RESUMO
:Aim To study the effects of continuous dai¬ly administration of ramelteon starting at the subacute period of cryogenic traumatic brain injury (cTBI) on neurological function and brain tissue repair in mice. Methods Thirty male C57BL/6 mice were randomly divided into sham group, vehicle group and ramelteon treatment groups. The right sensory-motor cortex was damaged by pressing a copper probe precooled by liq¬uid nitrogen onto the skull. Ramelteon ( 10 nig 'kg-1 • d"1) was administered by gavage every day starting at different time points after cTBI (1 h, 1 d,3 d) until sacrifice on day 14. Beam walking test and open field test were used to evaluate the motor function. Toluidine blue staining was used to measure the infarct volume. Immunofluorescence was used to detect the expression of GAP-43 and synaptophysin in peri-infarct area. Mi¬croglia activation was detected using Iba-1. The area and thickness of glial scars were analyzed by detecting GFAP positive areas. Results All three treatment ( 1 h - 14 d, 1 - 14 d, and 3 - 14 d) significantly im¬proved cTBI induced motor dysfunction, reduced the infarct volume, elevated the expression of GAP -43 and synaptophysin, and decreased the area and thick¬ness of glial scar and microglia activation. In addition, all ramelteon treatment groups had similar effects on the above indexes. Conclusions Delayed ramelteon treatment can improve neurological dysfunction after cTBI,and the therapeutic time window can be delayed for up to three days after cTBI. Inhibiting glial scar formation and microglia activation, and promoting ax- onal regeneration and synaptogenesis may contribute to the beneficial effects of ramelteon.