Real-time multi-site multi-parametric monitoring of rat brain subjected to traumatic brain injury

Assessment of cognitive dysfunction in traumatic brain injury patients: a review

Traumatic brain injury (TBI) is one of the major causes of human mortality and morbidity in the world. Brain injury could affect the core of a person's being - their thinking, memory, personality and behaviour. Electrophysiological markers from the human electroencephalogram and brain imaging provide a rich source of data which helps to elucidate specific processing impairments in TBI patients. To assess the cognitive and social function in traumatic brain injury patients, this review will focus on some of methods for assessing the disabling cognitive and social function deficits induced by TBI. There are many new technologies available to address TBI and recognition related questions. Integration of the various techniques will help to facilitate our comprehending of TBI, cognitive function and social function, and improve treatment and rehabilitation.

A User-Configurable Headstage for Multimodality Neuromonitoring in Freely Moving Rats

Multimodal monitoring of brain activity, physiology, and neurochemistry is an important approach to gain insight into brain function, modulation, and pathology. With recent progress in micro- and nanotechnology, micro-nano-implants have become important catalysts in advancing brain research. However, to date, only a limited number of brain parameters have been measured simultaneously in awake animals in spite of significant recent progress in sensor technology. Here we have provided a cost and time effective approach to designing a headstage to conduct a multimodality brain monitoring in freely moving animals. To demonstrate this method, we have designed a user-configurable headstage for our micromachined multimodal neural probe. The headstage can reliably record direct-current electrocorticography (DC-ECoG), brain oxygen tension (PbrO₂), cortical temperature, and regional cerebral blood flow (rCBF) simultaneously without significant signal crosstalk or movement artifacts for 72 h. Even in a noisy environment, it can record low-level neural signals with high quality. Moreover, it can easily interface with signal conditioning circuits that have high power consumption and are difficult to miniaturize. To the best of our knowledge, this is the first time where multiple physiological, biochemical, and electrophysiological cerebral variables have been simultaneously recorded from freely moving rats. We anticipate that the developed system will aid in gaining further insight into not only normal cerebral functioning but also pathophysiology of conditions such as epilepsy, stroke, and traumatic brain injury.

Mismatch negativity, social cognition, and functional outcomes in patients after traumatic brain injury

Mismatch negativity is generated automatically, and is an early monitoring indicator of neuronal integrity impairment and functional abnormality in patients with brain injury, leading to decline of cognitive function. Antipsychotic medication cannot affect mismatch negativity. The present study aimed to explore the relationships of mismatch negativity with neurocognition, daily life and social functional outcomes in patients after brain injury. Twelve patients with traumatic brain injury and 12 healthy controls were recruited in this study. We examined neurocognition with the Wechsler Adult Intelligence Scale-Revised China, and daily and social functional outcomes with the Activity of Daily Living Scale and Social Disability Screening Schedule, respectively. Mismatch negativity was analyzed from electroencephalogram recording. The results showed that mismatch negativity amplitudes decreased in patients with traumatic brain injury compared with healthy controls. Mismatch negativity amplitude was negatively correlated with measurements of neurocognition and positively correlated with functional outcomes in patients after traumatic brain injury. Further, the most significant positive correlations were found between mismatch negativity in the fronto-central region and measures of functional outcomes. The most significant positive correlations were also found between mismatch negativity at the FCz electrode and daily living function. Mismatch negativity amplitudes were extremely positively associated with Social Disability Screening Schedule scores at the Fz electrode in brain injury patients. These experimental findings suggest that mismatch negativity might efficiently reflect functional outcomes in patients after traumatic brain injury.

Reliability of VEP Recordings Using Chronically Implanted Screw Electrodes in Mice

PURPOSE

Visual evoked potentials (VEPs) are widely used to objectively assess visual system function in animal models of ophthalmological diseases. Although use of chronically implanted electrodes is common in longitudinal VEP studies using rodent models, reliability of recordings over time has not been assessed. We compared VEPs 1 and 7 days after electrode implantation in the adult mouse. We also examined stimulus-independent changes over time, by assessing electroencephalogram (EEG) power and approximate entropy of the EEG signal.

METHODS

Stainless steel screws (600-μm diameter) were implanted into the skull overlying the right visual cortex and the orbitofrontal cortex of adult mice (C57Bl/6J, n = 7). Animals were reanesthetized 1 and 7 days after implantation to record VEP responses (flashed gratings) and EEG activity. Brain sections were stained for glial activation (GFAP) and cell death (TUNEL).

RESULTS

Reliability analysis, using intraclass correlation coefficients, showed VEP recordings had high reliability within the same session, regardless of time after electrode implantation and peak latencies and approximate entropy of the EEG did not change significantly with time. However, there was poorer reliability between recordings obtained on different days, and a significant decrease in VEP amplitudes and EEG power. This amplitude decrease could be normalized by scaling to EEG power (within-subjects). Furthermore, glial activation was present at both time points but there was no evidence of cell death.

CONCLUSIONS

These results indicate that VEP responses can be reliably recorded even after a relatively short recovery period but decrease response peak amplitude over time. Although scaling the VEP trace to EEG power normalized this decrease, our results highlight that time-dependent cortical excitability changes are an important consideration in longitudinal VEP studies.

TRANSLATIONAL RELEVANCE

This study shows changes in VEP characteristics over time in chronically implanted mice. Thus, future preclinical longitudinal studies should consider time in addition to amplitude and latency when designing and interpreting research.

