Identification of a Molecular Target Mediating the General Anesthetic Actions of Pentobarbital

Abstract

Barbiturates were introduced into medical practice in 1934. They are widely used today as general anesthetics. Although in vitro studies revealed that the activity of a variety of ligandgated channels is modulated by barbiturates, the target(s) mediating the anesthetic actions of barbiturates in vivo are unknown. Studying pentobarbital action in ␤3(N265M) mice harboring ␤3-containing GABA A receptors insensitive to a variety of general anesthetic agents, we found that the immobilizing action of pentobarbital is mediated fully, and the hypnotic action is mediated in part by this receptor subtype. It was surprising that the respiratory depressant action of pentobarbital is indistinguishable between ␤3(N265M) and wild-type mice and thus is mediated by other as-yet-unidentified targets. Whereas the target for the immobilizing and hypnotic actions of pentobarbital seems to be the same as for etomidate and propofol, these latter agents' respiratory depressant actions are mediated by ␤3-containing GABA A receptors. Thus, in contrast to etomidate and propofol, pentobarbital can elicit respiratory depression by a ␤3-independent pathway. Pentobarbital reduced heart rate and body temperature to a slightly smaller extent in ␤3(N265M) mice compared with wild-type mice, indicating that these actions are largely mediated by other targets. Pentobarbital-induced increase of heart rate variability and prolongation of ECG intervals are seen in both ␤3(N265M) mice and wild-type mice, suggesting that they are not dependent on ␤3-containing GABA A receptors. In summary, we show a clear pharmacological dissociation of the immobilizing/hypnotic and respiratory/cardiovascular actions of pentobarbital.The introduction of general anesthetics into medical practice 160 years ago has revolutionized surgery. However, the mechanisms of action of this class of drugs are still only poorly understood. Although general anesthetics have been shown to modulate the activity of a number of proteins (e.g., ligand-gated ion channels; Krasowski and Harrison, 1999) and two-pore domain potassium channels in vitro (Franks and Honore, 2004), the identification of targets mediating specific actions of general anesthetics in vivo has only just begun.GABA A receptors are pentameric ligand-gated ion channels, the majority of them containing two ␣, two ␤, and one ␥ subunit (Backus et al., 1993;Chang et al., 1996). Mutagenesis studies have identified amino acid residues in GABA A receptor ␤ subunits that are crucial for the actions of the general anesthetics etomidate and propofol in vitro (Belelli et al., 1997;Mihic et al., 1997;Krasowski et al., 1998;Siegwart et al., 2002Siegwart et al., , 2003.It has been shown that ␤3(N265M) mice are insensitive to the immobilizing and respiratory depressant action of etomidate and propofol and have a reduced sensitivity to the hypnotic action of these drugs, suggesting that ␤3-containing GABA A receptors mediate these actions, whereas etomidate retains its sedative (motor depressant) action at subanesthetic doses (Jur...

Modulation of Presynaptic β3-Containing GABAAReceptors Limits the Immobilizing Actions of GABAergic Anesthetics

“…The capability of GABAergic anesthetics to produce immobility, despite their limited efficacy in reducing neuronal excitability in the spinal cord, can be explained by the involvement of supraspinal sites. It has been demonstrated previously that local administration of pentobarbital, another anesthetic acting predominantly via GABA A receptors (Zeller et al, 2007), into the mesopontine tegmental anesthesia locus can cause deep anesthesia (Devor and Zalkind, 2001;Sukhotinsky et al, 2005). This result, together with findings of the present study, allows the conclusion that the immobilizing properties of GABAergic anesthetics are mediated in part via the ventral horn of the spinal cord and, in part, via supraspinal structures, including the mesopontine tegmental anesthesia locus.…”

Implantation of Radiotelemetry Transmitters Yielding Data on ECG, Heart Rate, Core Body Temperature and Activity in Free-moving Laboratory Mice

“…Several other parameters can be established from the biopotentials curves. Examples for presentation of heart rate variability parameters 5 , QT interval and PQ interval 10,11 are published elsewhere. Table 1.…”

Inhalation Anesthesia Is Preferable for Recording Rat Cardiac Function Using an Electrocardiogram

“…Although they used mice, Zeller et al measured HRV as the standard deviation of the beat interval. 20) In their study, the intraperitoneal injection of pentobarbital increased the SDNN from 5.2± 0.2 ms 2 in a conscious baseline state to 40.4± 5.8 ms 2 under pentobarbital anesthesia. In this study, the SDNN under pentobarbital anesthesia was 18.8± 4.5 ms 2 .…”