Differences in time-frequency characteristics between healthy controls and TBI patients during hypercapnia assessed via fNIRS.

Damage to the cerebrovascular network is a universal feature of traumatic brain injury (TBI). This damage is present during different phases of the injury and can be non-invasively assessed using functional near infrared spectroscopy (fNIRS). fNIRS signals are influenced by partial arterial carbon dioxide (PaCO2), neurogenic, Mayer waves, respiratory and cardiac oscillations, whose characteristics vary in time and frequency and may differ in the presence of TBI. Therefore, this study aims to investigate differences in time-frequency characteristics of these fNIRS signal components between healthy controls and TBI patients and characterize the changes in their characteristics across phases of the injury. Data from 11 healthy controls and 21 TBI patients were collected during the hypercapnic protocol. Results demonstrated significant differences in low-frequency oscillations between healthy controls and TBI patients, with the largest differences observed in Mayer wave band (0.06 to 0.15 Hz), followed by the PaCO2 band (0.012 to 0.02 Hz). The effects within these bands were opposite, with (i) Mayer wave activity being lower in TBI patients during acute phase of the injury (d = 0.37 [0.16, 0.57]) and decreasing further during subacute (d = 0.66 [0.44, 0.87]) and postacute (d = 0.75 [0.50, 0.99]) phases; (ii) PaCO2 activity being lower in TBI patients only during acute phase of the injury (d = 0.36 [0.15, 0.56]) and stabilizing to healthy levels by the subacute phase. These findings demonstrate that TBI patients have impairments in low frequency oscillations related to different mechanisms and that these impairments evolve differently over the course of injury.

Evaluation of fNIRS signal components elicited by cognitive and hypercapnic stimuli.

Functional near infrared spectroscopy (fNIRS) measurements are confounded by signal components originating from multiple physiological causes, whose activities may vary temporally and spatially (across tissue layers, and regions of the cortex). Furthermore, the stimuli can induce evoked effects, which may lead to over or underestimation of the actual effect of interest. Here, we conducted a temporal, spectral, and spatial analysis of fNIRS signals collected during cognitive and hypercapnic stimuli to characterize effects of functional versus systemic responses. We utilized wavelet analysis to discriminate physiological causes and employed long and short source-detector separation (SDS) channels to differentiate tissue layers. Multi-channel measures were analyzed further to distinguish hemispheric differences. The results highlight cardiac, respiratory, myogenic, and very low frequency (VLF) activities within fNIRS signals. Regardless of stimuli, activity within the VLF band had the largest contribution to the overall signal. The systemic activities dominated the measurements from the short SDS channels during cognitive stimulus, but not hypercapnic stimulus. Importantly, results indicate that characteristics of fNIRS signals vary with type of the stimuli administered as cognitive stimulus elicited variable responses between hemispheres in VLF band and task-evoked temporal effect in VLF, myogenic and respiratory bands, while hypercapnic stimulus induced a global response across both hemispheres.

Minocycline plus N-acetylcysteine protect oligodendrocytes when first dosed 12 hours after closed head injury in mice.

The mouse closed head injury (CHI) model of traumatic brain injury (TBI) produces widespread demyelination. Myelin content is restored by minocycline (MINO) plus n-acetylcysteine (NAC) or MINO alone when first dosed at 12 h after CHI. In a rat controlled cortical impact model of TBl, a first dose of MINO plus NAC one h after injury protects resident oligodendrocytes that induce remyelination. In contrast, MINO less effectively protects oligodendrocytes and remyelination is mediated by oligodendrocyte precursor cell proliferation and differentiation. MINO plus NAC or MINO alone is hypothesized to work similarly in the CHI model as in the controlled cortical impact model even when first dosed at 12-h post-CHI. We tested this hypothesis by examining the time course of the changes in the oligodendrocyte antigenic markers CC1, 2',3'-Cyclic-nucleotide 3'-phosphodiesterase and phospholipid protein between 2 and 14 days post-CHI in mice treated with saline, NAC, MINO or MINO plus NAC. CHI produced a long-lasting loss of these markers that was not altered by NAC treatment. In contrast, oligodendrocyte marker expression was maintained by MINO plus NAC between 2 and 14 days post-injury. MINO alone did not prevent the early loss of oligodendrocyte markers, but marker expression significantly increased by 14-days post-injury. These data suggest that MINO plus NAC or MINO alone when first dosed 12 h after CHI increase myelin content using similar mechanisms seen when first dosed 1 h after closed head injury. These data also suggest that drugs protect oligodendrocytes with a clinically useful therapeutic time window.

