Helmut F. Cascorbi

Effect of Anesthetics and a Convulsant on Normal and Mutant Caenorhabditis elegans

The authors have developed a method for studying the action of volatile anesthetics in Caenorhabditis elegans (C.e.), a free living nematode. C.e. appears to be a useful model for the study of the influence of genetics on susceptibility to anesthetics. This worm has a small, completely defined nervous system, easily manipulated genetics, and a large number of nervous system mutants. Under normal conditions C.e. moves almost constantly. When exposed to anesthetics there is an initial phase of increased locomotion, followed by uncoordinated motion that progresses to immobility. Motion returns quickly when the nematodes are removed from the anesthetic. The authors called loss of locomotion “anesthesia.” The ED50s of various anesthetics with C.e. are as follows: methoxyflurane 0.45%, chloroform 1.25%, halothane 2.7%, enflurane 4.2%, isoflurane 5.6%, fluroxene 9.9%. The authors also studied the action of a convulsant, flurothyl, on C.e. Flurothyl has anesthetizing properties in these animals with an ED50 of 8.1%. No convulsant activity was noted. However, mixtures of halothane and flurothyl were antagonistic in their effects, while halothane and enflurane were additive. Furthermore, the authors isolated a mutant strain (HS1) of C.e. that shows altered responses to several anesthetics and a convulsant. HS1 is uncoordinated when not exposed to anesthetics. Like the normal strain (N2) HS1 loses mobility when exposed to anesthetics. The ED50s for various anesthetics in HS1 were as follows: methoxyflurane 0.04%, chloroform 0.52%, halothane 0.85%, isoflurane 4.9%, enflurane 6.0%, fluroxene 10.9%. When compared with the normal C.e., HS1 exhibits a marked increase in sensitivity to methoxyflurane, chloroform, and halothane. No alterations in sensitivity to isoflurane or fluroxene were noted. HS1 exhibited decreased sensitivity to enflurane. HS1 reverts to normal motion when exposed to low concentrations of flurothyl and shows decreased sensitivity to the anesthetic effects of flurothyl with an ED50 of 11.8%. The slope of the curve of the log ED50 versus the log oil/gas partition coefficient is steeper in mutant than in normal nematodes.

The effect of two genes on anesthetic response in the nematode Caenorhabditis elegans.

The authors studied the wild type strain, N2, and three mutant strains of the nematode, Caenorhabditis elegans, in order to measure genetically produced changes in responses to nine volatile anesthetics. They determined the anesthetic ED50s of N2 for thiomethoxyflurane, methoxyflurane, chloroform, halothane, enflurane, isoflurane, fluroxene, flurothyl, and diethylether. The log-log relationship of the oil-gas partition coefficients (O/G) and the ED50s of these agents for N2 yields a straight line with a slope of -.997 with a R2 of .98 over a range of O/G (at 37 degrees C) from 48 to 7230. When the O/Gs are corrected to 22 degrees C, the slope is -.964 with an R2 of .98. This relationship is similar to that found in other animals. Two mutant strains, unc-79 and unc-80, show altered responses to these anesthetics. These strains are two to three times more sensitive than N2 to anesthetics with an O/G greater than that of halothane (220 at 37 degrees C), yet they differ little from N2 in response to anesthetics with lower O/Gs. unc-79 and unc-80 are about 30% more sensitive than N2 to diethylether. The double mutant unc-79; unc-80 is more sensitive to halothane, isoflurane, and fluroxene than is either mutant alone. The authors believe these data indicate an alteration at the site of action of volatile anesthetics in unc-79 and unc-80. They also postulate that the interaction of unc-79 and unc-80 indicate these genes code for enzymes in a common pathway, and that unc-79 precedes unc-80 in this pathway.