| Popis: |
Serotonin is an ancient neurotransmitter. Phylogenetic comparisons suggest that the earliest serotonin receptor may have first appeared over 700 million years ago (Peroutka and Howell 1994). It is released from fiber tracts originating in primitive brainstem regions (the raphe nuclei of the brainstem reticular formation), and is found in species as ancient as Aplysia, Caenorhabditis elegans, and Drosophila. In addition, its synapses and receptors are widely distributed throughout the brain, serving many broad modulatory roles for diverse brain functions. It is not surprising, then, that serotonin receptors are primarily of the G-protein-coupled, 7-transmembrane receptor (7TM) class since these receptors couple to enzymatic and ion channel-modulating second messenger pathways (primarily adenylate cyclase, phosphoinositide turnover, and potassium channel modulation) which exhibit time constants in the second to millisecond range, consistent with broad signal modulation and gain-setting functions in the brain. |
