Dynamic changes in cerebral oxygenation in chemically induced seizures in rats: study by near-infrared spectrophotometry

Impact of repetitive transcranial magnetic stimulation on cortical activity: a systematic review and meta-analysis utilizing functional near-infrared spectroscopy evaluation

BACKGROUND

Repeated transcranial magnetic stimulation (rTMS) could induce alterations in cortical excitability and promote neuroplasticity. To precisely quantify these effects, functional near-infrared spectroscopy (fNIRS), an optical neuroimaging modality adept at detecting changes in cortical hemodynamic responses, has been employed concurrently alongside rTMS to measure and tailor the impact of diverse rTMS protocols on the brain cortex.

OBJECTIVE

This systematic review and meta-analysis aimed to elucidate the effects of rTMS on cortical hemodynamic responses over the primary motor cortex (M1) as detected by fNIRS.

METHODS

Original articles that utilized rTMS to stimulate the M1 cortex in combination with fNIRS for the assessment of cortical activity were systematically searched across the PubMed, Embase, and Scopus databases. The search encompassed records from the inception of these databases up until April, 2024. The assessment for risk of bias was also conducted. A meta-analysis was also conducted in studies with extractable raw data.

RESULTS

Among 312 studies, 14 articles were eligible for qualitative review. 7 studies were eligible for meta-analysis. A variety of rTMS protocols was employed on M1 cortex. In inhibitory rTMS, multiple studies observed a reduction in the concentration of oxygenated hemoglobin [HbO] at the ipsilateral M1, contrasted by an elevation at the contralateral M1. Meta-analysis also corroborated this consistent trend. Nevertheless, certain investigations unveiled diminished [HbO] in bilateral M1. Several studies also depicted intricate inhibitory or excitatory interplay among distinct cortical regions.

CONCLUSION

Diverse rTMS protocols led to varied patterns of cortical activity detected by fNIRS. Meta-analysis revealed a trend of increasing [HbO] in the contralateral cortices and decreasing [HbO] in the ipsilateral cortices following low frequency inhibitory rTMS. However, due to the heterogeneity between studies, further research is necessary to comprehensively understand rTMS-induced alterations in brain activity.

Multiarea Brain Activation and Gait Deterioration During a Cognitive and Motor Dual Task in Individuals With Parkinson Disease

BACKGROUND AND PURPOSE

In people with Parkinson disease (PD), gait performance deteriorating during dual-task walking has been noted in previous studies. However, the effects of different types of dual tasks on gait performance and brain activation are still unknown. The purpose of this study was to investigate cognitive and motor dual-task walking performance on multiarea brain activity in individuals with PD.

METHODS

Twenty-eight participants with PD were recruited and performed single walking (SW), walking while performing a cognitive task (WCT), and walking while performing a motor task (WMT) at their self-selected speed. Gait performance including walking speed, stride length, stride time, swing cycle, temporal and spatial variability, and dual-task cost (DTC) was recorded. Brain activation of the prefrontal cortex (PFC), premotor cortex (PMC), and supplementary motor areas (SMA) were measured using functional near-infrared spectroscopy during walking.

RESULTS

Walking performance deteriorated upon performing a secondary task, especially the cognitive task. Also, a higher and more sustained activation in the PMC and SMA during WCT, as compared with the WMT and SW, in the late phase of walking was found. During WMT, however, the SMA and PMC did not show increased activation compared with during SW. Moreover, gait performance was negatively correlated with PMC and SMA activity during different walking tasks.

DISCUSSION AND CONCLUSIONS

Individuals with mild to moderate PD demonstrated gait deterioration during dual-task walking, especially during WCT. The SMA and PMC were further activated in individuals with PD when performing cognitive dual-task walking.Supplemental Digital Content is Available in the Text.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A383 ).

Ventrolateral prefrontal hemodynamic responses in autism spectrum disorder with and without depression

In clinical settings, autism spectrum disorder (ASD) with comorbid depression is often difficult to diagnose, and should be considered in treatment. However, to our knowledge, no functional imaging study has examined the difference between ASD adolescents with and without comorbid depression. We aimed to compare the characteristics and prefrontal brain function of ASD with and without depression in order to identify a biological marker that can be used to detect the difference. Twenty-eight drug-naïve adolescents with ASD (14 ASD with and 14 ASD without depression) and 14 age- and gender-matched adolescents with typical development were evaluated using several variables. These included intelligence quotient, autism quotient, depression severity using the Beck Depression Inventory 2nd edition (BDI-II), and level of social functioning using the Social Adaptation Self-evaluation Scale (SASS). In addition, frontotemporal hemodynamic responses during a verbal fluency task (VFT) were measured using functional near-infrared spectroscopy (fNIRS). The ASD group, including both of the ASD with and ASD without depression groups, showed smaller hemodynamic responses than the typical development group in portions of the left dorsolateral prefrontal cortex (DLPFC), bilateral ventrolateral prefrontal cortex (VLPFC) and anterior part of the temporal cortex (aTC) during the VFT. Moreover, the smaller hemodynamic responses in the right VLPFC during the VFT in the ASD group were associated with the worse BDI-II and SASS scores. Furthermore, the ASD with depression group showed smaller hemodynamic responses in the right VLPFC during the VFT than the ASD without depression group in a direct comparison. Adolescents with ASD showed reduced activation in broad frontotemporal regions during a cognitive task compared with those with typical development. More specifically, the right VLPFC activation reflected the level of self-estimated depression and social functioning in the ASD subjects, and could be used to discriminate between ASD adolescents with and without depression.

