<Tr> <Td> 5 - HT </Td> <Td> 98.41 </Td> <Td> Cognition (antagonists ↑); antidepressant effects (agonists & antagonists ↑); anxiogenic effects (antagonists ↑). G signalling via activating adenylyl cyclase . </Td> </Tr> <Tr> <Td> 5 - HT </Td> <Td> 8.11 </Td> <Td> Cognition (antagonists ↑); antidepressant effects (antagonists ↑). Acts by G signalling via activating adenylyl cyclase . </Td> </Tr> <P> The neurons of the raphe nuclei are the principal source of 5 - HT release in the brain . There are nine raphe nuclei, designated B1 - B9, which contain the majority of serotonin - containing neurons (some scientists chose to group the nuclei raphes lineares into one nucleus), all of which are located along the midline of the brainstem, and centered on the reticular formation . Axons from the neurons of the raphe nuclei form a neurotransmitter system reaching almost every part of the central nervous system . Axons of neurons in the lower raphe nuclei terminate in the cerebellum and spinal cord, while the axons of the higher nuclei spread out in the entire brain . </P> <P> 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 . </P>

Where does serotonin come from in the brain