title: The involvement of hypothalamic sleep pathways in general anesthesia: testing the hypothesis using the GABAA receptor beta3N265M knock-in mouse.
abstract: The GABA(A) receptor has been identified as the single most important target for the intravenous anesthetic propofol. How effects at this receptor are then translated into a loss of consciousness, however, remains a mystery. One possibility is that anesthetics act on natural sleep pathways. Here, we test this hypothesis by exploring the anesthetic sensitivities of GABAergic synaptic currents in three specific brain nuclei that are known to be involved in sleep. Using whole-cell electrophysiology, we have recorded GABAergic IPSCs from the tuberomammillary nucleus (TMN), the perifornical area (Pef), and the locus ceruleus (LC) in brain slices from both wild-type mice and mice that carry a specific mutation in the GABA(A) receptor beta(3) subunit (N265M), which greatly reduces their sensitivity to propofol, but not to the neurosteroid alphaxalone. We find that this in vivo pattern of anesthetic sensitivity is mirrored in the hypothalamic TMN and Pef nuclei, consistent with their role as direct anesthetic targets. In contrast, anesthetic sensitivity in the LC was unaffected by the beta(3)N265M mutation, ruling out this nucleus as a major target for propofol. In support of the hypothesis that orexinergic neurons in the Pef are involved in propofol anesthesia, we further show that these neurons are selectively inhibited by GABAergic drugs in vivo during anesthesia, and that a modulation in the activity of Pef neurons alone can affect loss of righting reflex. Overall, our results support the idea that GABAergic anesthetics such as propofol exert their effects, at least in part, by modulating hypothalamic sleep pathways.
authors.affiliation: Biophysics Section, Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: Anna Y
authors.initials: AY
authors.lastname: Zecharia
authors.forename: Laura E
authors.initials: LE
authors.lastname: Nelson
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Gent
authors.forename: Mark
authors.initials: M
authors.lastname: Schumacher
authors.forename: Rachel
authors.initials: R
authors.lastname: Jurd
authors.forename: Uwe
authors.initials: U
authors.lastname: Rudolph
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Brickley
authors.forename: Mervyn
authors.initials: M
authors.lastname: Maze
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Franks
mesh_terms: D018681:Anesthetics, General / Q000494:pharmacology*; D000818:Animals; D055879:Gene Knock-In Techniques; D007026:Hypothalamic Area, Lateral / Q000187:drug effects / Q000378:metabolism; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008125:Locus Coeruleus / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D008822:Mice, Transgenic; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009479:Neuropeptides / Q000378:metabolism; D000068797:Orexins; D009924:Organ Culture Techniques; D015742:Propofol / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000235:genetics*; D012890:Sleep / Q000187:drug effects* / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D018681:Anesthetics, General; C546270:Gabrb3 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D015742:Propofol