Hello, I believe there are many ways to robustly disturb circadian rhythms in rats by photoperiod shifting. Constant conditions is one way but you can also use paradigms similar to those used by Robert J. McDonald (pubmed) where the animals are put through stages of phase shifting and recovery over many days. This seems to result in strong rhythm fragmentation in the rats, among other physiological deficits. I don't know about the particular schedule you've proposed but generally I've seen manipulations of light/dark cycles with varying proportions of light and darkness (eg. 18:6 or 6:18, etc.). Good luck! 

Hello Farzane,

Constant darkness will lead to the expression of a non entrained rhythm, named free running rhythm, in which the animal presents its endogenous period. I do not consider this condition a rhythm disturbance. If you kepp the animal in constant light (LL) for many days, it will eventually became arhythmic. Repeated phase shifting (advance or delay) of the light-dark cycle also induces rhythm disturbance. Using a 6 h light: 6 h dark or 48 h L: 48 h D would probably lead the animals to express their endogenous period, the free-running rhythm because the length is out of the circadian range, so the animals are not able to entrain. There is a condition of dissassociation beetwen ventral and dorsal SCN activity, and circadian rhythms, called forced desynchronization, in which the animals is kept in a 22 h light-dark cycle (11h light: 11h dark). 

http://www.ncbi.nlm.nih.gov/pubmed/15120072

http://www.ncbi.nlm.nih.gov/pubmed/17452631

http://www.ncbi.nlm.nih.gov/pubmed/19375313

I guess it all depends on what you mean by "disturbance", the LD of 22 hours we use leads to internal desynchrony, which I consider a disturbance. 

LD that are longer or much shorter will not lead to entrainment, but this does not mean the rhythm is free-running, because light still stimulates the PRC, so you will not get the endogenous period of the animal but a different period emerges, and its calculation is more complex. So, in this case the rhythm is somehow "disturbed"

Finally, chronic jet lags as suggested above, will also disturb the system

H

One method we have used to disrupt circadian rhythms is a 12L:12D schedule that "flips" every two days. This pattern resulted in very robust differences from a continuous 12L:12D cycle and pretty much obliterated circadian rhythms of locomotor activity. See https://www.jcircadianrhythms.com/articles/10.1186/1740-3391-6-7