Editing Serotonin (section)

====Ultrastructure and function====
The serotonin nuclei may also be divided into two main groups, the rostral and caudal containing three and four nuclei respectively. The rostral group consists of the caudal linear nuclei (B8), the dorsal raphe nuclei (B6 and B7) and the median raphe nuclei (B5, B8 and B9), that project into multiple cortical and subcortical structures. The caudal group consists of the nucleus raphe magnus (B3), raphe obscurus nucleus (B2), raphe pallidus nucleus (B1), and lateral medullary reticular formation, that project into the brainstem.<ref>{{cite book | veditors = Müller CP, Jacobs BL |title=Handbook of the behavioral neurobiology of serotonin |date=2009 |publisher= Academic |location=London |isbn=978-0-12-374634-4|pages=51–59|edition=1st}}</ref>

The serotonergic pathway is involved in sensorimotor function, with pathways projecting both into cortical (Dorsal and Median Raphe Nuclei), subcortical, and spinal areas involved in motor activity. Pharmacological manipulation suggests that serotonergic activity increases with motor activity while firing rates of serotonergic neurons increase with intense visual stimuli. Animal models suggest that kainate signaling negatively regulates serotonin actions in the retina, with possible implications for the control of the visual system.<ref>{{cite journal | vauthors = Passos AD, Herculano AM, Oliveira KR, de Lima SM, Rocha FA, Freitas HR, da Silva Sampaio L, Figueiredo DP, da Costa Calaza K, de Melo Reis RA, do Nascimento JL | title = Regulation of the Serotonergic System by Kainate in the Avian Retina | journal = Cellular and Molecular Neurobiology | volume = 39 | issue = 7 | pages = 1039–1049 | date = October 2019 | pmid = 31197744 | doi = 10.1007/s10571-019-00701-8 | s2cid = 189763144 | pmc = 11457822 }}</ref> The descending projections form a pathway that inhibits pain called the "descending inhibitory pathway" that may be relevant to a disorder such as fibromyalgia, migraine, and other pain disorders, and the efficacy of antidepressants in them.<ref>{{cite book | chapter = Serotonin in Pain and Pain Control | vauthors = Sommer C | veditors = Müller CP, Jacobs BL |title=Handbook of the behavioral neurobiology of serotonin|date=2009|publisher=Academic|location=London|isbn=978-0-12-374634-4|pages=457–460|edition=1st}}</ref>

Serotonergic projections from the caudal nuclei are involved in regulating mood and emotion, and hypo-<ref>{{cite book | chapter = Serotonin in Mode and Emotions | vauthors = Hensler JG | veditors = Müller CP, Jacobs BL | title=Handbook of the behavioral neurobiology of serotonin|date=2009|publisher=Academic|location=London|isbn=978-0-12-374634-4|pages=367–399|edition=1st}}</ref> or hyper-serotonergic<ref>{{cite journal | vauthors = Andrews PW, Bharwani A, Lee KR, Fox M, Thomson JA | title = Is serotonin an upper or a downer? The evolution of the serotonergic system and its role in depression and the antidepressant response | journal = Neuroscience and Biobehavioral Reviews | volume = 51 | pages = 164–188 | date = April 2015 | pmid = 25625874 | doi = 10.1016/j.neubiorev.2015.01.018 | s2cid = 23980182 }}</ref> states may be involved in depression and sickness behavior.