Treatment with low-dose methamphetamine improves behavioral and cognitive function after severe traumatic brain injury

Temporal expression of brainstem neurotrophic proteins following mild traumatic brain injury

BDNF, a neurotrophic factor, and its receptors have been implicated in the pathophysiology of mild traumatic brain injury (mTBI). The brainstem houses many vital functions, that are also associated with signs and symptoms of mTBI, but has been understudied in mTBI animal models. We determined the extent to which neurotrophic protein and associated receptor expression is affected within the brainstem of adult rats following mTBI. Their behavioral function was assessed and temporal expression of the 'negative' regulators of neuronal function (p75, t-TrkB, and pro-BDNF) and 'positive' neuroprotective (FL-TrkB and m-BDNF) protein isoforms were determined via western blot and immunohistochemistry at 1, 3, 7, and 14 post-injury days (PID) following mTBI or sham (control) procedure. Within the brainstem, p75 expression increased at PID 1 vs. sham animals. t-TrkB and pro-BDNF expression increased at PID 7 and 14. The 'positive' protein isoforms of FL-TrkB and m-BDNF expression were increased only at PID 7. The ratio of t-TrkB:FL-TrkB (negative:positive) was substantial across groups and time points, suggesting a negative impact of neurotrophic signaling on neuronal function. Additional NeuN experiments revealed cell death occurring within a subset of neurons within the medulla. While behavioral measures improved by PID 7-14, negative neurotrophic biochemical responses persisted. Despite the assertion that mTBI produces "mild" injury, evidence of cell death was observed in the medulla. Ratios of TrkB and BDNF isoforms with conflicting functions suggest that future work should specifically measure each subtype since they induce opposing downstream effects on neuronal function.

Trigeminal nerve stimulation restores hippocampal dopamine deficiency to promote cognitive recovery in traumatic brain injury

Cognitive impairment (CI) is a common neurological disease resulting from traumatic brain injury (TBI). Trigeminal nerve stimulation (TNS) is an emerging, non-invasive, and effective neuromodulation therapy especially for patients suffering from brain function disorders. However, the treatment and recovery mechanisms of TNS remain poorly understood. By using combined advanced technologies, we revealed here that the neuroprotective potential of TNS to improve CI caused by TBI. The study results found that 40Hz TNS treatment has the ability to improve CI in TBI mice and communicates with central nervous system via the trigeminal ganglion (TG). Transsynaptic virus experiments revealed that TG is connected to the hippocampus (HPC) through the corticotropin-releasing hormone (CRH) neurons of paraventricular hypothalamic nucleus (PVN) and the dopamine transporter (DAT) neurons of substantia nigra pars compacta/ventral tegmental area (SNc/VTA). Mechanistically, the data showed that TNS can increase the release of dopamine in the HPC by activating the following neural circuit: TG→CRH+ PVN→DAT+ SNc/VTA → HPC. Bulk RNA sequencing confirmed changes in the expression of dopamine-related genes in the HPC. This work preliminarily explains the efficacy and mechanism of TNS and adds to the increasing evidence demonstrating that nerve stimulation is an effective method to treat neurological diseases. DATA AVAILABILITY: The data that support the findings of this study are available from the corresponding author on reasonable request.

Differential Patterns of Change in Brain Connectivity Resulting from Severe Traumatic Brain Injury

Background: Traumatic brain injury (TBI) damages white matter tracts, disrupting brain network structure and communication. There exists a wide heterogeneity in the pattern of structural damage associated with injury, as well as a large heterogeneity in behavioral outcomes. However, little is known about the relationship between changes in network connectivity and clinical outcomes. Materials and Methods: We utilize the rat lateral fluid-percussion injury model of severe TBI to study differences in brain connectivity in 8 animals that received the insult and 11 animals that received only a craniectomy. Diffusion tensor imaging is performed 5 weeks after the injury and network theory is used to investigate changes in white matter connectivity. Results: We find that (1) global network measures are not able to distinguish between healthy and injured animals; (2) injury induced alterations predominantly exist in a subset of connections (subnetworks) distributed throughout the brain; and (3) injured animals can be divided into subgroups based on changes in network motifs-measures of local structural connectivity. In addition, alterations in predicted functional connectivity indicate that the subgroups have different propensities to synchronize brain activity, which could relate to the heterogeneity of clinical outcomes. Discussion: These results suggest that network measures can be used to quantify progressive changes in brain connectivity due to injury and differentiate among subpopulations with similar injuries, but different pathological trajectories.

Mitigated Oxidative Stress and Cognitive Impairments in Transient Global Ischemia using Niosomal Selegiline-NBP delivery

Stroke is the most common reason for adult disabilities and the second ground for death worldwide. Our previous study revealed that selegiline serves as an alternative candidate in transient hypoxia-ischemia. However, aggressive and restless behavior was observed in stroke-induced rats receiving 4 mg/kg selegiline. In comparison, 1 mg/kg selegiline could induce negligible therapeutic effects on mitochondrial dysfunction and histopathological changes. Therefore, we designed oral noisome-based selegiline attached to 4-(4-nitrobenzyl) pyridine to improve transient global ischemia by attenuating cognitive impairments, oxidative stress, and histopathological injury. The investigation was performed in transient hypoxia-ischemia-induced rats by oral administration of nanoformulation containing selegiline (0.25-1 mg/kg) for 4 weeks (3 times a week). Novel object recognition (NOR) was considered to evaluate their cognitive dysfunction. Oxidative stress parameters and brain histopathological assessments were determined following the scarification of rats. Outstandingly, our data demonstrated slower selegiline release from niosomes relative to free drug, which was also in a controlled manner. Our data confirmed significant improvement in cognitive behavior in the NOR test, an increase in glutathione level and total antioxidant power, a decline in MDA and protein carbonyl level, as well as a decreased number of dead cells in histopathological assessment after being exposed to (0.5-1 mg/kg) selegiline-NBP nanoformulation. These data manifested that the selegiline-NBP nanoformulation (0.5-1 mg/kg) could significantly reduce oxidative damage, cognitive dysfunction, and histopathological damage compared to transient hypoxia-ischemia rats, which is 20 times lower than the therapeutic dose in humans. Therefore, the proposed nanoformulation would be capable as an alternative candidate without side effects in stroke.

