Requirement of alpha5-GABAA receptors for the development of tolerance to the sedative action of diazepam in mice.
Despite its pharmacological relevance, the mechanism of the development of tolerance to the action of benzodiazepines is essentially unknown. The acute sedative action of diazepam is mediated via alpha1-GABA(A) receptors. Therefore, we tested whether chronic activation of these receptors by diazepam is sufficient to induce tolerance to its sedative action. Knock-in mice, in which thealpha1-,alpha2-,alpha3-, oralpha(5)-GABA(A) receptors had been rendered insensitive to diazepam by histidine-arginine point mutation, were chronically treated with diazepam (8 d; 15 mg x kg(-1) x d(-1)) and tested for motor activity. Wild-type, alpha2(H101R), and alpha3(H126R) mice showed a robust diminution of the motor-depressant drug action. In contrast, alpha5(H105R) mice failed to display any sedative tolerance. alpha1(H101R) mice showed no alteration of motor activity with chronic diazepam treatment. Autoradiography with [3H]flumazenil revealed no change in benzodiazepine binding sites. However, a decrease in alpha5-subunit radioligand binding was detected selectively in the dentate gyrus with specific ligands. This alteration was observed only in diazepam-tolerant animals, indicating that the manifestation of tolerance to the sedative action of diazepam is associated with a downregulation of alpha5-GABA(A) receptors in the dentate gyrus. Thus, the chronic activation of alpha(5)-GABA(A) receptors is crucial for the normal development of sedative tolerance to diazepam, which manifests itself in conjunction with alpha1-GABA(A) receptors.
Institute of Pharmacology and Toxicology, University of Zürich, 8057 Zürich, Switzerland.
Carolien
C
van Rijnsoever
Marcus
M
Täuber
Mohamed Khaled
MK
Choulli
Ruth
R
Keist
Uwe
U
Rudolph
Hanns
H
Mohler
Jean Marc
JM
Fritschy
Florence
F
Crestani
D000480:Alkynes; D000494:Allosteric Regulation / Q000187:drug effects; D019943:Amino Acid Substitution; D000818:Animals; D001569:Benzodiazepines / Q000493:pharmacokinetics; D001665:Binding Sites; D001923:Brain Chemistry / Q000187:drug effects*; D003342:Corpus Striatum / Q000737:chemistry; D003433:Crosses, Genetic; D018891:Dentate Gyrus / Q000737:chemistry; D003975:Diazepam / Q000494:pharmacology*; D015536:Down-Regulation; D004361:Drug Tolerance / Q000502:physiology; D005260:Female; D006624:Hippocampus / Q000737:chemistry; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D007093:Imidazoles / Q000493:pharmacokinetics; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D009044:Motor Cortex / Q000737:chemistry; D009714:Nucleus Accumbens / Q000737:chemistry; D017354:Point Mutation; D021122:Protein Subunits; D011869:Radioligand Assay; D011963:Receptors, GABA-A / Q000737:chemistry / Q000172:deficiency / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology
D000480:Alkynes; C546241:Gabra1 protein, mouse; C496250:Gabra5 protein, mouse; D006993:Hypnotics and Sedatives; D007093:Imidazoles; D021122:Protein Subunits; C109021:RY 80; D011963:Receptors, GABA-A; D011993:Recombinant Fusion Proteins; D001569:Benzodiazepines; D003975:Diazepam