A reproducible model of an epidural mass lesion in rodents. Part II: Characterization by in vivo magnetic resonance imaging

23Na chemical shift imaging in the living rat brain using a chemical shift agent, Tm[DOTP]5

OBJECTIVE

It is well known that the use of shift reagents (SRs) in nuclear magnetic resonance (NMR) studies is substantially limited by an intact blood-brain barrier (BBB). The current study aims to develop a method enabling chemical shift imaging in the living rat brain under physiological conditions using an SR, Tm[DOTP]^5-.

MATERIALS AND METHODS

Hyperosmotic mannitol bolus injection followed by 60 min infusion of a Tm[DOTP]^5- containing solution was administered via a catheter inserted into an internal carotid artery. We monitored the homeostasis of physiological parameters, and we measured the thulium content in brain tissue post mortem using total reflection fluorescence spectroscopy (T-XRF). The alterations of the ²³Na resonance spectrum were followed in a 9.4T small animal scanner.

RESULTS

Based on the T-XRF measurements, the thulium concentration was estimated at 2.3 ± 1.8 mM in the brain interstitial space. Spectroscopic imaging showed a split of the ²³Na resonance peak which became visible 20 min after starting the infusion. Chemical shift imaging revealed a significant decrease of the initial intensity level to 0.915 ± 0.058 at the end of infusion.

CONCLUSION

Our novel protocol showed bulk accumulation of Tm[DOTP]^5- thus enabling separation of the extra-/intracellular ²³Na signal components in the living rat brain while maintaining physiological homeostasis.

Acute brain trauma, lung injury, and pneumonia: more than just altered mental status and decreased airway protection

Traumatic brain injury (TBI) is a major cause of mortality and morbidity worldwide. Even when patients survive the initial insult, there is significant morbidity and mortality secondary to subsequent pulmonary edema, acute lung injury (ALI), and nosocomial pneumonia. Whereas the relationship between TBI and secondary pulmonary complications is recognized, little is known about the mechanistic interplay of the two phenomena. Changes in mental status secondary to acute brain injury certainly impair airway- and lung-protective mechanisms. However, clinical and translational evidence suggests that more specific neuronal and cellular mechanisms contribute to impaired systemic and lung immunity that increases the risk of TBI-mediated lung injury and infection. To better understand the cellular mechanisms of that immune impairment, we review here the current clinical data that support TBI-induced impairment of systemic and lung immunity. Furthermore, we also review the animal models that attempt to reproduce human TBI. Additionally, we examine the possible role of damage-associated molecular patterns, the chlolinergic anti-inflammatory pathway, and sex dimorphism in post-TBI ALI. In the last part of the review, we discuss current treatments and future pharmacological therapies, including fever control, tracheostomy, and corticosteroids, aimed to prevent and treat pulmonary edema, ALI, and nosocomial pneumonia after TBI.

Dietary Docosahexaenoic Acid Improves Cognitive Function, Tissue Sparing, and Magnetic Resonance Imaging Indices of Edema and White Matter Injury in the Immature Rat after Traumatic Brain Injury

Traumatic brain injury (TBI) is the leading cause of acquired neurologic disability in children. Specific therapies to treat acute TBI are lacking. Cognitive impairment from TBI may be blunted by decreasing inflammation and oxidative damage after injury. Docosahexaenoic acid (DHA) decreases cognitive impairment, oxidative stress, and white matter injury in adult rats after TBI. Effects of DHA on cognitive outcome, oxidative stress, and white matter injury in the developing rat after experimental TBI are unknown. We hypothesized that DHA would decrease early inflammatory markers and oxidative stress, and improve cognitive, imaging and histologic outcomes in rat pups after controlled cortical impact (CCI). CCI or sham surgery was delivered to 17 d old male rat pups exposed to DHA or standard diet for the duration of the experiments. DHA was introduced into the dam diet the day before CCI to allow timely DHA delivery to the pre-weanling pups. Inflammatory cytokines and nitrates/nitrites were measured in the injured brains at post-injury Day (PID) 1 and PID2. Morris water maze (MWM) testing was performed at PID41-PID47. T2-weighted and diffusion tensor imaging studies were obtained at PID12 and PID28. Tissue sparing was calculated histologically at PID3 and PID50. DHA did not adversely affect rat survival or weight gain. DHA acutely decreased oxidative stress and increased anti-inflammatory interleukin 10 in CCI brains. DHA improved MWM performance and lesion volume late after injury. At PID12, DHA decreased T2-imaging measures of cerebral edema and decreased radial diffusivity, an index of white matter injury. DHA improved short- and long-term neurologic outcomes after CCI in the rat pup. Given its favorable safety profile, DHA is a promising candidate therapy for pediatric TBI. Further studies are needed to explore neuroprotective mechanisms of DHA after developmental TBI.

