Cell proliferation is influenced by bulbectomy and normalized by imipramine treatment in a region-specific manner

Growing evidence indicates that alterations of neuroplasticity may contribute to the pathophysiology of depression. In contrast, various antidepressants increase adult hippocampal neurogenesis and block the effects of stress. These findings result in the 'neurogenesis hypothesis of depression'. The present study seeks to determine out whether cell proliferation is altered in the hippocampus, subventricular zone (SVZ), and basolateral amygdala of adult rats exposed to bilateral olfactory bulbectomy, another established model of depression and, if so, how imipramine effects bulbectomy-induced changes of cell genesis. Bulbectomy results in a significant reduction of cell proliferation in the hippocampus and SVZ, an effect that is normalized by subchronic doses of imipramine. Moreover, an increase in cell genesis in the basolateral amygdala, which is not affected by imipramine, is demonstrated. TUNEL staining indicates an enhanced apoptosis after bulbectomy in the SVZ that cannot be reduced by imipramine. Cell death rates in the hippocampus and amygdala are not affected by bulbectomy. The opposing effects of bulbectomy and imipramine treatment in the hippocampus and amygdala demonstrate that these structures of the limbic system, both integrated in emotional processing, react quite differently with regard to neuroplasticity. Further to this, we discuss a possible link between the pathogenesis of depression and changed neuronal plasticity in the SVZ.