Biomedical subjects

Antoni Díez-Noguera

Publications and source records attributed to Antoni Díez-Noguera.

7 recordsLinked to original sources

PubMed2006

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.

Animals↗

PubMed2006

History-dependent changes in entrainment of the activity rhythm in the Syrian hamster (Mesocricetus auratus).

The authors have studied the activity rhythm of Syrian hamsters exposed to square LD cycles with a 22-h period (T22) with the aim of testing the effects of the previous history on the rhythmic pattern. To do so, sequential changes of different lighting environments were established, followed by the same LD condition. Also, the protocol included T22 cycles with varying lighting contrasts to test the extent to which a computational model predicts experimental outcomes. At the beginning of the experiment, exposure to T22 with 300 lux and dim red light occurring respectively at photophase and scotophase (LD300/dim red) mainly generated relative coordination. Subsequent transfer to cycles with approximately 0.1-lux dim light during the scotophase (LD300/0.1) promoted entrainment to T22. However, a further reduction in light intensity to 10 lux during the photophase (LD10/0.1) generated weak and unstable T22 rhythms. When, after that, animals were transferred again to the initial LD300/dim red cycles, the amplitude of the rhythm still remained very low, and the phases were very unstable. Exposure to constant darkness partially restored the activity rhythm, and when, afterwards, the animals were submitted again to LD300/dim red cycles, a robust T22 rhythm appeared. The results demonstrate history-dependent changes in the hamster circadian system because the locomotor activity pattern under the same T22 cycle can show relative coordination or unstable or robust entrainment depending on the prior lighting condition. This suggests that the circadian system responds to environmental stimuli depending on its previous history. Moreover, computer simulations allow the authors to predict entrainment under LD300/0.1 cycles and indicate that most of the patterns observed in the animals due to the light in the scotophase can be explained by different degrees of coupling among the oscillators of the circadian system.

Animals↗

PubMed2005

Quantitative changes in neuronal and glial cells in the suprachiasmatic nucleus as a function of the lighting conditions during weaning.

To examine whether lighting conditions during the development of the rat circadian system affect the morphology of the suprachiasmatic nucleus (SCN), three groups of rats were born and maintained until they were 24 days old under constant light (LL), constant darkness (DD) or 24-h light-dark cycles (LD, 12-h light and 12-h darkness). We applied a stereological method to study whether these conditions lead to alterations in the volume of the SCN and changes in the total number of neurons and glial cells. While lighting conditions did not induce differences in the SCN volume, the number of both neurons and glial cells did differ between groups. The DD rats showed the lowest number of neurons. Glial cells were also lower in this group than in the other two groups; however the number of glial cells in LL rats was lower than in LD rats. Moreover, females had more glial cells than males but males and females showed a similar number of neurons. These findings indicate the plasticity of the SCN in response to lighting conditions during the developmental stage.

Analysis of Variance↗

PubMed2005

Effect of Robertsonian translocations on the motor activity rhythm in the house mouse.

Here we studied the circadian rhythm of motor activity in two groups of wild house mice from the chromosomal polymorphic zone of Barcelona, which differed in diploid number (2n): standard (2n = 40), with all acrocentric chromosomes, and Robertsonian (2n = 29-32), with several Robertsonian translocations. Motor activity under three lighting conditions, light-dark cycle, constant darkness, and constant light, was recorded for each mouse. The motor activity rhythm was examined by Fourier analysis and the daily power spectra were obtained. On the basis of the mean power spectrum of each animal and under each lighting condition, stepwise discriminant analyses were performed to classify the two chromosomal groups. This method allowed the correct classification of a large number of animals, the rhythms of about 2-2.6 hour periods being the most significant, with higher values in Robertsonian than in standard mice. Our results indicate that the daily motor activity pattern differs between the two chromosomal groups and its analysis may have a valuable interest for behavioral investigations on Robertsonian polymorphic zones of this species.

