A narrative literature review of depression following traumatic brain injury: prevalence, impact, and management challenges

Depression is one of the most common conditions to emerge after traumatic brain injury (TBI), and despite its potentially serious consequences it remains undertreated. Treatment for post-traumatic depression (PTD) is complicated due to the multifactorial etiology of PTD, ranging from biological pathways to psychosocial adjustment. Identifying the unique, personalized factors contributing to the development of PTD could improve long-term treatment and management for individuals with TBI. The purpose of this narrative literature review was to summarize the prevalence and impact of PTD among those with moderate to severe TBI and to discuss current challenges in its management. Overall, PTD has an estimated point prevalence of 30%, with 50% of individuals with moderate to severe TBI experiencing an episode of PTD in the first year after injury alone. PTD has significant implications for health, leading to more hospitalizations and greater caregiver burden, for participation, reducing rates of return to work and affecting social relationships, and for quality of life. PTD may develop directly or indirectly as a result of biological changes after injury, most notably post-injury inflammation, or through psychological and psychosocial factors, including pre injury personal characteristics and post-injury adjustment to disability. Current evidence for effective treatments is limited, although the strongest evidence supports antidepressants and cognitive behavioral interventions. More personalized approaches to treatment and further research into unique therapy combinations may improve the management of PTD and improve the health, functioning, and quality of life for individuals with TBI.

Modeling Fast-scan Cyclic Voltammetry Data from Electrically Stimulated Dopamine Neurotransmission Data Using QNsim1.0

Central dopaminergic (DAergic) pathways have an important role in a wide range of functions, such as attention, motivation, and movement. Dopamine (DA) is implicated in diseases and disorders including attention deficit hyperactivity disorder, Parkinson's disease, and traumatic brain injury. Thus, DA neurotransmission and the methods to study it are of intense scientific interest. In vivo fast-scan cyclic voltammetry (FSCV) is a method that allows for selectively monitoring DA concentration changes with fine temporal and spatial resolution. This technique is commonly used in conjunction with electrical stimulations of ascending DAergic pathways to control the impulse flow of dopamine neurotransmission. Although the stimulated DA neurotransmission paradigm can produce robust DA responses with clear morphologies, making them amenable for kinetic analysis, there is still much debate on how to interpret the responses in terms of their DA release and clearance components. To address this concern, a quantitative neurobiological (QN) framework of stimulated DA neurotransmission was recently developed to realistically model the dynamics of DA release and reuptake over the course of a stimulated DA response. The foundations of this model are based on experimental data from stimulated DA neurotransmission and on principles of neurotransmission adopted from various lines of research. The QN model implements 12 parameters related to stimulated DA release and reuptake dynamics to model DA responses. This work describes how to simulate DA responses using QNsim1.0 and also details principles that have been implemented to systematically discern alterations in the stimulated dopamine release and reuptake dynamics.

Ventricular fibrillation cardiac arrest produces a chronic striatal hyperdopaminergic state that is worsened by methylphenidate treatment

Cardiac arrest survival rates have improved with modern resuscitation techniques, but many survivors experience impairments associated with hypoxic-ischemic brain injury (HIBI). Currently, little is understood about chronic changes in striatal dopamine (DA) systems after HIBI. Given the common empiric clinical use of DA enhancing agents in neurorehabilitation, investigation evaluating dopaminergic alterations after cardiac arrest (CA) is necessary to optimize rehabilitation approaches. We hypothesized that striatal DA neurotransmission would be altered chronically after ventricular fibrillation cardiac arrest (VF-CA). Fast-scan cyclic voltammetry was used with median forebrain bundle (MFB) maximal electrical stimulations (60Hz, 10s) in rats to characterize presynaptic components of DA neurotransmission in the dorsal striatum (D-Str) and nucleus accumbens 14 days after a 5-min VF-CA when compared to Sham or Naïve. VF-CA increased D-Str-evoked overflow [DA], total [DA] released, and initial DA release rate versus controls, despite also increasing maximal velocity of DA reuptake (V_max ). Methylphenidate (10 mg/kg), a DA transporter inhibitor, was administered to VF-CA and Shams after establishing a baseline, pre-drug 60 Hz, 5 s stimulation response. Methylphenidate increased initial evoked overflow [DA] more-so in VF-CA versus Sham and reduced D-Str V_max in VF-CA but not Shams; these findings are consistent with upregulated striatal DA transporter in VF-CA versus Sham. Our work demonstrates that 5-min VF-CA increases electrically stimulated DA release with concomitant upregulation of DA reuptake 2 weeks after brief VF-CA insult. Future work should elucidate how CA insult duration, time after insult, and insult type influence striatal DA neurotransmission and related cognitive and motor functions.