Characteristic of Mayer Waves in Electrophysiological, Hemodynamic and Vascular Signals

We evaluated the properties of oscillations in the Mayer waves (MW) frequency range (∼0.1Hz) detected in blood pressure, heart rate variability, cerebral blood oxygenation changes and evolution of electroencephalographic (EEG) rhythms to elucidate the mechanisms of MW generation. We examined the persistence of MW in different signals and stability of their oscillations on the level of individual MW waveforms, which was achieved by applying matching pursuit (MP). MP yields adaptive time-frequency approximation of signal's structures in terms of frequency, amplitude, time occurrence, and time-span. The number of waveforms contributing to 95% of the energy of the signals was vastly different for the time series, but the average number of waveforms conforming to the MW criteria was almost the same (3.5 ± 0.4 per 120s epoch). In all the investigated signals, MW had the same distributions of frequency and the number of cycles. We show that the MW energy ratios in different signals varied strongly, p < 0.001. The highest percentage of MW energy was observed in blood pressure signals, heart rate variability, and reduced hemoglobin, in contrast to brain signals and oxygenated hemoglobin. The percentage of MW energy was related to the strength of causal influence exerted by them on the other signals. Our results indicate existence of a common mechanism of MW generation and support the hypothesis of MW generation in the baroreflex loop; however, they do not exclude the action of a central pacemaker.

Transcranial Recording of Electrophysiological Neural Activity in the Rodent Brain in vivo Using Functional Photoacoustic Imaging of Near-Infrared Voltage-Sensitive Dye

Minimally-invasive monitoring of electrophysiological neural activities in real-time-that enables quantification of neural functions without a need for invasive craniotomy and the longer time constants of fMRI and PET-presents a very challenging yet significant task for neuroimaging. In this paper, we present in vivo functional PA (fPA) imaging of chemoconvulsant rat seizure model with intact scalp using a fluorescence quenching-based cyanine voltage-sensitive dye (VSD) characterized by a lipid vesicle model mimicking different levels of membrane potential variation. The framework also involves use of a near-infrared VSD delivered through the blood-brain barrier (BBB), opened by pharmacological modulation of adenosine receptor signaling. Our normalized time-frequency analysis presented in vivo VSD response in the seizure group significantly distinguishable from those of the control groups at sub-mm spatial resolution. Electroencephalogram (EEG) recording confirmed the changes of severity and frequency of brain activities, induced by chemoconvulsant seizures of the rat brain. The findings demonstrate that the near-infrared fPA VSD imaging is a promising tool for in vivo recording of brain activities through intact scalp, which would pave a way to its future translation in real time human brain imaging.

Brain functional alterations observed 4-weekly in major depressive disorder following antidepressant treatment

BACKGROUND

Major depressive disorder (MDD) is a heterogeneous condition. Identifying the brain responses to antidepressant treatment is of particular interest as these may represent potential neural networks related to treatment response, forming one aspect of the biological markers of MDD. Near-infrared spectroscopy (NIRS) is suitable for repeated measurements with short intervals because of its noninvasiveness, and can provide detailed time courses of functional alterations in prefrontal regions.

METHODS

We conducted a 12-week longitudinal study to explore prefrontal hemodynamic changes at 4-week intervals following sertraline treatment in 11 medication-naïve participants with MDD using 52-channel NIRS.

RESULTS

While all participants achieved remission after treatment, intra-class correlation coefficient of oxygenated hemoglobin [oxy-Hb] values throughout the 12-week observation was moderate at the spatially and temporally contiguous cluster located in the left inferior frontal and temporal gyri. There was a significant negative correlation between mean [oxy-Hb] values in the significant cluster at 4 weeks and changes in Hamilton Rating Scale for Depression total score from 4 to 8 weeks (r = -0.73, P = 0.011) and from 4 to 12 weeks (r = -0.63, P = 0.039).

LIMITATIONS

Without healthy controls for comparison, we were unable to fully evaluate whether improvement of [oxy-Hb] activations after treatment in MDD reached normal levels or not.

CONCLUSION

Our NIRS findings of detailed prefrontal hemodynamic alterations over short interval observations such as 4 weeks may have revealed potential trait marker for MDD and biological maker for predicting clinical response to sertraline treatment in MDD.