Analysis of Variance↗

PubMed2005

Activity rhythm of golden hamster (Mesocricetus auratus) can be entrained to a 19-h light-dark cycle.

Both temporary access to a running wheel and temporary exposure to light systematically influence the phase producing entrainment of the circadian activity rhythm in the golden hamster (Mesocricetus auratus). However, precise determination of entrainment limits remains methodologically difficult, because such calculations may be influenced by varying experimental paradigms. In this study, effects on the entrainment of the activity pattern during successive light-dark (LD) cycles of stepwise decreasing periods, as well as wheel running activity, were investigated. In particular, the hamster activity rhythm under LD cycles with a period (T) shorter than 22 h was studied, i.e., when the LD cycle itself had been shown to be an insufficiently strong zeitgeber to synchronize activity rhythms. Indeed, it was confirmed that animals without a wheel do not entrain under 11:11-h LD cycles (T = 22 h). Subsequently providing hamsters continuous access to a running wheel established entrainment to T = 22 h. Moreover, this paradigm underwent further reductions of the T period to T = 19.6 h without loss of entrainment. Furthermore, restricting access to the wheel did not result in loss of entrainment, while even entrainment to T = 19 h was observed. To explain this observed shift in the lower entrainment limit, our speculation centers on changes in pacemaker response facilitated by stepwise changes of T spaced very far apart, thus allowing time for adaptation.

Activity Cycles↗

PubMed2004

Forced desynchronization of dual circadian oscillators within the rat suprachiasmatic nucleus.

The circadian clock in the suprachiasmatic nucleus of the hypothalamus (SCN) contains multiple autonomous single-cell circadian oscillators and their basic intracellular oscillatory mechanism is beginning to be identified. Less well understood is how individual SCN cells create an integrated tissue pacemaker that produces a coherent read-out to the rest of the organism. Intercellular coupling mechanisms must coordinate individual cellular periods to generate the averaged, genotype-specific circadian period of whole animals. To noninvasively dissociate this circadian oscillatory network in vivo, we (T.C. and A.D.-N.) have developed an experimental paradigm that exposes animals to exotic light-dark (LD) cycles with periods close to the limits of circadian entrainment. If individual oscillators with different periods are loosely coupled within the network, perhaps some of them would be synchronized to the external cycle while others remain unentrained. In fact, rats exposed to an artificially short 22 hr LD cycle express two stable circadian motor activity rhythms with different period lengths in individual animals. Our analysis of SCN gene expression under such conditions suggests that these two motor activity rhythms reflect the separate activities of two oscillators in the anatomically defined ventrolateral and dorsomedial SCN subdivisions. Our "forced desychronization" protocol has allowed the first stable separation of these two regional oscillators in vivo, correlating their activities to distinct behavioral outputs, and providing a powerful approach for understanding SCN tissue organization and signaling mechanisms in behaving animals.

Analysis of Variance↗

PubMed2004

Effects of photoperiod on rat motor activity rhythm at the lower limit of entrainment.

The experiment described here studied the rat motor activity pattern as a function of the photoperiod of circadian light-dark cycles in the limits of entrainment (22-and 23-h periods). In most cases, the overt rhythm showed 2 circadian components: 1 that followed the external LD cycle and a 2nd rhythm that was free run. The expression of these components was directly dependent on the photoperiod, and there was a gradual transition in the manifestation of 1 or the other. The component with a period equal to that of the external cycle was more manifested under long photoperiods, while the other 1 was more expressed during short photoperiods. Also, the period of the free-running component was longer under T22 than T23. For each period, the free-running component was longer under a longer photoperiod. At first sight, the presence of these 2 components in most of the rats might appear to be due to the fact that in the limits of entrainment, some rats do not entrain and thus show a free-running rhythm plus masking. However, the gradation observed in the different patterns of the overt motor activity rhythm, especially those patterns related to the different balance between the 2 components and the length of the period of the free-running component under LD as a function of the photoperiod, suggests that the circadian system can be functionally dissociated.

Animals↗