The aim of this review is to survey biochemical, electrophysiological and b
ehavioral evidence of the interactions between the cholinergic and histamin
ergic systems and evaluate their possible involvement in cognitive processe
s. The cholinergic system has long been implicated in cognition, and there
is a plethora of data showing that cholinergic deficits parallel cognitive
impairments in animal models and those accompanying neurodegenerative disea
ses or normal aging in humans. Several other neurotransmitters, though, are
clearly implicated in cognitive processes and interact with the cholinergi
c system. The neuromodulatory effect that histamine exerts on acetylcholine
release is complex and multifarious. There is clear evidence indicating th
at histamine controls the release of central acetylcholine (ACh) locally in
the cortex and amygdala, and activating cholinergic neurones in the nucleu
s basalis magnocellularis (NBM) and the medial septal area-diagonal band th
at project to the cortex and to the hippocampus, respectively. Extensive ex
perimental evidence supports the involvement of histamine in learning and m
emory and the procognitive effects of H-3 receptor antagonists. However, an
y attempt to strictly correlate cholinergic/histaminergic interactions with
behavioral outcomes without taking into account the contribution of other
neurotransmitter systems is illegitimate. Our understanding of the role of
histamine in learning and memory is still at its dawn, but progresses are b
eing made to the point of suggesting potential treatment strategies that ma
y produce beneficial effects on neurodegenerative disorders associated with
impaired cholinergic function. (C) 2001 Elsevier Science B.V. All rights r
eserved.