What if days were shorter? the behavioral effects of a 22-hour period on wistar rats

Light is a significant pacemaker for circadian, that is daily or ~24-h, rhythms that greatly influence mood and various physiological functions. As this connection is well known in psychology, there are many studies focusing on the seasonal affective disorder (SAD) and its connection to the light period (i.e. daytime) of the day. Briefly, when the light period in a circadian cycle is shortened, animals tend to be more vulnerable to mood alterations. Despite the effects of shortened light or dark periods are well-known in mood and mood disorders, there is no study investigating the effect of shortened days (i.e. < 24-h) on mood or locomotor activity. To this end, 27 naïve female Wistar rats (2-month-old, 203±6 g) were placed into two identical cabinets: the experimental group was exposed to shortened periods (22-h, 11:11 L:D cycle), whereas the controls were kept in a standard period (24-h, 12:12 L:D cycle). Two months later, both groups were tested in a classical rodent depression paradigm (behavioral despair), the Forced Swim Test (FST) as well as an anxiety-like behavior and locomotor activity test, the Open Field Test (OFT). The 22-h group showed no behavioral despair in the FST and no anxiety-like behavior in the OFT, and higher locomotor activity compared to the 24-h controls. These results indicate that moderately shorter, that is 22-hour, days can produce an antidepressant and anxiolytic effect in Wistar rats.