title: Targeted mutation of CCK2 receptor gene modifies the behavioural effects of diazepam in female mice.
abstract: BACKGROUND
  Evidence suggests that GABA and CCK have opposite roles in the regulation of anxiety.
  
  
  OBJECTIVE
  The aim of the present work was to study diazepam-induced anxiolytic-like action and impairment of motor co-ordination, and the parameters of benzodiazepine receptors in mice lacking CCK2 receptors.
  
  
  METHODS
  The action of diazepam (0.5-3 mg/kg i.p.) was studied in the elevated plus-maze model of anxiety and rotarod test using mice lacking CCK2 receptors. The parameters of benzodiazepine receptors were analysed using [3H]-flunitrazepam binding.
  
  
  RESULTS
  In the plus-maze test, the exploratory activity of the homozygous (-/-) mice was significantly higher compared to their wild-type (+/+) littermates. However, the wild-type (+/+) mice displayed higher sensitivity to the anxiolytic-like action of diazepam. Even the lowest dose of diazepam (0.5 mg/kg) induced a significant increase of open arm entries in the wild-type (+/+) mice. A similar effect in the homozygous (-/-) mice was established after the administration of diazepam 1 mg/kg. The highest dose of diazepam (3 mg/kg) caused a prominent anxiolytic-like effect in the wild-type (+/+) mice, whereas in the homozygous (-/-) animals suppression of locomotor activity was evident. The performance of the homozygous (-/-) mice in the rotarod test did not differ from that of the wild-type (+/+) littermates. However, a difference between the wild-type (+/+) and homozygous (-/-) animals became evident after treatment with diazepam. Diazepam (0.5 and 3 mg/kg) induced significantly stronger impairment of motor co-ordination in the homozygous (-/-) mice compared to their wild-type (+/+) littermates. The density of benzodiazepine binding sites was increased in the cerebellum, but not in the cerebral cortex and hippocampus, of the homozygous (-/-) mice.
  
  
  CONCLUSIONS
  Female mice lacking CCK2 receptors are less anxious than their wild-type (+/+) littermates. The reduced anxiety in homozygous (-/-) mice probably explains why the administration of a higher dose of diazepam is necessary to induce an anxiolytic-like action in these animals. The highest dose of diazepam (3 mg/kg) induced significantly stronger suppression of locomotor activity and impairment of motor co-ordination in the homozygous (-/-) mice compared to the wild-type (+/+) littermates. The increase in the action of diazepam is probably related to the elevated density of benzodiazepine receptors in the cerebellum of homozygous (-/-) mice. The present study seems to be in favour of increased tone of the GABAergic system in mice without CCK2 receptors.
authors.affiliation: Department of Physiology, Biomedicum, University of Tartu, 19 Ravila Street, 50411 Tartu, Estonia.
authors.forename: Sirli
authors.initials: S
authors.lastname: Raud
authors.forename: Kertu
authors.initials: K
authors.lastname: Rünkorg
authors.forename: Alar
authors.initials: A
authors.lastname: Veraksits
authors.forename: Ain
authors.initials: A
authors.lastname: Reimets
authors.forename: Aleksei
authors.initials: A
authors.lastname: Nelovkov
authors.forename: Urho
authors.initials: U
authors.lastname: Abramov
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Matsui
authors.forename: Michel
authors.initials: M
authors.lastname: Bourin
authors.forename: Vallo
authors.initials: V
authors.lastname: Volke
authors.forename: Sulev
authors.initials: S
authors.lastname: Kõks
authors.forename: Eero
authors.initials: E
authors.lastname: Vasar
mesh_terms: D000818:Animals; D001007:Anxiety / Q000188:drug therapy / Q000517:prevention & control; D002531:Cerebellum / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D002540:Cerebral Cortex / Q000737:chemistry / Q000187:drug effects; D003975:Diazepam / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005106:Exploratory Behavior / Q000187:drug effects*; D005260:Female; D005445:Flunitrazepam / Q000008:administration & dosage / Q000737:chemistry / Q000493:pharmacokinetics*; D018390:Gene Targeting; D006624:Hippocampus / Q000737:chemistry / Q000187:drug effects; D007274:Injections, Intraperitoneal; D008297:Male; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008817:Mice, Mutant Strains; D009043:Motor Activity / Q000187:drug effects / Q000235:genetics; D009154:Mutation; D011869:Radioligand Assay; D043887:Receptor, Cholecystokinin B / Q000172:deficiency / Q000187:drug effects* / Q000235:genetics*; D011963:Receptors, GABA-A / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D045442:Rotarod Performance Test; D014316:Tritium
chemical_list: D043887:Receptor, Cholecystokinin B; D011963:Receptors, GABA-A; D014316:Tritium; D005445:Flunitrazepam; D003975:Diazepam