Cross-Lagged Panel Analysis of Depression and Behavioral Dysfunction in the First Year After Moderate-to-Severe Traumatic Brain Injury

Timely treatment of depression and behavioral dysfunction after moderate-to-severe traumatic brain injury (TBI) could improve health, function, and quality of life. The authors hypothesized that 6-month depression would be the stronger contributor to later depression and behavioral dysfunction in a sample of 88 adults with moderate-to-severe TBI. A structural equation modeling cross-lagged panel analysis, adjusting for all 6-month predictors, revealed that 6-month depression had a stronger relationship to 12-month depression (βstand=0.55, p=0.002) and behavioral dysfunction (βstand=0.41, p=0.004) than did 6-month behavioral dysfunction (βstand=0.17, p=0.270, βstand=0.30, p=0.035). Depression may be in the developmental pathway to behavioral dysfunction, triggering a cycle of reciprocal causality.

Cerebrospinal Fluid Cortisol Mediates Brain-Derived Neurotrophic Factor Relationships to Mortality after Severe TBI: A Prospective Cohort Study

Distinct regulatory signaling mechanisms exist between cortisol and brain derived neurotrophic factor (BDNF) that may influence secondary injury cascades associated with traumatic brain injury (TBI) and predict outcome. We investigated concurrent CSF BDNF and cortisol relationships in 117 patients sampled days 0–6 after severe TBI while accounting for BDNF genetics and age. We also determined associations between CSF BDNF and cortisol with 6-month mortality. BDNF variants, rs6265 and rs7124442, were used to create a gene risk score (GRS) in reference to previously published hypothesized risk for mortality in “younger patients” (<48 years) and hypothesized BDNF production/secretion capacity with these variants. Group based trajectory analysis (TRAJ) was used to create two cortisol groups (high and low trajectories). A Bayesian estimation approach informed the mediation models. Results show CSF BDNF predicted patient cortisol TRAJ group (P = 0.001). Also, GRS moderated BDNF associations with cortisol TRAJ group. Additionally, cortisol TRAJ predicted 6-month mortality (P = 0.001). In a mediation analysis, BDNF predicted mortality, with cortisol acting as the mediator (P = 0.011), yielding a mediation percentage of 29.92%. Mediation effects increased to 45.45% among younger patients. A BDNF^*GRS interaction predicted mortality in younger patients (P = 0.004). Thus, we conclude 6-month mortality after severe TBI can be predicted through a mediation model with CSF cortisol and BDNF, suggesting a regulatory role for cortisol with BDNF's contribution to TBI pathophysiology and mortality, particularly among younger individuals with severe TBI. Based on the literature, cortisol modulated BDNF effects on mortality after TBI may be related to known hormone and neurotrophin relationships to neurological injury severity and autonomic nervous system imbalance.

Neuroproteomics and Systems Biology Approach to Identify Temporal Biomarker Changes Post Experimental Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) represents a critical health problem of which diagnosis, management, and treatment remain challenging. TBI is a contributing factor in approximately one-third of all injury-related deaths in the United States. The Centers for Disease Control and Prevention estimate that 1.7 million people suffer a TBI in the United States annually. Efforts continue to focus on elucidating the complex molecular mechanisms underlying TBI pathophysiology and defining sensitive and specific biomarkers that can aid in improving patient management and care. Recently, the area of neuroproteomics–systems biology is proving to be a prominent tool in biomarker discovery for central nervous system injury and other neurological diseases. In this work, we employed the controlled cortical impact (CCI) model of experimental TBI in rat model to assess the temporal–global proteome changes after acute (1 day) and for the first time, subacute (7 days), post-injury time frame using the established cation–anion exchange chromatography-1D SDS gel electrophoresis LC–MS/MS platform for protein separation combined with discrete systems biology analyses to identify temporal biomarker changes related to this rat TBI model. Rather than focusing on any one individual molecular entity, we used in silico systems biology approach to understand the global dynamics that govern proteins that are differentially altered post-injury. In addition, gene ontology analysis of the proteomic data was conducted in order to categorize the proteins by molecular function, biological process, and cellular localization. Results show alterations in several proteins related to inflammatory responses and oxidative stress in both acute (1 day) and subacute (7 days) periods post-TBI. Moreover, results suggest a differential upregulation of neuroprotective proteins at 7 days post-CCI involved in cellular functions such as neurite growth, regeneration, and axonal guidance. Our study is among the first to assess temporal neuroproteome changes in the CCI model. Data presented here unveil potential neural biomarkers and therapeutic targets that could be used for diagnosis, for treatment and, most importantly, for temporal prognostic assessment following brain injury. Of interest, this work relies on in silico bioinformatics approach to draw its conclusion; further work is conducted for functional studies to validate and confirm the omics data obtained.

Conceptual model and cluster analysis of behavioral symptoms in two cohorts of adults with traumatic brain injuries

INTRODUCTION

Behavioral changes often occur after moderate-to-severe traumatic brain injury (TBI) and can lead to poor health, psychosocial functioning, and quality of life. Challenges in evaluating these behaviors often result from the complexity and variability in the way they are conceptualized and defined. We propose and test a conceptual model that is specific to behavioral symptoms after TBI, to serve as a basis for better assessment and treatment. We hypothesized that clusters of individuals, with unique emotional, cognitive, and behavioral characteristics, would emerge that would illustrate this conceptual model.

