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.
Conclusion: 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.