Brain lipids that induce sleep are novel modulators of 5-hydroxytrypamine receptors

Amide derivatives of fatty acids were recently isolated from cerebrospinal fluid of sleep-deprived animals and found to induce sleep in rats. To determine which brain receptors might be sensitive to these novel neuromodulators, we tested them on a range of receptors expressed in Xenopus oocytes. cis-9,10-Octadecenamide (ODA) markedly potentiated the action of 5-hydroxytryptamine (5-HT) on 5-HT2A and 5-HT2C receptors, but this action was not shared by related compounds such as oleic acid and trans-9,10-octacenamide. ODA was active at concentrations as low as 1 nM. The saturated analog, octadecanamide, inhibited rather than potentiated 5-HT2C responses. ODA had either no effect or only weak effects on other receptors, including muscarinic cholinergic, metabotropic glutamate, GABA(A), N-methyl-D-asparate, or alpha-amino-3-hydroxy-5-methyl-4-isoxozolepropionic acid receptors. Modulation of 5-HT2 receptors by ODA and related lipids may represent a novel mechanism for regulation of receptors that activate G proteins and thereby play a role in alertness, sleep, and mood as well as disturbances of these states.