ABSTRACT
A wealth of evidence indicates that schizophrenia is heritable. However, the genetic mechanisms involved are poorly understood. Furthermore, it may be that genes conferring susceptibility interact with one another and with non-genetic factors to modulate risk status and/or the expression of symptoms. Genome-wide scanning and the mapping of several regions linked with risk for schizophrenia have led to the identification of several putative susceptibility genes including neuregulin-1 (NRG1), dysbindin (DTNBP1), regulator of G-protein signalling 4 (RGS4), catechol-o-methyltransferase (COMT), proline dehydrogenase (PRODH) and disrupted-in-schizophrenia 1 (DISC1). Genetic animal models involving targeted mutation via gene knockout or transgenesis have the potential to inform on the role of a given susceptibility gene on the development and behaviour of the whole organism and on whether disruption of gene function is associated with schizophrenia-related structural and functional deficits. This review focuses on data regarding the behavioural phenotype of mice mutant for schizophrenia susceptibility genes identified by positional candidate analysis and the study of chromosomal abnormalities. We also consider methodological issues that are likely to influence phenotypic effects, as well as the limitations associated with existing molecular techniques.
Subject(s)
Behavior, Animal , Genetic Predisposition to Disease/genetics , Genetics, Behavioral/methods , Multifactorial Inheritance/genetics , Schizophrenia/genetics , Animals , Disease Models, Animal , Gene Expression Profiling , Mice , Mice, Knockout , Mice, Transgenic , Nerve Tissue Proteins/genetics , Phenotype , Schizophrenic PsychologyABSTRACT
Non-selective benzodiazepines, such as diazepam, interact with equivalent affinity and agonist efficacy at GABA(A) receptors containing either an alpha1, alpha2, alpha3 or alpha5 subunit. However, which of these particular subtypes are responsible for the anticonvulsant effects of diazepam remains uncertain. In the present study, we examined the ability of diazepam to reduce pentylenetetrazoLe (PTZ)-induced and maximal electroshock (MES)-induced seizures in mice containing point mutations in single (alpha1H101R, alpha2H101R or alpha5H105R) or multiple (alpha125H-->R) alpha subunits that render the resulting GABA(A) receptors diazepam-insensitive. Furthermore, the anticonvulsant properties of diazepam, the alpha1- and alpha3-selective compounds zolpidem and TP003, respectively, and the alpha2/alpha3 preferring compound TP13 were studied against PTZ-induced seizures. In the transgenic mice, no single subtype was responsible for the anticonvulsant effects of diazepam in either the PTZ or MES assay and neither the alpha3 nor alpha5 subtypes appeared to confer anticonvulsant activity. Moreover, whereas the alpha1 and alpha2 subtypes played a modest role with respect to the PTZ assay, they had a negligible role in the MES assay. With respect to subtype-selective compounds, zolpidem and TP003 had much reduced anticonvulsant efficacy relative to diazepam in both the PTZ and MES assays whereas TP13 had high anticonvulsant efficacy in the PTZ but not the MES assay. Taken together, these data not only indicate a role for alpha2-containing GABA(A) receptors in mediating PTZ and MES anticonvulsant activity but also suggest that efficacy at more than one subtype is required and that these subtypes act synergistically.
Subject(s)
Anticonvulsants/pharmacology , Benzodiazepines/pharmacology , Receptors, GABA-A/physiology , Seizures/prevention & control , Animals , Binding Sites , Convulsants , Diazepam/pharmacology , Electroshock , GABA-A Receptor Agonists , Ligands , Mice , Mice, Mutant Strains , Mice, Transgenic , Pentylenetetrazole , Point Mutation , Protein Subunits/agonists , Protein Subunits/genetics , Protein Subunits/physiology , Pyridines/pharmacology , Receptors, GABA-A/genetics , Seizures/etiology , ZolpidemABSTRACT
Over the last decade, sequencing and characterisation of the mouse genome has been accompanied by unparalleled advances in functional genomics. In the context of drug action, we analyse the strengths and limitations of classical mutagenesis and gene targeting techniques, as well as alternative approaches such as chemical mutagenesis, gene trap, recombineering, transposon-mediated mutagenesis, chromosomal engineering, viral transgenesis and RNA interference. This review also focuses on the emerging importance of genetic manipulation in other species and related logistical issues of experimental work using mutants.:
ABSTRACT
Schizophrenia is a chronic and debilitating disease which is thought to arise from a neuro-developmental disorder. Both the stable tubule-only polypeptide (STOP) protein and the N-methyl-D-aspartate (NMDA) NR1 subunit are involved in neuronal development and physiology. It has therefore been postulated that transgenic mice lacking either the STOP or the NMDAR1 gene would show a 'schizophrenic-like' phenotype. Here, STOP knockout and NMDA NR1 hypomorphic mice were assessed in a behavioural measure that can be used to detect schizophrenic-like phenotypes: a change in sensorimotor gating, measured through prepulse inhibition (PPI). STOP knockout mice were further assessed in another measure of 'schizophrenic-like behaviour': hyperlocomotion. The PPI deficit exhibited by both the STOP knockout and NMDA knockdown mice could not be reversed by acute treatment with the atyptical antipsychotic, clozapine (1 mg/kg, i.p.) but the hyperlocomotion shown by the STOP knockout mice was reversed with the same acute dose of clozapine.
