Long photoperiod exposure did not produce anxious behaviors in the elevated plus maze or in a novel context.

<p>Histograms showing the average (mean ± SEM) percent of time that each group spent in the (A) open and (B) closed arms of the elevated plus maze, after a 2 week exposure to either NPP or LPP. Notice that there were no significant differences (unpaired t-test) in elevated plus maze performance were found between the two groups. Histograms showing (C) the average (mean ± SEM) distance traveled by each group, during the first exposure to each new context in the NOR chamber. Note that there were no significant differences (unpaired t-test) in locomotion between the NPP and LPP groups at any time point. Abbreviaions: NPP, normal photoperiod; LPP, long photoperiod.</p

Long photoperiod exposure negatively impacted novel object recognition by increasing familiar object exploration while sleep deprivation balanced performance between groups.

<p>Figures showing (A) average (mean ± SEM) time spent exploring familiar objects and (B) average time spent exploring novel objects. Notice that, after exposure to a LPP cycle, animals spent significantly more time exploring the familiar object during the test phase, which corresponds with a lack of recognition. Histograms in (C) plot each group’s average (mean ± SEM) Recognition Index, calculated as time spent exploring the novel object divided by the time total time spent exploring both novel and familiar objects. Notice that, after a 2 week exposure to their respective light cycles, the LPP group had significantly reduced recognition of the novel object compared to the NPP group. Also, the LPP group showed a significant impairment in novel object recognition compared to its baseline performance. After a three week exposure to respective light cycles and 3 h TSD following the familiarization phase, the LPP group still showed deficits in novel object recognition compared to its baseline performance, but their average RI was increased compared to 2 weeks LPP treatment without TSD. After 3 h TSD, the NPP group showed reduced novel object recognition, but the reduction proved to be insignificant. However, notice that the performances of each group become relatively equivalent after 3 h TSD. Exemplary heat maps shown in (D) plot nose-point exploration time during the test phases at each time point. Heat maps are plotted in a color spectrum from blue to red, with red indicating a high amount of time spent in the specified area. Circles labeled “N” and “F” indicate novel and familiar object locations, respectively. Notice the lack of discrimination between familiar and novel objects after LPP exposure. Asterisks indicate the levels of statistical significance (Tukey’s multiple comparisons test) of the differences between the NPP and LPP groups: *p<0.05, **p < 0.01. Delta indicates the level of stastical significance of the differences in the LPP group at different time points: Δp<0.05, ΔΔΔp<0.001. Abbreviaions: NPP, normal photoperiod; LPP, long photoperiod.</p

Experimental design and timeline.

<p>Week 1: All animals are kept in a 12L:12D cycle. Animals are habituated to the testing chamber for two days. On the third day, two identical objects are placed in the chamber, and the animal is allowed to familiarize with them for 10 minutes. On the fourth day, one familiar object is replaced with a novel object, and animals are allowed to freely explore for 2 minutes. Weeks 2 and 3: Group 1 is kept in a 12L:12D cycle; group 2 is housed in a 21L:3D cycle. Week 4: While being maintained on their respective light cycles, all animals undergo another NOR task. The context of the testing chamber is different from that of Week 1. The four-day NOR protocol is identical to that of Week 1, except that, after the second habituation, animals are placed in the elevated plus maze for 5 minutes. On the fifth day, animals undergo a 5 minute forced swim test. Week 5: Animals undergo another NOR task. The context of the testing chamber remains the same as Week 4. This NOR protocol is also identical to that of Week 1, except that, directly after the familiarization phase, animals are totally sleep deprived for 3 hours.</p