The effects of the photoperiod, the time of the day and the pineal gland on depression and agression like behaviours in wistar albino rats

Recently, with the development of technology, the differentiation of modern living conditions may cause the disturbance of the natural sleep rhythm and may trigger mental disorders such as anxiety, depression and aggression by changing the release rhythm of melatonin hormone. There are no studies in the literature that test the effects of different photoperiods, different measurement times of the day and the pineal gland together on these conditions. Our aim in this study, was to investigate the effects of the photoperiod, measurement time of the day and the pinealectomy on anxiety, depression and aggression-like behaviors in male Wistar albino rats by using open field, Porsolt forced swim test and resident-intruder test. The tested subjects were firstly divided into two groups as control and pinealectomy, then each group was divided into 3 subgroups as short (8L:16D), normal (12L:12D) and long (16L:8D) photoperiod, randomly. Experimental measurements were performed at the four different measurement time (6:00, 12:00, 18:00 and 24:00 h). In open field, pinealectomized subjects in the normal photoperiod at 24:00 h were the least anxious of all other conditions for most of the measurements. In Porsolt forced swim test, control subjects in the long photoperiod at 12:00 h were the least depressive of all other conditions for most of the measurements. In the resident-intruder test, the subjects in the short photoperiod were more aggressive than those in the normal and long photoperiod. Taken together these findings showed that the pinealectomized animals with low level of melatonin were less anxious, the subjects under the long photoperiod with low level of melatonin were less depressive compare to those in short photoperiod subjects with high level of melatonin. However, animals under the short photoperiod with high level of melatonin were more aggressive than those in long and normal photoperiod subjects. The outcomes of the study indicated that the effects of the pinealectomy, the measurement time of the day, and photoperiod were significant on the anxiety, depression and aggression-like behavior of the Wistar albino rats.