Thalamic Stimulation in Awake Rats Induces Neurogenesis in the Hippocampal Formation

Background Deep brain stimulation (DBS) provides clinical benefits for a variety of movement disorders and lately emerged as a potential treatment for cognitive and mood disorders. Modulation of adult hippocampal neurogenesis may play a role in mediating its effects. Objective To investigate the effects of unilateral anteromedial thalamic nucleus (AMN) stimulation on adult hippocampal neurogenesis in awake and unrestrained rats. Methods Four groups of adult Sprague-Dawley male and female rats received unilateral stimulation (n = 6 each) or sham surgery (n = 4 each) in the right AMN; another group of males (n = 4) was stimulated in the right ventral posterolateral thalamic nucleus (VPL). A naive group of males and females (n = 4 each) was also included. Rats received 4 injections (50 mg/kg/injection) of 5′-bromo-2′-deoxyuridine (BrdU) 3 days post-surgery and were euthanized 24 h later. The fractionator method was used together with confocal microscopy to count BrdU, GFAP and NeuN positive cells in the dentate gyrus (DG) and hilar zone of the hippocampus. Results Focal neurogenesis was induced in the ipsilateral DG after AMN but not VPL stimulation. Stimulation-induced effects were sex-independent and translated into a 76% increase in proliferation of neural stem/progenitor cells. Increased neurogenesis was most prominent at the caudal region of the DG, while no effect was detected in the hilar and the subventricular zones. Conclusions The exclusive hippocampal neurogenic response to AMN stimulation suggests an involvement of the Papez circuitry in mediating DBS effects and in the treatment of cognitive and behavioral disorders.