Sensitivity of unilateral- versus bilateral-onset spike-wave discharges to ethosuximide and carbamazepine in the fluid percussion injury rat model of traumatic brain injury

Unilateral-onset spike-wave discharges (SWDs) following fluid percussion injury (FPI) in rats have been used for nearly two decades as a model for complex partial seizures in human posttraumatic epilepsy (PTE). This study determined if SWDs with a unilateral versus bilateral cortical onset differed. In this experiment, 2-mo-old rats received severe FPI (3 atm) or sham surgery and were instrumented for chronic video-electrocorticography (ECoG) recording (up to 9 mo). The antiseizure drug, carbamazepine (CBZ), and the antiabsence drug, ethosuximide (ETX), were administered separately to determine if they selectively suppressed unilateral- versus bilateral-onset SWDs, respectively. SWDs did not significantly differ between FPI and sham rats on any measured parameter (wave-shape, frequency spectrum, duration, or age-related progression), including unilateral (∼17%) versus bilateral (∼83%) onsets. SWDs with a unilateral onset preferentially originated ipsilateral to the craniotomy in both FPI and sham rats, suggesting that the unilateral-onset SWDs were related to surgical injury and not specifically to FPI. ETX profoundly suppressed SWDs with either unilateral or bilateral onsets, and CBZ had no effect on either type of SWD. These results suggest that SWDs with either a unilateral or bilateral onset have a pharmacosensitivity similar to absence seizures and are very different from the complex partial seizures of PTE. Therefore, SWDs with a unilateral onset after FPI are not a model of the complex partial seizures that occur in PTE, and their use for finding new treatments for PTE could be counterproductive, particularly if their close similarity to normal brain oscillations is not acknowledged.NEW & NOTEWORTHY Unilateral-onset spike-wave discharges (SWDs) in rats have been used to model complex partial seizures in human posttraumatic epilepsy (PTE), compared to bilateral-onset SWDs thought to reflect human absence seizures. Here, we show that both unilateral- and bilateral-onset SWDs following traumatic brain injury are suppressed by the antiabsence drug ethosuximide and are unaffected by the antiseizure drug carbamazepine. We propose that unilateral-onset SWDs are not useful for studying mechanisms of, or treatments for, PTE.

Potential Neuroprotective Mechanisms of Methamphetamine Treatment in Traumatic Brain Injury Defined by Large-Scale IonStar-Based Quantitative Proteomics

Although traumatic brain injury (TBI) causes hospitalizations and mortality worldwide, there are no approved neuroprotective treatments, partly due to a poor understanding of the molecular mechanisms underlying TBI neuropathology and neuroprotection. We previously reported that the administration of low-dose methamphetamine (MA) induced significant functional/cognitive improvements following severe TBI in rats. We further demonstrated that MA mediates neuroprotection in part, via dopamine-dependent activation of the PI3K-AKT pathway. Here, we further investigated the proteomic changes within the rat cortex and hippocampus following mild TBI (TM), severe TBI (TS), or severe TBI plus MA treatment (TSm) compared to sham operated controls. We identified 402 and 801 altered proteins (APs) with high confidence in cortical and hippocampal tissues, respectively. The overall profile of APs observed in TSm rats more closely resembled those seen in TM rather than TS rats. Pathway analysis suggested beneficial roles for acute signaling through IL-6, TGFβ, and IL-1β. Moreover, changes in fibrinogen levels observed in TSm rats suggested a potential role for these proteins in reducing/preventing TBI-induced coagulopathies. These data facilitate further investigations to identify specific pathways and proteins that may serve as key targets for the development of neuroprotective therapies.

Selegiline (L-Deprenyl) Mitigated Oxidative Stress, Cognitive Abnormalities, and Histopathological Change in Rats: Alternative Therapy in Transient Global Ischemia

Selegiline (L-deprenyl) is the major drug which is used in the treatment of Parkinson's disease because of its neurotrophic and antiapoptotic properties. Previous studies suggested that low dose of L-methamphetamine (L-METH) caused lower mortality rate in patients with severe traumatic brain injury. As L-methamphetamine is one of the metabolites of selegiline, the present study aims to examine whether L-deprenyl can improve cognitive, biochemical, and histopathological injury in animal model of transient global ischemia. The animals were randomized in ten groups orally gavaged three times a week for 28 days. Then, novel object recognition (NOR) was conducted to assess their behavioral abnormality. After scarification of the rats, their brains were divided into two sections to measure oxidative stress parameters and perform pathological evaluations in rats. Our data revealed the involvement of oxidative stress, behavioral despair, and pathological data in transient global ischemia rats. Significant recovery in cognitive behavior, oxidative stress biomarker, and number of dead cell in histopathological assay was observed in rats treated with 1,2 and 4 mg/kg of selegiline. So, selegiline appears to be useful in alternative therapy of transient global ischemia.

Oxytocin inhibits methamphetamine-associated learning and memory alterations by regulating DNA methylation at the Synaptophysin promoter

Methamphetamine (METH) causes memory changes, but the underlying mechanisms are poorly understood. Epigenetic mechanisms, including DNA methylation, can potentially cause synaptic changes in the brain. Oxytocin (OT) plays a central role in learning and memory, but little is known of the impact of OT on METH-associated memory changes. Here, we explored the role of OT in METH-induced epigenetic alterations that underlie spatial and cognitive memory changes. METH (2.0 mg/kg, i.p.) was administered to male C57BL/6 mice once every other day for 8 days. OT (2.5 μg, i.c.v.) or aCSF was given prior to METH. Spatial and cognitive memory were assessed. In Hip and PFC, synaptic structures and proteins were examined, levels of DNA methyltransferases (DNMTs) and methyl CpG binding protein 2 (MECP2) were determined, and the DNA methylation status at the Synaptophysin (Syn) promoter was assessed. METH enhanced spatial memory, decreased synapse length, downregulated DNMT1, DNMT3A, DNMT3B, and MECP2, and induced DNA hypomethylation at the Syn promoter in Hip. In contrast, METH reduced cognitive memory, increased synapse thickness, upregulated DNMT1, DNMT3A, and MECP2, and induced DNA hypermethylation at the Syn promoter in PFC. OT pretreatment specifically ameliorated METH-induced learning and memory alterations, normalized synapse structures, and regulated DNMTs and MECP2 to reverse the DNA methylation status changes at the Syn promoter in Hip and PFC. DNA methylation is an important gene regulatory mechanism underlying METH-induced learning and memory alterations. OT can potentially be used to specifically manipulate METH-related memory changes.

