Figure 4. Serotonin pathways affected in PD and PD-D.
The two major serotonin nuclei with projections to the forebrain are the dorsal raphe containing B6/7 neurons, located in the periaqueductal grey matter of the midbrain, and the median raphe nucleus containing B5/8 neurons, located in the midline of the upper pons. The dorsal raphe projects to the striatum and cortex, while the median raphe projects to limbic regions and cortex. Only the median raphe is affected in PD, but whether this is associated with dementia or not is not clear. aq=aqueduct, N. acc=nucleus accumbens, V=fourth ventricle.