Long Photoperiod has Antidepressant Effects in Rats Shuntaro Tadano Program in Neuroscience Introduction • Seasonal Affective Disorder (SAD) patients develop symptoms in autumn or winter that diminish in spring or summer. • Photoperiod is considered as a primary variable for such seasonality. • Effect of photoperiod on the behavior of rats was tested by forced swim test (FST). • Developed by Porsolt et al. (1977) FST is a widely used tool to assess depressive activity in rats. • Since rats are nocturnal animals, it is hypothesized that long photoperiod has depressive effect on rats.

Episodes of mood disturbance (Teng, Akerman, Cordas, Kasper, & Vieira, 1995)

Materials and Methods •Subjects – Subjects were sixteen male Harlan Sprague Dawley® rats obtained from a supplier at approximately 40 days of age. – Eight of the rats were group-housed in normal photoperiod and another eight were group-housed in abnormal photoperiod. – The cages were transparent plastic with wood shaving (50 x 39 x 20 cm) and placed in the animal colony rooms in the Psychology Department at Muskingum College. – Under normal photoperiod, light was on at 0800h and off at 2000h (12L/ 12D), and under abnormal photoperiod, light was on at 1000h and off at 1400h (20L/ 4D).

•Apparatus

Controls of circadian rhythms by specific brain locations obtained

– A rectangular plastic container (25 x 33 x 51cm) was used for FST. – The container was filled with water to a depth of 30cm. – Water was maintained at room temperature (18.0-20.0ºC) and changed every session.

from http://www.nature.com/neuro/journal/v9/n3/fig_tab/nn0306-300_F1.html

•Procedure – The present experiment was approved by Muskingum College Institutional Animal Care and Use Committee. – Animals were placed into their respective lighting conditions for 28 days for control group and 22 days for experimental group. After this time the rats were tested on the FST. – One test consisted of two trials; habituation and test. On day of habituation, each rat was placed in water and allowed to swim for 15 minutes. After the swimming, they were removed, dried off with paper towels and returned to their home cage. In the following day, animals were tested. They were placed in apparatus and habituated for 1 minute and then amount of time spent immobile was recorded for 4 minutes. – Every habituation and test was conducted 90 minutes prior to the dark period. FST started at 1830h for a control group and at 0830h for an abnormal. After each trial, rats were removed from the container and dried with paper towels.

Mean time of immobility for the control and experimental group

Results * •Time of immobility was approximately 47 seconds on average for the control group while it was 22 seconds in an experimental group. This reduction in mobility was statistically significant, t(14) = 2.673, p = 0.018. •There was no difference in weight between a control and experimental group, t(14) = 0.239, p > 0.05.

Above and below from Saper, Scammell, & Lu, 2005

Conclusions • Contrary to prediction, long photoperiod did not induce depressive-like behavior in rats. • Instead, consistent with a previous study on the effect of long photoperiod (14L/10D) by Molina-Hernandez and Tellez-Alcantara (2000), a significant decrease in immobility was found that suggests antidepressant-like effects of long photoperiod. • Although implication of immobility shown in FST has been discussed, correlation between antidepressant effect of drug and immobility has been reported (Willner, 1984; Borsini & Meli, 1988). • Kobayashi, Hayashi, Shimamura, Kinoshita, & Murphy (2008) showed increased extracellular dopamine (DA) levels in prefrontal cortex (PFC). • DA projection in PFC comes from VTA that is projected by LHA containing ORX. LHA is projected by DMH. Saper, Scammell, and Lu (2005) suggested that DMH integrated information from suprachiasmatic nucleus (SCN) with external non-photic cues to provide flexible adaptation of behavioral and physiological cycle. • From the findings above, it can be suggested that SCN overly activates these hypothalamic regions in long photoperiod that are a part of the arousal/wake-regulatory system. It has not been reported whether over activation of these nuclei has antidepressant effects. However, irregularity of this system is clearly shown in depressive patients. Therefore, it implies dysfunctional integration of those photic-influenced areas may play a major role. •At last, it is noteworthy that this study was done under ordinary luminance. Therefore, it makes people wonder how artificial lights surrounding us can affect our affective state.

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