Executive (dys)function after traumatic brain injury: special considerations for behavioral pharmacology

Executive function is an umbrella term that includes cognitive processes such as decision-making, impulse control, attention, behavioral flexibility, and working memory. Each of these processes depends largely upon monoaminergic (dopaminergic, serotonergic, and noradrenergic) neurotransmission in the frontal cortex, striatum, and hippocampus, among other brain areas. Traumatic brain injury (TBI) induces disruptions in monoaminergic signaling along several steps in the neurotransmission process - synthesis, distribution, and breakdown - and in turn, produces long-lasting deficits in several executive function domains. Understanding how TBI alters monoamingeric neurotransmission and executive function will advance basic knowledge of the underlying principles that govern executive function and potentially further treatment of cognitive deficits following such injury. In this review, we examine the influence of TBI on the following measures of executive function - impulsivity, behavioral flexibility, and working memory. We also describe monoaminergic-systems changes following TBI. Given that TBI patients experience alterations in monoaminergic signaling following injury, they may represent a unique population with regard to pharmacotherapy. We conclude this review by discussing some considerations for pharmacotherapy in the field of TBI.

The Modulation of Gamma Oscillations by Methamphetamine in Rat Hippocampal Slices

Gamma frequency oscillations (γ, 30–100 Hz) have been suggested to underlie various cognitive and motor functions. The psychotomimetic drug methamphetamine (MA) enhances brain γ oscillations associated with changes in psychomotor state. Little is known about the cellular mechanisms of MA modulation on γ oscillations. We explored the effects of multiple intracellular kinases on MA modulation of γ induced by kainate in area CA3 of rat ventral hippocampal slices. We found that dopamine receptor type 1 and 2 (DR1 and DR2) antagonists, the serine/threonine kinase PKB/Akt inhibitor and N-methyl-D-aspartate receptor (NMDAR) antagonists prevented the enhancing effect of MA on γ oscillations, whereas none of them affected baseline γ strength. Protein kinase A, phosphoinositide 3-kinase and extracellular signal-related kinases inhibitors had no effect on MA. We propose that the DR1/DR2-Akt-NMDAR pathway plays a critical role for the MA enhancement of γ oscillations. Our study provides an new insight into the mechanisms of acute MA on MA-induced psychosis.

Visualization of thalamic calcium influx with quantitative susceptibility mapping as a potential imaging biomarker for repeated mild traumatic brain injury

A key event in the pathophysiology of traumatic brain injury (TBI) is the influx of substantial amounts of Ca²⁺ into neurons, particularly in the thalamus. Detection of this calcium influx in vivo would provide a window into the biochemical mechanisms of TBI with potentially significant clinical implications. In the present work, our central hypothesis was that the Ca²⁺ influx could be imaged in vivo with the relatively recent MRI technique of quantitative susceptibility mapping (QSM). Wistar rats were divided into five groups: naive controls, sham-operated experimental controls, single mild TBI, repeated mild TBI, and single severe TBI. We employed the lateral fluid percussion injury (FPI) model, which replicates clinical TBI without skull fracture, performed 9.4 Tesla MRI with a 3D multi-echo gradient-echo sequence at weeks 1 and 4 post-injury, computed susceptibility maps using V-SHARP and the QUASAR-HEIDI technique, and performed histology. Sham, experimental controls animals, and injured animals did not demonstrate calcifications at 1 week after the injury. At week 4, calcifications were found in the ipsilateral thalamus of 25-50% of animals after a single TBI and 83% of animals after repeated mild TBI. The location and appearance of calcifications on stained sections was consistent with the appearance on the in vivo susceptibility maps (correlation of volumes: r = 0.7). Our findings suggest that persistent calcium deposits represent a primary pathology of repeated injury and that FPI-QSM has the potential to become a sensitive tool for studying pathophysiology related to mild TBI in vivo.

Establishment of brain ischemia model in tree shrew

BACKGROUND

Tree shrew, as a kind of small and inexpensive animal between insectivores and primates with the general anatomy being similar to human, could be considered as developed animal model for brain ischemia (BI) study. However, there is no neural behavior scores criterion from tree shrew with BI up to now.

METHODS

To produce BI model of tree shrew, a novel systematic neurobehavioral assessment scale, named as neural behavior scores (NBS) including aggressive behavior, seeking behavior, gait, startle reflex, high jump and warped-tail phenomenon was firstly established and used in this study. Moreover, magnetic resonance imaging (MRI) was performed on the first day after the operation to detect the imaging changes caused by ischemia. Then TTC, HE staining and immunofluorescent staining for GFAP and NeuN, were performed 24 h after surgery respectively.

RESULTS

NBS in BI group were significantly higher than that of sham operation group at 1d, 3d, 5d and 7d after ischemia. Meanwhile, compared with the sham operation group, the T2 images demonstrated significant higher signal and local brain swelling after cerebral ischemia in tree shrews. The staining of TTC and HE showed apparent infarction and necrosis of the cerebral region, and most of neurons exhibited a shrink.

CONCLUSION

We have successfully established the BI model of tree shrew, confirmed by NBS (a new developed method), MRI, HE staining, TTC staining and immunofluorescence staining. It is the first time to report a novel neurobehavioral assessment scale for BI in tree shrew.

The Importance of Therapeutic Time Window in the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is a major cause of death and disability. Despite its importance in public health, there are presently no drugs to treat TBI. Many reasons underlie why drugs have failed clinical trials, one reason is that most drugs to treat TBI lose much of their efficacy before patients are first treated. This review discusses the importance of therapeutic time window; the time interval between TBI onset and the initiation of treatment. Therapeutic time window is complex, as brain injury is both acute and chronic, resulting in multiple drug targets that appear and disappear with differing kinetics. The speed and increasing complexity of TBI pathophysiology is a major reason why drugs lose efficacy as time to first dose increases. Recent Phase III clinical trials treated moderate to severe TBI patients within 4–8 h after injury, yet they turned away many potential patients who could not be treated within these time windows. Additionally, most head trauma is mild TBI. Unlike moderate to severe TBI, patients with mild TBI often delay treatment until their symptoms do not abate. Thus, drugs to treat moderate to severe TBI likely will need to retain high efficacy for up to 12 h after injury; drugs for mild TBI, however, will likely need even longer windows. Early pathological events following TBI progress with similar kinetics in humans and animal TBI models suggesting that preclinical testing of time windows assists the design of clinical trials. We reviewed preclinical studies of drugs first dosed later than 4 h after injury. This review showed that therapeutic time window can differ depending upon the animal TBI model and the outcome measure. We identify the few drugs (methamphetamine, melanocortin, minocycline plus N-acetylcysteine, and cycloserine) that demonstrated good therapeutic windows with multiple outcome measures. On the basis of their therapeutic window, these drugs appear to be excellent candidates for clinical trials. In addition to further testing of these drugs, we recommend that the assessment of therapeutic time window with multiple outcome measures becomes a standard component of preclinical drug testing.

