Estrous Correlated Modulations of Circadian and Ultradian Wheel-Running Activity Rhythms in LEW/Ztm Rats

Franziska Wollinik and Fred W. Turek

Physiology and Behavior – 1988

               

                Steroid hormones that are produced by females act to modulate the circadian rhythms of activity in female rats. This can occur on a daily basis. Furthermore, there are differences between males and females that are abolished when female are ovariectomized. This peaks interest in the question, what are the female hormones doing? The current study aimed to determine if the estrous cycle affected daily wheel-running activity in female rats.

                LEW/Ztm female rats were used in this study and were kept on a light dark cycle of 12:12. At 80 days of age all rats were placed in a cage with a wheel and at the beginning of the experiment half of the animals were blinded so they did not know whether it was dark or light. Estrous cycle was only monitored in three sighted and three blinded animals. For all animals the amount of wheel revolutions in a five minute period was measured and used to calculate the amount of activity. Out of the 20 animals used in the study there were a total of 17 animals that showed a consistent 4-5 day estrous cycle and it was these rats that were used in the analysis of the data.

                Rats showed increased levels of activity during the proestrus and estrus stages of the cycle and lower activities on the metestrus and diestrus stages. Measurements of daily activity and duration varied across the estrous cycle in the rats. This study showed that the biggest differences in the measurements of activity was consistently on the day of estrus. It was approximately two times higher than on the day of metestrus. The blinded rats also showed variations in activity based on the estrous cycle like the sighted animals. This study was important in showing that the voluntary wheel running activity of rats various with the estrous cycle as is supported by our data as well. In this study the day of estrus was shown to be the day of highest activity across both groups. This group suggests that it is estrogen and progesterone that modulate the rhythmic effects on activity seen in the estrous cycle. This current study was mostly focused on the effect that estrogen had on the circadian and ultradian rhythms. This is an interesting paper for sure because it does show that there are differences in the wheel running behavior based on the estrous cycle and it is suggested to be estrogen and progesterone. This can be the basis for further research in our lab, however, I feel there are definitely some methodology that needs to be reconsidered from this paper. Specifically, I am confused about how they determined the estrous cycle and feel that they were using some arbitrary parameters. Furthermore, this paper did not ovariectomize rats and replace with estrogen as the focus was the rhythms and not the wheel running, in this paper it seems the wheel running was just a way to measure rhythms.

Ben R