In vivo imaging allows regional analyses (from the whole brain to groups of neurons), whereas electron microscopy provides images … Cellular mapping of 5-HT-producing neurons in the CNS Due to the postmortem instability of 5-HT118 and other possible methodological bias,119 quantitative biochemical estimation of 5-HT in the human brain subdivisions should be interpreted with caution, as illustrated by the numerous discrepant data reported since the 1950s. For the same reason, morphological approaches by formaldehyde-induced fluorescence or immunohistochemistry using antibodies

against 5-HT are limited to biopsies and fetal brain tissues. Most Inhibitors,research,lifescience,medical of the anatomical studies in human are based on regional autoradiography of SERT binding sites to selective radioligands and immunohistochemical Inhibitors,research,lifescience,medical studies using antibodies against TPOH, which represent more stable postmortem markers. Therefore, from these studies and those performed in much detail in other species including rodents,120 cat,121 and nonhuman primates,122 it appears that the anatomy of the serotonergic system has remained somewhat similar between different species of mammals. The 5-HT systems belong to the neuronal systems composed of a restricted number of neurons emitting extensively branched, non- or poorly myelinated axons that innervate almost all brain nuclei. As first described

in human fetuses123,124 and later Inhibitors,research,lifescience,medical in adults by several authors,125-129 the distribution of the 5-HT cell bodies (approximately 350 000 cells) in the human brain is restricted to the brain stem. As illustrated in Figure 1, a large majority of them is concentrated along the midline in the raphe nuclei, extending from the caudalmost level Inhibitors,research,lifescience,medical of the medulla oblongata to mid-level of mesencephalon, but Inhibitors,research,lifescience,medical a substantial number is located in the reticular formation

lateral to these nuclei. The 5-HT neurons form a continuum of cells with loosely defined boundaries along the raphe nuclei. On the basis of studies of cell body localization and their respective projections, the 5-HT neurons can be separated into two groups: a rostral group located in the mesencephalic and rostral pons, sending axons to the forebrain, and a caudal group lying in the rostral pons and medulla oblongata, sending axons in the brain stem and spinal cord (refs in ref 128) In humans, the rostral group contains approximately 85% of the 5-HT neurons. It is composed of neurons located in four DZNeP cell line nuclei and one area, namely the interpeduncular, Microbiology and Molecular Biology Reviews the caudal linear, the dorsal raphe (DRN with 165 000 neurons) and the median raphe (MRN with 64 000 neurons) nuclei. The additional area corresponds to the caudal mesencephalic and rostral pontine reticular formation. 5-HT neurons spread in this area were already observed in the rat and cat species and their large number estimated in human (60 000 neurons). The caudal group accounts for 15% of all the 5-HT neurons.