Thymosin beta 4 induces significant changes in the plasma miRNA profile following severe traumatic brain injury in the rat lateral fluid percussion injury model

OBJECTIVES

Thymosin beta 4 (Tβ4) has demonstrated neuroprotective potential in models of neurlogical injury. The neuroprotective potential of Tβ4 has been associated with increased miR-200a and miR-200b within the brain following stroke. Here we tested the hypothesis that Tβ4 treatment could also alter miRNA profiles within the plasma following severe traumatic brain injury (TBI).

METHODS

We used the rat lateral fluid percusion injury model of severe TBI to test this hypothesis. Highly sensitive and quantitative droplet digital polymerase chain reaction (ddPCR) was used to measure the plasma concentrations of miR-200 family members. In addition, we conducted RNAseq analysis of plasma miRNA to further identify changes associated with TBI and treatment with Tβ4.

RESULTS

ddPCR demonstrated that miR-200a-3p andmiR-200b-3p were both significantly increased in plasma following treatment with Tβ4 after severe TBI. RNAseq analysis suggested that miR-300-3p and miR-598-3p increased while miR-450-3p and miR-194-5p significantly decreased following TBI. In contrast, miR-194-5p significantly increased in Tβ4 treated rats following TBI. In addition, we identified nine plasma miRNAs whose expression significantly changed following treatment with Tβ4.

CONCLUSIONS

Tβ4 treatment significantly increased plasma levels of miR-200a-3p and miR-200b-3p, while RNAseq analysis identified miR-194-5p as a candidate miRNA that may be critical for neuroprotection.

Convulsive seizures and EEG spikes after lateral fluid-percussion injury in the rat

The rat lateral fluid-percussion injury (FPI) model has been used extensively to study post-traumatic epilepsy (PTE). Epidemiological studies have reported that the risk of PTE is higher after more severe injury. Adult, male Wistar rats subjected to different atmospheric pressures of injury during FPI showed great variability in injury severity when functional behavior was determined based on the Neurological Severity Score (NSS) assessment. When NSS was used to select rats with the most severe FPI-induced brain injury, 63% of rats experienced at least one convulsive seizure 2-5 weeks after FPI. This same cohort of rats (i.e., selected for severe TBI based on NSS) were significantly more susceptible to PTZ-induced seizures compared to sham controls. Video/EEG recordings from a second cohort of rats with severe FPI-induced injury (based on NSS) showed a similar incidence and frequency of spike wave discharges between rats with severe TBI and sham controls. However, the rate of isolated EEG spikes was greater in rats with severe FPI-induced injury compared to sham controls. These data suggest that convulsive seizures can be obtained in FPI-treated rats when NSS is used as an inclusion criterion to select rats with severe injury. Furthermore, although spike-wave discharges were equally prevalent in rats with severe FPI and sham controls, spontaneous spikes were more prevalent in the rats with severe FPI.

Circulating microRNAs as biomarkers in traumatic brain injury

Preclinical and clinical studies can be greatly improved through the inclusion of diagnostic, prognostic, predictive or pharmacodynamics biomarkers. Circulating microRNAs (miRNAs) represent highly stable targets that respond to physiological and pathological changes. MicroRNA biomarkers can be detected by highly sensitive and absolutely quantitative methods currently available in most clinical laboratories. Here we review preclinical and clinical studies that have examined circulating miRNAs as potential diagnostic and prognostic biomarkers. We also present data that suggests pharmacodynamics biomarkers can be identified that are associated with neuroprotection in general. Although circulating miRNA can serve as useful tools, it is clear their expression profiles are highly sensitive to changing conditions and are influenced by a broad range of parameters including age, sex, body mass index, injury severity, time of collection, as well as methods of processing, purification and detection. Thus, considerable effort will be required to standardize methods and experimental design conditions before circulating miRNAs can prove useful in a heterologous injury like TBI. This article is part of the Special Issue entitled "Novel Treatments for Traumatic Brain Injury".

Methamphetamine Induces Apoptosis of Microglia via the Intrinsic Mitochondrial-Dependent Pathway

Methamphetamine (METH) is a drug of abuse, the acute and chronic use of which induces neurotoxic responses in the human brain, ultimately leading to neurocognitive disorders. Our goals were to understand the impact of METH on microglial mitochondrial respiration and to determine whether METH induces the activation of the mitochondrial-dependent intrinsic apoptosis pathway in microglia. We assessed the expression of pro- apoptosis genes using qPCR of RNA extracted from a human microglial cell line (HTHU). We examined the apoptosis-inducing effects of METH on microglial cells using digital holographic microscopy (DHM) to quantify real-time apoptotic volume decrease (AVD) in microglia in a noninvasive manner. METH treatment significantly increased AVD, activated Caspase 3/7, increased the gene expression levels of the pro- apoptosis proteins, APAF-1 and BAX, and decreased mitochondrial DNA content. Using immunofluorescence analysis, we found that METH increased the expression of the mitochondrial proteins cytochrome c and MCL-1, supporting the activation of mitochondrion-dependent (intrinsic) apoptosis pathway. Cellular bio-energetic flux analysis by Agilent Seahorse XF Analyzer revealed that METH treatment increased both oxidative and glycolytic respiration after 3 h, which was sustained for at least 24 h. Several events, such as oxidative stress, neuro-inflammatory responses, and mitochondrial dysfunction, may converge to mediate METH-induced apoptosis of microglia that may contribute to neurotoxicity of the CNS. Our study has important implications for therapeutic strategies aimed at preserving mitochondrial function in METH abusing patients.

Impact of Traumatic Brain Injury on Dopaminergic Transmission

Brain trauma is often associated with severe morbidity and is a major public health concern. Even when injury is mild and no obvious anatomic disruption is seen, many individuals suffer disabling neuropsychological impairments such as memory loss, mood dysfunction, substance abuse, and adjustment disorder. These changes may be related to subtle disruption of neural circuits as well as functional changes at the neurotransmitter level. In particular, there is considerable evidence that dopamine (DA) physiology in the nigrostriatal and mesocorticolimbic pathways might be impaired after traumatic brain injury (TBI). Alterations in DA levels can lead to oxidative stress and cellular dysfunction, and DA plays an important role in central nervous system inflammation. Therapeutic targeting of DA pathways may offer benefits for both neuronal survival and functional outcome after TBI. The purpose of this review is to discuss the role of DA pathology in acute TBI and the potential impact of therapies that target these systems for the treatment of TBI.

