Traumatic brain injury (TBI) is one of the leading causes of death and disability. TBI is associated with neuroinflammation, but temporal changes in immune and inflammatory signaling following TBI have not been fully elucidated. Furthermore, there have been no previous studies on changes in immune cell populations following TBI via the Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA). The current study aimed to determine the time course changes to inflammatory marker mRNA expression in the acute period following TBI in juvenile rats and to determine acute changes to brain and circulating immune cell populations. For this study, post-natal day (PND)-30 male Long Evans rats sustained a TBI or Sham TBI and were euthanized at 0, 3, 6, 12, 24, or 96 h post-injury. Prefrontal cortex and hippocampus samples were used to determine mRNA expression changes of inflammatory factors. The mRNA expression of the pro-inflammatory cytokine TNF-α was significantly elevated at 6 h post-injury in both regions evaluated. To evaluate immune cell populations, male Long Evans rats were euthanized at 48 h post-injury, and brain and blood samples were used for cell sorting by marker-specific antibodies. In the peripheral blood, there was an elevation in CD3⁺ total T cells, CD45R⁺ total B cells, and CD3⁺CD4⁺ helper T cells in the TBI subjects. However, there were no changes to natural killer cells or CD3⁺CD8⁺ cytotoxic T cell populations. In the brain, there was a reduction in CD11b/c⁺ monocytes/macrophages, but no changes in other immune cell populations. At 48 h post-injury, the TBI subjects also demonstrated expansion of the thymic medulla. These changes in the cerebral and blood immune cell populations and thymic medulla expansion may implicate the subacute recovery timeframe as a vulnerable window for the immune system in the pediatric population.

Juveniles are at increased risk for mild traumatic brain injury (mTBI) due to recreational activities, domestic violence, and vulnerabilities of the developing skull. In industrialized nations, adolescents often consume high-sugar, high-fat diets (HFD), which can impair CNS health and exacerbate mTBI outcomes. Secondary injury following mTBI is characterized by prolonged neuroinflammation, with nuclear factor kappa B (NF-κB) acting as a central regulator of these inflammatory responses. We developed a polypeptide biologic, SynB1-ELP-p50i, consisting of an elastin-like polypeptide delivered NF-κB inhibitor (p50i) and the cell-penetrating peptide SynB1. This study investigates the interaction between diet and NF-κB inhibition in juvenile rats with mTBI by examining SynB1-ELP-p50i biodistribution, pharmacokinetics, therapeutic efficacy, and cell-specific effects. Long Evans rats were assigned to chow or HFD groups at postnatal day 20 (PND20), and mTBI or sham injury was induced at PND30 using the CHIMERA TBI model. Rats received 50 mg/kg SynB1-ELP-p50i or saline post-injury. Behavioral outcomes were assessed with the Morris water maze (MWM), and neuroinflammatory markers were measured using RT-qPCR and single-nucleus RNA sequencing (snRNA-seq). SynB1-ELP-p50i accumulated at injury sites (p < 0.05), and SynB1-ELP-p50i treated chow-fed rats showed improved MWM performance compared to vehicle controls and HFD subjects (p < 0.05). RT-qPCR confirmed increased Aif1 and Gfap expression post-injury (p < 0.05), and snRNA-seq revealed upregulation of markers of microgliosis in activated microglia. These findings indicate that mTBI triggers acute cognitive deficits and neuroinflammation, worsened by HFD. SynB1-ELP-p50i mitigated memory deficits in chow-fed animals, supporting NF-κB inhibition as a promising therapeutic strategy for juvenile mTBI.

The following protocol is used to assess anxiety-related behaviors using the Elevated Plus Maze at the University of Alabama at Birmingham's Neuroscience Behavioral Assessment Core.

The following protocol is used to assess behavioral despair or learned helplessness using the University of Alabama at Birmingham's Neuroscience Behavioral Assessment Core.

The following protocol is used to assess spatial memory function using the Y Maze (novel arm variant) at the University of Alabama at Birmingham's Neuroscience Behavioral Assessment Core.