Minocycline plus N-Acetylcysteine Reduce Behavioral Deficits and Improve Histology with a Clinically Useful Time Window.

There are no drugs to manage traumatic brain injury (TBI) presently. A major problem in developing therapeutics is that drugs to manage TBI lack sufficient potency when dosed within a clinically relevant time window. Previous studies have shown that minocycline (MINO, 45 mg/kg) plus N-acetylcysteine (NAC, 150 mg/kg) synergistically improved cognition and memory, modulated inflammation, and prevented loss of oligodendrocytes that remyelinated damaged white matter when first dosed 1 h after controlled cortical impact (CCI) in rats. We show that MINO (45 mg/kg) plus NAC (150 mg/kg) also prevent brain injury in a mouse closed head injury (CHI) TBI model. Using the CHI model, the concentrations of MINO and NAC were titrated to determine that MINO (22.5 mg/kg) plus NAC (75 mg/kg) was more potent than the original formulation. MINO (22.5 mg/kg) plus NAC (75 mg/kg) also limited injury in the rat CCI model. The therapeutic time window of MINO plus NAC was then tested in the CHI and CCI models. Mice and rats could acquire an active place avoidance task when MINO plus NAC was first dosed at 12 h post-injury. A first dose at 12 h also limited gray matter injury in the hippocampus and preserved myelin in multiple white matter tracts. Mice and rats acquired Barnes maze when MINO plus NAC was first dosed at 24 h post-injury. These data suggest that MINO (22.5 mg/kg) plus NAC (75 mg/kg) remain potent when dosed at clinically useful time windows. Both MINO and NAC are drugs approved by the Food and Drug Administration and have been administered safely to patients in clinical trials at the doses in the new formulation. This suggests that the drug combination of MINO plus NAC may be effective in treating patients with TBI.

Minocycline plus N-acteylcysteine induces remyelination, synergistically protects oligodendrocytes and modifies neuroinflammation in a rat model of mild traumatic brain injury.

Mild traumatic brain injury afflicts over 2 million people annually and little can be done for the underlying injury. The Food and Drug Administration-approved drugs Minocycline plus N-acetylcysteine (MINO plus NAC) synergistically improved cognition and memory in a rat mild controlled cortical impact (mCCI) model of traumatic brain injury.3 The underlying cellular and molecular mechanisms of the drug combination are unknown. This study addressed the effect of the drug combination on white matter damage and neuroinflammation after mCCI. Brain tissue from mCCI rats given either sham-injury, saline, MINO alone, NAC alone, or MINO plus NAC was investigated via histology and qPCR at four time points (2, 4, 7, and 14 days post-injury) for markers of white matter damage and neuroinflammation. MINO plus NAC synergistically protected resident oligodendrocytes and decreased the number of oligodendrocyte precursor cells. Activation of microglia/macrophages (MP/MG) was synergistically increased in white matter two days post-injury after MINO plus NAC treatment. Patterns of M1 and M2 MP/MG were also altered after treatment. The modulation of neuroinflammation is a potential mechanism to promote remyelination and improve cognition and memory. These data also provide new and important insights into how drug treatments can induce repair after traumatic brain injury.

Righting Reflex Predicts Long-Term Histological and Behavioral Outcomes in a Closed Head Model of Traumatic Brain Injury.

Blunt impact produces a heterogeneous brain injury in people and in animal models of traumatic brain injury. We report that a single closed head impact to adult C57/BL6 mice produced two injury syndromes (CHI-1 and CHI-2). CHI-1 mice spontaneously reinitiated breathing after injury while CHI-2 mice had prolonged apnea and regained breathing only after cardiopulmonary resuscitation and supplementation of 100% O2. The CHI-1 group significantly regained righting reflex more rapidly than the CHI-2 group. At 7 days post-injury, CHI-1, but not CHI-2 mice, acquired but had no long-term retention of an active place avoidance task. The behavioral deficits of CHI-1 and CHI-2 mice were retained one-month after the injury. CHI-1 mice had loss of hippocampal neurons and localized white matter injury at one month after injury. CHI-2 had a larger loss of hippocampal neurons and more widespread loss of myelin and axons. High-speed videos made during the injury were followed by assessment of breathing and righting reflex. These videos show that CHI-2 mice experienced a larger vertical g-force than CHI-1 mice. Time to regain righting reflex in CHI-2 mice significantly correlated with vertical g-force. Thus, physiological responses occurring immediately after injury can be valuable surrogate markers of subsequent behavioral and histological deficits.