Causal Coupling Between Electrophysiological Signals, Cerebral Hemodynamics and Systemic Blood Supply Oscillations in Mayer Wave Frequency Range

The aim of the study was to assess causal coupling between neuronal activity, microvascular hemodynamics and blood supply oscillations in the Mayer wave frequency range. An electroencephalogram, cerebral blood oxygenation changes, an electrocardiogram and blood pressure were recorded during rest and during a movement task. Causal coupling between them was evaluated using directed transfer function, a measure based on the Granger causality principle. The multivariate autoregressive model was fitted to all the signals simultaneously, which made it possible to construct a complete scheme of interactions between the considered signals. The obtained pattern of interactions in the resting state estimated in the 0.05-0.15 Hz band revealed a predominant influence of blood pressure oscillations on all the other variables. Reciprocal connections between blood pressure and heart rate variability time series indicated the presence of feedback loops between these signals. During movement, the pattern of connections did not change dramatically. The number of connections decreased, but the couplings between blood pressure and heart rate variability signal were not significantly changed, and the strong influence of the decreased blood hemoglobin concentration on the oxygenated hemoglobin concentration persisted. For the first time our results provided a comprehensive scheme of interactions between electrical and hemodynamic brain signals, heart rate and blood pressure oscillations. Persistent reciprocal connections between blood pressure and heart rate variability time series suggest possible feedforward and feedback coupling of cardiovascular variables which may lead to the observed oscillations in Mayer wave range.

Aberrant Spatial and Temporal Prefrontal Activation Patterns in Medication-Naïve Adults with ADHD

Previous near-infrared spectroscopy (NIRS) studies using a verbal fluency task (VFT) have consistently reported that adults with attention-deficit hyperactivity disorder (ADHD) showed significantly smaller oxygenated-hemoglobin [oxy-Hb] activations in the prefrontal cortex (PFC) compared to those in healthy controls (HC). Despite this consistent evidence of brain dysfunction in ADHD, ADHD is currently diagnosed based only on subjective clinical and scoring measures, which are often unreliable. Hence, it is necessary to establish objective neuroimaging biomarkers for ADHD. While most NIRS studies have utilized averaged [oxy-Hb] values during the whole task period for group comparisons, we used a cluster-based non-parametric randomization test to compare the [oxy-Hb] time-course changes with a 0.1-s time resolution between drug-naïve adults with ADHD and HC, which may provide us with more details regarding abnormal prefrontal activation patterns in ADHD. A total of 101 participants, consisting of 63 drug-naïve adult individuals with ADHD and 38 HC, were included in this study. We identified that adults with ADHD showed significantly smaller [oxy-Hb] activations than those in HC at spatially and temporally connected clusters located in the bilateral PFC (more prominent on the left) and temporal brain region (more prominent on the left). We further found that aberrant [oxy-Hb] activation differs according to the time period during the task or according to brain location. Our findings indicate more detailed aberrant prefrontal and temporal activation patterns of ADHD compared with those in previous studies, possibly representing a biological marker for ADHD.

Maintaining Gait Performance by Cortical Activation during Dual-Task Interference: A Functional Near-Infrared Spectroscopy Study

In daily life, mobility requires walking while performing a cognitive or upper-extremity motor task. Although previous studies have evaluated the effects of dual tasks on gait performance, few studies have evaluated cortical activation and its association with gait disturbance during dual tasks. In this study, we simultaneously assessed gait performance and cerebral oxygenation in the bilateral prefrontal cortices (PFC), premotor cortices (PMC), and supplemental motor areas (SMA), using functional near-infrared spectroscopy, in 17 young adults performing dual tasks. Each participant was evaluated while performing normal-pace walking (NW), walking while performing a cognitive task (WCT), and walking while performing a motor task (WMT). Our results indicated that the left PFC exhibited the strongest and most sustained activation during WCT, and that NW and WMT were associated with minor increases in oxygenation levels during their initial phases. We observed increased activation in channels in the SMA and PMC during WCT and WMT. Gait data indicated that WCT and WMT both caused reductions in walking speed, but these reductions resulted from differing alterations in gait properties. WCT was associated with significant changes in cadence, stride time, and stride length, whereas WMT was associated with reductions in stride length only. During dual-task activities, increased activation of the PMC and SMA correlated with declines in gait performance, indicating a control mechanism for maintaining gait performance during dual tasks. Thus, the regulatory effects of cortical activation on gait behavior enable a second task to be performed while walking.

Prefrontal activation during inhibitory control measured by near-infrared spectroscopy for differentiating between autism spectrum disorders and attention deficit hyperactivity disorder in adults

The differential diagnosis of autism spectrum disorders (ASDs) and attention deficit hyperactivity disorder (ADHD) based solely on symptomatic and behavioral assessments can be difficult, even for experts. Thus, the development of a neuroimaging marker that differentiates ASDs from ADHD would be an important contribution to this field. We assessed the differences in prefrontal activation between adults with ASDs and ADHD using an entirely non-invasive and portable neuroimaging tool, near-infrared spectroscopy. This study included 21 drug-naïve adults with ASDs, 19 drug-naïve adults with ADHD, and 21 healthy subjects matched for age, sex, and IQ. Oxygenated hemoglobin concentration changes in the prefrontal cortex were assessed during a stop signal task and a verbal fluency task. During the stop signal task, compared to the control group, the ASDs group exhibited lower activation in a broad prefrontal area, whereas the ADHD group showed underactivation of the right premotor area, right presupplementary motor area, and bilateral dorsolateral prefrontal cortices. Significant differences were observed in the left ventrolateral prefrontal cortex between the ASDs and ADHD groups during the stop signal task. The leave-one-out cross-validation method using mean oxygenated hemoglobin changes yielded a classification accuracy of 81.4% during inhibitory control. These results were task specific, as the brain activation pattern observed during the verbal fluency task did not differentiate the ASDs and ADHD groups significantly. This study therefore provides evidence of a difference in left ventrolateral prefrontal activation during inhibitory control between adults with ASDs and ADHD. Thus, near-infrared spectroscopy may be useful as an auxiliary tool for the differential diagnosis of such developmental disorders.