METHODS

We conducted model-based cluster analyses in two cohorts, 6-months post-injury (n = 79) and >6 months post-injury (n = 62), of adults with moderate-to-severe TBI to explore the face validity of our conceptual model by evaluating how participants clustered with regard to emotional (Patient Health Questionnaire 9, Positive and Negative Affect Schedule), cognitive (neuropsychological test battery), and frontal behavioral (Frontal Systems Behavior Scale) symptoms.

RESULTS

In each cohort, unique clusters of participants emerged that differed significantly with regard to emotional state, cognition, and behavior (ps<.05). Those 6-months post-injury clustered along a general continuum of symptom severity in emotional and behavioral symptom domains, from no impairment to severe impairment. Clusters in the chronic cohort (>6 months) demonstrated a more complex pattern of symptoms; the most severe behavioral symptoms occurred in the context of severe emotional symptoms, even in the absence of cognitive impairment. However, problematic behavioral symptoms were also present in the context of severe cognitive impairment, even in the absence of emotional symptoms.

CONCLUSIONS

Emotional, cognitive, and behavioral characteristics were represented as expected, based on the proposed conceptual model of behavior. This conceptual model provides the basis for evaluating behavioral changes after moderate-to-severe TBI and identifying modifiable targets and relevant subpopulations for behavioral intervention, with the goal of improved evidence-based personalized medicine for this population.

Incidence and risk factors of posttraumatic seizures following traumatic brain injury: A Traumatic Brain Injury Model Systems Study

OBJECTIVE

Determine incidence of posttraumatic seizure (PTS) following traumatic brain injury (TBI) among individuals with moderate-to-severe TBI requiring rehabilitation and surviving at least 5 years.

METHODS

Using the prospective TBI Model Systems National Database, we calculated PTS incidence during acute hospitalization, and at years 1, 2, and 5 postinjury in a continuously followed cohort enrolled from 1989 to 2000 (n = 795). Incidence rates were stratified by risk factors, and adjusted relative risk (RR) was calculated. Late PTS associations with immediate (<24 h), early (24 h-7 day), or late seizures (>7 day) versus no seizure prior to discharge from acute hospitalization was also examined.

RESULTS

PTS incidence during acute hospitalization was highest immediately (<24 h) post-TBI (8.9%). New onset PTS incidence was greatest between discharge from inpatient rehabilitation and year 1 (9.2%). Late PTS cumulative incidence from injury to year 1 was 11.9%, and reached 20.5% by year 5. Immediate/early PTS RR (2.04) was increased for those undergoing surgical evacuation procedures. Late PTS RR was significantly greater for individuals who self-identified as a race other than black/white (year 1 RR = 2.22), and for black individuals (year 5 RR = 3.02) versus white individuals. Late PTS was greater for individuals with subarachnoid hemorrhage (year 1 RR = 2.06) and individuals age 23-32 (year 5 RR = 2.43) and 33-44 (year 5 RR = 3.02). Late PTS RR years 1 and 5 was significantly higher for those undergoing surgical evacuation procedures (RR: 3.05 and 2.72, respectively).

SIGNIFICANCE

In this prospective, longitudinal, observational study, PTS incidence was similar to that in studies published previously. Individuals with immediate/late seizures during acute hospitalization have increased late PTS risk. Race, intracranial pathologies, and neurosurgical procedures also influenced PTS RR. Further studies are needed to examine the impact of seizure prophylaxis in high-risk subgroups and to delineate contributors to race/age associations on long-term seizure outcomes.

Prognostic models for predicting posttraumatic seizures during acute hospitalization, and at 1 and 2 years following traumatic brain injury

OBJECTIVE

Posttraumatic seizures (PTS) are well-recognized acute and chronic complications of traumatic brain injury (TBI). Risk factors have been identified, but considerable variability in who develops PTS remains. Existing PTS prognostic models are not widely adopted for clinical use and do not reflect current trends in injury, diagnosis, or care. We aimed to develop and internally validate preliminary prognostic regression models to predict PTS during acute care hospitalization, and at year 1 and year 2 postinjury.

METHODS

Prognostic models predicting PTS during acute care hospitalization and year 1 and year 2 post-injury were developed using a recent (2011-2014) cohort from the TBI Model Systems National Database. Potential PTS predictors were selected based on previous literature and biologic plausibility. Bivariable logistic regression identified variables with a p-value < 0.20 that were used to fit initial prognostic models. Multivariable logistic regression modeling with backward-stepwise elimination was used to determine reduced prognostic models and to internally validate using 1,000 bootstrap samples. Fit statistics were calculated, correcting for overfitting (optimism).

