The serotonin pathways in the brain
The principal centres for serotonergic neurones are the rostral and caudal raphe nuclei. From the rostral raphe nuclei axons ascend to the cerebral cortex, limbic regions and specifically to the basal ganglia. Serotonergic nuclei in the brain stem give rise to descending axons, some of which terminate in the medulla, while others descend the spinal cord.
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References
5-Hydroxytryptamine. In: Neurotransmitters and drugs, 3rd edition. Kruk ZL and Pycock CJ. London, England: Chapman and Hall, 1993:116–132.