Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Methylene blue (MB) has known energy-enhancing and antioxidant properties. This study tested the hypothesis that MB treatment reduces lesion volume and behavioral deficits in a rat model of mild TBI. In a randomized double-blinded design, animals received either MB (n = 5) or vehicle (n = 6) after TBI. Studies were performed on 0, 1, 2, 7, and 14 days following an impact to the primary forelimb somatosensory cortex. MRI lesion was not apparent 1 h after TBI, became apparent 3 h after TBI, and peaked at 2 days for both groups. The MB-treated animals showed significantly smaller MRI lesion volume than the vehicle-treated animals at all time points studied. The MB-treated animals exhibited significantly improved scores on forelimb placement asymmetry and foot fault tests than did the vehicle-treated animals at all time points studied. Smaller numbers of darkstained Nissl cells and Fluoro-Jade Ò positive cells were observed in the MB-treated group than in vehicle-treated animals 14 days post-TBI. In conclusion, MB treatment minimized lesion volume, behavioral deficits, and neuronal degeneration following mild TBI. MB is already approved by the United States Food and Drug Administration (FDA) to treat a number of indications, likely expediting future clinical trials in TBI.

This study reports T 2 and diffusion-tensor magnetic resonance imaging (MRI) studies of a mild open-skull, controlled cortical impact injury in rats (n = 6) from 3 h to up to 14 d after traumatic brain injury (TBI). Comparison was made with longitudinal behavioral measurements and end-point histology. The impact was applied over the left primary forelimb somatosensory cortex (S1FL). The major findings were: 1) In the S1FL, T 2 increased and fractional anisotropy (FA) decreased at 3 h after TBI and gradually returned toward normal by Day 14; 2) in the S1FL, the apparent diffusion coefficient (ADC) increased at 3 h, peaked on Day 2, and gradually returned toward normal at Day 14; 3) in the corpus callosum underneath the S1FL, FA decreased at 3 h to Day 2 but returned to normal at Day 7 and 14, whereas T 2 and ADC were normal throughout; 4) heterogeneous hyperintense and hypointense T 2 map intensities likely indicated the presence of hemorrhage but were not independently verified; 5) lesion volumes defined by abnormal T 2 , ADC, and FA showed similar temporal patterns, peaking around Day 2 and returning toward normal on Day 14; 6) the temporal profiles of lesion volumes were consistent with behavioral scores assessed by forelimb placement and forelimb foot fault tests; and 7) at 14 d post-TBI, there was substantial tissue recovery by MRI, which could either reflect true tissue recovery or reabsorption of edema. Histology performed 14 d post-TBI, however, showed a small cavitation and significant neuronal degeneration surrounding the cavitation in S1FL. Thus, the observed improvement of behavioral scores likely involves both functional recovery and functional compensation.

Chronic hypertension alters cerebral vascular morphology, cerebral blood flow (CBF), cerebrovascular reactivity, increasing susceptibility to neurological disorders. This study evaluated: i) the lumen diameters of major cerebral and downstream arteries using magnetic resonance angiography, and ii) basal CBF, and iii) cerebrovascular reactivity to hypercapnia of multiple brain regions using arterial-spin-labeling technique in spontaneously hypertensive rats (SHR) at different stages. Comparisons were made with age-matched normotensive Wistar Kyoto (WKY) rats. In 10-week SHR, lumen diameter started to reduce, basal CBF, and hypercapnic CBF response were higher from elevated arterial blood pressure, but there was no evidence of stenosis, compared to age-matched WKY. In 20-week SHR, lumen diameter remained reduced, CBF returned toward normal from vasoconstriction, hypercapnic CBF response reversed and became smaller, but without apparent stenosis. In 40-week SHR, lumen diameter remained reduced and basal CBF further decreased, resulting in larger differences compared to WKY. There was significant stenosis in main supplying cerebral vessels. Hypercapnic CBF response further decreased, with some animals showing negative hypercapnic CBF responses in some brain regions, indicative of compromised cerebrovascular reserve. The territory with negative hypercapnia CBF responses corresponded with the severity of stenosis in arteries that supplied those territories. We also found enlargement of downstream vessels and formation of collateral vessels as compensatory responses to vasoconstriction upstream vessels. The middle cerebral and azygos arteries were amongst the most susceptible to hypertension-induced changes. Multimodal MRI provides clinically relevant data that might be useful to characterize disease pathogenesis, stage disease progression, and monitor treatment effects in hypertension.

