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. Author manuscript; available in PMC: 2012 Mar 10.
Published in final edited form as: Neuroscience. 2010 Dec 24;176:284–295. doi: 10.1016/j.neuroscience.2010.12.022

Figure 1.

Figure 1

Protocol for photoperiod shifts during CPP. Rats were initially housed on a 12L:12D schedule (arrow, Start) for CPP training, testing in the drug-free state, and for the first reinstatement. Separate groups of rats were then shifted to either shorter or longer days, followed by a shift to constant dark (0L:24D) or constant light (24L:0D), respectively, and then shifted back to the original 12L:12D photoperiod. Numbers in parentheses indicate the maximum number of days between photoperiods to allow for re-entrainment (range: 1-16) depending on the magnitude of the photoperiod shift (see Methods for details). Separate groups of rats were trained and tested at ZT4, ZT12, or ZT20. White bars represent the light period; black bars represent the dark period.