Seizure-induced formation of isofurans: novel products of lipid peroxidation whose formation is positively modulated by oxygen tension

We have previously shown that seizures induce the formation of F(2)-isoprostanes (F(2)-IsoPs), one of the most reliable indices of oxidative stress in vivo. Isofurans (IsoFs) are novel products of lipid peroxidation whose formation is favored by high oxygen tensions. In contrast, high oxygen tensions suppress the formation of F(2)-IsoPs. The present study determined seizure-induced formation of IsoFs and its relationship with cellular oxygen levels (pO2). Status epilepticus (SE) resulted in F(2)-IsoP and IsoF formation, with overlapping but distinct time courses in hippocampal subregions. IsoF, but not F(2)-IsoP formation coincided with mitochondrial oxidative stress. SE resulted in a transient decrease in hippocampal pO2 measured by in vivo electron paramagnetic resonance oximetry suggesting an early phase of seizure-induced hypoxia. Seizure-induced F(2)-IsoP formation coincided with the peak hypoxia phase, whereas IsoF formation coincided with the 'reoxygenation' phase. These results demonstrate seizure-induced increase in IsoF formation and its correlation with changes in hippocampal pO2 and mitochondrial dysfunction.

Bilateral, vascular and perivascular glial upregulation of heat shock protein-27 after repeated epileptic seizures

Heat shock protein-27 (HSP-27) is an inducible stress response protein. It inhibits apoptotic cell death and is a reliable marker for oxidative stress. We studied the induction of HSP-27 in rat brains on days 1, 4 and 14 after repeated, pentylenetetrazole (PTZ)-induced seizures using immunohistochemisty. Saline treated control rats showed no induction of HSP-27. HSP-27 reactive astrocytes were rarely seen 1 or 4 days after PTZ injection. When present, single astrocytes were located in the cortex and/or the hippocampus. After 14 days PTZ treatment, a bilateral distribution of HSP-27 immunoreactive glia was present in piriform and entorhinal cortices and in the dentate gyrus of most brains. Rats with most intense HSP-27 upregulation showed HSP-27 in amygdala and thalamic nuclei. Astrocytes associated with blood vessels presented strongest HSP-27 staining, but did not show upregulation of gial fibrillary acidic protein and none responded with HSP-47 expression. Additionally, HSP-27 immunoreactivity increased in the endothelial cells of blood vessels in the affected brain regions, although no neuronal induction occurred. Contrastingly, a subconvulsive dose of the glutamine synthetase inhibitor L-methionine sulfoxime, which acts directly on astrocytes, resulted in a rapid, homogeneous astrocyte-specific HSP-27 upregulation within 24 h. Thus, repeated PTZ-induced seizure activity elicits a focal "heat shock" response in endothelial cells and astrocytes of selected cerebral regions indicating that expression of HSP-27 occurred in a seizure-dependent manner within the affected cerebral circuitries. Therefore, this PTZ-model of repeated seizure activity exhibited a cortical pattern of HSP-27 expression which is most comparable to that known from patients with epilepsy.

Heat Shock Protein-27 Is Upregulated in the Temporal Cortex of Patients with Epilepsy

PURPOSE

Heat shock protein-27 (HSP-27) belongs to the group of small heat shock proteins that become induced in response to various pathologic conditions. HSP-27 has been shown to protect cells and subcellular structures, particularly mitochondria, and serves as a carrier for estradiol. It is a reliable marker for tissues affected by oxidative stress. Oxidative stress and related cellular defence mechanisms are currently thought to play a major role during experimentally induced epileptic neuropathology. We addressed the question whether HSP-27 becomes induced in the neocortex resected from patients with pharmacoresistant epilepsy.

METHODS

Human epileptic temporal neocortex was obtained during neurosurgery, and control tissue was obtained at autopsy from subjects without known neurologic diseases. The tissues were either frozen for Western blot analysis or fixed in Zamboni's fixative for the topographic detection of HSP-27 at the cellular level by means of immunohistochemistry.

RESULTS

HSP-27 was highly expressed in all epilepsy specimens and in the cortex of a patient who died in the final stage of multiple sclerosis (positive control), whereas only low amounts of HSP-27 were detectable in control brains. In epilepsy patients, HSP-27 was present in astrocytes and in the walls of blood vessels. The intracortical distribution patterns varied strongly among the epilepsy specimens.

CONCLUSIONS

These results demonstrate that HSP-27 becomes induced in response to epileptic pathology. Although the functional aspects of HSP-27 induction during human epilepsy have yet to be elucidated, it can be concluded that HSP-27 is a marker for cortical regions in which a stress response has been caused by seizures.