This study investigated the effects of perturbed cerebral blood flow (CBF) and cerebrovascular reactivity (CR) on relaxation time constant (T 2 ), apparent diffusion coefficient (ADC), fractional anisotropy (FA), and behavioral scores at 1 and 3 hours, 2, 7, and 14 days after traumatic brain injury (TBI) in rats. Open-skull TBI was induced over the left primary forelimb somatosensory cortex (N = 8 and 3 sham). We found the abnormal areas of CBF and CR on days 0 and 2 were larger than those of the T 2 , ADC, and FA abnormalities. In the impact core, CBF was reduced on day 0, increased to 2.5 times of normal on day 2, and returned toward normal by day 14, whereas in the tissue surrounding the impact, hypoperfusion was observed on days 0 and 2. CR in the impact core was negative, most severe on day 2 but gradually returned toward normal. T 2 , ADC, and FA abnormalities in the impact core were detected on day 0, peaked on day 2, and pseudonormalized by day 14. Lesion volumes peaked on day 2 and were temporally correlated with forelimb asymmetry and foot-fault scores. This study quantified the effects of perturbed CBF and CR on structural magnetic resonance imaging and behavioral readouts.

Impaired white matter integrity in traumatic brain injury (TBI) can lead to deficits in various neurological functions. Differentiation of the underlying pathological processes, e.g. edema, demyelination, axonal damage to name a few, is of key clinical interest for assessing white matter injury. In this study, a combination of T2, diffusion and susceptibility MRI were used to study the spatiotemporal changes in white matter at 1 hour, 3 hours, 1, 2, 7, and 14 days following TBI, using a rat controlled cortical impact (CCI) model. Based on radial diffusivity (RD), the rats were divided into two groups: group 1 showed widespread increases of RD along the corpus callosum of the ipsilesional hemisphere at day 2, and group 2 showed normal RD. Based on this group separation, group 1 also showed similar widespread changes of fractional anisotropy (FA) and T2 at day 2, and group 2 showed normal FA and T2. The widespread changes in RD and T2 in group 1 on day 2 were apparently dominated by edema, which obscured possible myelin and axonal damage. In contrast, the susceptibility of group 1 showed more localized increases near the impact site on day 2, and otherwise similar contrast to the contralesional hemisphere. The localized susceptibility increase is likely due to demyelination and axonal injury. The extent of brain damage between the two groups revealed by MRI was consistent with behavioral results where the first group showed significantly increased forelimb asymmetry and increased forelimb foot fault deficits. Our results suggest that the combination of T2, diffusion and susceptibility MRI may provide an opportunity for differential assessment of edema and axonal damage in TBI.

Blood-brain barrier (BBB) disruption is common following traumatic brain injury (TBI). Dynamic contrast enhanced (DCE) MRI can longitudinally measure the transport coefficient Ktrans which reflects BBB permeability. Ktrans measurements however are not widely used in TBI research because it is generally considered to be noisy and possesses low spatial resolution. We improved spatiotemporal resolution and signal sensitivity of Ktrans MRI in rats by using a high-sensitivity surface transceiver coil. To overcome the signal drop off profile of the surface coil, a pre-scan module was used to map the flip angle (B1 field) and magnetization (M0) distributions. A series of T1-weighted gradient echo images were acquired and fitted to the extended Kety model with reversible or irreversible leakage, and the best model was selected using F-statistics. We applied this method to study the rat brain one hour following controlled cortical impact (mild to moderate TBI), and observed clear depiction of the BBB damage around the impact regions, which matched that outlined by Evans Blue extravasation. Unlike the relatively uniform T2 contrast showing cerebral edema, Ktrans shows a pronounced heterogeneous spatial profile in and around the impact regions, displaying a nonlinear relationship with T2. This improved Ktrans MRI method is also compatible with the use of high-sensitivity surface coil and the high-contrast two-coil arterial spin-labeling method for cerebral blood flow measurement, enabling more comprehensive investigation of the pathophysiology in TBI.

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Traumatic brain injury (TBI) remains a primary cause of death and disability in both civilian and military populations worldwide. There is a critical need for the development of neuroprotective agents that can circumvent damage and provide functional recovery. We previously showed that methylene blue (MB), a U.S. Food and Drug Administration-grandfathered drug with energy-enhancing and antioxidant properties, given 1 and 3 h post-TBI, had neuroprotective effects in rats. This study aimed to further investigate the neuroprotection of delayed MB treatment (24 h postinjury) post-TBI as measured by lesion volume and functional outcomes. Comparisons were made with vehicle and acute MB treatment. Multi-modal magnetic resonance imaging and behavioral studies were performed at 1 and 3 h and 2, 7, and 14 days after an impact to the primary forelimb somatosensory cortex. We found that delaying MB treatment 24 h postinjury still minimized lesion volume and functional deficits, compared to vehicle-treated animals. The data further support the potential for MB as a neuroprotective treatment, especially when medical teatment is not readily available. MB has an excellent safety profile and is clinically approved for other indications. MB clinical trials on TBI can thus be readily explored.