The impact of methamphetamines in patients with traumatic brain injury, a retrospective review

OBJECTIVE

Both neurotoxic and neuroprotective effects of methamphetamines (METH) are being studied. There are few studies evaluating the effects of METH on patients with traumatic brain injury (TBI). The objective of this study is to compare clinical outcomes after TBI in METH users versus non-METH users.

PATIENT AND METHODS

A retrospective review of 304 patients with severe traumatic head injury were performed. Patients were evaluated and stratified based on toxicology screening for methamphetamines (METH) or none. Of the patients reviewed with a full toxicology, 24 of those patients were positive for METH, and 60 patients were negative. Patients were evaluated based on demographics, type of injury, Glasgow Coma Scale (GCS), and Glasgow Outcome Scale (GOS).

RESULTS

METH patients were younger upon presentation (43.5 versus 55.8, p = 0.003), with a larger improvement in GCS and GOS upon discharge (P = 0.012, 0.0001 respectively). There was no significant difference in length of hospital stay, initial presenting GCS and GOS, or discharge GCS and GOS.

CONCLUSIONS

Our findings demonstrate an improved change in GCS and GOS for those positive with METH than those without. Surprisingly, substance positive patients did not have a worse outcome score. Further investigation is necessary to evaluate the potential neuro-protective effects of METH in TBI.

Applications of the Morris water maze in translational traumatic brain injury research

Acquired traumatic brain injury (TBI) is frequently accompanied by persistent cognitive symptoms, including executive function disruptions and memory deficits. The Morris Water Maze (MWM) is the most widely-employed laboratory behavioral test for assessing cognitive deficits in rodents after experimental TBI. Numerous protocols exist for performing the test, which has shown great robustness in detecting learning and memory deficits in rodents after infliction of TBI. We review applications of the MWM for the study of cognitive deficits following TBI in pre-clinical studies, describing multiple ways in which the test can be employed to examine specific aspects of learning and memory. Emphasis is placed on dependent measures that are available and important controls that must be considered in the context of TBI. Finally, caution is given regarding interpretation of deficits as being indicative of dysfunction of a single brain region (hippocampus), as experimental models of TBI most often result in more diffuse damage that disrupts multiple neural pathways and larger functional networks that participate in complex behaviors required in MWM performance.

Do psychoactive drugs have a therapeutic role in compulsivity? Studies on schedule-induced polydipsia

RATIONALE

Clinical studies have shown that some psychoactive recreational drugs have therapeutic applications in anxiety, depression, and schizophrenia. However, to date, there are few studies on the therapeutic potential efficacy of recreational drugs in compulsive neuropsychiatric disorders.

OBJECTIVES

We explored the therapeutic potential of different psychoactive and psychedelic drugs in a preclinical model of compulsive behavior.

METHODS

Outbred male Wistar rats were selected as either high (HD) or low (LD) drinkers according to their behavior in schedule-induced polydipsia (SIP). Subsequently, we assessed the effects of acute administration of scopolamine (0.125, 0.25, and 0.5 mg/kg), methamphetamine (0.25, 0.5, 1.25, and 2.5 mg/kg), ketamine (1.25, 2.5, 5, and 10 mg/kg), cannabidiol (1 and 3 mg/kg), WIN21255-2 (0.5, 075, and 1 mg/kg), and AM404 (0.25 and 0.5 mg/kg) on compulsive drinking in SIP.

RESULTS

Scopolamine reduced dose-dependent compulsive drinking in HD compared with LD rats in SIP. Methamphetamine induced a dose-dependent inverted U-curve effect in both groups, in which lower doses increased and higher doses reduced compulsive drinking in SIP. Ketamine, cannabidiol, WIN21255-2, and AM404 did not have any relevant effects in SIP.

CONCLUSIONS

These data provide new evidence that low doses of scopolamine and intermediate doses of methamphetamine might therapeutically reduce compulsive behaviors and suggest that there is not a direct participation of the endocannabinoid system in compulsive behavior on SIP. The research in the underlying neurochemical mechanisms of these psychoactive drugs might provide an additional insight on new therapeutic targets in compulsive neuropsychiatric disorders.

Are changes in excitability in the hippocampus of adult male rats induced by prenatal methamphetamine exposure or stress?

Prenatal stress and drug exposure induce permanent alterations of the brain. Even though different brain structures are involved, alterations almost always refer to the hippocampus. The aim of this study was to investigate the excitability of hippocampal slices in low-magnesium epilepsy model of prenatally methamphetamine (MA, 5mg/kg sc.) or saline (sc., stress model) exposed animals in adult male rats. The second aim was to investigate, if a low dose of MA (1ml/kgs.c.) administered in adulthood changes the hippocampal activity of these animals. Adult Wistar male rats were divided into groups according to their prenatal treatment (C - naïve control; Sa - saline; MA - MA administration). One half of the animals was treated with a challenge dose of MA (1mg/kg sc.) 45min before hippocampal slices were cut. The activity of 350μ thick transversal slices of CA1 hippocampi was recorded (latencies of the first epileptiform discharge and the regular epileptiform activity) and evaluated in ACSF with low-magnesium concentration. Effects of prenatal exposure: The highest excitability was found in the Sa (prenatally stressed) group in respect to C and MA groups. This group developed also the highest number of seizure-like events. In addition, the prenatally MA treated group had also higher excitability than C group. Effects of the MA challenge dose: The challenge dose decreased the excitability of prenatally SA- exposed group. To conclude, even a mild prenatal stress significantly increases hippocampal excitability in adulthood and a challenge dose of MA is able to dampen it.

