Depresyon, anksiyete ve öğrenme ile biyolojik ritimler arasındaki ilişkinin fotoperiyod, maternal transfer ve suprakiyazmatik nukleus çalışmaları çerçevesinde incelenmesi

Some internal factors such as suprachiasmatic nucleus (SCN), pineal gland and melatonin hormone which play important role in the generation and the regulation of the rhythms as well as the environmental factors such as day length (photoperiod) are effective on mood states (anxiety and depression) and memory (spatial memory). However, in the literature, there was no comprehensive study which examines the reciprocal relationship among these variables and it was not known yet the practical and theoretical results of this study or relationship. In this planned thesis, these topics were investigated, related hypothesis were tested, new research models and techniques were implemented and the originality and the applicability of the results were presented. The planned studies in this thesis were classified into 3 main topics: The investigation of the relationship among photoperiod, pineal gland and behaviors. Mood differences in different seasons were considered to be based on the different day lengths in these seasons. In the present study, the effects of different day lengths and pineal gland on mood (anxiety and depression) and spatial memory performance were investigated. Furthermore, whether or not these different day lengths had some effects on the infants through the maternal transfer were investigated. For this aim, in the first study, control (sham pinealectomized) and pinealectomized hamsters were used. Photoperiodic adult male and female Syrian hamsters (Mesocricetus auratus) were exposed to the long (18L), short (6L) and normal (14L) photoperiods for 14 weeks period. At the end of this period, anxiety (open field and elevated plus maze), depression (porsolt), and spatial memory (T-maze) tests were applied to the groups. In all tests, long photoperiod and pinealectomy reduced the anxiety, depression, and improved spatial learning in this study. We also found sex differences in these tests. In the second study, the juvenile hamsters borned to the mothers being exposed to these short, long and normal photoperiods were tested by the same experimental design when they were weaned. In this way, whether there was an effect of the maternal transfer on these behaviors or not were tested. In all tests, the behavior of the anxiety was transferred to the juveniles but not the depression, and spatial memory behaviors in this study. In mammals, SCN which located in the hypothalamus of the brain is responsible for the generation and the regulation of the circadian rhythms. The third study investigated, whether the electrolytic lesions of the SCN eliminate the variations of the behaviors such as anxiety, depression, and spatial memory in different time points of the day. This result could indicate for the first time that the circadian control of the behaviors via the SCN. For this aim, the rats coming from LD 12:12 photoperiod were SCN lesioned. The anxiety, depression and memory experiments were performed in SCN lesioned, sham SCN lesioned and intact rats in different time points of the day (06:00, 12:00, 18:00 and 24:00). In such way, it were realized whether or not these behaviors had a circadian rhythm and this rhythm is controlled by the SCN. The results of the present study indicated that SCN lesions changed the circadian rhythms of the anxiety, depression, and spatial memory.