Method for studying behavioural activity patterns during long-term recordings using a force-plate actometer.
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.
Chiesa
Juan José
JJ
Departament de Fisiologia, Facultat de Farmacia, Universitat de Barcelona, Av Joan XXIII s/n, 08028 Barcelona, Spain. jchiesa@ub.edu
Araujo
John Fontenele
JF
Díez-Noguera
Antoni
A
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