Multiple mild traumatic brain injury in the rat produces persistent pathological alterations in the brain

Multiple mild traumatic brain injury (mmTBI), in certain cases, produces persistent symptoms. However, the molecular mechanisms underlying these symptoms remain unclear. Here, we demonstrate extended pathological changes in the rat brain following mmTBI. Using the lateral fluid percussion (LFP) technique we exposed adult male Wistar rats to a mild TBI (mTBI) once a week for four weeks and compared them to surgical shams. At 90days following the last TBI or sham procedure the animals were cognitively tested in the Morris Water Maze (MWM), euthanized, and the brains removed for immunohistochemistry. At 90days following the last mTBI, NRF-2 staining was significantly decreased in the hilus of the hippocampus and cortex on the injured side, but did not significantly differ from shams on the un-injured side. CD68 positive microglia were significantly increased in the ipsilateral corpus callosum, cortex, and internal capsule of injured animals. Reactive astrocytosis, determined by increased GFAP staining, was also evident in the corpus callosum, cortex, internal capsule and thalamus on the injured side. Interestingly, the corpus callosum thickness at the midline was decreased in injured animals and had evident demyelination when compared to sham animals. Despite these findings, there were no significant differences in neurological assessments at 90days following the last injury. In MWM testing there were not significant differences in the training phase, the time spent in the thigmotaxia zone, or the target quadrant during the probe trial. However, there were significant differences between shams and injured animals in platform zone crossings during the probe trial. These results demonstrate that repetitive head trauma may produce persistent, long-term pathological alterations in brain architecture that may be difficult to detect using standard cognitive and neurological assessments.

The Forensic Implications of Amphetamine Intoxication in Cases of Inflicted Blunt Craniocerebral Trauma

The effects of D-amphetamine on outcome after blunt craniocerebral trauma are characterized and the potential legal implications discussed. Traumatic brain injury (TBI) was induced under general anesthesia in adult, male Sprague Dawley rats using the impact acceleration model. At 10 min prior to injury, D-amphetamine (5 mg/kg) or saline vehicle was administered subcutaneously; animals were subsequently assessed over a 7-day period post-trauma for motor outcome using a rotarod device. D-amphetamine treated animals performed significantly better (p < 0.001; ANOVA) than vehicle treated controls on their motor assessment, suggesting that D-amphetamine exposure prior to injury either is neuroprotective or enhances motor performance. It is possible, therefore, that an individual who has taken amphetamines may function at a better motor level after head trauma than one who has not been exposed to the drug. Future interpretations of the potential effects of amphetamines on TBI should include this possibility.

Factors affecting increased risk for substance use disorders following traumatic brain injury: What we can learn from animal models

Recent studies have helped identify multiple factors affecting increased risk for substance use disorders (SUDs) following traumatic brain injury (TBI). These factors include age at the time of injury, repetitive injury and TBI severity, neurocircuits, neurotransmitter systems, neuroinflammation, and sex differences. This review will address each of these factors by discussing 1) the clinical and preclinical data identifying patient populations at greatest risk for SUDs post-TBI, 2) TBI-related neuropathology in discrete brain regions heavily implicated in SUDs, and 3) the effects of TBI on molecular mechanisms that may drive substance abuse behavior, like dopaminergic and glutamatergic transmission or neuroimmune signaling in mesolimbic regions of the brain. Although these studies have laid the groundwork for identifying factors that affect risk of SUDs post-TBI, additional studies are required. Notably, preclinical models have been shown to recapitulate many of the behavioral, cellular, and neurochemical features of SUDs and TBI. Therefore, these models are well suited for answering important questions that remain in future investigations.

Astrocyte-specific overexpressed gene signatures in response to methamphetamine exposure in vitro

BACKGROUND

Astrocyte activation is one of the earliest findings in the brain of methamphetamine (Meth) abusers. Our goal in this study was to identify the characteristics of the astrocytic acute response to the drug, which may be critical in pathogenic outcomes secondary to the use.

METHODS

We developed an integrated analysis of gene expression data to study the acute gene changes caused by the direct exposure to Meth treatment of astrocytes in vitro, and to better understand how astrocytes respond, what are the early molecular markers associated with this response. We examined the literature in search of similar changes in gene signatures that are found in central nervous system disorders.

RESULTS

We identified overexpressed gene networks represented by genes of an inflammatory and immune nature and that are implicated in neuroactive ligand-receptor interactions. The overexpressed networks are linked to molecules that were highly upregulated in astrocytes by all doses of methamphetamine tested and that could play a role in the central nervous system. The strongest overexpressed signatures were the upregulation of MAP2K5, GPR65, and CXCL5, and the gene networks individually associated with these molecules. Pathway analysis revealed that these networks are involved both in neuroprotection and in neuropathology. We have validated several targets associated to these genes.

CONCLUSIONS

Gene signatures for the astrocytic response to Meth were identified among the upregulated gene pool, using an in vitro system. The identified markers may participate in dysfunctions of the central nervous system but could also provide acute protection to the drug exposure. Further in vivo studies are necessary to establish the role of these gene networks in drug abuse pathogenesis.

Adolescent Traumatic Brain Injury Induces Chronic Mesolimbic Neuroinflammation with Concurrent Enhancement in the Rewarding Effects of Cocaine in Mice during Adulthood

Clinical psychiatric disorders of depression, anxiety, and substance abuse are most prevalent after traumatic brain injury (TBI). Pre-clinical research has focused on depression and anxiety post-injury; however, virtually no data exist examining whether the preference for illicit drugs is affected by traumatic injury in the developing adolescent brain. Using the controlled cortical impact (CCI) model of TBI and the conditioned place preference (CPP) assay, we tested the underlying hypothesis that brain injury during adolescence exacerbates the rewarding properties of cocaine in adulthood possibly through an active inflammatory status in the mesolimbic pathway. Six-week old, C57BL/6 mice sustained a single CCI-TBI to the right somatosensory cortex. CPP experiments with cocaine began 2 weeks post-TBI. Animals receiving cocaine displayed significant place preference shifts compared to saline controls. Further, within the cocaine-experienced cohort, moderate CCI-TBI during adolescence significantly increased the preference shift in adulthood when compared to naïve controls. Additionally, persistent neuroinflammatory responses were observed in the cortex, nucleus accumbens (NAc), and ventral tegmental area post-CCI-TBI. Significant increases in both astrocytic, glial fibrillary acidic protein, and microglial, ionization basic acid 1, markers were observed in the NAc at the end of CPP testing. Moreover, analysis using focused array gene expression panels identified the upregulation of numerous inflammatory genes in moderate CCI-TBI animals, compared to naïve controls, both in the cortex and NAc at 2 weeks post-TBI, before onset of cocaine administration. These results suggest that sustaining moderate TBI during adolescence may augment the rewarding effects of psychostimulants in adulthood, possibly by induction of chronic mesolimbic neuroinflammation.

