aura (MO); the method is associated with minimal side effects, validating its use as an experimental tool in patients with migraine to test the stress axis.