The dorsal raphe nucleus (DRN) is an origin of the central serotonergic system. About 50% of the serotonin neurons in the rat brain are in the DRN, although fewer than 50% of the neurons in the DRN are serotonergic (Waselus et al., 2011). The DRN has projections into numerous brain regions, including the mesolimbic regions important in reward and addiction (amygdala, hippocampus, caudate putamen, substantia nigra and ventral tegmental area). Projections from the raphe nuclei mediate dopamine release in the ventral tegmental area (Liu et al., 2006b; Rodd et al., 2007; Sari et al., 2011). Ethanol-naïve P rats have fewer serotonergic neurons in the DRN than ethanol-naïve NP rats and decreased serotonergic projections into terminal regions (Zhou et al., 1994). Postmortem studies of the DRN of alcoholics (Underwood et al., 2007) found less serotonin transporter in the brainstem of alcoholics.
