Effects of bifemelane on discrimination learning of serotonergic-dysfunction rats.

To investigate the effect of bifemelane hydrochloride on learning achievements of serotonin-deficient rats, animals were fed with tryptophan-deficient diets and operant type discrimination learning tests were performed. In general, serotonin-deficient rats show hyperactivity. In this study, total number of responses in reverse learning experiments was lower in rats that received 50 mg/kg bifemelane compared to the other serotonin-deficient groups. The ratio of correct responses to the total number of responses revealed low learning achievements in the control and low-dose groups, whereas the ratio in the high-dose group was nearly the same as in normal rats in the final few sessions of both the primary and reverse learning experiments. Throughout this study, the high-dose group showed a better improvement in learning achievement than the low-dose group. Therefore, bifemelane has certain effects on learning achievement from a) the functional activation of the serotonergic nervous system and b) changes in neurotransmitter levels in the brain (e.g., acetylcholine, noradrenaline) and overall energy metabolism.