RESULTS

The prognostic models identified sex, craniotomy, contusion load, and pre-injury limitation in learning/remembering/concentrating as significant PTS predictors during acute hospitalization. Significant predictors of PTS at year 1 were subdural hematoma (SDH), contusion load, craniotomy, craniectomy, seizure during acute hospitalization, duration of posttraumatic amnesia, preinjury mental health treatment/psychiatric hospitalization, and preinjury incarceration. Year 2 significant predictors were similar to those of year 1: SDH, intraparenchymal fragment, craniotomy, craniectomy, seizure during acute hospitalization, and preinjury incarceration. Corrected concordance (C) statistics were 0.599, 0.747, and 0.716 for acute hospitalization, year 1, and year 2 models, respectively.

SIGNIFICANCE

The prognostic model for PTS during acute hospitalization did not discriminate well. Year 1 and year 2 models showed fair to good predictive validity for PTS. Cranial surgery, although medically necessary, requires ongoing research regarding potential benefits of increased monitoring for signs of epileptogenesis, PTS prophylaxis, and/or rehabilitation/social support. Future studies should externally validate models and determine clinical utility.

Abbreviated levetiracetam treatment effects on behavioural and histological outcomes after experimental TBI

OBJECTIVE

Long-term prophylactic treatment with levetiracetam (LEV) has multiple neuroprotective effects in a traumatic brain injury (TBI) rat model. Although a rational time-frame of seizure prophylactic treatment with LEV for after TBI is not well established, clinical prophylaxis with LEV often includes treatment duration similar to clinical treatment guidelines with Phenytoin. Thus, this study investigated the effects of abbreviated LEV treatment on behavioural function and histological evidence of neuroprotection.

RESEARCH DESIGN

Pre-clinical trial of abbreviated LEV dosing in an experimental model of TBI Methods: After either controlled cortical impact (CCI) injury or sham surgery, rats received three 50 mg kg(-1) doses over 24 hours or vehicle. After injury/sham surgery, beam performance, spatial learning, contusion volume size and hippocampal neuron survival were assessed.

RESULTS

Abbreviated LEV did not improve motor or cognitive performance after TBI. Further, abbreviated LEV did not improve hippocampal neuron sparing or contusion volumes compared with vehicle controls.

CONCLUSIONS

Together with previous work assessing daily LEV treatment, these results suggest that longer-term therapy may be required to confer beneficial effects within these domains. These findings may guide (1) future experimental studies assessing minimal effective dosing for neuroprotection and anti-epileptogenesis and (2) treatment guideline updates for seizure prophylaxis post-TBI.

Genetic variation in neuronal glutamate transport genes and associations with posttraumatic seizure

OBJECTIVE

Posttraumatic seizures (PTS) commonly occur following severe traumatic brain injury (sTBI). Risk factors for PTS have been identified, but variability in who develops PTS remains. Excitotoxicity may influence epileptogenesis following sTBI. Glutamate transporters manage glutamate levels and excitatory neurotransmission, and they have been associated with both epilepsy and TBI. Therefore, we aimed to determine if genetic variation in neuronal glutamate transporter genes is associated with accelerated epileptogenesis and increased PTS risk after sTBI.

METHODS

Individuals (N = 253) 18-75 years of age with sTBI were assessed for genetic relationships with PTS. Single nucleotide polymorphisms (SNPs) within SLC1A1 and SLC1A6 were assayed. Kaplan-Meier estimates and log-rank statistics were used to compare seizure rates from injury to 3 years postinjury for SNPs by genotype. Hazard ratios (HRs) were estimated using Cox proportional hazards regression for SNPs significant in Kaplan-Meier analyses adjusting for known PTS risk factors.

RESULTS

Thirty-two tagging SNPs were examined (SLC1A1: n = 28, SLC1A6: n = 4). Forty-nine subjects (19.37%) had PTS. Of these, 18 (36.7%) seized within 7 days, and 31 (63.3%) seized between 8 days and 3 years post-TBI. With correction for multiple comparisons, genotypes at SNP rs10974620 (SLC1A1) were significantly associated with time to first seizure across the full 3-year follow-up (seizure rates: 77.1% minor allele homozygotes, 24.8% heterozygotes, 16.6% major allele homozygotes; p = 0.001). When seizure follow-up began day 2 postinjury, genotypes at SNP rs7858819 (SLC1A1) were significantly associated with PTS risk (seizure rates: 52.7% minor allele homozygotes, 11.8% heterozygotes, 21.1% major allele homozygotes; p = 0.002). After adjusting for covariates, we found that rs10974620 remained significant (p = 0.017, minor allele versus major allele homozygotes HR 3.4, 95% confidence interval [CI] 1.3-9.3). rs7858819 also remained significant in adjusted models (p = 0.023, minor allele versus major allele homozygotes HR 3.4, 95%CI 1.1-10.5).

SIGNIFICANCE

Variations within SLC1A1 are associated with risk of epileptogenesis following sTBI. Future studies need to confirm findings, but variation within neuronal glutamate transporter genes may represent a possible pharmaceutical target for PTS prevention and treatment.

