Anatomical distribution of the central serotonergic system
Neurons containing 5-HT are restricted to clusters of cells around the midline of the pons and upper brainstem; this is known as the raphe´ area of the midbrain. In addition, according to studies of rat brain, cells containing 5-HT are located in the area postrema and in the caudal locus coeruleus, which forms an anatomical basis for a direct connection between the serotonergic and noradrenergic systems. The more caudal groups of cells in the raphe´ project largely to the medulla and the spinal cord, the latter projections being physiologically important in the regulation of pain perception at the level of the dorsal horn. Conversely, the more rostral cells of the dorsal and median raphe´ project to limbic structures such as the hippocampus and, in particular, to innervate extensively the cortex. Unlike the noradrenergic cortical projections, there does not appear to be an organized pattern of serotonergic terminals in the cortex. In general, it would appear that the noradrenergic and serotonergic systems are colocalized in most limbic areas of the brain, which may provide the anatomical basis for the major involvement of these transmitters in the affective disorders.
Neurons containing 5-HT are restricted to clusters of cells around the midline of the pons and upper brainstem; this is known as the raphe´ area of the midbrain. In addition, according to studies of rat brain, cells containing 5-HT are located in the area postrema and in the caudal locus coeruleus, which forms an anatomical basis for a direct connection between the serotonergic and noradrenergic systems. The more caudal groups of cells in the raphe´ project largely to the medulla and the spinal cord, the latter projections being physiologically important in the regulation of pain perception at the level of the dorsal horn. Conversely, the more rostral cells of the dorsal and median raphe´ project to limbic structures such as the hippocampus and, in particular, to innervate extensively the cortex. Unlike the noradrenergic cortical projections, there does not appear to be an organized pattern of serotonergic terminals in the cortex. In general, it would appear that the noradrenergic and serotonergic systems are colocalized in most limbic areas of the brain, which may provide the anatomical basis for the major involvement of these transmitters in the affective disorders.
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