Altered Responses to Propofol, but Not Ketamine, in Mice Deficient in the 65-Kilodalton Isoform of Glutamate Decarboxylase

• Published in: The Journal of pharmacology and experimental therapeutics 2009-05, Vol.329 (2), p.592-599
• Main Authors: Kubo, Kazuhiro, Nishikawa, Koichi, Hardy-Yamada, Makiko, Ishizeki, Junko, Yanagawa, Yuchio, Saito, Shigeru
• Format: Article
• Language: English
• Subjects: Anesthetics, Intravenous - administration & dosage; Anesthetics, Intravenous - pharmacology; Animals; Behavior, Animal - drug effects; Electrophysiology; Excitatory Postsynaptic Potentials - drug effects; Frontal Lobe - drug effects; Frontal Lobe - metabolism; Glutamate Decarboxylase - deficiency; Glutamate Decarboxylase - genetics; Hippocampus - drug effects; Hippocampus - metabolism; Ketamine - administration & dosage; Ketamine - pharmacology; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Motor Activity - drug effects; Neurons - drug effects; Neurons - metabolism; Propofol - administration & dosage; Propofol - pharmacology
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.109.151456

GABA is synthesized by two isoforms of glutamate decarboxylase (GAD), GAD65, and GAD67. However, the relative contributions of GAD65-mediated GABA synthesis to the in vivo actions of anesthetics remain unknown. To address this issue, we used mice deficient in the 65-kDa isoform of GAD and tested the hypothesis that partial reduction of GABA content in GAD65-deficient mice [GAD65(-/-)] would contribute to hypnotic and immobilizing actions of the anesthetics. The open field test, loss of righting reflex (LORR), loss of tail-pinch withdrawal response (LTWR), and locomotor activity were compared between wild-type (WT) mice and GAD65(-/-) mice. Effects of general anesthetics on both phasic and tonic GABAergic currents were examined using the patch-clamp method in frontal cortex pyramidal neurons in brain slices. The duration of propofol (100 mg/kg i.p.)-induced LORR and the duration of propofol (150 mg/kg i.p.)-induced LTWR in GAD65(-/-) mice were significantly reduced compared with WT mice. In contrast, no difference was seen for ketamine. Preinjection of the GABA transporter 1 inhibitor, NO-711 (C 21 H 22 N 2 O 3 · HCl) (0.75 mg/kg i.p.), reinstated diminished actions of propofol in GAD65(-/-) mice. Cortical pyramidal neurons in GAD65(-/-) mice had smaller tonic conductances, and propofol-induced enhancement of tonic inhibition was smaller than in WT mice, suggesting that genotype differences in GAD65-mediated GABAergic inhibitory tone may be, at least in part, a cellular basis underlying behavioral differences. In conclusion, GAD65(-/-) mice show a diminished response to propofol, but not ketamine, indicating that GAD65-mediated GABA synthesis plays an important role in hypnotic and immobilizing actions of propofol.