The neuroprotective potential of low-dose methamphetamine in preclinical models of stroke and traumatic brain injury

Methamphetamine is a psychostimulant that was initially synthesized in 1920. Since then it has been used to treat attention deficit hyperactive disorder (ADHD), obesity and narcolepsy. However, methamphetamine has also become a major drug of abuse worldwide. Under conditions of abuse, which involve the administration of high repetitive doses, methamphetamine can produce considerable neurotoxic effects. However, recent evidence from our laboratory indicates that low doses of methamphetamine can produce robust neuroprotection when administered within 12h after severe traumatic brain injury (TBI) in rodents. Thus, it appears that methamphetamine under certain circumstances and correct dosing can produce a neuroprotective effect. This review addresses the neuroprotective potential of methamphetamine and focuses on the potential beneficial application for TBI.

The Controlled Cortical Impact Model of Experimental Brain Trauma: Overview, Research Applications, and Protocol

Controlled cortical impact (CCI) is a commonly used and highly regarded model of brain trauma that uses a pneumatically or electromagnetically controlled piston to induce reproducible and well-controlled injury. The CCI model was originally used in ferrets and it has since been scaled for use in many other species. This chapter will describe the historical development of the CCI model, compare and contrast the pneumatic and electromagnetic models, and summarize key short- and long-term consequences of TBI that have been gleaned using this model. In accordance with the recent efforts to promote high-quality evidence through the reporting of common data elements (CDEs), relevant study details-that should be reported in CCI studies-will be noted.

Catecholaminergic based therapies for functional recovery after TBI

Among the many pathophysiologic consequences of traumatic brain injury are changes in catecholamines, including dopamine, epinephrine, and norepinephrine. In the context of TBI, dopamine is the one most extensively studied, though some research exploring epinephrine and norepinephrine have also been published. The purpose of this review is to summarize the evidence surrounding use of drugs that target the catecholaminergic system on pathophysiological and functional outcomes of TBI using published evidence from pre-clinical and clinical brain injury studies. Evidence of the effects of specific drugs that target catecholamines as agonists or antagonists will be discussed. Taken together, available evidence suggests that therapies targeting the catecholaminergic system may attenuate functional deficits after TBI. Notably, it is fairly common for TBI patients to be treated with catecholamine agonists for either physiological symptoms of TBI (e.g. altered cerebral perfusion pressures) or a co-occuring condition (e.g. shock), or cognitive symptoms (e.g. attentional and arousal deficits). Previous clinical trials are limited by methodological limitations, failure to replicate findings, challenges translating therapies to clinical practice, the complexity or lack of specificity of catecholamine receptors, as well as potentially counfounding effects of personal and genetic factors. Overall, there is a need for additional research evidence, along with a need for systematic dissemination of important study details and results as outlined in the common data elements published by the National Institute of Neurological Diseases and Stroke. Ultimately, a better understanding of catecholamines in the context of TBI may lead to therapeutic advancements. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Chronic Histopathological and Behavioral Outcomes of Experimental Traumatic Brain Injury in Adult Male Animals

The purpose of this review is to survey the use of experimental animal models for studying the chronic histopathological and behavioral consequences of traumatic brain injury (TBI). The strategies employed to study the long-term consequences of TBI are described, along with a summary of the evidence available to date from common experimental TBI models: fluid percussion injury; controlled cortical impact; blast TBI; and closed-head injury. For each model, evidence is organized according to outcome. Histopathological outcomes included are gross changes in morphology/histology, ventricular enlargement, gray/white matter shrinkage, axonal injury, cerebrovascular histopathology, inflammation, and neurogenesis. Behavioral outcomes included are overall neurological function, motor function, cognitive function, frontal lobe function, and stress-related outcomes. A brief discussion is provided comparing the most common experimental models of TBI and highlighting the utility of each model in understanding specific aspects of TBI pathology. The majority of experimental TBI studies collect data in the acute postinjury period, but few continue into the chronic period. Available evidence from long-term studies suggests that many of the experimental TBI models can lead to progressive changes in histopathology and behavior. The studies described in this review contribute to our understanding of chronic TBI pathology.

The cross-talk of HIV-1 Tat and methamphetamine in HIV-associated neurocognitive disorders

Antiretroviral therapy has dramatically improved the lives of human immunodeficiency virus 1 (HIV-1) infected individuals. Nonetheless, HIV-associated neurocognitive disorders (HAND), which range from undetectable neurocognitive impairments to severe dementia, still affect approximately 50% of the infected population, hampering their quality of life. The persistence of HAND is promoted by several factors, including longer life expectancies, the residual levels of virus in the central nervous system (CNS) and the continued presence of HIV-1 regulatory proteins such as the transactivator of transcription (Tat) in the brain. Tat is a secreted viral protein that crosses the blood–brain barrier into the CNS, where it has the ability to directly act on neurons and non-neuronal cells alike. These actions result in the release of soluble factors involved in inflammation, oxidative stress and excitotoxicity, ultimately resulting in neuronal damage. The percentage of methamphetamine (MA) abusers is high among the HIV-1-positive population compared to the general population. On the other hand, MA abuse is correlated with increased viral replication, enhanced Tat-mediated neurotoxicity and neurocognitive impairments. Although several strategies have been investigated to reduce HAND and MA use, no clinically approved treatment is currently available. Here, we review the latest findings of the effects of Tat and MA in HAND and discuss a few promising potential therapeutic developments.

Negative neuroplasticity in chronic traumatic brain injury and implications for neurorehabilitation

Based on growing findings of brain volume loss and deleterious white matter alterations during the chronic stages of injury, researchers posit that moderate-severe traumatic brain injury (TBI) may act to “age” the brain by reducing reserve capacity and inducing neurodegeneration. Evidence that these changes correlate with poorer cognitive and functional outcomes corroborates this progressive characterization of chronic TBI. Borrowing from a framework developed to explain cognitive aging (Mahncke et al., Progress in Brain Research, 157, 81–109, 2006a; Mahncke et al., Proceedings of the National Academy of Sciences of the United States of America, 103(33), 12523–12528, 2006b), we suggest here that environmental factors (specifically environmental impoverishment and cognitive disuse) contribute to a downward spiral of negative neuroplastic change that may modulate the brain changes described above. In this context, we review new literature supporting the original aging framework, and its extrapolation to chronic TBI. We conclude that negative neuroplasticity may be one of the mechanisms underlying cognitive and neural decline in chronic TBI, but that there are a number of points of intervention that would permit mitigation of this decline and better long-term clinical outcomes.