A perfused rat brain model maintaining the connection between the central and peripheral nervous systems

We have developed a new perfused brain model in rats. In this model, the cerebral circulation is separated from the systemic circulation, while the connections between the central and peripheral nervous systems are preserved. After bilateral common carotid, external carotid and vertebral artery ligation, bilateral common carotid arteries were cannulated to infuse rinsed human type O red blood cells mixed with modified Ringer's solution. To drain cerebral venous blood, external jugular veins were cannulated. Normal electrocortical activities were observed on electroencephalograms (EEGs) for more than 1h after the beginning of the perfusion. Somatosensory evoked potentials (SEPs) were also recorded. Direct infusion of pentylenetetrazol (PTZ) into the brain induced epileptic discharges on the EEGs and active dilation of cerebral arterioles, which was accompanied by an increase in systemic blood pressure (BP). The present model, in which we can change cerebral blood flow (CBF) and/or cerebral metabolism without directly affecting the systemic circulation, will provide a new approach to brain research.

Bilateral near-infrared monitoring of the cerebral concentration and oxygen-saturation of hemoglobin during right unilateral electro-convulsive therapy

Reductions in right prefrontal cerebral blood flow have been correlated with symptomatic improvement in depressed individuals receiving electroconvulsive therapy (ECT). Non-invasive near infrared spectroscopy has previously been shown to reliably measure changes in cerebral hemoglobin concentrations and oxygen saturation. In this study, we measured the concentration and oxygen saturation of hemoglobin on the right and left frontal brain regions of nine patients during right unilateral ECT. In all patients, we have found that the electrically induced seizure causes a stronger cerebral deoxygenation on the side ipsilateral to the electrical current (-21+/-5%) with respect to the contralateral side (-6+/-4%). On the brain side ipsilateral to the ECT electrical discharge, we have consistently observed a discharge-induced decrease in the total hemoglobin concentration, i.e. in the cerebral blood volume, by -7+/-3 microM, as opposed to an average increase by 6+/-3 microM on the contralateral side. The ipsilateral decrease in blood volume is assigned to a vascular constriction associated with the electrical discharge, as indicated by the observed decrease in cerebral oxy-hemoglobin concentration and minimal change in deoxy-hemoglobin concentration during the electrical discharge on the side of the discharge. These findings provide indications about the cerebral hemodynamic/metabolic mechanisms associated with ECT, and may lead to useful parameters to predict the individual clinical outcome of ECT.

Novel role for the NMDA receptor redox modulatory site in the pathophysiology of seizures

Redox-active compounds modulate NMDA receptors (NMDARs) such that reduction of NMDAR redox sites increases, and oxidation decreases, NMDAR-mediated activity. Because NMDARs contribute to the pathophysiology of seizures, redox-active compounds also may modulate seizure activity. We report that the oxidant 5, 5'-dithio-bis(2-nitrobenzoic acid) (DTNB) and the redox cofactor pyrroloquinoline quinone (PQQ) suppressed low Mg(2+)-induced hippocampal epileptiform activity in vitro. Additionally, in slices exposed to 4-7 microM bicuculline, DTNB and PQQ reversed the potentiation of evoked epileptiform responses by the reductants dithiothreitol and Tris(2-carboxyethyl)phosphine (TCEP). NMDA-evoked whole-cell currents in CA1 neurons in slices were increased by TCEP and subsequently decreased by DTNB or PQQ at the same concentrations that modulated epileptiform activity. However, DTNB and PQQ had little effect on baseline NMDA-evoked currents in control medium, and PQQ did not alter NMDAR-dependent long-term potentiation. In contrast, in slices returned to control medium after low Mg(2+)-induced ictal activity, DTNB significantly inhibited NMDAR-mediated currents, indicating endogenous reduction of NMDAR redox sites under this epileptogenic condition. These data suggested that PQQ and DTNB suppressed spontaneous ictal activity by reversing pathological NMDAR redox potentiation without inhibiting physiological NMDAR function. In vivo, PQQ decreased the duration of chemoconvulsant-induced seizures in rat pups with no effect on baseline behavior. Our results reveal endogenous potentiation of NMDAR function via mass reduction of redox sites as a novel mechanism that may enhance epileptogenesis and facilitate the transition to status epilepticus. The results further suggest that redox-active compounds may have therapeutic use by reversing NMDAR-mediated pathophysiology without blocking physiological NMDAR function.

c-fos expression and redox state of cytochrome oxidase of rat brain in hypoxia

Hypoxic induction of c-fos was studied in rat brains as a function of the cerebral oxygenation state using near-infrared spectroscopy by which the hemoglobin oxygenation state and redox state of mitochondrial cytochrome oxidase could be monitored noninvasively. Following reoxygenation after hypoxia, the expression of c-fos and MAP2 mRNAs was followed by reverse transcription-coupled PCR. The expression of MAP2 remained unchanged throughout all the conditions from 21 to 8% FiO2. Under mildly hypoxia conditions, c-fos mRNA was not induced. Hemoglobin was partially deoxygenated but cytochrome oxidase remained fully oxidized. Severe hypoxia, where cytochrome oxidase was reduced, caused a significant induction of c-fos mRNA At this stage, the oxygen concentration in cerebral tissue fell to < 10(-7) M. These data suggest that the decline in oxidative phosphorylation might be a trigger for the induction of c-fos mRNA.

