title: Swimming behaviour and post-swimming activity in Vitamin D receptor knockout mice.
abstract: Animal experiments have shown that Vitamin D plays a role in both brain development and adult brain function. The adult Vitamin D receptor null mutant mouse (VDR -/-) is reported to be less active and more anxious than wild-type litter mate controls and to have poor swimming ability. However, an "anxious" behavioural phenotype is inferred from differences in locomotor behaviour. This is a general problem in behavioural phenotyping where a neurological phenotype is inferred from changes in locomotion which will be affected by non-neurological factors, such as muscle fatigue. In this study of VDR -/-, we conducted a detailed examination of one form of motor behaviour, swimming, compared to wildtype littermate controls. Swimming was assessed using a forced swim test, a laneway swimming test and a watermaze test using a visible platform. Post-swimming activity was assessed by comparing grooming and rearing behaviour before, and 5 min after, the forced swimming test. We replicated previous findings in which VDR -/- mice demonstrate more sinking episodes than wildtype controls in the forced swim test but they were similar to controls in the time taken to swim a 1m laneway, and in the time taken to reach a visible platform in the watermaze. Thus, the VDR -/- mice were able to swim but were not able to float. Grooming and rearing behaviour of the VDR -/- mice was similar to wildtype controls before the forced swim but the VDR -/- were much less active after the swim compared with wildtype mice which displayed high levels of grooming and rearing. We conclude that VDR -/- mice have muscular and motor impairments that do not affect their ability to swim but significantly alters the ability to float as well as their post-swimming activity. Differences in muscle strength may confound tests of activity that are used to infer an "anxious" phenotype.
authors.affiliation: Neurobiology Program, Institute for Cell and Molecular Therapies, Griffith University, Brisbane, Qld 4111, Australia. t.burne@griffith.edu.au
authors.forename: Thomas H J
authors.initials: TH
authors.lastname: Burne
authors.forename: Amy N B
authors.initials: AN
authors.lastname: Johnston
authors.forename: John J
authors.initials: JJ
authors.lastname: McGrath
authors.forename: Alan
authors.initials: A
authors.lastname: Mackay-Sim
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009043:Motor Activity / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010641:Phenotype; D018167:Receptors, Calcitriol / Q000235:genetics* / Q000378:metabolism; D013315:Stress, Psychological / Q000378:metabolism; D013550:Swimming / Q000502:physiology*
chemical_list: D018167:Receptors, Calcitriol