MMP-9 inhibitor SB-3CT attenuates behavioral impairments and hippocampal loss after traumatic brain injury in rat

The aim of this study was to evaluate the potential efficacy of SB-3CT, a matrix metallopeptidase 9 inhibitor, on behavioral and histological outcomes after traumatic brain injury (TBI) in rats. Adult male Sprague-Dawley rats were randomly divided into three groups (n=15/group): TBI with SB-3CT treatment, TBI with saline, and sham injury. The TBI model was induced by a fluid percussion TBI device. SB-3CT (50 mg/kg in 10% dimethyl sulfoxide) was administered intraperitoneally at 30 min, 6 h, and 12 h after the TBI. Motor function (beam-balance/beam-walk tests) and spatial learning/memory (Morris water maze) were assessed on post-operative Days 1-5 and 11-15, respectively. Fluoro-Jade staining, immunofluorescence, and cresyl violet-staining were carried out for histopathological evaluation at 24 h, 72 h, and 15 days after TBI, respectively. It was shown that TBI can result in significant behavioral deficit induced by acute neurodegeneration, increased expression of cleaved caspase-3, and long-term neuronal loss. SB-3CT intervention via the current regime provides robust behavioral protection and hippocampal neurons preservation from the deleterious effects of TBI. Hence, the efficacy of SB-3CT on TBI prognosis could be ascertained. It is believed that the current study adds to the growing literature in identifying SB-3CT as a potential therapy for human brain injury.

Functional assessment of long-term deficits in rodent models of traumatic brain injury

Traumatic brain injury (TBI) ranks as the leading cause of mortality and disability in the young population worldwide. The annual US incidence of TBI in the general population is estimated at 1.7 million per year, with an estimated financial burden in excess of US$75 billion a year in the USA alone. Despite the prevalence and cost of TBI to individuals and society, no treatments have passed clinical trial to clinical implementation. The rapid expansion of stem cell research and technology offers an alternative to traditional pharmacological approaches targeting acute neuroprotection. However, preclinical testing of these approaches depends on the selection and characterization of appropriate animal models. In this article we consider the underlying pathophysiology for the focal and diffuse TBI subtypes, discuss the existing preclinical TBI models and functional outcome tasks used for assessment of injury and recovery, identify criteria particular to preclinical animal models of TBI in which stem cell therapies can be tested for safety and efficacy, and review these criteria in the context of the existing TBI literature. We suggest that 2 months post-TBI is the minimum period needed to evaluate human cell transplant efficacy and safety. Comprehensive review of the published TBI literature revealed that only 32% of rodent TBI papers evaluated functional outcome ≥1 month post-TBI, and only 10% evaluated functional outcomes ≥2 months post-TBI. Not all published papers that evaluated functional deficits at a minimum of 2 months post-TBI reported deficits; hence, only 8.6% of overall TBI papers captured in this review demonstrated functional deficits at 2 months or more postinjury. A 2-month survival and assessment period would allow sufficient time for differentiation and integration of human neural stem cells with the host. Critically, while trophic effects might be observed at earlier time points, it will also be important to demonstrate the sustainability of such an effect, supporting the importance of an extended period of in vivo observation. Furthermore, regulatory bodies will likely require at least 6 months survival post-transplantation for assessment of toxicology/safety, particularly in the context of assessing cell abnormalities.

Phenoxybenzamine is neuroprotective in a rat model of severe traumatic brain injury

Phenoxybenzamine (PBZ) is an FDA approved α-1 adrenergic receptor antagonist that is currently used to treat symptoms of pheochromocytoma. However, it has not been studied as a neuroprotective agent for traumatic brain injury (TBI). While screening neuroprotective candidates, we found that phenoxybenzamine reduced neuronal death in rat hippocampal slice cultures following exposure to oxygen glucose deprivation (OGD). Using this system, we found that phenoxybenzamine reduced neuronal death over a broad dose range (0.1 μM–1 mM) and provided efficacy when delivered up to 16 h post-OGD. We further tested phenoxybenzamine in the rat lateral fluid percussion model of TBI. When administered 8 h after TBI, phenoxybenzamine improved neurological severity scoring and foot fault assessments. At 25 days post injury, phenoxybenzamine treated TBI animals also showed a significant improvement in both learning and memory compared to saline treated controls. We further examined gene expression changes within the cortex following TBI. At 32 h post-TBI phenoxybenzamine treated animals had significantly lower expression of pro-inflammatory signaling proteins CCL2, IL1β, and MyD88, suggesting that phenoxybenzamine may exert a neuroprotective effect by reducing neuroinflammation after TBI. These data suggest that phenonxybenzamine may have application in the treatment of TBI.

MRI of neuronal recovery after low-dose methamphetamine treatment of traumatic brain injury in rats

We assessed the effects of low dose methamphetamine treatment of traumatic brain injury (TBI) in rats by employing MRI, immunohistology, and neurological functional tests. Young male Wistar rats were subjected to TBI using the controlled cortical impact model. The treated rats (n = 10) received an intravenous (iv) bolus dose of 0.42 mg/kg of methamphetamine at eight hours after the TBI followed by continuous iv infusion for 24 hrs. The control rats (n = 10) received the same volume of saline using the same protocol. MRI scans, including T2-weighted imaging (T2WI) and diffusion tensor imaging (DTI), were performed one day prior to TBI, and at 1 and 3 days post TBI, and then weekly for 6 weeks. The lesion volumes of TBI damaged cerebral tissue were demarcated by elevated values in T2 maps and were histologically identified by hematoxylin and eosin (H&E) staining. The fractional anisotropy (FA) values within regions-of-interest (ROI) were measured in FA maps deduced from DTI, and were directly compared with Bielschowsky's silver and Luxol fast blue (BLFB) immunohistological staining. No therapeutic effect on lesion volumes was detected during 6 weeks after TBI. However, treatment significantly increased FA values in the recovery ROI compared with the control group at 5 and 6 weeks after TBI. Myelinated axons histologically measured using BLFB were significantly increased (p<0.001) in the treated group (25.84±1.41%) compared with the control group (17.05±2.95%). Significant correlations were detected between FA and BLFB measures in the recovery ROI (R = 0.54, p<0.02). Methamphetamine treatment significantly reduced modified neurological severity scores from 2 to 6 weeks (p<0.05) and foot-fault errors from 3 days to 6 weeks (p<0.05) after TBI. Thus, the FA data suggest that methamphetamine treatment improves white matter reorganization from 5 to 6 weeks after TBI in rats compared with saline treatment, which may contribute to the observed functional recovery.