MODULATION OF GABA(A) RECEPTORS AND INHIBITORY SYNAPTIC CURRENTS BY THE ENDOGENOUS CNS SLEEP REGULATOR CIS-9,10-OCTADECENOAMIDE (COA)

1 Cis-9,10-octadecenoamide (cOA) accumulates in the CSF of sleep-depri ved cats and may represent a novel signalling molecule. Synthetic cOA has been shown to induce physiological sleep when injected into labora tory rats. Here we assess the cellular mode of action of cOA in vitro. 2 In all rat cultured cortical neurones (pyramidal cells) examined, t he synthetic brain lipid (3.2-64 mu M) enhanced the responses to subsa turating GABA concentrations (up to circa 2x) in a concentration-depen dent manner (EC50, circa 15 mu M). 3 (20 mu M) cOA significantly enhan ced the affinity of exogenous GABA for its receptor without changing t he Hill slope or the maximal response. These effects were not voltage- dependent or secondary to shifts in E-Cl. 4 In the absence of GABA, cO A directly evoked small inhibitory currents in a subpopulation (<7%) o f sensitive cells. 5 20 mu M cOA reversibly enhanced the duration of s pontaneous inhibitory post synaptic currents (cii.ca 2 fold) without s ignificantly altering their amplitude. 6 At 32-64 mu M, cOA reversibly reduced the incidence and amplitude of both inhibitory post synaptic currents (i.p.s.cs) and excitatory post synaptic currents (e.p.s.cs) i n the cultured neuronal circuits in common with other depressant drugs acting at the GABAA receptor. 7 32 mu M Oleic acid did not modulate e xogenous GABA currents or synaptic activity suggesting that cOAs actio ns are mediated through a specific receptor. 8 A specific, protein-dep endent interaction with GABA(A) receptors was confirmed in Xenopus ooc ytes. Recombinant human receptors were modulated by 10 mu M cOA (and d iazepam) only when a gamma(2) subunit was co-expressed with alpha(1)be ta(2): the cOA response was not sensitive to the specific benzodiazepi ne antagonist flumazenil(1 mu M). 8 cOA may represent an endogenous li gand for allosteric modulatory sites on isoforms of GABA(A) receptors which are crucial for the regulation of arousal and have recently been implicated in the circadian control of physiological sleep.