Responses of rat brain to induced spreading depression following exposure to carbon monoxide

Effects of passive smoking on cortical spreading depolarization in male and female mice

BACKGROUND

Patients with migraine are typically advised to avoid passive smoking because it may aggravate headaches and other health conditions. However, there is insufficient high-quality evidence on the association between passive smoking and migraine, which warrants further investigation using animal models. Therefore, using a mouse model, we examined the effect of passive smoking on susceptibility to cortical spreading depolarization (CSD), the biological basis of migraine with aura.

FINDINGS

Fifty C57BL/6 mice (25 males and 25 females) were exposed for one hour to cigarette smoke or room air. Subsequently, potassium chloride (KCl) was administered under isoflurane anesthesia to induce CSD, and the CSD threshold, frequency of induction, and propagation velocity were determined. The threshold to induce CSD (median [interquartile range (IQR)]) was significantly lower in female mice (adjusted p = 0.01) in the smoking group (0.05 [0.05, 0.088]) than in the sham group (0.125 [0.1, 0.15]); however, there was no significant difference in the male mice (adjusted p = 0.77). CSD frequency or propagation velocity did not differ significantly between the two groups for either sex.

CONCLUSIONS

Female mice in the smoking group showed lower CSD threshold compared to the sham group, suggesting a potential sex-specific difference in the effect of smoking on the pathogenesis of CSD and migraine with aura. This finding may contribute to the understanding of migraine pathophysiology in association with passive smoking and sex difference.

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.

Mitochondrial function in vivo evaluated by NADH fluorescence: from animal models to human studies

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. The goals of the present review are the following: 1) to provide an historical overview of NADH fluorescence monitoring and its physiological significance; 2) to present the solid scientific ground underlying NADH fluorescence measurements based on published materials; 3) to provide the reader with basic information on the methodologies used in the past and the current state of the art fluorometers; and 4) to clarify the various factors affecting monitored signals, including artifacts. 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 understand tissue function better, the multiparametric approach has been developed where NADH serves as the key parameter. The development of new light sources in UV and visible spectra has led to the development of small compact units applicable in clinical conditions for better diagnosis of patients.

Blockade of haem oxygenase and nitric oxide synthetase causes cortical dysfunction in sheep exposed to carbon monoxide

Twenty adult ewes underwent common surgery and following recovery were exposed to 1% carbon monoxide (CO) for 2 h. Ten of these sheep were randomly selected for treatment with haem oxygenase (HO) and nitric oxide synthetase (NOS) blockers. All sheep were killed 5 days later. The CO exposure was narcotic and EEG frequency was suppressed. The EEG recovery was rapid in the control sheep and both slow and incomplete in the treated sheep. This difference was statistically significant (P<0.05). For the first time in our CO studies in sheep, one showed multiple cortical infarcts. This sheep was blocked for HO and NOS function. No significant differences were seen in peri-ventricular white matter infarction distribution and frequency. We have previously shown brain protection against CO- and inert diluent-hypoxemia by way of an increase in brain blood flow (BBF) that maintains adequate brain O2 uptake, and by an increase in circulating red blood cells. From this study, we propose that the induction of neuronal and glial HO and NOS in sheep exposed to CO is protective, especially for the cortex. We intend to study this further by both selective and collective enzyme blockade and by measuring regional BBF changes.

Blood flow and ionic responses in the awake brain due to carbon monoxide

This study examined the effect of 2000 ppm CO on the brain of an awake rat. Measurements of regional perfusion as well as metabolic, ionic and electrical activities were used to examine whether mechanisms responsible for changes in brain perfusion were separable from those attributable to compromises in neuronal metabolism. Exposure to 2000 ppm CO resulted in elevation of cerebral blood flow. The stability of mitochondrial NADH redox level during CO exposure indicated that tissue hypoxia did not develop. The elevation in blood flow was inhibited by L-nitroarginine methyl ester, indicating that nitric oxide was responsible for the CO-induced elevation in blood flow. Exposure to 2000 ppm CO also triggered a significant decrease in pH and rise in extracellular potassium ion, possibly due to ion-pump inhibition. The amplitude of the electrocorticogram wave activity decreased, indicative of a compromise to physiological activity. These changes were not observed in rats anesthetized with pentobarbital during CO exposure, although anesthesia had no effect on the CO-induced elevation in blood flow and there was still no change in mitochondrial NADH redox level. We concluded that CO acts by separate mechanisms to alter cerebral vasoactivity and neuronal metabolic responses and that both processes are independent of hypoxic stress.

Effects of single and repetitive spreading depression on cerebral blood flow and glucose metabolism in cats: a PET study

To clarify the effects of spreading depression (SD) on cerebral circulation and metabolism, we elicited a single or repetitive episode of SD and evaluated CBF and CMRglc three-dimensionally in normal cats (n=4, in each group) using a high-resolution positron emission tomography (PET) scanner. SD was evoked by applying KCl to the left occipital cortex. We then monitored DC potential changes with tungsten electrodes inserted into the left temporal cortex. CBF was measured twice before and three times (immediately, 30-60 min, and 60-120 min) following KCl application using [15O]H(2)O, and CMRglc was determined using 2-[18F]fluoro-2-deoxy-D-glucose immediately following the last CBF measurement. The following results were obtained: (1) a single episode of SD produced a temporary CBF increase, followed by a long-lasting hypoperfusion in the cortex, with no significant changes to CBF observed in the subcortex; (2) no significant CMRglc changes were observed in either cortical or subcortical regions following a single episode of SD; (3) a flow-metabolism uncoupling was observed in the cortical regions concurrently with persistent hypoperfusion; (4) repetitive SD produced significant CBF changes in the cortex; and (5) the cortical CMRglc increased as a result of repeated episodes of SD, with no significant changes observed in the subcortex. Thus, we succeeded in determining three-dimensionally the effects of single and repetitive SD on CBF and CMRglc in cats using a high-resolution PET scanner. The present study provides the first direct evidence of CBF-CMRglc uncoupling occurring concurrently with persistent hypoperfusion following SD.