Traumatic brain injury (TBI) is a cause of disability and a risk factor for the development of epilepsy, partially mediated by reactive gliosis. The aim of this project was to observe astroglial and microglial reactions to brain injury and identify sex differences in the process of glial scar formation.Penetrating cortical brain injury was induced on postnatal day 30 (P30) in male and female rats. The animals were perfused on P32, P38, P46, or P60. Brain tissue was sectioned and stained against glial fibrillary acidic protein (GFAP, astrocyte marker) and ionized calcium-binding adapter molecule 1 (Iba1, microglial marker).GFAP-positive and Iba1-positive areas were analysed in perilesional cortex and in the contralateral hemisphere of injured animals and non-injured controls.Increased GFAP-positive area was observed in perilesional cortex on P32 and P38 compared to P46 and P60, in males and females. Increased astrogliosis and microgliosis in injured hemisphere were observed at every stage after TBI compared to non-injured controls. The highest value of Iba1-positive area was observed on P32, with a tendency to decline on P38 in females and on P46 in males. Significant astroglial contralateral reaction was observed in females on P32 and in males on P38.To conclude, TBI is related to persistent gliosis in perilesional area, both in male and female rats, and a temporal contralateral astrocytic reaction. Further analyses will include the morphological analysis of astrocytes and microglia and evaluation of the impact of oestrous cycle on gliosis in females.Funding: National Science Centre Preludium 21 Grant 2022/45/N/NZ4/03028