Age affects acute traumatic brain injury outcomes in rats exposed to the same impact setting

In an animal study of acute traumatic brain injury, 8-week-old male Sprague–Dawley rats showed greater neurological deficits, neuronal loss, axonal injury and molecular responses than 10- and 12-week-old rats exposed to the same nominal impact setting. The findings indicate that animal age should be treated as an important source of variability in closed-head injury experiments.

The study, published in Frontiers in Neurology on 19 October 2026, compared 8-, 10- and 12-week-old rats in a closed-head injury model. The experimental cohort comprised 48 rats, with each age cohort divided into injured and sham groups of eight. An additional seven animals died after impact, producing an overall mortality of 12.7%, and replacements were added to maintain the planned group sizes. The study was approved by the Institutional Animal Care and Use Committee of Army Medical University.

Injuries were produced with a pneumatically driven BIM-IV impactor at a driving pressure of 0.7 MPa. A steel helmet was fixed to the midline of the skull to reduce the risk of fracture, while sensors recorded linear acceleration and angular velocity during impact at a sampling rate of 10 kHz. Rotational acceleration was calculated from angular velocity. Head mass and skull thickness were also measured to assess possible biomechanical differences among the age groups.

The youngest animals recorded the highest peak linear and rotational accelerations, followed by the 10-week-old and 12-week-old groups. The 10- and 12-week-old groups had significantly lower peak rotational acceleration than the 8-week-old group, while the 12-week-old group also had significantly lower peak linear acceleration. Head mass and skull thickness increased with age. The authors considered these structural differences plausible contributors to the varying kinematic responses, but the experimental design did not establish which factor was responsible for the subsequent differences in injury severity.

Behavioral assessments were conducted during the acute period. All injured groups had a longer loss of righting reflex and higher modified Neurological Severity Scores than their age-matched sham groups. The 8-week-old injured rats also had a significantly longer loss-of-righting-reflex period than the 12-week-old injured rats, and their neurological severity scores were higher than those of both older injured cohorts. On the rotarod test, all injured groups performed worse than their shams, but differences among the three injured groups did not reach statistical significance. In the elevated plus maze, injured rats spent significantly less time in open arms than their shams, a pattern interpreted as increased anxiety-like behavior, while differences among injured age groups were not significant.

Histological analysis showed injury in all three age groups. Nissl staining identified shrunken neuronal cell bodies, condensed chromatin, blurred contours and vacuolar degeneration after injury. The 8-week-old group had the greatest neuronal loss and disorganization in the cerebral cortex, with some areas nearly devoid of intact neurons, and the most severe changes in the hippocampal CA3 region. The 12-week-old group retained comparatively well-preserved neuronal morphology. Cortical neuronal counts were significantly higher in the 12-week-old injured group than in the 8-week-old injured group.

Axonal injury in the corpus callosum was assessed with beta-amyloid precursor protein immunohistochemistry. Injured rats showed increased staining relative to their age-matched shams, with dense, widespread deposits in the 8-week-old group, intermediate staining in the 10-week-old group and sparse deposits in the 12-week-old group. The integrated optical density was significantly lower in the 12-week-old injured group than in the 8-week-old injured group. These findings associated the youngest animals with more extensive axonal pathology under the tested conditions.

Western blot measurements of tissue from the cerebral cortex, hippocampus and corpus callosum showed significantly elevated glial fibrillary acidic protein, cleaved caspase-3 and interleukin-1 beta in the 8- and 10-week-old injured groups compared with their shams. None of the three markers differed significantly from sham levels in the 12-week-old group, and each was significantly lower in the 12-week-old injured group than in the 8-week-old injured group. The authors associated these markers with astrocyte reactivity, apoptotic pathways and neuroinflammation, respectively, but the restricted molecular panel did not establish the underlying regulatory mechanisms.

The experiment was limited to one impact intensity and acute-phase outcomes, so it did not determine whether the pattern extends to milder injuries or persists during recovery. Only three molecular markers were measured, and systemic metabolic disturbance, oxidative stress and peripheral inflammation were not assessed. No post-injury analgesic was administered and pain was not independently evaluated, meaning pain or stress could have influenced behavioral and pathological results. The authors also cautioned that the findings do not show that increasing age is generally protective against traumatic brain injury in humans, where outcomes also depend on developmental stage, injury severity, comorbidities and recovery time.

Subject of Research: Effects of rat age on acute outcomes in a closed-head traumatic brain injury model

Article Title: Comparative study of acute-phase traumatic brain injury in rats of different weeks of age under identical impact force

Article References: Chen, D., Wang, P., Zhang, L., Qiu, J., Zhu, X., Xiang, H., Wang, Q., Guo, Y., Zhao, H., & Xiong, K. (2026). Comparative study of acute-phase traumatic brain injury in rats of different weeks of age under identical impact force. Frontiers in Neurology, 17, Article 1928195. https://doi.org/10.3389/fneur.2026.1928195

Image Credits: AI Generated

DOI: 10.3389/fneur.2026.1928195

Keywords: traumatic brain injury, closed-head injury, rat age, biomechanical response, neurological deficits, neuronal loss, axonal injury, neuroinflammation, animal model, Comparative, acute-phase, traumatic