MARTA MARTINEZ MORGA¹, Angel Toval², Yevheniy Kutsenko², Daniel Garrigos², Alberto Barreda², Bruno Ribeiro Do-Couto³, Jose Luis Ferran²

(1) Universidad de Murcia, Facultad de Medicina, Dpto. Anatomía Humana y Psicobiología, 30006, España (Región de Murcia)
(2) Universidad de Murcia, Facultad de Medicina, Dpto. Anatomía Humana y Psicobiología, España (Región de Murcia)
(3) Universidad de Murcia, Facultad de Psicología, España (Región de Murcia)

The sedentary lifestyle is defined by the World Health Organization as a person with less than 90 minutes of weekly physical activity. According to several published studies, the sedentary life increases the obesity rates, becoming a problem that occurs worldwide in developed and developing countries. The current scientific knowledge strongly supports that being physically active or sedentary results in consequences on health of people. However, the brain causal mechanisms that affects peripheral tissues by which physical activity produces these effects are poorly understood. If the aim is to learn about the central nervous system networks working in the physical activity responses, the forced running system in rodents is one of the main options. Forced exercise systems like forced running wheel are a guaranty of experimental repeatability allowing to all the animals running the same volume and speed. One of the main difficulties in the rat forced wheel trainings was the 10% of failure in the running response. However, recent works have demonstrated that a habituation phase will produce a 100% of rodent response in the main training program. This habituation phase consists of 10 sessions developed for 8 days, where the intensity and volume are progressively increased. Once finished the habituation phase was evaluated by an incremental test. The efficiency of habituation phase improving the motor response has been demonstrated, but there is no data informing about consequences of shortening the time of this phase. We consider this exploration as the first step to compare in further experiments the molecular mechanisms activated in habituation periods with differences in time of running but with similar intensity of exercise.

Six motor running-wheels were used for this study and the habituations phases were comprised of different sessions distributed across 2, 4 and 8 days of training. During these sessions, both intensity (speed) and volume (time) were increased following an upward progressive pattern. When the habituation phases were completed, rats were subjected to an incremental exercise test 24 h after the last habituation session. The time spent in the running wheel was determined from the beginning of the test to its termination when the animal fails to maintain a running pattern. At the age of 20 days, all the male Sprague-Dawley rats were assigned to either a group that received an exercise habituation protocol, a wheel control group, or a cage control group as described below: 2,4 or 8 days habituation group (n=6 each one), 2,4 or 8 days wheel control (n=6 each one), and one cage control (n=6).

The total time of running during the incremental test was of 37.78 ± 2.65 min for 8 days habituated rats but 15.84 ± 1.22 min for non-habituated rats (wheel control). In the case of 4 days habituated rats the total time of running was 36.02 ± 2.67 min with 17.35 ± 2.86 for the control. Finally, we found that after 2 days of habituation, rats run during the incremental test 28.95 ± 3.94 min, but 19.97 ± 2.57 min in the case of the control. We didn´t observed any differences in weight during all the period analyzed.

Shortening of habituation period to 4 days produce similar effect in the incremental test than 8-day habituation period. However, 2 days habituation period produce a decreased response during the incremental test compared with 4- and 8-day habituated rats.