COMT and ANKK1 Genetics Interact With Depression to Influence Behavior Following Severe TBI: An Initial Assessment

OBJECTIVE

Genetic variations in the dopamine (DA) system are associated with cortical-striatal behavior in multiple populations. This study assessed associations of functional polymorphisms in the ankyrin repeat and kinase domain (ANKK1; Taq1a) and catechol-O-methyltransferase (COMT; Val158Met) genes with behavioral dysfunction following traumatic brain injury (TBI).

PARTICIPANTS

This was a prospective study of 90 survivors of severe TBI recruited from a level 1 trauma center.

MAIN MEASURES

The Frontal Systems Behavior Scale, a self- or family report questionnaire evaluating behavior associated with frontal lobe dysfunction, was completed 6 and 12 months postinjury. Depression was measured concurrently with the Patient Health Questionnaire-9. Study participants were genotyped for Val158Met and Taq1a polymorphisms.

RESULTS

No statistically significant behavioral differences were observed by Taq1a or Val158Met genotype alone. At 12 months, among those with depression, Met homozygotes (Val158Met) self-reported worse behavior than Val carriers (P = .015), and A2 homozygotes (Taq1a) self-reported worse behavior than A1 carriers (P = .028) in bivariable analysis. Multivariable models suggest an interaction between depression and genetic variation with behavior at 12 months post-TBI, and descriptive analysis suggests that carriage of both risk alleles may contribute to worse behavioral performance than carriage of either risk allele alone.

CONCLUSION

In the context of depression, Val158Met and Taq1a polymorphisms are individually associated with behavioral dysfunction 12 months following severe TBI, with preliminary evidence suggesting cumulative, or perhaps epistatic, effects of COMT and ANKK1 on behavioral dysfunction.

Longitudinal sex and stress hormone profiles among reproductive age and post-menopausal women after severe TBI: A case series analysis

PRIMARY OBJECTIVES

To describe hormone profiles for pre-/post-menopausal women, to monitor time to resumption of menstruation among pre-menopausal women and to describe cortisol associated LH suppression and phasic variation in other sex hormones over timeMethods and procedures: This study determined amenorrhea duration and characterized acute (days 0-7) and chronic (months 1-6) gonadotropins [luteinizing hormone and follicle stimulating hormone (LH, FSH)], sex hormones (progesterone, estradiol) and stress hormone (cortisol) profiles. Women were pre-menopausal (n = 3) or post-menopausal (n = 3). Among pre-menopausal women, menstrual cycle resolution and phase association (luteal/follicular) was monitored using self-report monthly reproductive history questionnaires. This study compared post-TBI hormone profiles, stratified by menopausal status, to hormone levels from seven controls and described 6- and 12-month outcomes for these women.

MAIN OUTCOMES AND RESULTS

Consistent with functional hypothalamic amenorrhea (FHA), menstruation resumption among pre-menopausal women occurred when serum cortisol normalized to luteal phase control levels. For post-menopausal women, serum cortisol reductions corresponded with resolution of suppressed LH levels.

CONCLUSIONS

The stress of TBI results in anovulation and central hypothalamic-pituitary-ovarian (HPG) axis suppression. Future work will examine acute/chronic consequences of post-TBI hypercortisolemia and associated HPG suppression, the temporal association of HPG suppression with other neuroendocrine adaptations and how HPG suppression impacts multidimensional recovery for women with TBI.

Principal components derived from CSF inflammatory profiles predict outcome in survivors after severe traumatic brain injury

Studies have characterized absolute levels of multiple inflammatory markers as significant risk factors for poor outcomes after traumatic brain injury (TBI). However, inflammatory marker concentrations are highly inter-related, and production of one may result in the production or regulation of another. Therefore, a more comprehensive characterization of the inflammatory response post-TBI should consider relative levels of markers in the inflammatory pathway. We used principal component analysis (PCA) as a dimension-reduction technique to characterize the sets of markers that contribute independently to variability in cerebrospinal (CSF) inflammatory profiles after TBI. Using PCA results, we defined groups (or clusters) of individuals (n=111) with similar patterns of acute CSF inflammation that were then evaluated in the context of outcome and other relevant CSF and serum biomarkers collected days 0-3 and 4-5 post-injury. We identified four significant principal components (PC1-PC4) for CSF inflammation from days 0-3, and PC1 accounted for the greatest (31%) percentage of variance. PC1 was characterized by relatively higher CSF sICAM-1, sFAS, IL-10, IL-6, sVCAM-1, IL-5, and IL-8 levels. Cluster analysis then defined two distinct clusters, such that individuals in cluster 1 had highly positive PC1 scores and relatively higher levels of CSF cortisol, progesterone, estradiol, testosterone, brain derived neurotrophic factor (BDNF), and S100b; this group also had higher serum cortisol and lower serum BDNF. Multinomial logistic regression analyses showed that individuals in cluster 1 had a 10.9 times increased likelihood of GOS scores of 2/3 vs. 4/5 at 6 months compared to cluster 2, after controlling for covariates. Cluster group did not discriminate between mortality compared to GOS scores of 4/5 after controlling for age and other covariates. Cluster groupings also did not discriminate mortality or 12 month outcomes in multivariate models. PCA and cluster analysis establish that a subset of CSF inflammatory markers measured in days 0-3 post-TBI may distinguish individuals with poor 6-month outcome, and future studies should prospectively validate these findings. PCA of inflammatory mediators after TBI could aid in prognostication and in identifying patient subgroups for therapeutic interventions.

