Sex-dependent and chronic alterations in behavior and mitochondrial function in a rat model of pediatric mild traumatic brain injury

Pathophysiology of Pediatric Traumatic Brain Injury

The national incidence of traumatic brain injury (TBI) exceeds that of any other disease in the pediatric population. In the United States the Centers for Disease Control and Prevention (CDC) reports 697,347 annual TBIs in children ages 0–19 that result in emergency room visits, hospitalization or deaths. There is a bimodal distribution within the pediatric TBI population, with peaks in both toddlers and adolescents. Preclinical TBI research provides evidence for age differences in acute pathophysiology that likely contribute to long-term outcome differences between age groups. This review will examine the timecourse of acute pathophysiological processes during cerebral maturation, including calcium accumulation, glucose metabolism and cerebral blood flow. Consequences of pediatric TBI are complicated by the ongoing maturational changes allowing for substantial plasticity and windows of vulnerabilities. This review will also examine the timecourse of later outcomes after mild, repeat mild and more severe TBI to establish developmental windows of susceptibility and altered maturational trajectories. Research progress for pediatric TBI is critically important to reveal age-associated mechanisms and to determine knowledge gaps for future studies.

The ketogenic diet raises brain oxygen levels, attenuates postictal hypoxia, and protects against learning impairments

OBJECTIVES

A prolonged vasoconstriction/hypoperfusion/hypoxic event follows self-terminating focal seizures. The ketogenic diet (KD) has demonstrated efficacy as a metabolic treatment for intractable epilepsy and other disorders but its effect on local brain oxygen levels is completely unknown. This study investigated the effects of the KD on tissue oxygenation in the hippocampus before and after electrically elicited (kindled) seizures and whether it could protect against a seizure-induced learning impairment. We also examined the effects of the ketone β-hydroxybutyrate (BHB) as a potential underlying mechanism.

METHODS

Male and female rats were given access to one of three diet protocols 2 weeks prior to the initiation of seizures: KD, caloric restricted standard chow, and ad libitum standard chow. Dorsal hippocampal oxygen levels were measured prior to initiation of diets as well as before and after a 10-day kindling paradigm. Male rats were then tested on a novel object recognition task to assess postictal learning impairments. In a separate cohort, BHB was administered 30 min prior to seizure elicitation to determine whether it influenced oxygen dynamics.

RESULTS

The KD increased dorsal hippocampal oxygen levels, ameliorated postictal hypoxia, and prevented postictal learning impairments. Acute BHB administration did not alter oxygen levels before or after seizures.

INTERPRETATION

The ketogenic diet raised brain oxygen levels and attenuated severe postictal hypoxia likely through a mechanism independent of ketosis and shows promise as a non-pharmacological treatment to prevent the postictal state.

Drosophila Exhibit Divergent Sex-Based Responses in Transcription and Motor Function After Traumatic Brain Injury

Every year, millions of people in the US suffer brain damage from mild to severe traumatic brain injuries (TBI) that result from a sudden impact to the head. Despite TBI being a leading cause of death and disability worldwide, sex differences that contribute to varied outcomes post-injury are not extensively studied and therefore, poorly understood. In this study, we aimed to explore biological sex as a variable influencing response to TBI using Drosophila melanogaster as a model, since flies have been shown to exhibit symptoms commonly seen in other mammalian models of TBI. After inflicting TBI using the high-impact trauma device, we isolated w¹¹¹⁸ fly brains and assessed gene transcription changes in male and female flies at control and 1, 2, and 4 hr after TBI. Our results suggest that overall, Drosophila females show more gene transcript changes than males. Females also exhibit upregulated expression changes in immune response and mitochondrial genes across all time-points. In addition, we looked at the impact of injury on mitochondrial health and motor function in both sexes before and after injury. Although both sexes report similar changes in mitochondrial oxidation and negative geotaxis, locomotor activity appears to be more impaired in males than females. These data suggest that sex-differences not only influence the response to TBI but also contribute to varied outcomes post-injury.

