Serotonergic Autoinhibition within Dorsal Raphe Nucleus Modulates Sodium Appetite

Excerpt

Serotonin [5-hydroxytryptamine (5-HT)] is a widespread monoaminergic neurotransmitter in the brain. Its neuronal population is among the first to differentiate in the mammalian brain (Gaspar et al. 2003), playing an important role in neurogenesis (Lauder and Krebs 1978) and in several normal physiological functions and pathological disorders throughout the mammalian life. There are 235,000 serotonergic neurons in the human midbrain raphe and 10,000–12,000 multipolar cell in rats (Abrams et al. 2004; Adell et al. 2002). The 5-HT neurons exist in a widespread distributed system in the mammalian brain (Jacobs and Azmitia 1992), with a peculiar elevated density of serotonergic perikarya dispersed on or near the brainstem’s midline, where they are primarily located in the median (MRN) and dorsal raphe (DRN) nuclei (Azmitia and Segal 1978; Parent et al. 1981). The DRN is located in the ventral part of the midbrain periaqueductal gray matter and extends caudally, bordering the anterior portion of the pons. The DRN’s serotonergic neurons are organized into a cluster arranged in several topographical subdivisions. Rostral projections of the DRN are arranged in a conspicuous manner, connected to an extensive collaborative distribution in the terminal fields (Azmitia 1987, 2001). According to Azmitia, different subsets of serotonergic neurons take part in the integrated coordination of neural control systems (Azmitia 1987, 2001; Jacobs and Azmitia 1992). This idea has been revisited by Abrams et al. (2004) through morphological and functional approaches.