Recovery From Repeat Mild Traumatic Brain Injury in Adolescent Rats Is Dependent on Pre-injury Activity State

Risk of Two Sport-Related Concussions in the Same Year: Is the Second Concussion Worse?

OBJECTIVES

1) Evaluate the frequency of same-year, repeat concussions; (2) assess predictors of sustaining a repeat concussion; and (3) compare outcomes of athletes with repeat concussions with athletes with single concussion.

DESIGN

A retrospective, case-control study.

SETTING

Regional sports concussion center.

PATIENTS

Adolescents sustaining a sport-related concussions (SRC) from November 2017 to October 2020.

INDEPENDENT VARIABLES

Participants were dichotomized into 2 groups: (1) athletes with a single concussion; and (2) athletes with repeat concussions.

MAIN OUTCOME MEASURES

Between group and within group analyses were completed to look for differences in demographics, personal and family history, concussion history, and recovery metrics between the 2 groups.

RESULTS

Of 834 athletes with an SRC, 56 (6.7%) sustained a repeat concussion and 778 (93.3%) had a single concussion. Between group: Personal history of migraines (19.6% vs 9.5%, χ 2 = 5.795, P = 0.02), family history of migraines (37.5% vs 24.5%, χ 2 = 4.621, P = 0.03), and family history of psychiatric disorders (25% vs 13.1%, χ 2 = 6.224, P = 0.01) were significant predictors of sustaining a repeat concussion. Within group: Among those with a repeat concussion, initial symptom severity was greater (Z = -2.422; P = 0.02) during the repeat concussion and amnesia was more common (χ 2 = 4.775, P = 0.03) after the initial concussion.

CONCLUSIONS

In a single-center study of 834 athletes, 6.7% suffered a same-year, repeat concussion. Risk factors included personal/family migraine history and family psychiatric history. For athletes with repeat concussions, initial symptom score was higher after the second concussion, yet amnesia was more common after the initial concussion.

Chronic running-wheel exercise from adolescence leads to increased anxiety and depression-like phenotypes in adulthood in rats: Effects on stress markers and interaction with BDNF Val66Met genotype

Exercise has been shown to be beneficial in reducing symptoms of affective disorders and to increase the expression of brain-derived neurotrophic factor (BDNF). The BDNF Val66Met polymorphism is associated with reduced activity-dependent BDNF release and increased risk for anxiety and depression. Male and female Val66Met rats were given access to running wheels from 3 weeks of age and compared to sedentary controls. Anxiety- and depression-like behaviors were measured in adulthood using the elevated plus maze (EPM), open field (OF), and forced swim test (FST). Expression of BDNF and a number of stress-related genes, the glucocorticoid receptor (Nr3c1), serum/glucocorticoid-regulated kinase 1 (Sgk1), and FK506 binding protein 51 (Fkbp5) in the hippocampus were also measured. Rats given access to running wheels developed high levels of voluntary exercise, decreased open-arm time on the EPM and center-field time in the OF, reduced overall exploratory activity in the open field, and increased immobility time in the FST with no differences between genotypes. Chronic exercise induced a significant increase in Bdnf mRNA and BDNF protein levels in the hippocampus with some of these effects being genotype specific. Exercise decreased the expression of Nr3c1 and Sgk1, but increased the expression of Fkbp5. These results suggest that chronic running-wheel exercise from adolescence increased anxiety and depression-like phenotypes in adulthood, independent of BDNF Val66Met genotype. Further studies are required to confirm that increased indices of anxiety-like behavior are independent from reduced overall locomotor activity.

Monoamine control of descending pain modulation after mild traumatic brain injury

Traumatic brain injury (TBI) is a significant public health concern, with the majority of injuries being mild. Many TBI victims experience chronic pain. Unfortunately, the mechanisms underlying pain after TBI are poorly understood. Here we examined the contribution of spinal monoamine signaling to dysfunctional descending pain modulation after TBI. For these studies we used a well-characterized concussive model of mild TBI. Measurements included mechanical allodynia, the efficacy of diffuse noxious inhibitory control (DNIC) endogenous pain control pathways and lumber norepinephrine and serotonin levels. We observed that DNIC is strongly reduced in both male and female mice after mild TBI for at least 12 weeks. In naïve mice, DNIC was mediated through α2 adrenoceptors, but sensitivity to α2 adrenoceptor agonists was reduced after TBI, and reboxetine failed to restore DNIC in these mice. The intrathecal injection of ondansetron showed that loss of DNIC was not due to excess serotonergic signaling through 5-HT₃ receptors. On the other hand, the serotonin-norepinephrine reuptake inhibitor, duloxetine and the serotonin selective reuptake inhibitor escitalopram both effectively restored DNIC after TBI in both male and female mice. Therefore, enhancing serotonergic signaling as opposed to noradrenergic signaling alone may be an effective pain treatment strategy after TBI.