Noninvasive continuous monitoring of cerebral oxygenation periictally using near-infrared spectroscopy: a preliminary report

PURPOSE

To report on the use of near-infrared spectroscopy (NIRS) to examine the changes in cerebral oxygenation in the periictal period in patients with seizures.

METHODS

Cerebral hemoglobin oxygen availability was monitored continuously and noninvasively with NIRS in three patients (one in the pediatric intensive care unit (ICU) and two in epilepsy-monitoring units) in conjunction with continuous EEG monitoring. Ictal events were recorded and compared with the pre-, intra-, and postictal periods for cerebral oxygen availability, as defined by oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (Hb), and the redox state of cytochrome oxidase (cytox).

RESULTS

Several important preliminary observations were made by using this technology. First, a preictal increase in cerebral oxygenation began between 1 and 2 h and >10 h before the ictal event. Second, despite adequate perfusion, based on an observed increased HbO2, reduction in cytox indicates a perfusion-metabolism mismatch during seizure activity. Third, continued seizure activity and even isolated ictal events were associated with decreased cerebral oxygen availability. Fourth, differences in cerebral oxygen availability were noted between different types of seizures (e.g., electrographic seizures were accompanied by rapid reductions in HbO2 and cerebral blood volume without reduction of cytox, whereas electroclinical seizures were characterized by marked increases in HbO2 with or without reduction of cytox).

CONCLUSIONS

In this preliminary report on the use of NIRS for patients with seizures, we believe that NIRS allows continuous and noninvasive monitoring of changes in cerebral oxygenation periictally, thereby permitting investigations into the pathophysiology of seizures and the exploration of the potential of cerebral oximetry as a tool for seizure localization.

Energy-dependent redox state of heme a + a3 and copper of cytochrome oxidase in perfused rat brain in situ

Using the blood-free perfused rat brain, we examined the redox behavior of cytochrome oxidase of two chromophores, heme a + a3 and copper. When perfusate inflow was stopped to induce global ischemia, the reduction of heme a + a3 was triphasic, with a rapid phase, a slow phase, and a second rapid phase. In contrast, the reduction of copper was monophasic after the rapid phase of heme a + a3. The triphasic reduction of heme a + a3 was diminished by energy-depleting treatments, such as addition of an uncoupler. The time course of the reduction of copper was not affected by the energy depletion. During global ischemia the decrease in creatine phosphate nearly paralleled the reduction of heme a + a3, whereas ATP remained at the control level until approximately 60% of heme a + a3 was reduced in the rapid phase. In the slow phase, ATP started to decrease with the reduction of copper. The redox behavior of copper was similar to the slow phase of the reduction of heme a + a3 because of the higher oxygen affinity of copper than of heme a + a3. Therefore, the rapid phase of the reduction of heme a + a3 can be used as an alarm before a decrease in ATP, whereas the reduction of copper indicates a decrease in ATP under severe hypoxia. Thus the copper signal in noninvasive near-infrared spectroscopy is a useful parameter for the clinical setting.

Optical characterization of heme a + a3 and copper of cytochrome oxidase in blood-free perfused rat brain

For the precise examination of the optical characteristics of cerebral tissue, we prepared hemoglobin-free perfused rat heads, from which trace amounts of blood were completely removed. In this preparation at 30 degrees C, the redox responses of the cytochrome oxidase components, heme a + a3 and copper, were followed spectrophotometrically in visible and near-infrared regions, and were correlated with the changes in neural activity as monitored by electroencephalography (EEG). During the aerobic-anaerobic transition, there was clear dissociation of the time courses of the reduction of heme a + a3 and copper; the reduction of heme a + a3 preceded the reduction of copper. The EEG activity decreased earlier than the reduction of heme a + a3. Pentylenetetrazole administration in normoxia caused the partial reduction of heme a + a3 but not of copper. The redox behaviors of cytochrome oxidase components in the brain were identical to those observed in isolated mitochondria. The usefulness of brain preparation for bridging the in vivo and in vitro studies is documented where various circulatory parameters could be controlled artificially.

Redox behavior of cytochrome oxidase in the rat brain measured by near-infrared spectroscopy

Using near-infrared spectroscopy, we developed a new approach for measuring the redox state of cytochrome oxidase in the brain under normal blood-circulation conditions. Our algorithm does not require the absorption coefficient of cytochrome oxidase, which differs from study to study. We employed this method for evaluation of effects of changes in oxygen delivery on cerebral oxygenation in rats. When fractional inspired oxygen was decreased in a stepwise manner from 100 to <10%, at which point the concentration of oxygenated hemoglobin ([HbO2]) decreased by approximately 60%, cytochrome oxidase started to be reduced. Increases in arterial PO2 under hyperoxic conditions caused an increase in [HbO2], whereas further oxidation of cytochrome oxidase was not observed. The dissociation of the responses of hemogloblin and cytochrome oxidase was also clearly observed after the injection of epinephrine under severely hypoxic conditions; that is, cytochrome oxidase was reoxidized with increasing blood pressure, whereas hemoglobin oxygenation was not changed. These data indicated that oxygen-dependent redox changes in cytochrome oxidase occur only when oxygen delivery is extremely impaired. This is consistent with the in vitro data of our previous study.

