behavioralmouseF2 hybrid (129/Sv × C57BL/6), 129/SvEv, C57BL/6, and congenic strains
Objective: Measurement of horizontal locomotor activity in an open field to assess spontaneous movement and exploration in D2 dopamine receptor-deficient mice
Materials & Equipment Checklist
6 items2 from ConductScience
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Equipment2
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Protocol Steps
View Abstract
Locomotor activity is a polygenic trait that varies widely among inbred strains of mice (Flint et al., 1995). To characterize the role of D2 dopamine receptors in locomotion, we generated F 2 hybrid (129/Sv × C57BL/6) D2 dopamine receptor (D2R)-deficient mice by gene targeting and investigated the contribution of genetic background to open-field activity and rotarod performance. Horizontal activity of D2R−/− mice was approximately half that of drug-naive, strain-matched controls but was significantly greater than haloperidol-treated controls, which were markedly hypokinetic. Wild-type 129/SvEv and C57BL/6 mice with functional D2 receptors had greater interstrain differences in spontaneous activity than those among the F 2 hybrid mutants. Incipient congenic strains of D2R-deficient mice demonstrated an orderly gene dosage reduction in locomotion superimposed on both extremes of parental background locomotor activity. In contrast, F 2 hybrid D2R−/− mice had impaired motor coordination on the rotarod that was corrected in the congenic C57BL/6 background. Wild-type 129/SvEv mice had the poorest rotarod ability of all groups tested, suggesting that linked substrain 129 alleles, not the absence of D2 receptors per se, were largely responsible for the reduced function of the F 2 hybrid D2R−/− and D2R+/− mice. Neurochemical and pharmacological studies revealed unexpectedly normal tissue striatal monoamine levels and no evidence for supersensitive D1, D3, or D4 dopamine receptors in the D2R−/− mice. However, after acute monoamine depletion, akinetic D2R+/− mice had a significantly greater synergistic restoration of locomotion in response to SKF38393 and quinpirole compared with any group of D2R+/+ controls. We conclude that D2R-deficient mice are not a model of Parkinson’s disease. Our studies highlight the interaction of multiple genetic factors in the analysis of complex behaviors in gene knock-out mice.
1
Animal preparation and grouping
Generate or obtain F2 hybrid (129/Sv × C57BL/6) D2 dopamine receptor-deficient mice, wild-type controls, and congenic strains. Include drug-naive strain-matched controls and haloperidol-treated controls.
Not specifiedNot specified
Note: Multiple genotypes tested: D2R−/−, D2R+/−, and D2R+/+ mice across different genetic backgrounds
View evidence from paper
“we generated F2 hybrid (129/Sv × C57BL/6) D2 dopamine receptor (D2R)-deficient mice by gene targeting and investigated the contribution of genetic background to open-field activity”
2
Open field activity testing
Place mice in open field apparatus and measure horizontal locomotor activity. Test drug-naive controls, D2R-deficient mice, and haloperidol-treated controls.
Note: Horizontal activity is the primary outcome measure; interstrain differences in spontaneous activity are compared
View evidence from paper
“Horizontal activity of D2R−/− mice was approximately half that of drug-naive, strain-matched controls but was significantly greater than haloperidol-treated controls, which were markedly hypokinetic”
3
Rotarod performance testing
Test motor coordination and balance using rotarod apparatus in F2 hybrid D2R−/− mice, congenic strains, and wild-type controls.
Note: F2 hybrid D2R−/− mice showed impaired motor coordination that was corrected in congenic C57BL/6 background
View evidence from paper
“F2 hybrid D2R−/− mice had impaired motor coordination on the rotarod that was corrected in the congenic C57BL/6 background”
4
Neurochemical analysis
Measure tissue striatal monoamine levels in D2R-deficient mice to assess dopamine and related neurotransmitter content.
Not specifiedNot specified
Note: Results showed unexpectedly normal tissue striatal monoamine levels in D2R−/− mice
View evidence from paper
“Neurochemical and pharmacological studies revealed unexpectedly normal tissue striatal monoamine levels”
5
Dopamine receptor sensitivity assessment
Evaluate D1, D3, and D4 dopamine receptor sensitivity in D2R-deficient mice compared to wild-type controls.
Not specifiedNot specified
Note: No evidence for supersensitive D1, D3, or D4 dopamine receptors was found in D2R−/− mice
View evidence from paper
“no evidence for supersensitive D1, D3, or D4 dopamine receptors in the D2R−/− mice”
6
Acute monoamine depletion and pharmacological challenge
Deplete monoamines acutely and then administer SKF38393 and quinpirole to assess synergistic restoration of locomotion in D2R+/− mice versus D2R+/+ controls.
Not specifiedNot specified
Note: D2R+/− mice showed significantly greater synergistic restoration of locomotion compared to D2R+/+ controls
View evidence from paper
“after acute monoamine depletion, akinetic D2R+/− mice had a significantly greater synergistic restoration of locomotion in response to SKF38393 and quinpirole compared with any group of D2R+/+ controls”
Subjects / Specimens
Species
mouse
Strain
F2 hybrid (129/Sv × C57BL/6), 129/SvEv, C57BL/6, and congenic strains
Age
Not specified
Sex
unknown
Weight
Not specified
D2R-deficient (D2R−/−), heterozygous (D2R+/−), and wild-type (D2R+/+) mice; drug-naive and haloperidol-treated controls included