Effects of Methylphenidate on the Hyperemotional Behavior in Olfactory Bulbectomized Mice by Using the Hole-Board Test

Abstract

The most consistent behavioral changes caused by olfactory bulbectomy are hyperemotional responses such as hyperactivity in a novel environment. However, the changes in the emotional behavior of mice after undergoing olfactory bulbectomy have not yet been described in detail. The effects of methylphenidate on the hyperemotional behavior of olfactory bulbectomized (OBX) mice were examined by using the hole-board test. Mice (4-week-old) were subjected to olfactory bulbectomy, and the behavioral test was performed 2 weeks after surgery. OBX mice showed a significant increase in the number of head-dips as compared to the sham-operated mice. This increase was significantly decreased after treatment with methylphenidate (10 µg/kg, s.c.). The norepinephrine (NE) turnover ratio in the frontal cortex in OBX mice was significantly less than that in the sham-operated mice. However, the decreased NE ratio in OBX mice normalized after treatment with methylphenidate. Our results suggest that the increased head-dipping behavior in OBX mice might reflect an impulsive-like behavior. In addition, we proposed that the improvement in the noradrenergic abnormalities in the frontal cortex due to methylphenidate treatment may play a key role in the improvement of impulsive-like behaviors observed in OBX mice. Keywords:: olfactory bulbectomy, hole-board test, methylphenidate, norepinephrine