Non-invasive optical spectroscopy and imaging of human brain function

Brain activity is associated with changes in optical properties of brain tissue. Optical measurements during brain activation can assess haemoglobin oxygenation, cytochrome-c-oxidase redox state, and two types of changes in light scattering reflecting either membrane potential (fast signal) or cell swelling (slow signal), respectively. In previous studies of exposed brain tissue, optical imaging of brain activity has been achieved at high temporal and microscopical spatial resolution. Now, using near-infrared light that can penetrate biological tissue reasonably well, it has become possible to assess brain activity in human subjects through the intact skull non-invasively. After early studies employing single-site near-infrared spectroscopy, first near-infrared imaging devices are being applied successfully for low-resolution functional brain imaging. Advantages of the optical methods include biochemical specificity, a temporal resolution in the millisecond range, the potential of measuring intracellular and intravascular events simultaneously and the portability of the devices enabling bedside examinations.

A novel near infra-red spectrophotometry system using microprobes: its evaluation and application for monitoring neuronal activity in the visual cortex

A novel near-infrared (NIR) spectrophotometry system with microprobes of optical transmitter and receivers (550 and 410 microm in diameter, respectively) has been developed. A three-dimensional profile of the signal source estimated in in vitro experiments showed two spindle-shaped regions around the respective probes, suggesting that the signal detected by the present system comes from a relatively restricted region around each probe. Next, we examined how the concentration of oxygen in inspired gas affected the NIR signals in the rat cerebral cortex in vivo. Calculated concentrations of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) in the rat cortex changed in mirror-image fashion in response to the change in the O2 concentration in the inspired gas. Finally, NIR responses to visual stimulation were recorded from the striate cortex of conscious adult cats that had been monocularly deprived since the peak of the sensitive period. Corresponding to the results of previous electrophysiological studies, stimulation of the normal eye induced significant NIR signals, whereas that of the deprived eye evoked no response. These results indicate that this new NIR system can be applied to study changes in oxygen metabolism in relatively restricted regions following neuronal activation in the brain.

Relationship between time-resolved and non-time-resolved Beer-Lambert law in turbid media

The time-resolved Beer-Lambert law proposed for oxygen monitoring using pulsed light was extended to the non-time-resolved case in a scattered medium such as living tissues with continuous illumination. The time-resolved Beer-Lambert law was valid for the phantom model and living tissues in the visible and near-infrared regions. The absolute concentration and oxygen saturation of haemoglobin in rat brain and thigh muscle could be determined. The temporal profile of rat brain was reproduced by Monte Carlo simulation. When the temporal profiles of rat brain under different oxygenation states were integrated with time, the absorbance difference was linearly related to changes in the absorption coefficient. When the simulated profiles were integrated, there was a linear relationship within the absorption coefficient which was predicted for fractional inspiratory oxygen concentration from 10 to 100% and, in the case beyond the range of the absorption coefficient, the deviation from linearity was slight. We concluded that an optical pathlength which is independent of changes in the absorption coefficient is a good approximation for near-infrared oxygen monitoring.

Interpretation of BOLD MRI signals in rat brain using simultaneously measured near-infrared spectrophotometric information

The purpose of this paper is to investigate the origin of the signal changes in the blood oxygenation level dependent effect (BOLD) and the influence of oxygen metabolism by utilizing near-infrared spectrophotometry (NIRS), which can measure deoxyhemoglobin (deoxyHb) content in blood vessels and redox states of cytochrome oxidase in whole tissue. Simultaneous MRI and NIRS measurements of the rat head were performed by changing oxygen concentrations in the inhalant gas. The signal intensity based on the BOLD effect depended on the influence of both arterial and venous blood deoxygenation in the brain, whose relative contributions differed at various points. In this paper, it is noteworthy that the differential apparent transverse relaxation rate between two conditions in the brain areas was linearly correlated with deoxyHb content determined by NIRS, except in severe hypoxia, and that no reduction of cytochrome oxidase occurred under the same conditions. These results indicate that the influence of hemodynamic changes on the signal intensity of the BOLD effect, and therefore functional MRI, can be elucidated by the NIRS information to determine actual changes of blood deoxygenation and blood volume.