Fast-scan cyclic voltammetry demonstrates that L-DOPA produces dose-dependent, regionally selective bimodal effects on striatal dopamine kinetics in vivo

Parkinson's disease (PD) is a debilitating condition that is caused by a relatively specific degeneration of dopaminergic (DAergic) neurons of the substantia nigra pars compacta. L-DOPA was introduced as a viable treatment option for PD over 40 years ago and still remains the most common and effective therapy for PD. Though the effects of L-DOPA to augment striatal DA production are well known, little is actually known about how L-DOPA alters the kinetics of DA neurotransmission that contribute to its beneficial and adverse effects. In this study, we examined the effects of L-DOPA administration (50 mg/kg carbidopa + 0, 100, and 250 mg/kg L-DOPA) on regional electrically stimulated DA response kinetics using fast-scan cyclic voltammetry in anesthetized rats. We demonstrate that L-DOPA enhances DA release in both the dorsal striatum (D-STR) and nucleus accumbens (NAc), but surprisingly causes a delayed inhibition of release in the D-STR. In both regions, L-DOPA progressively attenuated reuptake kinetics, predominantly through a decrease in Vmax . These findings have important implications on understanding the pharmacodynamics of L-DOPA, which may be informative for understanding its therapeutic effects and also common side effects like L-DOPA-induced dyskinesias (LID). L-DOPA is commonly used to treat Parkinsonian symptoms, but little is known about how it affects presynaptic DA neurotransmission. Using in vivo fast-scan cyclic voltammetry, we show L-DOPA inhibits DA reuptake in a region-specific and dose-dependent manner, and L-DOPA has paradoxical effects on release. These findings may be important when considering mechanisms for L-DOPA's therapeutic benefits and adverse side-effects.

Trajectories of life satisfaction after traumatic brain injury: Influence of life roles, age, cognitive disability, and depressive symptoms

OBJECTIVES

(a) Identify life satisfaction trajectories after moderate to severe traumatic brain injury (TBI); (b) establish a predictive model for these trajectories across the first 5 years postinjury; and (c) describe differences in these life satisfaction trajectory groups, focusing on age, depressive symptoms, disability, and participation in specific life roles.

RESEARCH METHOD

Analysis of the longitudinal TBI Model Systems National Database was performed on data collected prospectively at 1-, 2-, and 5-years post-TBI. Participants (n = 3,012) had a moderate to severe TBI and were 16 years old and older.

RESULTS

Four life satisfaction trajectories were identified across the first 5 years postinjury, including: stable satisfaction, initial satisfaction declining, initial dissatisfaction improving, and stable dissatisfaction. Age, depressive symptoms, cognitive disability, and life role participation as a worker, leisure participant, and/ or religious participant at 1-year postinjury significantly predicted trajectory group membership. Life role participation and depressive symptoms were strong predictors of life satisfaction trajectories across the first 5 years post-TBI.

CONCLUSIONS

The previously documented loss of life roles and prevalence of depression after a moderate to severe TBI make this a vulnerable population for whom low or declining life satisfaction is a particularly high risk. Examining individual life role participation may help to identify relevant foci for community-based rehabilitation interventions or supports.

Chronic Inflammation After Severe Traumatic Brain Injury: Characterization and Associations With Outcome at 6 and 12 Months Postinjury

OBJECTIVE

Examine associations between chronic inflammatory profiles and outcome 6 to 12 months following severe traumatic brain injury (TBI).

SETTING

University-affiliated level 1 trauma center and community.

PARTICIPANTS

Adults with severe TBI (n = 87); healthy controls (n = 7).

DESIGN

Prospective cohort study.

MAIN MEASURES

Glasgow Outcome Scale; serum cytokines (interleukin [IL]-1β, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, tumor necrosis factor α), 2 weeks to 3 months, 4- to 6-month averages, 6- and 12-month levels.

RESULTS

Serum levels of IL-1β, IL-6, IL-8, IL-10, and tumor necrosis factor α were elevated over 3 months following TBI. Multivariate analysis showed that increased cytokine load score was associated with a 1.21 (95% confidence interval, 1.06-1.38) and 1.18 (95% confidence interval, 1.02-1.37) increase in odds of unfavorable Glasgow Outcome Scale score at 6 and 12 months, respectively. Also, elevated IL-6/IL-10 ratios were associated with increased odds of unfavorable outcomes at 6 months (adjusted odds ratio = 1.76; 95% confidence interval, 1.08-2.88).

