The anatomical organization of monoaminergic systems shares a number of common features. Monoaminergic systems are strikingly divergent: monoaminergic cell bodies are generally found in aggregates located in a few restricted subcortical brain regions. Individual monoaminergic neurons typically possess long and extensively branched axonal processes, innervating a large number of postsynaptic cells. This organization may permit monoaminergic systems to exert control in a coordinated manner over diverse brain regions. The actions of monoamines in particular brain areas are determined not only by the extent of monoamine innervation, but also by the receptor subtypes expressed in these regions. Monoaminergic receptors are diverse with regard to their regional and synaptic localization within the brain, and to the intracellular signaling systems to which they couple. This receptor diversity provides a means through which a single signaling molecule may produce effects that vary in different postsynaptic neurons.
[...] The hypothalamus receives the densest histaminergic innervation, consistent with a role for this transmitter in the regulation of autonomic and neuroendocrine processes. Acetylcholine The axonal processes of cholinergic neurons may either project to distant brain regions (projection neurons) or contact local cells within the same structure (interneurons). Two large clusters of cholinergic projection neurons are found within the brain: the basal forebrain complex and the mesopontine complex. The basal forebrain complex provides the vast majority of the cholinergic innervation to the nonstriatal telencephalon. [...]
[...] These axons show differential sensitivity to the neurotoxic effects of the amphetamine analog 3,4-methylene-dioxymethamphetamine (MDMA, “ecstasy”). This agent produces a selective loss of fine axons while sparing the larger beaded projections derived from the median raphe. The significance of the morphological differences in these projection fibers remains to be determined. Both types of fibers are found in the neocortex, which receives a rich serotonergic innervation derived from both nuclei. The divergent nature of serotonergic projections is illustrated by this innervation; it has been estimated that each serotonergic neuron may influence 500,000 target neurons. [...]
[...] This projection modulates motor function, as highlighted by the motor disturbances of Parkinson's disease, a disorder characterized by degeneration of the nigrostriatal system. In addition, the extrapyramidal adverse effects of antipsychotic drugs are believed to result from the blockade of striatal dopamine receptors. The midbrain ventral tegmental area lies medial to the substantia nigra and contains dopaminergic neurons that give rise to the mesocorticolimbic dopamine system. These neurons send ascending projections that innervate limbic structures, such as the nucleus accumbens and amygdala, as well as associated cortical structures, particularly the prefrontal cortex. [...]
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