Does the redox state of cytochrome aa3 reflect brain energy level during hypoxia? Simultaneous measurements by near infrared spectrophotometry and 31P nuclear magnetic resonance spectroscopy

We studied cerebral oxygen metabolism during hypoxia to demonstrate whether the redox state of cytochrome aa3 (cyt.aa3), as measured by near infrared spectrophotometry (NIRS), reflects brain energy level. Rats (n = 6) subjected to hypoxia were simultaneously monitored by NIRS and 31P nuclear magnetic resonance spectroscopy (NMRS). Brain function was evaluated using the electroencephalogram (EEG). After a reduction of the fraction of inspired oxygen FIO2 from 0.21 to 0.15, we observed a significant increase in reduced cyt.aa3 (from 16.5% +/- 2.1% to 41.2% +/- 2.8%; P < 0.01), without significant changes in phosphocreatine (PCr) and beta-adenosine triphosphate (beta-ATP) levels. The PCr decreased significantly at a FIO2 of 0.10 (53.8% +/- 6.4% as compared with 97.7% +/- 10.9% at a FIO2 of 0.21; P < 0.05), and reached a minimum at a FIO2 of 0.04. beta-ATP did not change significantly at a FIO2 of 0.10 or 0.08. With a FIO2 of less than 0.08, cyt.aa3 was almost totally reduced. EEG activity slowed at a FIO2 of 0.08 and became isoelectric at 0.04. Significant correlations were found between the levels of cyt.aa3 and PCr (P < 0.001, r = 0.83) as well as between cyt.aa3 and beta-ATP (P < 0.001, r = 0.73) by using the overall values at FIO2 levels from 0 to 1.0. However, no significant correlations were observed among these variables when the FIO2 was less than 0.10. These findings suggest that the increase in reduced cyt.aa3 reflects brain energy depletion; however, the redox state of cyt.aa3 will not indicate brain energy depletion during extreme hypoxia because cyt.aa3 is reduced totally during hypoxia insufficient to deplete intracellular ATP.

Near-infrared monitoring of cerebral oxygenation state during carotid endarterectomy

BACKGROUND

Recent studies have indicated that near-infrared spectroscopy (NIRS) could continuously and noninvasively observe the changes in cerebral oxygenation state during hypoxia and ischemia, using their optical properties. Its validity and usefulness during cerebrovascular surgery, however, still remain to be clarified.

METHODS

Using NIRS, we continuously monitored the changes in the concentration of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin ([oxy-HB], [deoxy-Hb], and [total Hb], respectively) and redox state of cytochrome oxidase (cyt ox) during carotid endarterectomy for 22 patients, and we compared the NIRS responses with those of intraoperative somatosensory evoked potentials (SEP) and regional cerebral blood flow (rCBF).

RESULTS

In 9 of 22 patients, cross-clamping of the carotid artery caused a continuous decrease [oxy-Hb] and [total Hb], and an increase in [deoxy-Hb]. Cyt ox was partially reduced during the clamping. These NIRS responses demonstrated the occurrence of severe hypoxia in the ipsilateral cerebral tissue. These patients showed a marked decrease in the N20 amplitude of SEP and rCBF. In contrast, the other 13 patients did not show a significant decrease in the cerebral oxygenation state, which showed no remarkable changes in either SEP or in rCBF.

CONCLUSIONS

NIRS could successfully jude the cerebral oxygenation state noninvasively during carotid surgery and was more sensitive to ischemic crisis than other indirect methods.

Near-infrared spectroscopy: theory and applications

In conclusion, NIRS appears to offer both a new monitoring modality and new information about cerebral oxygenation. Technical problems in the application of this technology persist, most notably determination of pathlength and the volume of tissue interrogated. Those familiar with the history of pulse oximetry will recall that although Millikan developed an ear oximeter in 1947, it was not until Aoyagi combined recognition of the pulse signal with spectroscopy in the 1970s that oximetry was transformed into a clinically applicable monitor. In much the same way, NIRS may find the same tremendous usefulness as a noninvasive monitor of cerebral oxygen utilization, pending resolution of the remaining technical problems.

The cerebral hemodynamic response to electrically induced seizures in man

The hemodynamic response to seizure has long been a topic for discussion in association with the neuronal damage resulting from convulsion. Electroconvulsive therapy (ECT) is an appropriate clinical model for the investigation of the cerebral physiology of seizure. In this study, we monitored the oxygenation state of brain tissue using near infrared (NIR) spectrophotometry, and flow velocity at the middle cerebral artery (MCA) using transcranial Doppler ultrasonography (tc-Doppler) in ninety cases where flow velocity at the middle cerebral artery (MCA) using transcranial Doppler ultrasonography (tc-Doppler) in ninety cases where ECT was prescribed to patients suffering from endogenous depression. Under general anesthesia with thiopental and succinyl choline, an electrical current was applied bilaterally at the minimal energy level. Throughout the therapy, end-tidal CO2 tension was maintained at 30-35 mmHg, and the SpO2 value was maintained above 98% by manual ventilation assistance. The total- and oxy-hemoglobin contents in the brain were reduced during the electrical shock, and then recovered to the pre-shock value (total-hemoglobin; 44.13 +/- 12.88 s after the shock, oxy-hemoglobin; 88.62 +/- 11.69 s after the shock). Subsequently, these values further increased beyond the preshock value. On the other hand, the deoxy-hemoglobin content increased for 90.73 +/- 15.88 s during and after the electrical shock, and decreased afterward. Reduction of cytochrome aa3 began 3.04 +/- 0.51 s after the electrical shock, and this was reoxygenated at 171.88 +/- 12.95 s after the shock.(ABSTRACT TRUNCATED AT 250 WORDS)