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Rebekah Mannix, Jacqueline Berglass, Justin Berkner, Philippe Moleus, Jianhua Qiu, Lauren L. Jantzie, William P. Meehan III, Rachel M. Stanley and Shenandoah Robinson

Object

While progesterone has been well studied in experimental models of adult traumatic brain injury (TBI), it has not been evaluated in pediatric models. The study of promising interventions in pediatric TBI is important because children have the highest public health burden of such injuries. Therapies that are beneficial in adults may not necessarily be effective in the pediatric population. The purpose of this study was to evaluate whether progesterone treatment improves outcomes in an experimental model of pediatric TBI.

Methods

The authors determined whether progesterone administered after controlled cortical impact (CCI) improves functional and histopathological outcomes in 4-week-old mice. Both male and female mice (58 mice total) were included in this study, as the majority of prior studies have used only male and/or reproductively senescent females. Mice were randomized to treatment with progesterone or vehicle and to CCI injury or sham injury. Motor (wire grip test) and memory (Morris water maze) testing were performed to determine the effect of progesterone on TBI. Lesion volume was also assessed.

Results

Compared with their vehicle-treated counterparts, the progesterone-treated CCI-injured male mice had improved motor performance (p < 0.001). In contrast, progesterone-treated CCI-injured female mice had a worse performance than their vehicle-treated counterparts (p = 0.001). Progesterone treatment had no effect on spatial memory performance or lesion volume in injured male or female mice.

Conclusions

These data suggest a sex-specific effect of progesterone treatment after CCI in adolescent mice and could inform clinical trials in children.

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Rebekah Mannix, Jacqueline Berglass, Justin Berkner, Philippe Moleus, Jianhua Qiu, Nick Andrews, Georgia Gunner, Laura Berglass, Lauren L. Jantzie, Shenandoah Robinson and William P. Meehan III

Object

With the recent increasing interest in outcomes after repetitive mild traumatic brain injury (rmTBI; e.g., sports concussions), several models of rmTBI have been established. Characterizing these models in terms of behavioral and histopathological outcomes is vital to assess their clinical translatability. The purpose of this study is to provide an in-depth behavioral and histopathological phenotype of a clinically relevant model of rmTBI.

Methods

The authors used a previously published weight-drop model of rmTBI (7 injuries in 9 days) in 2- to 3-month-old mice that produces cognitive deficits without persistent loss of consciousness, seizures, gross structural imaging findings, or microscopic evidence of structural brain damage. Injured and sham-injured (anesthesia only) mice were subjected to a battery of behavioral testing, including tests of balance (rotarod), spatial memory (Morris water maze), anxiety (open field plus maze), and exploratory behavior (hole-board test). After behavioral testing, brains were assessed for histopathological outcomes, including brain volume and microglial and astrocyte immunolabeling.

Results

Compared with sham-injured mice, mice subjected to rmTBI showed increased exploratory behavior and had impaired balance and worse spatial memory that persisted up to 3 months after injury. Long-term behavioral deficits were associated with chronic increased astrocytosis and microgliosis but no volume changes.

Conclusions

The authors demonstrate that their rmTBI model results in a characteristic behavioral phenotype that correlates with the clinical syndrome of concussion and repetitive concussion. This model offers a platform from which to study therapeutic interventions for rmTBI.

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Shenandoah Robinson, Jesse L. Winer, Justin Berkner, Lindsay A. S. Chan, Jesse L. Denson, Jessie R. Maxwell, Yirong Yang, Laurel O. Sillerud, Robert C. Tasker, William P. Meehan III, Rebekah Mannix and Lauren L. Jantzie

OBJECTIVE

Traumatic brain injury (TBI) is a leading cause of death and severe morbidity for otherwise healthy full-term infants around the world. Currently, the primary treatment for infant TBI is supportive, as no targeted therapies exist to actively promote recovery. The developing infant brain, in particular, has a unique response to injury and the potential for repair, both of which vary with maturation. Targeted interventions and objective measures of therapeutic efficacy are needed in this special population. The authors hypothesized that MRI and serum biomarkers can be used to quantify outcomes following infantile TBI in a preclinical rat model and that the potential efficacy of the neuro-reparative agent erythropoietin (EPO) in promoting recovery can be tested using these biomarkers as surrogates for functional outcomes.

METHODS

With institutional approval, a controlled cortical impact (CCI) was delivered to postnatal Day (P)12 rats of both sexes (76 rats). On postinjury Day (PID)1, the 49 CCI rats designated for chronic studies were randomized to EPO (3000 U/kg/dose, CCI-EPO, 24 rats) or vehicle (CCI-veh, 25 rats) administered intraperitoneally on PID1–4, 6, and 8. Acute injury (PID3) was evaluated with an immunoassay of injured cortex and serum, and chronic injury (PID13–28) was evaluated with digitized gait analyses, MRI, and serum immunoassay. The CCI-veh and CCI-EPO rats were compared with shams (49 rats) primarily using 2-way ANOVA with Bonferroni post hoc correction.

RESULTS

Following CCI, there was 4.8% mortality and 55% of injured rats exhibited convulsions. Of the injured rats designated for chronic analyses, 8.1% developed leptomeningeal cyst–like lesions verified with MRI and were excluded from further study. On PID3, Western blot showed that EPO receptor expression was increased in the injured cortex (p = 0.008). These Western blots also showed elevated ipsilateral cortex calpain degradation products for αII-spectrin (αII-SDPs; p < 0.001), potassium chloride cotransporter 2 (KCC2-DPs; p = 0.037), and glial fibrillary acidic protein (GFAP-DPs; p = 0.002), as well as serum GFAP (serum GFAP-DPs; p = 0.001). In injured rats multiplex electrochemiluminescence analyses on PID3 revealed elevated serum tumor necrosis factor alpha (TNFα p = 0.01) and chemokine (CXC) ligand 1 (CXCL1). Chronically, that is, in PID13–16 CCI-veh rats, as compared with sham rats, gait deficits were demonstrated (p = 0.033) but then were reversed (p = 0.022) with EPO treatment. Diffusion tensor MRI of the ipsilateral and contralateral cortex and white matter in PID16–23 CCI-veh rats showed widespread injury and significant abnormalities of functional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD); MD, AD, and RD improved after EPO treatment. Chronically, P13–P28 CCI-veh rats also had elevated serum CXCL1 levels, which normalized in CCI-EPO rats.

CONCLUSIONS

Efficient translation of emerging neuro-reparative interventions dictates the use of age-appropriate preclinical models with human clinical trial–compatible biomarkers. In the present study, the authors showed that CCI produced chronic gait deficits in P12 rats that resolved with EPO treatment and that chronic imaging and serum biomarkers correlated with this improvement.