LSD connects with 5-HT receptor
Pharmacology
Pharmacodynamics
Most serotonergic psychedelics are not significantly dopaminergic, and LSD is therefore atypical in this regard. The agonism of the D2 receptor by LSD may contribute to its psychoactive effects in humans.LSD binds to most serotonin receptor subtypes except for the 5-HT3 and 5-HT4 receptors. However, most of these receptors are affected at too low affinity to be sufficiently activated by the brain concentration of approximately 10–20 nM. In humans, recreational doses of LSD can affect 5-HT1A (Ki=1.1nM), 5-HT2A (Ki=2.9nM), 5-HT2B (Ki=4.9nM), 5-HT2C (Ki=23nM), 5-HT5A (Ki=9nM [in cloned rat tissues]), and 5-HT6 receptors (Ki=2.3nM). Although not present in humans, 5-HT5B receptors found in rodents also have a high affinity for LSD. The psychedelic effects of LSD are attributed to cross-activation of 5-HT2A receptor heteromers. Many but not all 5-HT2A agonists are psychedelics and 5-HT2A antagonists block the psychedelic activity of LSD. LSD exhibits functional selectivity at the 5-HT2A and 5HT2C receptors in that it activates the signal transduction enzyme phospholipase A2 instead of activating the enzyme phospholipase C as the endogenous ligand serotonin does.Exactly how LSD produces its effects is unknown, but it is thought that it works by increasing glutamate release in the cerebral cortex and therefore excitation in this area, specifically in layers IV and V. LSD, like many other drugs of recreational use, has been shown to activate DARPP-32-related pathways. The drug enhances dopamine D2 receptor protomer recognition and signaling of D2–5-HT2A receptor complexes, which may contribute to its psychotropic effects. LSD has been shown to have low affinity for H1 receptors, displaying antihistamine effects.LSD is a biased agonist that induces a conformation in serotonin receptors that preferentially recruits β-arrestin over activating G proteins. LSD also has an exceptionally long residence time when bound to serotonin receptors lasting hours, consistent with the long lasting effects of LSD despite its relatively rapid clearance. A crystal structure of 5-HT2B bound to LSD reveals an extracellular loop that forms a lid over the diethylamide end of the binding cavity which explains the slow rate of LSD unbinding from serotonin receptors. The related lysergamide lysergic acid amide (LSA) that lacks the diethylamide moiety is far less hallucinogenic in comparison.