Neurogenesis inhibition in the dorsal vagal complex by chronic immobilization stress in the adult rat.
Résumé
The dorsal vagal complex (DVC) is the brainstem integrative center that mediates the satiety reflex and relays autonomic neural responses to stress. The DVC displays adult neurogenesis, intrinsic neural stem cells and a high brain-derived neurotrophic factor (BDNF) content, effectors of plasticity that are modulated by stress in the hippocampus. In this study we asked whether neurogenesis and BDNF expression in the DVC are altered by stress, in parallel with food intake reduction. To this end, neurogenesis was assessed in adult rats in vivo by repetitive 5-bromo-2'-deoxyuridine (BrdU) administration without (controls) or with daily sessions of immobilization stress (1 h/day), and were allowed to survive for 2 weeks after the end of BrdU treatment. Neurogenic proliferation in the brainstem was detected by immunohistochemistry and confocal microscopy mainly in the area postrema and the nucleus tractus solitarius; newly formed neurons amounted to about 35% of all BrdU-labeled cells in the DVC of control rats. Chronic immobilization stress induced a significant decrease in neurogenic proliferation in the DVC which reached 50% in the area postrema. The number of newly-formed neurons was also decreased by chronic immobilization stress in the DVC, and this effect was again maximal in the area postrema; the proportion of BrdU-labeled cells that were neurons was unchanged. In vitro neurosphere assay was then performed on microdissected DVC tissue from another cohort of chronically stressed and control rats. Chronic immobilization stress induced a significant decrease of the total neurosphere number per rat DVC in both primary and secondary cultures, indicating that intrinsic neural stem cell frequency was decreased by chronic stress in DVC tissue. Tissue BDNF concentration in the DVC, as assessed by enzyme-linked immunosorbent assay, was not significantly altered when compared with controls after 3, 6, 9 or 13 days of chronic immobilization stress. These results further characterize neurogenesis in the DVC and suggest its involvement in the long-term regulation of food intake.