CONCLUSIONS

Chronic inflammation has not been well characterized following TBI. Our subacute cytokine load score classifies individuals at risk for unfavorable outcomes following injury. Higher proinflammatory burden with IL-6, relative to the anti-inflammatory marker IL-10, is significantly associated with outcome. Further research should examine whether inflammatory genes and other inflammatory biomarkers affect risk for unfavorable outcomes and TBI complications.

Visual Priming Enhances the Effects of Nonspatial Cognitive Rehabilitation Training on Spatial Learning After Experimental Traumatic Brain Injury

Previous work demonstrates that spatial (explicit) and nonspatial (implicit) elements of place learning in the Morris water maze (MWM) task can be dissociated and examined in the context of experimental traumatic brain injury (TBI). Providing nonspatial cognitive training (CT) after injury can improve place learning compared with untrained controls. In the present study, we hypothesized that brief exposure to extra-maze cues, in conjunction with CT, may further improve MWM performance and extra-maze cue utilization compared with CT alone. Adult male Sprague-Dawley rats (n = 66) received controlled cortical impact (CCI) injury or sham surgery. Beginning day 8 postsurgery, CCI and sham rats received 6 days of no training (NT) or CT with/without brief, noncontextualized exposure to extra-maze cues (BE and CT, respectively). Acquisition (days 14-18), visible platform (VP; day 19), carryover (CO; days 20-26), and periodic probe trials were performed. Platform latencies, peripheral and target zone time allocation, and search strategies were assessed. CCI/BE rats had shorter acquisition trial latencies than CCI/NT (P < .001) and tended to have shorter latencies than CCI/CT rats (P < .10). Both BE and CT reduced peripheral zone swimming for CCI rats versus CCI/NT. CCI/BE animals increased spatial swim strategies from day 14 to day 18 relative to CCI/CT and showed similar swim strategy selection to the Sham/NT group. These data suggest that visual priming improves initial place learning in the MWM. These results support the visual priming response as another clinically relevant experimental rehabilitation construct, to use when assessing injury and treatment effects of behavioral and pharmacological therapies on cognition after TBI.

IL-1β associations with posttraumatic epilepsy development: A genetics and biomarker cohort study

OBJECTIVE

Posttraumatic epilepsy (PTE) is a significant complication following traumatic brain injury (TBI), yet the role of genetic variation in modulating PTE onset is unclear. We hypothesized that TBI-induced inflammation likely contributes to seizure development. We assessed whether genetic variation in the interleukin-1beta (IL-1β) gene, Il-1β levels in cerebral spinal fluid (CSF) and serum, and CSF/serum IL-1β ratios would predict PTE development post-TBI.

METHODS

We investigated PTE development in 256 Caucasian adults with moderate-to-severe TBI. IL-1β tagging and functional single nucleotide polymorphisms (SNPs) were genotyped. Genetic variance and PTE development were assessed. Serum and CSF IL-1β levels were collected from a subset of subjects (n = 59) during the first week postinjury and evaluated for their associations with IL-1β gene variants, and also PTE. Temporally matched CSF/serum IL-1β ratios were also generated to reflect the relative contribution of serum IL-1β to CSF IL-1β.

RESULTS

Multivariate analysis showed that higher CSF/serum IL-1β ratios were associated with increased risk for PTE over time (p = 0.008). Multivariate analysis for rs1143634 revealed an association between the CT genotype and increased PTE risk over time (p = 0.005). The CT genotype group also had lower serum IL-1β levels (p = 0.014) and higher IL-1β CSF/serum ratios (p = 0.093).

SIGNIFICANCE

This is the first report implicating IL-1β gene variability in PTE risk and linking (1) IL-1β gene variation with serum IL-1β levels observed after TBI and (2) IL-1β ratios with PTE risk. Given these findings, we propose that genetic and IL-1β ratio associations with PTE may be attributable to biologic variability with blood-brain barrier integrity during TBI recovery. These results provide a rationale for further studies (1) validating the impact of genetic variability on IL-1β production after TBI, (2) assessing genetically mediated signaling mechanisms that contribute to IL-1β CSF/serum associations with PTE, and (3) evaluating targeted IL-1β therapies that reduce PTE. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

Preliminary Associations Between Brain-Derived Neurotrophic Factor, Memory Impairment, Functional Cognition, and Depressive Symptoms Following Severe TBI

Background Traumatic brain injury (TBI) often leads to mood and cognitive complications, affecting functional recovery. Understanding neurobiological alterations common in post-TBI depression (PTD) and cognition may identify novel biomarkers for TBI complications. Brain-derived neurotrophic factor (BDNF) is a likely target based on evidence of reduced BDNF signaling in experimental TBI and depression models and its role in learning and memory. Objective To evaluate BDNF as a biomarker for PTD, cognitive impairment, and functional cognition in a prospective cohort with severe TBI. Methods Participants with TBI (n = 113) were evaluated for PTD (Patient Health Questionnaire-9 [PHQ-9]), cognitive impairment (cognitive composite score), and functional cognition (Functional Independence Measure-Cognition, FIM-Cog). BDNF levels were measured in cerebrospinal fluid and serum at 0 to 6 days postinjury and in serum at 6 and 12 months postinjury.

