Spectral analysis of body weight, food and water consumption and spontaneous motor activity in male Sprague-Dawley rats.

Abstract

Spectral analyses by maximum entropy method were performed on the time-series data of body weight, food and water consumption and spontaneous motor activity in Sprague-Dawley rats. These parameters were recorded by a monitoring system collected every 30 min for 10 days. All the parameters had circadian (24 +/- 4 hr) and ultradian (less than 20 hr) rhythms. From the logarithmic transformation of spectral frequencies and their power spectral densities, the characteristics of the spectrum of body weight showed 1/f fluctuation and those of food and water consumption were white noises. The spectrum of the spontaneous motor activity showed complex characters. The range of frequencies lower than 0.1 Hz showed white noise while the range of those higher than 0.1 Hz were 1/f or 1/f2 fluctuations, especially in the range between 0.5 and 1.0 Hz (1-2 hours cycle). The auto-correlation coefficients of body weight did not declined suggesting that 24 hours cycle is only periodic phenomenon in body weight changes. Though the auto-correlation coefficients of food and water consumption also did not declined, they had not enough auto-correlations. This was consistent with the appearance of white noise in spectral analyses. The auto-correlation coefficients of spontaneous motor activity declined remarkably, and this suggests that there are various periodic changes in spontaneous motor activity including one to two hours cycles. These results suggest that the possibility of further extension of research is expected by using rhythmicity. It is also indicated that the time of measurement of body weight must be taken into consideration in experiments because of the presence of the circadian rhythmic changes.