Effects of milnacipran and fluvoxamine on hyperemotional behaviors and the loss of tryptophan hydroxylase-positive cells in olfactory bulbectomized rats

Rationale It has been reported that many of the behavioral and serotonergic neuronal changes observed in olfactory bulbectomy (OBX) were improved by subchronic administration of a variety of antidepressants. Objective We examined the effects of subchronic treatment with milnacipran, a dual serotonin and noradrenaline reuptake inhibitors (SNRIs) and fluvoxamine, selective serotonin reuptake inhibitors (SSRI) in the OBX-induced hyperemotional behaviors and tryptophan hydroxylase (TPH), rate-limiting enzyme of 5-HT. Materials and methods The olfactory bulbs were removed by suction. Drugs were administered p.o. once daily for 8 days beginning 14 days post-surgery. The hyperemotionality behaviors of OBX rats were measured by rating scale and in the elevated plus-maze test. Results OBX rats, after milnacipran or fluvoxamine treatment, showed significant decrease in the score of hyperemotional responses on 7th day as compared with vehicle-treated OBX rats. In addition, milnacipran and fluvoxamine in OBX rats respectively produced a significant increase in the percentage of time spent in and number of entries into open arms in the elevated plus maze test. Furthermore, when 5-HTnergic neuronal function was examined using antibodies against tryptophan hydroxylase (TPH) following the behavioral tests, fluvoxamine significantly reversed the loss of TPH-positive cells produced by OBX in the dorsal raphe. Conclusions We demonstrated that chronic treatment with milnacipran or fluvoxamine was effective to improve both the hyperemotional behavior and the loss of TPH-positive cells seen in OBX rats.