Effect of MGHPPGP Peptide Administered during the Post-Traumatic Period on Morphometric Parameters of the Neocortex and Hippocampus, Hepatocytes, and Epithelium of the Tongue and Small Intestine in Rats

The effect of glyproline-containing peptide MGHPPGP (Met-Glu-His-Phe-Pro-Gly-Pro) was studied in experiments on male Wistar rats with modeled traumatic brain injury. The peptide was administered intraperitoneally in a dose of 1 mg/kg in 3 h and on days 2, 3, 4, 5 after injury. We evaluated morphometric parameters of the epithelial cells of the tongue, small intestine, and liver cells (AgNOR staining), neuronal layers II and V of the neocortex of the parietal lobe and hippocampal CA1 field (staining with gallocyanin) were evaluated in the post-traumatic period. Traumatic brain injury (TBI) was induced in rats by using the impact model (WDM; weight drop method). MGHPPGP peptide corrected the activity indicators of the nuclear organizer regions in epitheliocytes of the tongue.

The emerging role of neutrophils as modifiers of recovery after traumatic injury to the developing brain

The innate immune response plays a critical role in traumatic brain injury (TBI), contributing to ongoing pathogenesis and worsening long-term outcomes. Here we focus on neutrophils, one of the "first responders" to TBI. These leukocytes are recruited to the injured brain where they release a host of toxic molecules including free radicals, proteases, and pro-inflammatory cytokines, all of which promote secondary tissue damage. There is mounting evidence that the developing brain is more vulnerable to injury that the adult brain. This vulnerability to greater damage from TBI is, in part, attributed to relatively low antioxidant reserves coupled with an early robust immune response. The latter is reflected in enhanced sensitivity to cytokines and a prolonged recruitment of neutrophils into both cortical and subcortical regions. This review considers the contribution of neutrophils to early secondary pathogenesis in the injured developing brain and raises the distinct possibility that these leukocytes, which exhibit phenotypic plasticity, may also be poised to support wound healing. We provide a basic review of the development, life cycle, and granular contents of neutrophils and evaluate their potential as therapeutic targets for early neuroprotection and functional recovery after injury at early age. While neutrophils have been broadly studied in neurotrauma, we are only beginning to appreciate their diverse roles in the developing brain and the extent to which their acute manipulation may result in enduring neurological recovery when TBI is superimposed upon brain development.

Polydatin prevents the induction of secondary brain injury after traumatic brain injury by protecting neuronal mitochondria

Polydatin is thought to protect mitochondria in different cell types in various diseases. Mitochondrial dysfunction is a major contributing factor in secondary brain injury resulting from traumatic brain injury. To investigate the protective effect of polydatin after traumatic brain injury, a rat brain injury model of lateral fluid percussion was established to mimic traumatic brain injury insults. Rat models were intraperitoneally injected with polydatin (30 mg/kg) or the SIRT1 activator SRT1720 (20 mg/kg, as a positive control to polydatin). At 6 hours post-traumatic brain injury insults, western blot assay was used to detect the expression of SIRT1, endoplasmic reticulum stress related proteins and p38 phosphorylation in cerebral cortex on the injured side. Flow cytometry was used to analyze neuronal mitochondrial superoxide, mitochondrial membrane potential and mitochondrial permeability transition pore opened. Ultrastructural damage in neuronal mitochondria was measured by transmission electron microscopy. Our results showed that after treatment with polydatin, release of reactive oxygen species in neuronal mitochondria was markedly reduced; swelling of mitochondria was alleviated; mitochondrial membrane potential was maintained; mitochondrial permeability transition pore opened. Also endoplasmic reticulum stress related proteins were inhibited, including the activation of p-PERK, spliced XBP-1 and cleaved ATF6. SIRT1 expression and activity were increased; p38 phosphorylation and cleaved caspase-9/3 activation were inhibited. Neurological scores of treated rats were increased and the mortality was reduced compared with the rats only subjected to traumatic brain injury. These results indicated that polydatin protectrd rats from the consequences of traumatic brain injury and exerted a protective effect on neuronal mitochondria. The mechanisms may be linked to increased SIRT1 expression and activity, which inhibits the p38 phosphorylation-mediated mitochondrial apoptotic pathway. This study was approved by the Animal Care and Use Committee of the Southern Medical University, China (approval number: L2016113) on January 1, 2016.