Ultrastructural localization of vimentin immunoreactivity and gene expression in tanycytes and their alterations in hamsters kept under different photoperiods.

Tanycytes are located in the basolateral walls of the third ventricle. By light- and electron-microscopic immunohistochemistry, we demonstrated that the tanycytes of Djungarian hamsters were intensely immunostained with the vimentin monoclonal antibody V9. The cells always extended long radial processes in which aggregations of vimentin-immunoreactive intermediate filaments were prominent. The tanycytes showed photoperiod-dependent changes. The population of vimentin-immunoreactive tanycytes was increased in hamsters exposed to continuous lighting for 1 month or to a long photoperiod (16 h light:8 h dark) for 2 months. On the other hand, the immunoreactive cells were significantly decreased in hamsters exposed to complete darkness for 1 month or to a short photoperiod (8 h light:16 h dark) for 2 months. The pericapillary spaces of the primary plexus of the portal circulation system were lined by the end-feet of tanycytic processes. Electron microscopy confirmed that the tanycytic processes were markedly decreased in number and size after exposure to complete darkness. Expression of vimentin mRNA in the hamster mediobasal hypothalamus was detected by the reverse transcription-polymerase chain reaction (RT-PCR). The alterations of vimentin mRNA expression under different photoperiods were analyzed using laser capture microdissection and real-time quantitative PCR. The level of vimentin mRNA in the mediobasal hypothalamus was enhanced after exposure to continuous lighting for 1 month or to a long photoperiod for 2 months, whereas it was significantly diminished after exposure to constant darkness or short photoperiod. These changes in the tanycytes under different photoperiods may influence the portal circulation system and also the cell activity of the pars tuberalis, and may thus participate in photoperiodic regulation of the endocrine system.