*1.2.3. Pinealectomy*

Pinealectomy is one of the methods to investigate the effect of melatonin in animals. It eliminates the melatonin hormone from blood circulation. It is well-recognized that the removal of the pineal gland abolishes the rhythmic endogenous melatonin release and decreases the plasma levels of melatonin significantly (Hoffman and Reiter, 1965). It prevents the animal from responding against the changes in day length (Hoffmann and Reiter, 1965; Hoffmann, 1974).

The effects of pinealectomy have been mostly studied on the reproductive system. The reproductive cycle desynchronizes from the environmental photoperiodic cycle by the pinealectomy. The effects of pinealectomy on reproductive system have been well documented in some hamster species. Pinealectomy prevents the regression effect of short photoperiods while gonadal maintenance on long photoperiods is not affected in Syrian hamster (Hoffmann and Reiter, 1965). Pinealectomy blocks short photoperiod induced gonadal regression of hamsters previously housed on long photoperiod (Hoffmann, 1974).

In addition to studies on the effects of regulatory function of pinealectomy on the reproductive system, it has been received a research attention in the behavioral studies. However, these studies have provided rather inconsistent findings. For instance, while the pinealectomy itself did not have a detrimental effect on cognitive performance in rats, the interaction of it with the other lesion (i.,e, lesion on habenula) impaired such performance (Lecourtier et al., 2005). Many studies have shown that pinealectomy did not have a significant effect on the acquisition and extinction of the active avoidance behavior (Appenrodt and Schwarzberg, 2003), anxiety behavior (Appenrodt and Schwarzberg, 2000), passive avoidance learning (Appenrodt and Schwarzberg, 1999), open field exploratory activity (Kovács et al., 1974), and social recognition (Appenrodt et al., 2002).
