title: Evidence that sensitivity to steroid anesthetics appears late in evolution.
abstract: The effects of pregnanolone, a steroid anesthetic, were compared with diethyl ether and short chain alkanols in 21 aquatic species from 7 phyla. Loss of righting reflex and escape response were used as indicators of anesthesia. All organisms were anesthetized by diethyl ether and short chain alkanols, but pregnanolone affected only organisms belonging to the phylum Chordata. It is probable that pregnanolone exerts its effect on the gamma-aminobutyric acid (GABA) receptor. Because many invertebrates do possess GABA receptors, our results suggest that a binding site at which steroid binding causes organismal anesthesia appeared early in chordate evolution on a previously existing GABA receptor. The results also appear to exclude a primary lipid bilayer site for steroid anesthetic action.
authors.affiliation: Department of Zoology, University of California, Davis 95616.
authors.forename: A E
authors.initials: AE
authors.lastname: Oliver
authors.forename: D W
authors.initials: DW
authors.lastname: Deamer
authors.forename: M
authors.initials: M
authors.lastname: Akeson
mesh_terms: D000438:Alcohols / Q000494:pharmacology; D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D000845:Annelida; D001181:Arthropods; D005075:Biological Evolution; D002816:Chordata, Nonvertebrate; D004447:Echinodermata; D004924:Escape Reaction / Q000187:drug effects; D004986:Ether / Q000494:pharmacology; D056890:Eukaryota; D008565:Membrane Proteins / Q000378:metabolism; D008974:Mollusca; D010852:Picrotoxin / Q000037:antagonists & inhibitors; D010986:Platyhelminths; D004856:Postural Balance / Q000187:drug effects; D011284:Pregnenolone / Q000494:pharmacology*; D012018:Reflex / Q000187:drug effects; D013045:Species Specificity
chemical_list: D000438:Alcohols; D000777:Anesthetics; D004986:Ether; D008565:Membrane Proteins; D010852:Picrotoxin; D011284:Pregnenolone