The Histaminergic System in Brain: Memory and Synaptic Plasticity

Among the aminergic systems in the brain the histaminergic system has received the least attention although it is equally important. The relatively small groups of neurons containing acetylcholine, noradrenaline, dopamine, serotonin and histamine display comparable electrophysiological properties and morphological features. They all project with multifold arborintion to most regions of the central nervous system with some notable distinctions between them. They form mutual connections and act in concert to maintain the homoeostasis of many basic body functions and behavioral state. They switch and modulate higher brain functions and hormonal states during sleep and waking, during stress and contemplative life, during dosing and attention, during reproduction and cognition. Memory formation and retrieval relies on synchronous activities in selected groups of neurons located in the hippocampus. the amygdala, the cerebral cortex, cerebellum and the basal ganglia. Aminergic systems can enable such synchronous discharges through modulation of the cortical excitability by using a number of sophisticated mechanisms. The histaminergic neurons are unique with respect t o their localisation in the tuberomamillary nucleus of the posterior hypothalamus. They establish a particularly close partnership to the orexinergic neurons in the perifornical area which serve as the conductor in the aminergic orchestra. The involvement of histamine in long lasting changes of synaptic transmission and memory functions is reviewed.