Defining Experimental Variability in Actuator-Driven Closed Head Impact in Rats

Traumatic brain injury (TBI) is a world-wide health challenge that lacks tools for diagnosis and treatment. There is a need for translational preclinical models to effectively design clinical tools, however, the diversity of models is a barrier to reproducible studies. Actuator-driven closed head impact (AD-CHI) models have translational advantages in replicating the pathophysiological and behavioral outcomes resulting from impact TBI. The main advantages of AD-CHI protocols include versatility of impact parameters such as impact angle, velocity, depth, and dwell time with the ability to interchange tip types, leading to consistent outcomes without the need for craniectomy. Sources of experimental variability within AD-CHI rat models are identified within this review with the aim of supporting further characterization to improve translational value. Primary areas of variability may be attributed to lack of standardization of head stabilization methods, reporting of tip properties, and performance of acute neurological assessments. AD-CHI models were also found to be more prevalently used among pediatric and repeated TBI paradigms. As this model continues to grow in use, establishing the relationships between impact parameters and associated injury outcomes will reduce experimental variability between research groups and encourage meaningful discussions as the community moves towards common data elements.

A Pro-social Pill? The Potential of Pharmacological Treatments to Improve Social Outcomes After Pediatric Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of injury-induced disability in young children worldwide, and social behavior impairments in this population are a significant challenge for affected patients and their families. The protracted trajectory of secondary injury processes triggered by a TBI during early life-alongside ongoing developmental maturation-offers an extended time window when therapeutic interventions may yield functional benefits. This mini-review explores the scarce but promising pre-clinical literature to date demonstrating that social behavior impairments after early life brain injuries can be modified by drug therapies. Compounds that provide broad neuroprotection, such as those targeting neuroinflammation, oxidative stress, axonal injury and/or myelination, may prevent social behavior impairments by reducing secondary neuropathology. Alternatively, targeted treatments that promote affiliative behaviors, exemplified by the neuropeptide oxytocin, may reduce the impact of social dysfunction after pediatric TBI. Complementary literature from other early life neurodevelopmental conditions such as hypoxic ischemic encephalopathy also provides avenues for future research in neurotrauma. Knowledge gaps in this emerging field are highlighted throughout, toward the goal of accelerating translational research to support optimal social functioning after a TBI during early childhood.

Sex Differences in Neurophysiological Changes Following Voluntary Exercise in Adolescent Rats

Background: Adolescence is a period of time characterized by the onset of puberty and is marked by cognitive and social developments and gross physical changes that can play a role in athletic performance. Sex differences are present with differences in body size, height, physiology and behavior which contribute to differences in athletic performance as well. Pre-clinical studies representing this active group are lacking.

Methods: Acute and chronic effects of exercise were evaluated. Male and female adolescent rats were given voluntary access to a running wheel for 10 consecutive days. Running behavior (males and females) and estrous cycling (females only) were analyzed daily. A second group was given 10 days of voluntary access to a running wheel, then rested for 10 days to determine the long-term effects of exercise on the adolescent brain. Brain and muscle tissue were harvested at 10 and 20 day time points to understand exercise-dependent changes in mitochondrial activity and neuroplasticity. Animal cohorts were carried out at two different sites: University of California Los Angeles and Pepperdine University.

Results: On average, running distance, intensity of run, and length of running bout increased for both male and female rats across the 10 days measured. Females ran significantly further and for longer intervals compared to males. Cortical and muscle expression of PGC1α showed similar levels at 10 days regardless of sex and exercise. There was a significant increase in expression at 20 days in all groups correlating with body size (p's < 0.05). Cortical and hippocampal levels of BDNF were similar across all groups, however, BDNF was significantly higher in exercised females at the acute compared to long-term time point.

Discussion: Adolescent rats allowed 10 days of exercise show changes in physiologic function. There are sex differences in running behavior not impacted by sex hormones. These results are important to further our understanding of how exercise impacts the adolescent brain.

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.