Visualisation of cortical pO(2) during an epidural mass lesion in rodents

Monitoring p(bt)O(2) is a valuable supplemental -procedure for neurocritically ill patients. Here, we utilise an opto-chemical method for measuring cortical pO(2) during a reversibly introduced epidural mass lesion in a rat model. The sensor was placed in a cortical window of 17 ventilated Wistar rats. Inflating the balloon device over the contralateral hemisphere increased ICP. Physiological parameters and cortical pO(2) were recorded. The ICP increased from 6.2 ± 4.6 to 44.6 ± 12.6 mmHg (p < 0.001). Cortical pO(2) over arterioles changed from 28.9 ± 2.1 to 19.0 ± 2.1 mmHg (p < 0.001), over venules from 14.8 ± 1.2 to 9.9 ± 1.5 mmHg (p = 0.002) and over parenchyma from 4.1 ± 0.7 to 2.4 ± 0.8 mmHg respectively (p < 0.001), while basic physiological parameters remained constant (p > 0.05). During baseline, arterial pO(2) correlated significantly with cortex arteriole and venole pO(2), but not with cortex parenchyma pO(2). While ICP was raised, cortical pO(2) did not correlate with arterial pO(2). In this model, a moderate epidural mass lesion causes a significant decrease in cortical pO(2). Cortex parenchyma pO(2) appeared to be independent from arterial pO(2). The correlation of cortex vessel pO(2) with arterial pO(2) disappeared during the epidural mass lesion. These findings show the capability of the device to elucidate the behaviour of functionally different cortex areas at pathophysiological conditions.

Neuropathological differences between rats and mice after spinal cord injury

PURPOSE

To investigate the utility of noninvasive magnetic resonance imaging (MRI) protocols to demonstrate pathological differences between rats and mice after spinal cord injury (SCI). Rats and mice are commonly used to model SCI; however, histology and immunohistochemistry have shown differences in neuropathology between the two species, including cavity formation and scar/inflammatory responses.

MATERIALS AND METHODS

Moderate contusion SCI was performed on adult male rats and mice. At 28 days postinjury, animals underwent T1-weighted (T1W), with or without gadolinium contrast, or T2-weighted (T2W) magnetic resonance imaging (MRI), to be compared with histology at the same timepoint.

RESULTS

In both species, all MRI methods demonstrated changes in spinal cord anatomy. Immunohistochemistry indicated that T2W accurately reflected areas of inflammation and glial scar formation in rats and mice. Quantitation of lesion volume by histology and functional performance correlated best with T2W measurements in both species. Gadolinium contrast accurately reflected the blood-spinal cord-barrier permeability in both species, which appeared greater in rats than in mice.

CONCLUSION

These data demonstrate that MRI, with either a T1W or T2W protocol, can effectively distinguish pathological differences between rats and mice.

The salicylate trapping method: is oxidation of salicylic acid solution oxygen and time dependent and metal catalysed?

For a microdialytic trapping method we systematically investigated changes in concentrations of 2,5-dihydroxy-benzoic acid (2,5-DHBA) and 2,3-dihydroxy-benzoic acid (2,3-DHBA) in freshly prepared solutions of salicylic acid (SA). The solvent was 0.9% saline exposed to different atmospheric concentrations of oxygen (0, 21, and 100%). The solutions were treated by freezing-thawing and an ultrasonic bath in presence and absence of aluminium foil. Without aluminium the concentrations of 2,5-DHBA and 2,3-DHBA kept constant over an observed period of 160 min on different levels from below 20 ng/ml to about 100 ng/ml. In presence of aluminium the concentrations increased to maximum 307 ng/ml after 160 min. Ultrasonic irradiation amplified this effect to maximum 341 ng/ml. HPLC/ECD processing and quantitative analysis of dihydroxy-benzoic acids (DHBAs) in microdialysis may be artificially influenced by varying oxygen environment and metal catalysis.

Neurophysiological monitoring, magnetic resonance imaging, and histological assays confirm the beneficial effects of moderate hypothermia after epidural focal mass lesion development in rodents

OBJECTIVE

To assess the effects of moderate intraischemic hypothermia on neurophysiological parameters in an epidural balloon compression model in rats and to correlate the results with magnetic resonance imaging and histological findings.

METHODS

Neurophysiological monitoring included laser Doppler flow, tissue partial oxygen pressure, and intracranial pressure measurements and electroencephalographic assessments during balloon expansion, sustained inflation, and reperfusion. Moderate intraischemic cooling of animals was extended throughout the reperfusion period, and results were compared with those for normothermic animals. Moreover, histological morphometric and magnetic resonance imaging volumetric analyses of the lesions were performed.

