title: Method for studying behavioural activity patterns during long-term recordings using a force-plate actometer.
abstract: The motor activity (MA) patterns of rodents are commonly detected in the laboratory using infrared photo-beams or running wheels. In chronobiological studies, the MA rhythm is considered as a behavioural output of the circadian pacemaker. This paper describes a method to obtain long-term records of MA in rodents, with a 1mm spatial resolution and a 1s temporal resolution. The device comprised a square platform laid on top of three force transducers, allowed the calculation of the coordinates of the centre of force exerted by a freely moving rodent, and continuously monitored its displacements. A specific computer program processed the trajectories, providing an exhaustive analysis of motion. To test this method, motor behavioural activity was studied in rats exposed to conditions that favoured rhythmicity: light-dark cycles of both 24 h (LD) and 22 h (T22), and constant darkness (DD). In addition, arrhythmicity patterns were studied under constant light (LL) conditions, and in animals with permanent lesions of the hypothalamic suprachiasmatic nucleus (SCNx). A single description of the general MA distribution at 24 h was obtained using infrared photo-beams. By contrast, under LD conditions, a 24-h rhythm with ultradian components was seen in the total distance travelled, whereas that detected in the number of slow motions showed less ultradian components. In addition, a regional preference in the nesting place was detected under both LD and DD conditions. In one SCNx animal and another exposed to LL conditions, both showing arrhythmicity in photo-beam-detected MA, a 24 h rhythm was observed in regional preference; other LL animal presented a 24 h rhythm in the number of slow motions. This method has capabilities lacking in commonly used techniques. The potential uses of this approach, principally in cronobiological studies, are discussed.
authors.affiliation: Departament de Fisiologia, Facultat de Farmacia, Universitat de Barcelona, Av Joan XXIII s/n, 08028 Barcelona, Spain. jchiesa@ub.edu
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Chiesa
authors.forename: John Fontenele
authors.initials: JF
authors.lastname: Araujo
authors.forename: Antoni
authors.initials: A
authors.lastname: Díez-Noguera
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D035843:Biomedical Research; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D008027:Light; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D010507:Periodicity; D051381:Rats; D013493:Suprachiasmatic Nucleus / Q000166:cytology