Cortical Glutamatergic Neurons Mediate the Motor Sedative Action of Diazepam

A. Zeller, F. Crestani, I. Camenisch, T. Iwasato, S. Itohara, J. M. Fritschy, and U. Rudolph

Institute of Pharmacology and Toxicology, University of Zürich, Zürich, Switzerland (A.Z., F.C., I.C., J.M.F., U.R.); PRESTO, Japan Science and Technology Agency, Saitama, Japan (T.I.); Laboratory for Behavioral Genetics, RIKEN Brain Science Institute, Saitama, Japan (T.I., S.I.); and Laboratory of Genetic Neuropharmacology, McLean Hospital and Department of Psychiatry, Harvard Medical School, Belmont, Massachusetts (U.R.)

The neuronal circuits mediating the sedative action of diazepamare unknown. Although the motor-depressant action of diazepamis suppressed in ${alpha}$ 1(H101R) homozygous knockin mice expressingdiazepam-insensitive ${alpha}$ 1-GABA_A receptors, global ${alpha}$ 1-knockout miceshow greater motor sedation with diazepam. To clarify this paradox,attributed to compensatory up-regulation of the ${alpha}$ 2 and ${alpha}$ 3 subunits,and to further identify the neuronal circuits supporting diazepam-inducedsedation, we generated Emx1-cre-recombinase-mediated conditionalmutant mice, selectively lacking the ${alpha}$ 1 subunit (forebrain-specific ${alpha}$ 1^-/-) or expressing either a single wild-type (H) or a singlepoint-mutated (R) ${alpha}$ 1 allele (forebrain-specific ${alpha}$ 1^-/H and ${alpha}$ 1^-/Rmice, respectively) in forebrain glutamatergic neurons. In therest of the brain, ${alpha}$ 1^-/R mutants are heterozygous ${alpha}$ 1(H101R) mice.Forebrain-specific ${alpha}$ 1^-/- mice showed enhanced diazepam-inducedmotor depression and increased expression of the ${alpha}$ 2 and ${alpha}$ 3 subunitsin the neocortex and hippocampus, in comparison with their pseudo-wild-typelittermates. Forebrain-specific ${alpha}$ 1^-/R mice were less sensitivethan ${alpha}$ 1^-/H mice to the motor-depressing action of diazepam, buteach of these conditional mutants had a similar behavioral responseas their corresponding control littermates. Unexpectedly, expressionof the ${alpha}$ 1 subunit was reduced in forebrain, notably in ${alpha}$ 1^-/R mice,and the ${alpha}$ 3 subunit was up-regulated in neocortex, indicatingthat proper ${alpha}$ 1 subunit expression requires both alleles. In conclusion,conditional manipulation of GABA_A receptor ${alpha}$ 1 subunit expressioncan induce compensatory changes in the affected areas. Specifically,alterations in GABA_A receptor expression restricted to forebrainglutamatergic neurons reproduce the behavioral effects seenafter a global alteration, thereby implicating these neuronsin the motor-sedative effect of diazepam.

Received June 6, 2007; accepted October 26, 2007

Address correspondence to: Dr. Uwe Rudolph, Laboratory of Genetic Neuropharmacology, McLean Hospital, Department of Psychiatry, Harvard Medical School, 115 Mill St., Belmont, MA 02478. E-mail: urudolph{at}mclean.harvard.edu