Exposure to 56Fe-particle radiation accelerates electrophysiological alterations in the hippocampus of APP23 transgenic mice

Abstract An unavoidable complication of space travel is exposure to high-charge, high-energy (HZE) particles. In animal studies, exposure of the CNS to HZE-particle radiation leads to neurological alterations similar to those seen in aging or Alzheimer's disease. In this study we examined whether HZE-particle radiation accelerated the age-related neuronal dysfunction that was previously described in transgenic mice overexpressing human amyloid precursor protein (APP). These APP23 transgenic mice exhibit age-related behavioral abnormalities and deficits in synaptic transmission. We exposed 7-week-old APP23 transgenic males to brain-only (56)Fe-particle radiation (600 MeV/nucleon; 1, 2, 4 Gy) and recorded synaptic transmission in hippocampal slices at 2, 6, 9, 14 and 18-24 months. We stimulated Schaeffer collaterals and recorded field excitatory postsynaptic potentials (fEPSP) and population spikes (PS) in CA1 neurons. Radiation accelerated the onset of age-related fEPSP decrements recorded at the PS threshold from 14 months of age to 9 months and reduced synaptic efficacy. At 9 months, radiation also reduced PS amplitudes. At 6 months, we observed a temporary deficit in paired-pulse inhibition of the PS at 2 Gy. Radiation did not significantly affect survival of APP23 transgenic mice. We conclude that irradiation of the brain with HZE particles accelerates Alzheimer's disease-related neurological deficits.

Radiation exposure prior to ischemia decreases lesion volume, brain edema and cell death

PURPOSE

To investigate the neuronal response to ischemic injury following exposure to whole brain proton irradiation.

METHODS

Brain only proton irradiation (8 Gy, 250 MeV) was performed ten days prior to middle cerebral artery occlusion (MCAO) in 1 year old male Sprague Dawley rats. MCAO was induced in two animal groups: proton irradiated (MCAO + Rad) and MCAO only. Magnetic resonance imaging (MRI) and quantitative analysis were performed prior to and 2 days after irradiation, and then 2, 14 and 28 days after MCAO. After the last imaging time point animals were sacrificed and TUNEL staining was performed on 4% paraformaldehyde - fixed brain sections.

RESULTS

Neuroimaging demonstrated a reduction in ischemic lesion volume in the MCAO + Rad group compared with MCAO alone. Neurological deficits did not differ between ischemia groups. Interestingly, there was a 34% decrease in the number of TUNEL-positive cells in MCAO + Rad brains compared to MCAO alone.

CONCLUSION

Our results suggest that radiation treatment reduces brain edema, ischemic lesion volume and peri-ischemic apoptosis. The underlying mechanisms are currently unknown and additional studies will elucidate the significance of these results.

Long-term effects of melatonin after intracerebral hemorrhage in rats

Free radical scavengers have been shown to improve short-term outcome after intracerebral hemorrhage (ICH). The purpose of this study was to evaluate whether melatonin (a potent free radical scavenger and an indirect antioxidant) can improve short- and/or long-term neurological function after ICH, which was induced by collagenase injection into the striatum of adult rats. Melatonin (15 mg/kg) was administered by intraperitoneal injection at 1, 24, 48, and 72 h. Neurological and behavioral testing was performed at several time points from 1 day to 8 weeks post-ICH. Neurological and behavioral deficits were observed in ICH rats at all time points, but the melatonin treatment regimen did not improve performance or level of brain injury.

Deficiency of CD18 gene reduces brain edema in experimental intracerebral hemorrhage in mice

Experimental studies of intracerebral hemorrhage (ICH) point toward leukocytes as a major contributor to ICH-induced brain injury. Leukocyte and endothelial cell adhesion molecules are responsible for injurious neutrophil-endothelial cell interactions in vasculature. Since deficiency of leukocyte-expressed CD18 protects against ischemia-reperfusion injury, we hypothesized that such deficiency may have similar effect in ICH-induced injury. Our aim was to investigate whether CD18 deficiency affords neuroprotection by decreasing ICH-induced brain injury, thereby improving neurological function and reducing mortality. A total of 20 males wild-type CDI8+/+ mice and 12 CD18-/- knockout mice were used in our study. ICH was induced by collagenase injection. Mortality, neurological function, and brain edema were measured at 24h after ICH. Data were analyzed by ANOVA, Chi-square, and Student t-test. Differences of p < 0.05 were considered statistically significant. Our study showed that the increase in brain water content caused by ICH was significantly smaller in CD18 knockout mice compared with wild-type mice (p < 0.05, Student t-test). This result correlated with a tendency toward improvement of neurological function and a decrease in mortality. We conclude that CD18 deficiency significantly reduces brain edema after ICH, which corresponds with a trend toward reduction in neurological deficit and mortality.

Effects of superoxide dismutase and catalase derivates on intracerebral hemorrhage-induced brain injury in rats

The use of exogenous superoxide dismutase (SOD) and catalase (CAT) has been previously evaluated against various reactive oxygen species-mediated brain injuries, especially those associated with ischemia/ reperfusion. In this study, we investigated effects of these enzymatic antioxidants on intracerebral hemorrhage (ICH)-induced brain injury. A total of 65 male Sprague-Dawley rats (300-380 g) were divided into a sham group, an untreated ICH group, 3 groups of ICH rats treated with lecithinized SOD (PC-SOD) at doses of 0.1, 0.3, and 1 mg/kg, and a group treated with polyethylene glycol conjugated CAT (PEG-CAT) at a dose of 10,000 U/kg. An additional group of ICH rats received a combination of PC-SOD (1 mg/kg) and PEG-CAT (10,000 U/kg). ICH was induced by collagenase injection. All drugs were administered intravenously immediately after ICH induction. Brain injury was evaluated by scoring neurological function and measuring brain edema at 24 h after ICH induction. Our results demonstrated that ICH caused significant neurological deficit associated with remarkable brain edema. Treatment with PC-SOD, PEG-CAT, or PC-SOD in combination with PEG-CAT did not reduce brain edema or neurological deficit after ICH. We conclude that intravenously administered PC-SOD and/or PEG-CAT do not reduce brain injury in the collagenase-induced ICH rat model.