RESULTS

Laser Doppler flow decreased slightly during ischemia (P < 0.05) in animals treated with hypothermia, and flow values demonstrated complete reperfusion, compared with incomplete flow restoration in untreated animals (P < 0.05). During ischemia, the tissue partial oxygen pressure was less than 4.3 mm Hg in both groups. After reperfusion, values returned to the normal range in both groups, but the tissue partial oxygen pressure in hypothermic animals was significantly higher (P = 0.042) and demonstrated 19% higher values, compared with normothermic animals, before rewarming. Moderate hypothermia attenuated a secondary increase in intracranial pressure (P < 0.05), and electroencephalographic findings indicated a trend toward faster recovery (P > 0.05) after reperfusion. Lesion size was reduced by 35% in magnetic resonance imaging volumetric evaluations and by 24.5% in histological morphometric analyses.

CONCLUSION

Intraischemic hypothermia improves cerebral microcirculation, attenuates a secondary increase in intracranial pressure, facilitates electroencephalographic recovery, and reduces the lesion size.

Moderate hypothermia improves neurobehavioral deficits after an epidural focal mass lesion in rodents

The objective of this study was to evaluate the effects of a moderate, intraischemic hypothermia on the behavorial deficits up to 4 weeks after induction of a focal mass lesion. A focal epidural mass lesion was induced by an epidural balloon. The severity of the trauma was defined by the balloon volume and flattening of electroencephalography. Hypothermia (32 degrees C) was induced as soon as maximum balloon infIation was reached. Ischemia was extended over 30 min. After reperfusion, normothermic (n = 24) and hypothermic animals (n = 25) were monitored for 3 h followed by a rewarming of the cooled animals. Results were compared to sham-operated animals (n = 10). Behavioral deficits were assessed by postural reflex (PR), open field (OF), beam balance (BB), beam walking (BW), and water maze tests (WMT). MRI follow-up and histology was evaluated. Sham-operated rats showed normal test results. Rats with normothermia showed worsening of test performance (PR, p < 0.05; OF, p < 0.05; BB, p < 0.05; BW, p < 0.05; WMT, p < 0.05) compared to controls over the whole observation period. A significantly better behavioral outcome was observed in animals treated with hypothermia which showed no differences from controls 3-4 days after injury (PR, OF, BB, BW, WMT, p > 0.05). Lesion induced mortality was reduced in cooled animals but overall mortality rates were not influenced by this therapeutic measure. Neuronal cell loss in the CA1-CA4 region (p < 0.05) was reduced and the lesion size smaller (21%/p > 0.05) in hypothermic animals. Magnetic resonance imaging revealed that the lesion was more pronounced in the cortical grey matter after normothermia, whereas hypothermic animals showed more subcortical brain lacerations. In conclusion, intraischemic hypothermia significantly improved the behavioral outcome, and decreased lesion-induced mortality and the size of the lesion after an epidural focal mass lesion.

A new reproducible model of an epidural mass lesion in rodents. Part I: Characterization by neurophysiological monitoring, magnetic resonance imaging, and histopathological analysis

OBJECT

The goal of this study was to characterize a new model of an epidural mass lesion in rodents by means of neurophysiological monitoring, magnetic resonance imaging, and histopathological analysis.

METHODS

Changes in intracranial pressure (ICP), cerebral perfusion pressure (CPP), and laser Doppler flowmetry (LDF) values, intraparenchymal tissue partial oxygen pressure (PtiO2), and electroencephalography (EEG) activity were evaluated in the rat during controlled, epidural expansion of a latex balloon up to a maximum ICP of 60 mm Hg. The initial balloon inflation was followed by periods of sustained inflation (30 +/- 1 minute) and reperfusion (180 +/- 5 minutes). Histopathological analysis and magnetic resonance (MR) imaging were performed to characterize the lesion. The time to maximum balloon expansion and the average balloon volume were highly reproducible. Alterations in EEG activity during inflation first appeared when the CPP decreased to 57 mm Hg, the LDF value to 66% of baseline values. and the PtiO2 to 12 mm Hg. During maximum compression, the CPP was reduced to 34 mm Hg, the LDF value to 40% of baseline, and the PtiO2 to 4 to 5 mm Hg. The EEG tracing was isoelectric during prolonged inflation and the values of LDF and PtiO2 decreased due to accompanying hypotonia. After reperfusion, the CPP was significantly decreased (p < 0.05) due to the elevation of ICP. Both the LDF value and EEG activity displayed incomplete restoration, whereas the value of PtiO2 returned to normal. Histological analysis and MR imaging revealed brain swelling with a midline shift and a combined cortical-subcortical ischemic lesion beyond the site of balloon compression.

CONCLUSIONS

This novel model of an epidural mass lesion in rodents closely resembles the process observed in humans. Evaluation of pathophysiological and morphological changes was feasible by using neurophysiological monitoring and MR imaging.