Subject(s)
Gait Disorders, Neurologic/genetics , Gait Disorders, Neurologic/physiopathology , Microtubule-Associated Proteins/deficiency , Receptors, N-Methyl-D-Aspartate/deficiency , Somatosensory Cortex/physiopathology , Acoustic Stimulation/methods , Animals , Antipsychotic Agents/administration & dosage , Body Temperature/drug effects , Body Temperature/genetics , Body Weight/drug effects , Body Weight/genetics , Clozapine/administration & dosage , Dose-Response Relationship, Drug , Dose-Response Relationship, Radiation , Drug Interactions , Enzyme Inhibitors/pharmacology , Gait Disorders, Neurologic/drug therapy , Mice , Mice, Inbred C57BL , Mice, Knockout , Motor Activity/drug effects , Motor Activity/genetics , Neural Inhibition/drug effects , Neural Inhibition/genetics , Phencyclidine/pharmacology , Reflex, Acoustic/drug effects , Reflex, Acoustic/genetics , Rotarod Performance Test/methods , Somatosensory Cortex/drug effects , Swimming , Time FactorsABSTRACT
The i.v. agent etomidate exerts its anaesthetic actions through potentiation of gamma-aminobutyric acid-A receptors containing beta2 and beta3 subunits. It was recently shown that the beta2 subunit contributes to the sedative properties of etomidate, whereas the beta3 subunit is responsible for its anaesthetic properties. However, these studies evaluated anaesthetic effects in point mutation mice in which the effect of etomidate was decreased, but not abolished, at the beta2 subunit. Here we have used beta2 knockout mice to completely remove any contribution of the beta2 subunit to the effects of etomidate. Etomidate was equally anaesthetic in wildtype and knockout mice, thus further confirming that efficacy at the beta3 subunit only is sufficient to induce general anaesthesia.
Subject(s)
Anesthesia , Anesthetics, Intravenous , Etomidate , Protein Subunits/physiology , Receptors, GABA-A/physiology , Animals , Behavior, Animal , Dose-Response Relationship, Drug , Female , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Motor Activity/drug effects , Protein Subunits/genetics , Receptors, GABA-A/genetics , Recovery of Function/drug effects , Reflex/drug effects , Reflex/physiology , Time FactorsABSTRACT
BACKGROUND: The authors have previously described that the gamma-aminobutyric acid type A (GABAA) receptor beta 2N265S mutation results in a knock-in mouse with reduced sensitivity to etomidate. After recovery from etomidate anesthesia, these mice have improved motor performance and less slow wave sleep. Because most clinically used anesthetics produce hypothermia, the effect of this mutation on core body temperature was investigated. METHODS: The effect of etomidate and propofol on core body temperature were measured using radiotelemetry in freely moving GABAA receptor beta 2N265S mutant mice and wild-type controls. RESULTS: beta 2N265S mutant mice have a reduced hypothermic response to anesthetic doses of etomidate compared with wild-type controls and after a transient loss of righting reflex regain normothermia more rapidly compared with wild-type controls. Subanesthetic doses of etomidate produce hypothermia, which was not observed in the mutant mice. Vehicle administration resulted in a stress-induced hyperthermic response in both genotypes. Propofol produced a hypothermic response that was similar in both genotypes. CONCLUSIONS: The GABAA receptor beta 2 subunit mediates a significant proportion of the hypothermic effects of etomidate. As the beta 2 subunit mediates postrecovery ataxia and sedation, anesthetic agents that do not have in vivo potency at beta 2 subunit-containing receptors offer the potential for surgical anesthesia with improved recovery characteristics.
Subject(s)
Body Temperature/drug effects , Etomidate/toxicity , Hypothermia/chemically induced , Hypothermia/physiopathology , Protein Subunits/physiology , Receptors, GABA/physiology , Animals , Body Temperature/genetics , Etomidate/antagonists & inhibitors , Hypothermia/genetics , Mice , Mice, Mutant Strains , Protein Subunits/genetics , Receptors, GABA/genetics , Receptors, GABA-A , Time FactorsABSTRACT
The specific mechanisms underlying general anesthesia are primarily unknown. The intravenous general anesthetic etomidate acts by potentiating GABA(A) receptors, with selectivity for beta2 and beta3 subunit-containing receptors determined by a single asparagine residue. We generated a genetically modified mouse containing an etomidate-insensitive beta2 subunit (beta2 N265S) to determine the role of beta2 and beta3 subunits in etomidate-induced anesthesia. Loss of pedal withdrawal reflex and burst suppression in the electroencephalogram were still observed in the mutant mouse, indicating that loss of consciousness can be mediated purely through beta3-containing receptors. The sedation produced by subanesthetic doses of etomidate and during recovery from anesthesia was present only in wild-type mice, indicating that the beta2 subunit mediates the sedative properties of anesthetics. These findings show that anesthesia and sedation are mediated by distinct GABA(A) receptor subtypes.
