Brain histamine: psychoneuroimmune regulator in physiological and pathological conditions.

HA is a biogenic amine widely distributed in the CNS, with neurons located in the posterior hypothalamus. HA acts as a neurotransmitter and/or neuromodulator regulating neuroendocrine and neuroimmune functions, circadian rhythms, sleep-wakefulness cycle, body temperature, centrally-mediated neurovegetative functions, cerebrovascular control, and behavior and learning. Changes in brain HA are observed in aging. High levels of HA in CSF and CNS of AD patients might reflect a reactive response to neuroimmune activation and tissue damage.