The distribution of neurons, containing 5-HT is very widespread, and is similar to that of NA. The cells occur in several large clusters in the pons and upper medulla, which lie close to the midline (raphe) and are often referred to as raphe nuclei. The rostrally situated nuclei project, via the medial forebrain bundle, to many parts of the cortex, hippocampus, basal ganglia, limbic system and hypothalamus. The caudally situated cells project to the cerebellum, medulla and spinal cord (Fig.3).