Real-time optical diagnosis of the rat brain exposed to a laser-induced shock wave: observation of spreading depolarization, vasoconstriction and hypoxemia-oligemia

Despite many efforts, the pathophysiology and mechanism of blast-induced traumatic brain injury (bTBI) have not yet been elucidated, partially due to the difficulty of real-time diagnosis and extremely complex factors determining the outcome. In this study, we topically applied a laser-induced shock wave (LISW) to the rat brain through the skull, for which real-time measurements of optical diffuse reflectance and electroencephalogram (EEG) were performed. Even under conditions showing no clear changes in systemic physiological parameters, the brain showed a drastic light scattering change accompanied by EEG suppression, which indicated the occurrence of spreading depression, long-lasting hypoxemia and signal change indicating mitochondrial energy impairment. Under the standard LISW conditions examined, hemorrhage and contusion were not apparent in the cortex. To investigate events associated with spreading depression, measurement of direct current (DC) potential, light scattering imaging and stereomicroscopic observation of blood vessels were also conducted for the brain. After LISW application, we observed a distinct negative shift in the DC potential, which temporally coincided with the transit of a light scattering wave, showing the occurrence of spreading depolarization and concomitant change in light scattering. Blood vessels in the brain surface initially showed vasodilatation for 3-4 min, which was followed by long-lasting vasoconstriction, corresponding to hypoxemia. Computer simulation based on the inverse Monte Carlo method showed that hemoglobin oxygen saturation declined to as low as ∼35% in the long-term hypoxemic phase. Overall, we found that topical application of a shock wave to the brain caused spreading depolarization/depression and prolonged severe hypoxemia-oligemia, which might lead to pathological conditions in the brain. Although further study is needed, our findings suggest that spreading depolarization/depression is one of the key events determining the outcome in bTBI. Furthermore, a rat exposed to an LISW(s) can be a reliable laboratory animal model for blast injury research.

Shedding light on mitochondrial function by real time monitoring of NADH fluorescence: I. Basic methodology and animal studies

Normal mitochondrial function in the process of metabolic energy production is a key factor in maintaining cellular activities. Many pathological conditions in animals, as well as in patients, are directly or indirectly related to dysfunction of the mitochondria. Monitoring the mitochondrial activity by measuring the autofluorescence of NADH has been the most practical approach since the 1950s. This review presents the principles and technological aspects, as well as typical results, accumulated in our laboratory since the early 1970s. We were able to apply the fiber-optic-based NADH fluorometry to many organs monitored in vivo under various pathophysiological conditions in animals. These studies were the basis for the development of clinical monitoring devices as presented in accompanying article. The encouraging experimental results in animals stimulated us to apply the same technology in patients after technological adaptations as described in the accompanying article. Our medical device was approved for clinical use by the FDA.

Cortical excitation and inhibition following focal traumatic brain injury

Cortical compression can be a significant problem in many types of brain injuries, such as brain trauma, localized brain edema, hematoma, focal cerebral ischemia, or brain tumors. Mechanical and cellular alterations can result in global changes in excitation and inhibition on the neuronal network level even in the absence of histologically significant cell injury, often manifesting clinically as seizures. Despite the importance and prevalence of this problem, however, the precise electrophysiological effects of brain injury have not been well characterized. In this study, the changes in electrophysiology were characterized following sustained cortical compression using large-scale, multielectrode measurement of multiunit activity in primary somatosensory cortex in a sensory-evoked, in vivo animal model. Immediately following the initiation of injury at a distal site, there was a period of suppression of the evoked response in the rat somatosensory cortex, followed by hyper-excitability that was accompanied by an increase in the spatial extent of cortical activation. Paired-pulse tactile stimulation revealed a dramatic shift in the excitatory/inhibitory dynamics, suggesting a longer term hyperexcitability of the cortical circuit following the initial suppression that could be linked to the disruption of one or more inhibitory mechanisms of the thalamocortical circuit. Together, our results showed that the use of a sensory-evoked response provided a robust and repeatable functional marker of the evolution of the consequences of mild injury, serving as an important step toward in vivo quantification of alterations in excitation and inhibition in the cortex in the setting of traumatic brain injury.

Use of NADH fluorescence to determine mitochondrial function in vivo

Normal mitochondrial function is a critical factor in maintaining cellular homeostasis in various organs of the body. Due to the involvement of mitochondrial dysfunction in many pathological states, the real-time in vivo monitoring of the mitochondrial metabolic state is crucially important. This type of monitoring in animal models as well as in patients provides real-time data that can help interpret experimental results or optimize patient treatment. In this paper we are summarizing the following items: (1) presenting the solid scientific ground underlying nicotine amide adenine dinucleotide (NADH) NADH fluorescence measurements based on published materials. (2) Presenting NADH fluorescence monitoring and its physiological significance. (3) Providing the reader with basic information on the methodologies of the fluorometers reflectometers. (4) Clarifying various factors affecting the monitored signals, including artifacts. (5) Presenting the potential use of monitoring mitochondrial function in vivo for the evaluation of drug development. The large numbers of publications by different groups testify to the valuable information gathered in various experimental conditions. The monitoring of NADH levels in the tissue provides the most important information on the metabolic state of the mitochondria in terms of energy production and intracellular oxygen levels. Although NADH signals are not calibrated in absolute units, their trend monitoring is important for the interpretation of physiological or pathological situations. To better understand the tissue function, the multiparametric approach has been developed where NADH serves as the key parameter to be monitored.