Emotional Disturbance in Two Models of Melatonin Deficiency: A Comparative Study

Abstract

In the present study, the aim was to compare the role of melatonin deficiency on emotional status in two different models, chronic constant light (CCL) and pinealectomy in male Wistar rats. While the rats with pinealectomy (Pin) showed impulsive behaviour (increased motor activity and lack of anxiety), CCL-rats demonstrated higher anxiety in the elevated plus-maze test (EPM). Slight differences in depressive-like behaviour, measured by the saccharine preference test (SPT) and the forced swimming test (FST), were also detected. The CCL-rats exhibited anhedonia only during the active (dark) phase of the light-dark cycle whereas rats with removed pineal gland showed depressive behaviour without diurnal variations. Immobility in the FST was increased in the two models of melatonin deficiency. Exposure to CCL and removal of the pineal gland abolished the circadian fluctuations in plasma melatonin levels. Both models of melatonin deficit exhibited higher plasma corticosterone levels during the light period and blunted diurnal variations of the hormone. Our findings suggest that models of melatonin deficiency recapitulate several neurobiological alterations associated with melancholic depression. Future studies are needed to elucidate the precise mechanism related to the model-specific difference in emotional status.