RESULTS

Serum BDNF was reduced after TBI versus controls at all time points. Acute serum BDNF positively correlated with memory composites (6 months: r = 0.43, P = .019, n = 30; 12 months: r = 0.53, P = .005, n = 26) and FIM-Memory scores (6 months: r = 0.35, P = .019, n = 45; 12 months: r = 0.38, P = .018, n = 38). Acute serum BDNF negatively correlated with 12-month PHQ-9 scores (r = -0.38; P = .044; n = 29). At 12 months, chronic serum BDNF tended to be lower in participants with PTD (P = .07) and correlated with PHQ-9 scores (r = -0.41; P = .019; n = 32). Conclusions Acute BDNF associations with memory recovery may implicate hippocampal damage/degeneration. Comparatively, BDNF associations with PTD status were not as strong as associations with PTD severity. Further investigation may delineate longitudinal BDNF patterns, and BDNF responsive treatments, reflecting mood and cognitive recovery following TBI.

Pilot feasibility of an mHealth system for conducting ecological momentary assessment of mood-related symptoms following traumatic brain injury

OBJECTIVE

This study assessed pilot feasibility and validity of a mobile health (mHealth) system for tracking mood-related symptoms after traumatic brain injury (TBI).

DESIGN

A prospective, repeated measures design was used to assess compliance with daily ecological momentary assessments (EMA) conducted via a smartphone application over an 8-week period.

METHODS

An mHealth system was developed specifically for individuals with TBI and utilized previously validated tools for depressive and anxiety symptoms (Patient Health Questionnaire-9, Generalized Anxiety Disorder-7). Feasibility was assessed in 20 community-dwelling adults with TBI via an assessment of compliance, satisfaction and usability of the smartphone applications. The authors also developed and implemented a clinical patient safety management mechanism for those endorsing suicidality.

RESULTS

Participants correctly completed 73.4% of all scheduled assessments, demonstrating good compliance. Daily assessments took <2 minutes to complete. Participants reported high satisfaction with smartphone applications (6.3 of 7) and found them easy to use (6.2 of 7). Comparison of assessments obtained via telephone-based interview and EMA demonstrated high correlations (r = 0.81-0.97), supporting the validity of conducting these assessments via smartphone application in this population.

CONCLUSIONS

EMA conducted via smartphone demonstrates initial feasibility among adults with TBI and presents numerous opportunities for long-term monitoring of mood-related symptoms in real-world settings.

Genetic variation in the adenosine regulatory cycle is associated with posttraumatic epilepsy development

OBJECTIVE

Determine if genetic variation in enzymes/transporters influencing extracellular adenosine homeostasis, including adenosine kinase (ADK), [ecto-5'-nucleotidase (NT5E), cluster of differentiation 73 (CD73)], and equilibrative nucleoside transporter type-1 (ENT-1), is significantly associated with epileptogenesis and posttraumatic epilepsy (PTE) risk, as indicated by time to first seizure analyses.

METHODS

Nine ADK, three CD73, and two ENT-1 tagging single nucleotide polymorphisms (SNPs) were genotyped in 162 white adults with moderate/severe traumatic brain injury (TBI) and no history of premorbid seizures. Kaplan-Meier models were used to screen for genetic differences in time to first seizure occurring >1 week post-TBI. SNPs remaining significant after correction for multiple comparisons were examined using Cox proportional hazards analyses, adjusting for subdural hematoma, injury severity score, and isolated TBI status. SNPs significant in multivariate models were then entered simultaneously into an adjusted Cox model.

RESULTS

Comparing Kaplan-Meier curves, rs11001109 (ADK) rare allele homozygosity and rs9444348 (NT5E) heterozygosity were significantly associated with shorter time to first seizure and an increased seizure rate 3 years post-TBI. Multivariate Cox proportional hazard models showed that these genotypes remained significantly associated with increased PTE hazard up to 3 years post-TBI after controlling for variables of interest (rs11001109: hazard ratio (HR) 4.47, 95% confidence interval (CI) 1.27-15.77, p = 0.020; rs9444348: HR 2.95, 95% CI 1.19-7.31, p = 0.019) .

SIGNIFICANCE

Genetic variation in ADK and NT5E may help explain variability in time to first seizure and PTE risk, independent of previously identified risk factors, after TBI. Once validated, identifying genetic variation in adenosine regulatory pathways relating to epileptogenesis and PTE may facilitate exploration of therapeutic targets and pharmacotherapy development.